HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

What caps should I use for a resonant loop antenna for VLF? I have
some antenna plans and need .2 uf total capacitance to resonate a loop
antenna at 60 Khz.

I know I should avoid electrolytic and tantalum due to their poor
temperature stability.

Disc ceramics are so poor thermally that they are out of the question,
especially since the caps are going to be outdoors.

Silver Mica's are horribly expensive these days, and aren't available
much past .01uf anyway.

I have a Mouser catalog and plan to order from them soon, but it's not
clear which type of cap I should order.

Any suggestions for 50,000 pF caps that don't cost a fortune?

Note that this is a receive only antenna so voltage rating and current
carrying capacity are not an issue.

Thanks.

T

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

TRABEM wrote in message
...
What caps should I use for a resonant loop antenna for VLF? I have
some antenna plans and need .2 uf total capacitance to resonate a
loop
antenna at 60 Khz.

I know I should avoid electrolytic and tantalum due to their poor
temperature stability.

Disc ceramics are so poor thermally that they are out of the
question,
especially since the caps are going to be outdoors.

Silver Mica's are horribly expensive these days, and aren't
available
much past .01uf anyway.

I have a Mouser catalog and plan to order from them soon, but it's
not
clear which type of cap I should order.

Any suggestions for 50,000 pF caps that don't cost a fortune?

Note that this is a receive only antenna so voltage rating and
current
carrying capacity are not an issue.

Thanks.

T
===================================
Avoid electrolytics and ceramics like the plague!

Since whatever you do, 90 percent of losses will be in the coil
resistance you have a good choice of capacitor types. Any type of
plastic film insulation will do fine. You may wish to have a 2000pF
air-spaced variable in parallel to cover a small frequency range.

0.2 uF = 10 times 0.02 uF. In any case you will need a number of
small value components in parallel for exact tuning of a high-Q
circuit.

The normal 5 or 10 percent tolerance means that you will have to
measure and select values from a larger batch of inexpensive
capacitors.

Don't forget you will have to select from a small number of standard
values such as 0.22, 0.1, 0.047, 0.033, etc.

Specially manufactured close tolerance capacitors will cost the Earth.

Temperature coefficients don't matter very much but if you have a
choice then select those with the lowest coefficient. But TC is seldom
specified by manufacturers. You would need a very good capacitance
bridge to measure the small TCs involved although it is easy to make
TC measurements.

To reduce size of the capacitor just increase the number of coil
turns. You will notice little or no difference in operation.

The most efficient loop has a single turn of very thick wire.
The ONLY reason for multiple coil turns at VLF is to avoid impractical
values of capacitance. Receiving sensitivity does not depend on the
number of turns, only on the area enclosed by the loop.

A change in the number of coil turns involves only a change in how the
loop is Z-matched to the receiver. With a single-turn coupling loop
no changes are needed.

You may find program RJELOOP3 useful. It covers multi-turn square
loops and other regular shapes of the same enclosed area.

Download program from website below in a few seconds and run
immediately.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

TRABEM wrote in message ...
What caps should I use for a resonant loop antenna for VLF? I have
some antenna plans and need .2 uf total capacitance to resonate a loop
antenna at 60 Khz.

I know I should avoid electrolytic and tantalum due to their poor
temperature stability.

Disc ceramics are so poor thermally that they are out of the question,
especially since the caps are going to be outdoors.

Silver Mica's are horribly expensive these days, and aren't available
much past .01uf anyway.

I have a Mouser catalog and plan to order from them soon, but it's not
clear which type of cap I should order.

Any suggestions for 50,000 pF caps that don't cost a fortune?

Note that this is a receive only antenna so voltage rating and current
carrying capacity are not an issue.

Thanks.

T

Polystyrene caps are very temperature stable, typically changing only 0.5%
over their full temp range. And they're available in high capacitance
values. Check Mouser and Digikey for good prices.
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Hi Reg,

Didn't know you monitored here!



The normal 5 or 10 percent tolerance means that you will have to
measure and select values from a larger batch of inexpensive
capacitors.

Don't forget you will have to select from a small number of standard
values such as 0.22, 0.1, 0.047, 0.033, etc.


I've ordered a good supply of polystyrene caps in the standard values.
I also have an RCL meter, which is cheap and not accurate, but I can
measure the actual value of the caps I get from Mouser and assemble
them to hit the target frequency pretty easily. So, I'm actually
hoping the values they send are somewhat dispersed from the marked
values.


Specially manufactured close tolerance capacitors will cost the Earth.

Temperature coefficients don't matter very much but if you have a
choice then select those with the lowest coefficient. But TC is seldom
specified by manufacturers. You would need a very good capacitance
bridge to measure the small TCs involved although it is easy to make
TC measurements.

I learned about TC in the WB4VVF Accukeyer days when I was much
younger and foolish. I built one, it worked great. But, I used a disc
ceramic cap for the clock speed generator. I could actually detect the
keyer changing speed as I sent cw, which I assumed was due to the TC
of the disc ceramic. Touching a soldering iron to the outside of the
cap drove the keyer speed wild. Anyway, I learned my lesson about
disk ceramic caps the hard way and didn't want to repeat the error 25
years later by using a cap that didn't have a good temco.


To reduce size of the capacitor just increase the number of coil
turns. You will notice little or no difference in operation.

The most efficient loop has a single turn of very thick wire.

Which is exactly what I intend to do! I had a choice between large
copper welding cable and 3 inch copper pipe. I chose the welding cable
because it was actually cheaper although I'm not sure which would have
the best Q.

The ONLY reason for multiple coil turns at VLF is to avoid impractical
values of capacitance. Receiving sensitivity does not depend on the
number of turns, only on the area enclosed by the loop.

A change in the number of coil turns involves only a change in how the
loop is Z-matched to the receiver. With a single-turn coupling loop
no changes are needed.


Actually, I have a receiver with a 2 ohm input impedance Reg. So, it
can be fed directly from the series tuned loop. My only selectivity in
the front end of the receiver will be the loop tuning, so Q is
important.

The receiver is small and draws low power, so I am going to locate the
receiver at the antenna and feed the audio to teh house with common
mode audio transformers...thus avoiding the chance to conduct
household noise from the house to the receiver through the connecting
cable.

You may find program RJELOOP3 useful. It covers multi-turn square
loops and other regular shapes of the same enclosed area.

Download program from website below in a few seconds and run
immediately.

Already got RJELOOP3 and love it Reg. It has helped immensely and
saved me so much time because it allows me to evaluate how good
antennas will work without having to assemble them! Thanks for making
the software available.

GL.

T

................................................. ..........

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Sun, 23 Oct 2005 21:08:29 -0400, TRABEM wrote:

Hi Reg,

Didn't know you monitored here!

Try googling the archives to see he does more than monitor.

The normal 5 or 10 percent tolerance means that you will have to
measure and select values from a larger batch of inexpensive
capacitors.

Don't forget you will have to select from a small number of standard
values such as 0.22, 0.1, 0.047, 0.033, etc.


I've ordered a good supply of polystyrene caps in the standard values.
I also have an RCL meter, which is cheap and not accurate, but I can
measure the actual value of the caps I get from Mouser and assemble
them to hit the target frequency pretty easily.

Most capacitors are rated at the same frequency that most RCL meters
(for good reason) run at: 1KHz. This is not to say capacitance is the
same at 60KHz. It would be simpler to build your antenna with a
tickler coil in an oscillator circuit and measure the resonance
frequency.

So, I'm actually hoping the values they send are somewhat
dispersed from the marked values.

They usually are, but are also within the stated error band. That is
to say if they are spec'd at ±5% you might them spread from +1% to
+5% of nominal rather than across the full range of -5% to +5%. The
upside is tighter matching, the downside is no offsetting average
centered around nominal.

To reduce size of the capacitor just increase the number of coil
turns. You will notice little or no difference in operation.

The most efficient loop has a single turn of very thick wire.

Which is exactly what I intend to do! I had a choice between large
copper welding cable and 3 inch copper pipe. I chose the welding cable
because it was actually cheaper although I'm not sure which would have
the best Q.

And this is where most of the advice so far (and the perception of the
problem) comes into a clash with reality. I will quote from your
earlier post to make the point:

Note that this is a receive only antenna so voltage rating and current
carrying capacity are not an issue.

Current carrying capacity is an issue, that is why it is called Q!

Simply having smaller currents does not boost the Q of these pitifully
meager leads on the capacitors going to the comparatively garganthuan
copper pipe. Even more, and especially at this frequency, contact
resistance of the plates of the capacitor to the leads is an issue
that has been studied and resolved for designers of switching power
supplies (which typically run in this frequency neighborhood).

What you need to research for are caps with low ESR (Equivalent Series
Resistance), or test your selections along the lines offered at:
http://octopus.freeyellow.com/99.html

This returns us to the discussion of Q (we never really left), but for
capacitors is measured as DF (dissipation factor, something that is
generally ignored for transmission lines because the loaded Q is so
very low - as Dorothy would offer "Toto, we're not in Kansas
anymore!"). You could be killed by ESR and not know what hit you.

The suggestion for Polystyrene may be good, but only for a particular
manufacturer or for a particular run. It requires individual
examination and specification, especially when you've been warned away
from ceramics which can exhibit ±15ppm/°C (how good do you want it?).
The real trick is to simply accept you are going to get some that
drift and plan to offset that drift with another parallel formula that
drifts in the opposite direction such as: polyester and polypropylene,
or polystyrene and polycarbonate.

73's
Richard Clark, KB7QHC

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

"TRABEM" bravely wrote to "All" (23 Oct 05 21:08:29)
--- on the heady topic of " HIGH Q CAPS FOR VLF LOOP ANTENNA?"

TR From: TRABEM
TR Xref: core-easynews rec.radio.amateur.antenna:219247

TR I learned about TC in the WB4VVF Accukeyer days when I was much
TR younger and foolish. I built one, it worked great. But, I used a disc
TR ceramic cap for the clock speed generator. I could actually detect the
TR keyer changing speed as I sent cw, which I assumed was due to the TC
TR of the disc ceramic. Touching a soldering iron to the outside of the
TR cap drove the keyer speed wild. Anyway, I learned my lesson about
TR disk ceramic caps the hard way and didn't want to repeat the error 25
TR years later by using a cap that didn't have a good temco.

Hey those tiny square blue bypass caps are great for measuring
temperature. I had one on the workbench in a bridge and the IR heat
from my bare hand was changing the reading from at least a foot away!
Ceramic bypass types vary their capacitance a lot with temperature and
voltage.

A*s*i*m*o*v

.... Hanging: Early form of bungee jumping practiced in the old west.

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Caps to consider: as you've already figured, polypropylenes can do
very well. Mylars/polyesters are not very stable, and don't have as
high a Q as polyprops. They also show greater distortion, which may or
may not be an issue to you. C0G ceramics should work fine. Be aware
that the loop inductance will change with temperature, too, as the loop
size changes. Presumably your loaded Q won't be so high that it's a
problem: 50ppm/C over 20C is 0.1%, which wouldn't be noticable, most
likely, with a loaded Q of up to 500 or so. At 60kHz, Q=600 is only
about a 100Hz bandwidth, so I suppose you won't want a higher Q than
that anyway (assuming you could get it). I'm curious: what loaded Q
do YOU expect to get? How big is your loop going to be? What
impedance do you expect with the loop resonated?

Cheers,
Tom

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

"Richard Clark" wrote -

Try googling the archives to see he does more than monitor.

Richard,

I'm a little surprised you have time to spy on my activities. I trust
you are not a spare-time member of the CIA which appears to take an
interest in most things which go on on this planet. By the way, your
use of the English Language has recently improved. I have been able to
understand better what you are talking about.

But your concern about Effective Series Resistance (ESR) of the tuning
capacitors in connection with VLF tuned loops is a bit overdone.
Remembering Lord Kelvin, let's crudely quantify things.

All we have to go on is Trabem's value of the tuning capacitor of 0.2
uF.

Therefore the size of his loop is a square of sides = 5 metres. Total
length of wire = 20 metres. Or somehing similar.

Assume the wire diameter is a conservative thick 2mm.

Therefore we have L = 31 microHenrys, Reactance at 60 KHz = 12 ohms,
and RF resistance 0.23 ohms.

From which the intrinsic Q of the loop inductance = 50.

Assume the tuning capacitor is comprised of ten 0.02 uF capacitors in
parallel. The resistance of 10 capacitor leads in parallel is
negligible in comparison with the loop's single-turn conductor RF
resistance of 0.23 ohms.

He, Trabem, will be obliged to use a bundle of capacitors to make an
EXACT value for the tuning capacitor because of the impossibiltity of
obtaining a single capacitor of exactly the correct value, at a
particular temerature, and of sufficient long-term stability. He
can't afford it!

Immediately, the ESR of a 0.02 uF capacitor, whatever it is, is
divided by 10. Yes, I know that the ESR of a capacitor at 60 KHz
involves a little more than lead resistance. But it's too small for an
American General Radio bridge to accurately measure it.

But to return to Earth, the working Q of the 5-metre-per-side loop is
a function of the sum of the conductor resistance, plus the small ESR,
plus the radiation resistance (which is also negligible), PLUS the
loss resistance due interaction of the loop with its environment.

Unless the loop is removed from ground and other foreign structures by
at least 1/3 of its diameter the losses due to its environment will
greatly exeed all other losses.

If the environmental loss is equal only to conductor resistance loss,
the working Q of the loop will be reduced to 25.

With a Q of 25 the bandwidth will be of the order of 60/25 = 2.4 KHz,
or enough to accommodate an audio SSB transmission.

And getting down to practicalities, this means that the 0.2 uF tuning
capacitor has to be adjusted to an accuracy of about 0.3 percent, or
within a few hundred pF.

That is why I suggested a 2000 pF variable capacitor be included in
the bunch. A 2000 pF variable capacitor consists of an old fashioned
4-gang, 500 pF, receiving-type capacitor with all sections connected
in parallel.

As the loop is to be installed outdoors (with 5 metre sides it HAS to
be) the variable 2000 pF component might be useful to re-tuning it
between summer and winter temperature variations.

It's surprising what can be gleaned from a knowledge only of the value
of the proposed tuning capacitor.

Its all guesswork of course.

Incidentally, if Trabem obtains batchea of nominally identical value
capacitors, he will probably find they are all on the same side of the
tolerance. They probably all came from the same production line and
machine settings. Production values are not distributed at random.
This can seriously handicap his choice of particalar values to make up
the total of 0.2 uF.
----
Regards, Reg, G4FGQ.

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Mon, 24 Oct 2005 18:12:32 +0000 (UTC), "Reg Edwards"
wrote:
"Richard Clark" wrote -
Try googling the archives to see he does more than monitor.

Richard,
I'm a little surprised you have time to spy on my activities.

Hi Reggie,

There is no room for surprise and even less interest in your
"activities" whatever that term means. As for the time to accomplish
such a simple act - that is eclipsed in simply responding with these
first two sentences.

But your concern about Effective Series Resistance (ESR) of the tuning
capacitors in connection with VLF tuned loops is a bit overdone.

Clearly you in over your head, Old Son. I would suggest you exercise
your own skills in spying out common literature on the subject.

Remembering Lord Kelvin, let's crudely quantify things.

Sure, this exercise is going to floor you because you are clearly
quantifying only those things you are aware of. ESR is clearly beyond
your experience horizon given the howlers of dismissal you offer.

All we have to go on is Trabem's value of the tuning capacitor of 0.2
uF.

Therefore the size of his loop is a square of sides = 5 metres. Total
length of wire = 20 metres. Or somehing similar.

We have a loop so small, by your own reckoning, that its Radiation
Resistance amounts to barely 20 nanoOhms. This is not outside of the
realm of a simple reckoning - Lord Kelvinator would roll his eyes at
such omissions. The same efficiency issues that plague driving this
as a transmission antenna also plague it as a receiving antenna. I
see you neglect your own Kelvinator assessment of efficiency in your
cavalier dismissal.

Assume the wire diameter is a conservative thick 2mm.

In the face of a stated choice of:
I had a choice between large copper welding cable and
3 inch copper pipe. I chose the welding cable

Therefore we have L = 31 microHenrys, Reactance at 60 KHz = 12 ohms,
and RF resistance 0.23 ohms.

Adding loss seems to serve the argument rather than the plan.

From which the intrinsic Q of the loop inductance = 50.

Lord Kelvinator would throw his chalk at you for such reliance on what
is so easily measurable instead of being conjectured.

Assume the tuning capacitor is comprised of ten 0.02 uF capacitors in
parallel.

This is another failure that Lord Kelvinator would dope slap you with.
WHAT capacitors? What materials are being used, what vendor? what
specification? You are egregiously deficient in the particular of
MEASURABLES and you simply skip the SWAG. Is this the Kelvinator
ethic at work? This is lower 4th form effort. You are simply arguing
what you are familiar with and what follows reveals a vast
intellectual hole:
the ESR of a 0.02 uF capacitor, whatever it is, is
divided by 10. Yes, I know that the ESR of a capacitor at 60 KHz
involves a little more than lead resistance. But it's too small for an
American General Radio bridge to accurately measure it.

You clearly left the bench before the General Radio 1650-B became
commonly available to the calibration labs 40 years ago. There is
also the ESI Electro Scientific Inc. 250 DA Impedance Bridge. Both
bridges span 6 orders of magnitude for D measurement. We can presume
you have no experience with the Hewlett Packard HP 4270A either.

Going further (and certainly more modern) we have the ANDEEN-HAGERLING
AH 2700A which offers loss down to a dissipation factor of 1.5x10-8
tan d. This, by the way, does not extend above 20KHz but certainly
blows away any argument of anything being too small for its 12 ORDERS
of magnitude to encompass.

I could offer more examples, but that would be like shooting fish in a
barrel.

Reggie, you are simply gusting on with confirmed bafflegab:
Its all guesswork of course.

Incidentally, if Trabem obtains batchea of nominally identical value
capacitors, he will probably find they are all on the same side of the
tolerance.
Let's see, I said that already and you parrot it either
1. without attribution (plagiarizing);
2. responding without reading;
3. both.

73's
Richard Clark, KB7QHC

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

"Reg Edwards" wrote in message
...

"Richard Clark" wrote -

Try googling the archives to see he does more than monitor.

Richard,


Snippppppp
Assume the tuning capacitor is comprised of ten 0.02 uF capacitors in
parallel. The resistance of 10 capacitor leads in parallel is
negligible in comparison with the loop's single-turn conductor RF
resistance of 0.23 ohms.

He, Trabem, will be obliged to use a bundle of capacitors to make an
EXACT value for the tuning capacitor because of the impossibiltity of
obtaining a single capacitor of exactly the correct value, at a
particular temerature, and of sufficient long-term stability. He
can't afford it!

Immediately, the ESR of a 0.02 uF capacitor, whatever it is, is
divided by 10. Yes, I know that the ESR of a capacitor at 60 KHz
involves a little more than lead resistance. But it's too small for an
American General Radio bridge to accurately measure it.

But to return to Earth, the working Q of the 5-metre-per-side loop is
a function of the sum of the conductor resistance, plus the small ESR,
plus the radiation resistance (which is also negligible), PLUS the
loss resistance due interaction of the loop with its environment.

Unless the loop is removed from ground and other foreign structures by
at least 1/3 of its diameter the losses due to its environment will
greatly exeed all other losses.

If the environmental loss is equal only to conductor resistance loss,
the working Q of the loop will be reduced to 25.

With a Q of 25 the bandwidth will be of the order of 60/25 = 2.4 KHz,
or enough to accommodate an audio SSB transmission.

And getting down to practicalities, this means that the 0.2 uF tuning
capacitor has to be adjusted to an accuracy of about 0.3 percent, or
within a few hundred pF.

That is why I suggested a 2000 pF variable capacitor be included in
the bunch. A 2000 pF variable capacitor consists of an old fashioned
4-gang, 500 pF, receiving-type capacitor with all sections connected
in parallel.

As the loop is to be installed outdoors (with 5 metre sides it HAS to
be) the variable 2000 pF component might be useful to re-tuning it
between summer and winter temperature variations.

It's surprising what can be gleaned from a knowledge only of the value
of the proposed tuning capacitor.

Its all guesswork of course.

Incidentally, if Trabem obtains batchea of nominally identical value
capacitors, he will probably find they are all on the same side of the
tolerance. They probably all came from the same production line and
machine settings. Production values are not distributed at random.
This can seriously handicap his choice of particalar values to make up
the total of 0.2 uF.
----
Regards, Reg, G4FGQ.



The idea of having to use identical values of caps is a bit off track. You
build the capacitor bank up with obtainable value units, but add smaller
values (it's called trimming) to get to the exact capacitance you need.
I saw a VLF loop antenna that used such an arrangement, and as the fine
tuning element, there was a couple varicaps in parallel. There was also a
thermistor that fed temperature data back to an opamp circuit that
controlled the bias on the varicaps. The end result was an antenna that was
very well compensated for temperature. The loop stayed tuned within a few
hertz of it's tuned frequency over temperatures ranging from around 0F to
over 100F. The antenna was part of a VLF frequency calibration system.
Can't remember the make/model... it was a number of years ago. Tracor
seems to ring a bell, but not sure.

Cheers!!!
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Therefore the size of his loop is a square of sides = 5 metres. Total
length of wire = 20 metres. Or somehing similar.

Assume the wire diameter is a conservative thick 2mm.


Assume nothing Reg.

The loop is indeed 5M per side.

But, it is however made out or 2/0 copper cable used for arc welding.

I got a good deal on it. It has many many fine strands, never bothered
to count them or to measure the diameter of the individual strands.

But, suffice it to say that it is much larger than 2 mm.

I'm hoping for a Q of 600 at 60 Khz.

I looked at 3 inch copper pipe, couldn't estimate which had the better
ac resistance, so I went with the welding cable rather than the large
copper pipe.



And getting down to practicalities, this means that the 0.2 uF tuning
capacitor has to be adjusted to an accuracy of about 0.3 percent, or
within a few hundred pF.

That is why I suggested a 2000 pF variable capacitor be included in
the bunch. A 2000 pF variable capacitor consists of an old fashioned
4-gang, 500 pF, receiving-type capacitor with all sections connected
in parallel.

As the loop is to be installed outdoors (with 5 metre sides it HAS to
be) the variable 2000 pF component might be useful to re-tuning it
between summer and winter temperature variations.


I have some 365 pF air variables I planned to use one for fine tuning
the loop.

There will be no ssb reception. Generally I'm interested in 6 to 10 Hz
wide channels at 185.3 Khz and in the 137 KHz ham band.

Fortunately, I have a DDS with a tcxo, so I can spot the frequencies I
want to listen on and then tweek the loop with the variable cap.

Regards,

T

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Thanks Tom,

I hope for a Q of 600.

At 60kHz, Q=600 is only
about a 100Hz bandwidth, so I suppose you won't want a higher Q than
that anyway (assuming you could get it). I'm curious: what loaded Q
do YOU expect to get?

How big is your loop going to be?

Around 5.2 Meters per side.

What
impedance do you expect with the loop resonated?

It should be under 1 ohm. I don't exactly know the ac resistance or
how the Q of the C and the Q of the inductor combine.

My loop material is 2/0 copper welding cable, many fine starnds. I
considered 3 inch copper pipe, but couldn't get an estimate of the ac
resistance for either, so I chose the copper cable.


Regards,

T

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

I'm puzzled. My copy of rjeloop3 suggests the Q will be about 200 at
60kHz with a 9mm wire diameter, and you'll see about 2kohms when it's
resonated. Are you not taking the output across the ends of the loop
(across the capacitor)? And with a skin depth of about 0.01" at 60kHz
in copper, certainly 3" diameter soft copper pipe would have the lower
resistance. You might have some trouble finding soft copper pipe,
though. But even hard copper pipe should have a low RF resistance.
"Reference Data for Radio Engineers" (or "Reference Data for Engineers"
in newer incarnations) has lots of good info for figuring out things
like RF resistance of copper wire. I assume your welding cable doesn't
have strands that are insulated from each other like Litz wire.

Consider that Q is energy stored divided by energy dissipated per
radian (1/2pi of a cycle). Then the net Q will be 1/(1/Q(inductor) +
1/Q(capacitor)). So if the cap and inductor have the same Q, the net Q
will be half that. And if you put a resistive load across the
coil+cap, that will dissipate power and lower the Q further.

Cheers,
Tom

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Stranded, layer-wound wire, even when strands are individually
insulated, behaves similar to solid wire of slightly smaller diameter.

The strands in true Litz are WOVEN such that every strand spends the
same length in inside and outside and intermediate layers of the
cable.

Current is then more uniformly distributed throughout the conductor's
cross-section.

The diameter of an individal strand should not be greater than about
about twice skin depth. Otherwise effectiveness decreases. Thus, at
high frequences where skin depth is very small, very fine wire must be
used.

There are practical and economic limits to the fineness of drawn
copper wire. There is little to be gained by using ordinary Litz
above 3 or 4 MHz. At high frequencies with small coils of few turns,
such as receiving coils, tank and loading coils, it is far more
economic to increase Q just by increasing the diameter of solid copper
wire. Litz is at its best from VLF to IF and MF.
----
Reg.

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Another set of questions: Given the high atmospheric noise level at
LF/VLF, is there really a need for such a large loop as you propose,
for receiving? How quiet is your receiver front end? In other words,
will such a large loop significantly improve your SNR on weak signals?
Do you have a reason other than signal level for using such a large
loop? What about the response to nearby strong electric-field noise
generators of a large loop versus a smaller one?

Cheers,
Tom

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

You are absolutely right about the size of the loop.

A larger loop might not enhance the ability to copy a weaker signal.
And, I spent a small fortune in buying big wire just to make it have a
reasonably high Q. My question about the caps was merely to make sure
that I was buying the right type of caps, so that the investment in
the larger sized wire didn't get negated by having the wrong type of
cap.

At some time I might like to evaluate a smaller loop against the big
one in terms of the actual weak signal reception capability.

The receiver is hot on HF and should be just as good on LF and VLF.

Ultimately I'd like a shielded loop, but the effect of the stray
capacitance seems to really kill the Q. The shielded loop camp makes a
convincing argument in that the magnetic field is significantly
quieter than the electrical field is. But, how to do a shielded loop
without knocking the Q all to Hell is a significant issue. Needless to
say the potential for interference by strong LF broadcasters is much
reduced by shielding the loop as well.

One user I spoke to recently commented on the quality of reception
with his shielded loop.....signals that were buried in noise by quite
a few db seem to pop up into Q5 readability when the shielded loop
antenna is switched in. So, I know they work. Just not sure how to
implement them without incurring a lot of loss in Q from the stray
capacitance introduced by the shielding.

T


On 25 Oct 2005 09:22:10 -0700, "K7ITM" wrote:

Another set of questions: Given the high atmospheric noise level at
LF/VLF, is there really a need for such a large loop as you propose,
for receiving? How quiet is your receiver front end? In other words,
will such a large loop significantly improve your SNR on weak signals?
Do you have a reason other than signal level for using such a large
loop? What about the response to nearby strong electric-field noise
generators of a large loop versus a smaller one?

Cheers,
Tom

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Tue, 25 Oct 2005 19:43:42 -0400, TRABEM wrote:

The shielded loop camp makes a
convincing argument in that the magnetic field is significantly
quieter than the electrical field is. But, how to do a shielded loop
without knocking the Q all to Hell is a significant issue. Needless to
say the potential for interference by strong LF broadcasters is much
reduced by shielding the loop as well.

You are tap dancing in the mine field of nonsense. Once you strip
this stuff out of your thinking, you might find your way to a more
sensible antenna design (maybe even a good shielded one - and shielded
for better reasons than those above).

73's
Richard Clark, KB7QHC

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

You need first to realize that the "shield" IS the antenna. The whole
point of the "shielded loop" is that you can make it very symmetrical,
which is just what's needed to reject strong local electrical fields.
The symmetry does nothing to reject electromagnetic signals. BUT you
can make an "unshielded" loop which is as symmetrical as a "shielded",
if you are careful, and get the same advantages. If you really want to
build one like a classical "shielded loop" and maintain high Q, just
build the "shield" out of copper pipe and put the capacitor across the
gap. The wire inside the pipe is just the center conductor of a short
piece of coax connected to the feedpoint.

If you don't understand this, please see King, Mimno and Wing's
"Transmission Lines, Antennas and Waveguides." It's explained quite
nicely in the "antennas": chapter. It's also explained reasonably well
in Johnson and Jasik's "Antenna Engineering Handbook."

Cheers,
Tom

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On 25 Oct 2005 17:31:02 -0700, "K7ITM" wrote:

You need first to realize that the "shield" IS the antenna. The whole
point of the "shielded loop" is that you can make it very symmetrical,
which is just what's needed to reject strong local electrical fields.
The symmetry does nothing to reject electromagnetic signals. BUT you
can make an "unshielded" loop which is as symmetrical as a "shielded",
if you are careful, and get the same advantages. If you really want to
build one like a classical "shielded loop" and maintain high Q, just
build the "shield" out of copper pipe and put the capacitor across the
gap. The wire inside the pipe is just the center conductor of a short
piece of coax connected to the feedpoint.

If you don't understand this, please see King, Mimno and Wing's
"Transmission Lines, Antennas and Waveguides." It's explained quite
nicely in the "antennas": chapter. It's also explained reasonably well
in Johnson and Jasik's "Antenna Engineering Handbook."


Hi Tom,

No, I don't understand this. I thought a shielded loop meant the loop
antenna wire was shielded by the copper (non-ferrous) surrounding the
wire. The shield tends to protect the wire from electrical field
inputs and allows it to only respond to magnetic field variations.

I thought the capacitance between the wire and the surrounding shield
material represented a loss in Q, therefore a loss in output voltage.
So, a loop that might have a Q of 100 in free space would have a much
lower Q if the loop wire was enclosed in a non-ferrous pipe.

There are countless horror stories about those attempting to use
surplus hardline as shielded loops on LF and VLF, all with
disappointing results. The predominate attitude was that the
capacitive coupling between the wire and the shielding material was
the cause. I don't say the predominate attitude is correct.but, if it
is a false assumption, then I am not the only one who needs
revision:))

If the copper pipe IS the antenna, then why have the wire inside it at
all??

I must say I'm more confused now than I was before reading your
message.

I'm sorry, I have to leave now. The director of the asylum is
calling.......

T

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Tue, 25 Oct 2005 23:01:01 -0400, TRABEM wrote:

No, I don't understand this. I thought a shielded loop meant the loop
antenna wire was shielded by the copper (non-ferrous) surrounding the
wire.

It is not an effective antenna shield if it is wholly continuous - and
it is not, it has a gap opposite the mounting point which is generally
at ground/reference potential. Part of the point of being "shielded"
is to enforce a symmetry and that ground/reference is electrically
neutral as long as you guarantee it is equidistant both sides around
the loop to that gap.

The shield tends to protect the wire from electrical field
inputs and allows it to only respond to magnetic field variations.

There is no such thing as "only" magnetic fields variations.

I thought the capacitance between the wire and the surrounding shield
material represented a loss in Q,

Q is a simple relation between loss and storage. Lower Q for the same
storage (be it in a capacitor or an inductor) can only result from
resistive loss of Ohmic conduction or radiation. Any loss
attributable to a capacitor is conductive loss - hence the discussion
of ESR. You would have to go back to the stone age of electronics
with paper and wax dielectrics to find loss BETWEEN the plates.
Equivalent Series Resistance for garden variety capacitors, when
compared to radiation resistance, is not trivial. That is, unless,
you swamp that loss by putting your loop in the closet with your
mothballed summer wardrobe or burying it in the garden mud. Design
for failure is easily achieved if you need a rationale to ignore
simple considerations.

Consult:
http://www.w8ji.com/magnetic_receiving_loops.htm

There are countless horror stories about those attempting to use
surplus hardline as shielded loops on LF and VLF, all with
disappointing results.

Such disasters that arise are one of two possible scenarios:
1. They don't have a gap (short circuit city);
2. They don't guarantee symmetry (poor balance, poor tuning, poor
response).

The predominate attitude was that the
capacitive coupling between the wire and the shielding material was
the cause. I don't say the predominate attitude is correct.but, if it
is a false assumption, then I am not the only one who needs
revision:))

We get that traffic - yes. They suffer the same learning slope.

If the copper pipe IS the antenna, then why have the wire inside it at
all??

Because you have to have a conductor pair back to the receiver. The
grounded "shield" serves as one half of the pair, the other spans the
gap connecting to the other half's "shield" (it looks like you are
shorting the inner conductor to ground) to thus pick up the opposite
potential. The voltage across the gap is thus sensed and it only
takes one wire. Look closely at any such standard "shielded" loop.
The sense of what is being shielded is THAT conductor which you
contrive to keep in a controlled environment (a coaxial shield) and
away from the imbalance of nearby capacitive couplings. The
"shielded" inner conductor spans a very small distance whose opposite
poles' capacity is balanced to all neighboring paths to ground. That
is, unless you push one side up against the wall.

Stretch out the gap of the shield loop and you have a conventional
dipole. A conventional dipole exhibits high Z and high V at its tips.
The middle of such a dipole has a low Z and a high I. With respect to
both ends, the middle is neutral and strapping it to a conductor does
nothing to change that topology (and is a common tower mounting
benefit). Being curved into a loop does not change this and allows
you to connect your transmission line to both sides without greatly
exposing a significant length of the transmission line (and thus
forcing an unbalance and upsetting the applecart).

This dipole is obviously very small with respect to its wavelength and
thus some form of end loading is required. Thus the capacitor arrives
on the scene. The circulating currents and potentials become
astronomic for progressively smaller antennas. Those currents flow
through and to the plates of the capacitor. If you don't choose the
right components for that capacitor (and manufacturers of HF loops
like to crow how they achieve this) then your design efficiency goes
TU. Hence to speak of capacitor Q is not appropriate as the correct
term is D (dissipation factor). It is certainly related (an inverse
relation) and despite comments to the contrary, D is resolvable with
standard bridges (although those bridges are of considerable design
sophistication in maintaining balance and their own shielding - not a
trivial matter).

There are simpler ways of achieving the same thing by building a
completely exposed loop with capacitor (still paying attention to the
ESR and keeping the whole shebang out of the mud), and simply building
a shielded coupling loop. Reg has adequately described this before
many times.

73's
Richard Clark, KB7QHC

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Thanks Richard,

I have a bunch of reading to do. Appreciate your time and the
explanation that you gave.

My receiver has a 2 to 3 ohm input impedance, my hope was to use a
series tuned loop that was entirely floating (with no ground anywhere)
and feed it to the house with a balanced line. Since it's a short run
to the house (in terms of wavelength, I had hoped the impedance
mismatch between the 90 ohm impedance twisted pair transmission line
would not produce a big loss.

The receiver input is also untuned, so the only selectivity available
to it will be the antenna selectivity, which I think I can get away
with since the antenna is relatively high Q.

Again, thanks for the info and for the web resource. I have some more
studying to do!

Regards,

T




On Tue, 25 Oct 2005 23:01:01 -0400, TRABEM wrote:

No, I don't understand this. I thought a shielded loop meant the loop
antenna wire was shielded by the copper (non-ferrous) surrounding the
wire.

It is not an effective antenna shield if it is wholly continuous - and
it is not, it has a gap opposite the mounting point which is generally
at ground/reference potential. Part of the point of being "shielded"
is to enforce a symmetry and that ground/reference is electrically
neutral as long as you guarantee it is equidistant both sides around
the loop to that gap.

The shield tends to protect the wire from electrical field
inputs and allows it to only respond to magnetic field variations.

There is no such thing as "only" magnetic fields variations.

I thought the capacitance between the wire and the surrounding shield
material represented a loss in Q,

Q is a simple relation between loss and storage. Lower Q for the same
storage (be it in a capacitor or an inductor) can only result from
resistive loss of Ohmic conduction or radiation. Any loss
attributable to a capacitor is conductive loss - hence the discussion
of ESR. You would have to go back to the stone age of electronics
with paper and wax dielectrics to find loss BETWEEN the plates.
Equivalent Series Resistance for garden variety capacitors, when
compared to radiation resistance, is not trivial. That is, unless,
you swamp that loss by putting your loop in the closet with your
mothballed summer wardrobe or burying it in the garden mud. Design
for failure is easily achieved if you need a rationale to ignore
simple considerations.

Consult:
http://www.w8ji.com/magnetic_receiving_loops.htm

There are countless horror stories about those attempting to use
surplus hardline as shielded loops on LF and VLF, all with
disappointing results.

Such disasters that arise are one of two possible scenarios:
1. They don't have a gap (short circuit city);
2. They don't guarantee symmetry (poor balance, poor tuning, poor
response).

The predominate attitude was that the
capacitive coupling between the wire and the shielding material was
the cause. I don't say the predominate attitude is correct.but, if it
is a false assumption, then I am not the only one who needs
revision:))

We get that traffic - yes. They suffer the same learning slope.

If the copper pipe IS the antenna, then why have the wire inside it at
all??

Because you have to have a conductor pair back to the receiver. The
grounded "shield" serves as one half of the pair, the other spans the
gap connecting to the other half's "shield" (it looks like you are
shorting the inner conductor to ground) to thus pick up the opposite
potential. The voltage across the gap is thus sensed and it only
takes one wire. Look closely at any such standard "shielded" loop.
The sense of what is being shielded is THAT conductor which you
contrive to keep in a controlled environment (a coaxial shield) and
away from the imbalance of nearby capacitive couplings. The
"shielded" inner conductor spans a very small distance whose opposite
poles' capacity is balanced to all neighboring paths to ground. That
is, unless you push one side up against the wall.

Stretch out the gap of the shield loop and you have a conventional
dipole. A conventional dipole exhibits high Z and high V at its tips.
The middle of such a dipole has a low Z and a high I. With respect to
both ends, the middle is neutral and strapping it to a conductor does
nothing to change that topology (and is a common tower mounting
benefit). Being curved into a loop does not change this and allows
you to connect your transmission line to both sides without greatly
exposing a significant length of the transmission line (and thus
forcing an unbalance and upsetting the applecart).

This dipole is obviously very small with respect to its wavelength and
thus some form of end loading is required. Thus the capacitor arrives
on the scene. The circulating currents and potentials become
astronomic for progressively smaller antennas. Those currents flow
through and to the plates of the capacitor. If you don't choose the
right components for that capacitor (and manufacturers of HF loops
like to crow how they achieve this) then your design efficiency goes
TU. Hence to speak of capacitor Q is not appropriate as the correct
term is D (dissipation factor). It is certainly related (an inverse
relation) and despite comments to the contrary, D is resolvable with
standard bridges (although those bridges are of considerable design
sophistication in maintaining balance and their own shielding - not a
trivial matter).

There are simpler ways of achieving the same thing by building a
completely exposed loop with capacitor (still paying attention to the
ESR and keeping the whole shebang out of the mud), and simply building
a shielded coupling loop. Reg has adequately described this before
many times.

73's
Richard Clark, KB7QHC

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

I could perhaps scan the relevant pages of the references I
mentioned...

How are you planning to couple your 2-ohm load to your loop without
doing really bad things to its Q? (And just what sort of detector do
you have that represents a 2 ohm load?)

Cheers,
Tom

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

"K7ITM" wrote in message
ups.com...
I could perhaps scan the relevant pages of the references I
mentioned...

How are you planning to couple your 2-ohm load to your loop without
doing really bad things to its Q? (And just what sort of detector do
you have that represents a 2 ohm load?)

Cheers,
Tom


He probably measured the DC resistance at the antenna input connector. If
there's an inductance path to ground, then that's probably what he measured.
The DC resistance is NOT the RF impedance of the input.

Cheers!!!!


--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in
the address)

Never take a laxative and a sleeping pill at the same time!!

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Wed, 26 Oct 2005 20:58:26 -0400, "DaveM"
wrote:

"K7ITM" wrote in message
oups.com...
I could perhaps scan the relevant pages of the references I
mentioned...

How are you planning to couple your 2-ohm load to your loop without
doing really bad things to its Q? (And just what sort of detector do
you have that represents a 2 ohm load?)

Cheers,
Tom


He probably measured the DC resistance at the antenna input connector. If
there's an inductance path to ground, then that's probably what he measured.
The DC resistance is NOT the RF impedance of the input.


NO.

Cheers!!!!

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Thu, 27 Oct 2005 00:36:07 -0400, TRABEM wrote:

NO.

The group deserves a better specification for the input Z of your amp
than that.

73's
Richard Clark, KB7QHC

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On 26 Oct 2005 09:27:44 -0700, "K7ITM" wrote:

I could perhaps scan the relevant pages of the references I
mentioned...


No, I can get them att he schools library I think. thanks for the
offer.

How are you planning to couple your 2-ohm load to your loop without
doing really bad things to its Q?

Is it better to convert the loop to a higher impedance just to feed it
into the house? It appears that anything I do is going to knock the
heck out of the antennas Q though.

I have not decided whether to mount the receiver at the antenna yet,
or whether to run the twisted line directly into the house from the
antenna (since it's a short run). Most likely it will have a short run
of cat 5 cable going from the antenna to a 1 to 1 toroid transformer
located in the receiver. The only selectivity for the receiver will be
the antenna itself. The receiver is very small, and uses very little
power, so it's pretty feasible to mount the entire receiver at the
antenna and run a balanced line feed of the audio into the house.

(And just what sort of detector do
you have that represents a 2 ohm load?)

Is it better to convert the loop to a higher impedance just to feed it
into the house?

It's an analog switch input, modified by my neighbor that gave me one
of them. The switch vendor says the switch series resistance should be
around 3 ohms, but it measures around 2.5 ohms. Probably is a little
lower than expected due to the integrating capacitors (.1 uF) which
are hung on the output of each switch. The .1's go to ground.

I measured it twice, once with a 1:1:1 isolation transformer and once
with a 6:1:1 isolation transformer....The tester looses accuracy at
low impedances, so we repeated the measurement with the generator
feeding the high impedance side of the a transformer also. I got
nearly the same reading after correcting for the transformers
impedance step down value, since both readings agree pretty well with
the switch vendors ratings, it's very likely that the receiver input
impedance is around 2 ohms.

(And just what sort of detector do
you have that represents a 2 ohm load?)

Cheers,
Tom

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Wed, 26 Oct 2005 22:07:48 -0700, Richard Clark
wrote:

On Thu, 27 Oct 2005 00:36:07 -0400, TRABEM wrote:

NO.

The group deserves a better specification for the input Z of your amp
than that.


Yes, of course they do Richard.

However, the reply was more than Dave deserved after the statement
that he made. Maybe that's how he measures receiver input impedance, I
certainly don't measure it like that.

You should have the schematic in your mailbox by the time you get this
message.

I can't post a schematic here.

T

73's
Richard Clark, KB7QHC

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

The point is that the loop's inductive reactance is on the order of 10
ohms in the frequency range you're talking about. When resonated with
a capacitor, if the Q is, say, 300, then the impedance at resonance
will be about 3000 ohms, resistive, as seen across the capacitor.
Reg's program gives you an estimate of what it will be. If you put a
low-resistance load across that, the Q will drop drastically. And if
you put your 2 ohms (which it won't be at the received frequency, if I
understand what you have) in series with the loop and capacitor, it
will also drastically lower the Q. So my question remains: how will
you couple to the loop and maintain the Q?

When you measure the input impedance of your detector, you should do it
while the detector is operating, and do it versus frequency. I expect
you'll see a large increase in impedance at the operating frequency.

Cheers,
Tom

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Mon, 24 Oct 2005 18:03:49 -0400, TRABEM wrote:


Assume the wire diameter is a conservative thick 2mm.


Assume nothing Reg.

Well T, reading through the thread you seem to be real short on
relevant information (ie you don't adequately anticipate the
information people need to answer your questions), then very ready to
deal abruptly with people who make the wrong assumptions about the
context.

Owen
--

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Thu, 27 Oct 2005 02:02:53 -0400, TRABEM wrote:

You should have the schematic in your mailbox by the time you get this
message.

If I am to translate the annotation correctly (and it is obviously in
error - R10 and R12 are not the pair being changed), then Input Z
somewhere in your frequencies of interest (you've named several) runs
around 10 Ohms with the switch itself attenuating your signal by 6 to
10dB. This, of course, says nothing of the abysmal match to the
antenna whose Q will be buried in potter's field.

I gather that the switch operates as a baseband quadrature/synchronous
detector. It looks suspiciously like it will either short the input,
or leave one half dangling, but I trust you got the schematic from a
good source. I won't bother to try to verify the logic.

The roll-off frequency of the amplifier(s) is at the bottom of the AM
band, it would do better to track the oscillator frequency about one
seventh below so that AM signals are depressed below WWVB instead of
competing with it. Increase the caps from 470pF to 3300pF.

The reason why you want low front end Input Z is to satisfy the
amplifier topology (the gain will be roughly half what it is probably
specified at). This could have been done better in half a dozen
different ways with the same active parts.

The problem here is some bozo marked the input "antenna" and removed
the necessary follower amplifier that would have been fed by the
antenna which would in turn feed this circuit through the transformer.
This sucker, as drawn, is going to be deaf, deaf, DEAF. If you hear
WWVB it will be by virtue of their strong power, not by any quality of
design here.

To unplug this design's ears and make up for the massive goof, add a
FET follower. Load the FET drain with a 2.2 Ohm resistor and make
sure you couple the signal through a large cap feeding the
transformer. Also, bias the FET on with a hi Z divider so you don't
wipe out the Q of the antenna. I will bet that even the proposed "I"
and "Q" paths are mislabled or missapplied.

73's
Richard Clark, KB7QHC

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

You should have the schematic in your mailbox by the time you get this
message.

If I am to translate the annotation correctly (and it is obviously in
error - R10 and R12 are not the pair being changed), then Input Z
somewhere in your frequencies of interest (you've named several) runs
around 10 Ohms with the switch itself attenuating your signal by 6 to
10dB. This, of course, says nothing of the abysmal match to the
antenna whose Q will be buried in potter's field.

Hi Richard,

You are correct, the resistors being changed at R11 and R12, sorry for
the error. To correct the statement on the schematic, consider R11 and
R12 as being changed from 10 ohms to .2 ohms.

I'm not sure what the 'abysmal match to the antenna whose Q will be
buried in potter's field' statement is about. With my antenna being in
the 2 ohm impedance range, and the receiver being at 10 ohms (I'll use
your figure), how can the match be abysmal? Granted, it's not anywhere
near ideal. Have you assumed I was using a parallel tuned loop?

Since power transfer is the goal, and the antenna has a lot of ability
to reject out of band signals, it was my hope to use the antenna
itself as the only (purposely) tuned circuit in the system. Wouldn't
converting the antenna impedance to a more traditional 50 ohms with a
toroid, and then having a second toroid to convert it back down to 10
ohms also be destructive to the antenna Q and lossy?


I gather that the switch operates as a baseband quadrature/synchronous
detector. It looks suspiciously like it will either short the input,
or leave one half dangling, but I trust you got the schematic from a
good source. I won't bother to try to verify the logic.


The logic is good, trust me, the receiver as shown outperforms many
much more expensive ones on the market currently. It is based on the
receiver shown at:

http://www.qrp2001.freeserve.co.uk/qrp2001rf.gif

It's design has been around for awhile, the first prototype was built
in 2000. While I disagree with the use of resistive matching, it
should be ok at VLF as the signals are usually quite large there to
begin with. For a simple receiver, it is the best answer. Although
ideally, each switch should have it's own 1 ohm variable resistor for
absolute best results...the purpose being to swamp out the dynamic
switch series resistance differences.

Note the receiver has no rf amp, it isn't needed. The gain is provided
by some low noise op amps, and no rf stage is needed. The QRP2001
receiver is designed for 100 KHz to 30 Mhz, but it is only rated down
to 1.8 MHz. However, it's worst case sensitivity is .4uV for 10 db
sinad.


The roll-off frequency of the amplifier(s) is at the bottom of the AM
band, it would do better to track the oscillator frequency about one
seventh below so that AM signals are depressed below WWVB instead of
competing with it. Increase the caps from 470pF to 3300pF.


Agreed. Thanks.

The 470 pF value was chosen for a wide band spectral display from DC
to 96 KHz, which is about the best that generic PC sound cards can do
today. If the panoramic view of the surrounding spectrum wasn't
necessary, these caps would be much larger in value. As it sits
however, it's nice to have a panoramic view of the surrounding
spectrum, so the caps might not be changed.

For my purposes, they don't need to be nearly as small as they are,
but the original design was for HF...where a wiew of the surrounding
spectrum was handy.

The reason why you want low front end Input Z is to satisfy the
amplifier topology (the gain will be roughly half what it is probably
specified at). This could have been done better in half a dozen
different ways with the same active parts.

The problem here is some bozo marked the input "antenna" and removed
the necessary follower amplifier that would have been fed by the
antenna which would in turn feed this circuit through the transformer.
This sucker, as drawn, is going to be deaf, deaf, DEAF. If you hear
WWVB it will be by virtue of their strong power, not by any quality of
design here.


WRONG, but I think I understand your error. BTW, the 'bozo' was me::.

Again, I think you've assumed it would be fed with a parallel loop
resonant antenna.

And, no active components are needed for outstanding performance.

It is possible that the antenna circuit might need to be tuned with
passive components, but that possibility needs further evaluation.

To unplug this design's ears and make up for the massive goof, add a
FET follower. Load the FET drain with a 2.2 Ohm resistor and make
sure you couple the signal through a large cap feeding the
transformer. Also, bias the FET on with a hi Z divider so you don't
wipe out the Q of the antenna. I will bet that even the proposed "I"
and "Q" paths are mislabled or missapplied.


OK, this is a fair request...from someone without experience in this
type of receiver. However, in reality, an rf stage of any sort is
unnecessary.

Again, I think you're trying to match a 2 K parallel tuned loop to the
relatively low impedance of the receiver input. I noticed you said
'follower'. Which, I think means unity gain, but is used for impedance
matching.

Any active component before the audio op amp is STRONGLY
DISCOURAGED in this type of receiver. This includes back to back
diodes as the receiver switches can handle 4v p-p. It also includes
varicap tuning diodes. A front end rf amp should be avoided at all
costs, it can only degrade the performance of this type of receiver.

The receiver has incredible immunity to strong out of band signals,
much more than any superhet. The nature of the beast is that the
quadrature detector cancels them out by (effectively) NOT reinforcing
them. The desired signal is however very strongly reinforced. Since we
don't need an rf amp to get good sensitivity, any active component
before the load capacitors is strongly discouraged.

Even at 60 MHz, the performance is only slightly degraded, and that is
due to the inability of the analog switch to enable and disable fast
enough to allow reception there. There is a commercial application
using this technology that implements receive and transmit with analog
switch method and it does not have an RF amp.

Of course, there is a trade off. In order to obtain immunity from
strong adjacent out of band signals, we give up the ability to reject
harmonics. Harmonics are only attenuated 6 db....so a tuned input must
be used if the antenna cannot adequately prevent harmonics of the
receiver frequency from entering the receiver.

In theory, a minimum of 6db enhancement is available because there is
no mixer, so there is no conversion loss!

The susceptibility to harmonics is a small trade off. Remember, a
receiver of this type is wideband, needs no conventional mixers, no
detector diode, no transformers, no crystal filters, no IF amps, has
no conversion loss and no major non-linear components...thus offers
outstanding performance with the cost to build very much reduced
(relative to a superhet). What you don't see on the schematic is the
incredible sound of the receiver audio which is clean and crisp...it's
not quantifiable by bench measurements however.

I've put some links to web references of this technology at the end of
the message.

In the meantime, I'd appreciate comments regarding the issue of how
well the loop will feed the antenna input for the modified receiver
schematic I sent you by email.

Regards,

T

PS:I hope Dave is still with us. Although he probably left when he
assumed I measured the input impedance with an ohm meter:: Dave, are
you able to concede that the input impedance of the receiver might be
around 2 (or 10) ohms now?


-----------------------------------------------------------

If you want read up on this type of receiver, I can recommend the
following:


http://www.qrp2001.freeserve.co.uk/contact.htm

http://www.flex-radio.com/

Flex-Radio makes the quadrature based SDR-1000 transceiver. For a very
detailed explanation (without heavy math) of the detector theory,
check out the QEX article, part 1 at:

http://www.flex-radio.com/articles_files/SDRFMP1.pdf

And, there are independent product reviews for the SDR-1000 at:

http://www.flex-radio.com/articles_files/index.htm

Dan Tayloes NC2030 high performance signle band transceiver is
detailed at:

http://www.qslnet.de/member/df7tv/nc...es_2004_10.pdf

The complete schematics for the NC2030 are at:

http://www.norcalqrp.org/nc2030.htm

Note that the NC2030 uses the same type of detector, but does not use
a sound card and does not rely on a computer at all. It is a stand
alone transceiver.

There is also a 9Y4 who home brewed a complete transceiver, details
at:

http://9y4ar.tripod.com/tayloe_mixer.htm

Although slightly off topic, a low power ssb/cw exciter can be made
just as easily as the receiver using the same analog switch
technology. The process is simply the reverse process of the detector.
To see how simple a high quality transmitter is, try:

http://www.w1tag.com/Phasing.htm


..

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Thu, 27 Oct 2005 06:37:17 GMT, Owen Duffy wrote:

On Mon, 24 Oct 2005 18:03:49 -0400, TRABEM wrote:


Assume the wire diameter is a conservative thick 2mm.


Assume nothing Reg.

Well T, reading through the thread you seem to be real short on
relevant information (ie you don't adequately anticipate the
information people need to answer your questions), then very ready to
deal abruptly with people who make the wrong assumptions about the
context.



Owen,

You're right of course. Although there is a balance needed as the
complete details would fill a small book...no one would read it to the
very end.

Check the thread a little later in it's history, I think there has
been additional pertinent information goven.

Enjoy.

T

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

May I ask, what is with the almost fanitical adherence to Q?

TRABEM wrote in message ...
On 26 Oct 2005 09:27:44 -0700, "K7ITM" wrote:

I could perhaps scan the relevant pages of the references I
mentioned...


No, I can get them att he schools library I think. thanks for the
offer.

How are you planning to couple your 2-ohm load to your loop without
doing really bad things to its Q?

Is it better to convert the loop to a higher impedance just to feed it
into the house? It appears that anything I do is going to knock the
heck out of the antennas Q though.

I have not decided whether to mount the receiver at the antenna yet,
or whether to run the twisted line directly into the house from the
antenna (since it's a short run). Most likely it will have a short run
of cat 5 cable going from the antenna to a 1 to 1 toroid transformer
located in the receiver. The only selectivity for the receiver will be
the antenna itself. The receiver is very small, and uses very little
power, so it's pretty feasible to mount the entire receiver at the
antenna and run a balanced line feed of the audio into the house.

(And just what sort of detector do
you have that represents a 2 ohm load?)

Is it better to convert the loop to a higher impedance just to feed it
into the house?

It's an analog switch input, modified by my neighbor that gave me one
of them. The switch vendor says the switch series resistance should be
around 3 ohms, but it measures around 2.5 ohms. Probably is a little
lower than expected due to the integrating capacitors (.1 uF) which
are hung on the output of each switch. The .1's go to ground.

I measured it twice, once with a 1:1:1 isolation transformer and once
with a 6:1:1 isolation transformer....The tester looses accuracy at
low impedances, so we repeated the measurement with the generator
feeding the high impedance side of the a transformer also. I got
nearly the same reading after correcting for the transformers
impedance step down value, since both readings agree pretty well with
the switch vendors ratings, it's very likely that the receiver input
impedance is around 2 ohms.

(And just what sort of detector do
you have that represents a 2 ohm load?)

Cheers,
Tom

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Hooey Boy, are you gonna get an earfull now! How dare you ask something
like that! You just evoked the wrath of flag, momma, and God! har..

J

"Fred W4JLE" wrote in message
...
May I ask, what is with the almost fanitical adherence to Q?

TRABEM wrote in message
...
On 26 Oct 2005 09:27:44 -0700, "K7ITM" wrote:

I could perhaps scan the relevant pages of the references I
mentioned...


No, I can get them att he schools library I think. thanks for the
offer.

How are you planning to couple your 2-ohm load to your loop without
doing really bad things to its Q?

Is it better to convert the loop to a higher impedance just to feed it
into the house? It appears that anything I do is going to knock the
heck out of the antennas Q though.

I have not decided whether to mount the receiver at the antenna yet,
or whether to run the twisted line directly into the house from the
antenna (since it's a short run). Most likely it will have a short run
of cat 5 cable going from the antenna to a 1 to 1 toroid transformer
located in the receiver. The only selectivity for the receiver will be
the antenna itself. The receiver is very small, and uses very little
power, so it's pretty feasible to mount the entire receiver at the
antenna and run a balanced line feed of the audio into the house.

(And just what sort of detector do
you have that represents a 2 ohm load?)

Is it better to convert the loop to a higher impedance just to feed it
into the house?

It's an analog switch input, modified by my neighbor that gave me one
of them. The switch vendor says the switch series resistance should be
around 3 ohms, but it measures around 2.5 ohms. Probably is a little
lower than expected due to the integrating capacitors (.1 uF) which
are hung on the output of each switch. The .1's go to ground.

I measured it twice, once with a 1:1:1 isolation transformer and once
with a 6:1:1 isolation transformer....The tester looses accuracy at
low impedances, so we repeated the measurement with the generator
feeding the high impedance side of the a transformer also. I got
nearly the same reading after correcting for the transformers
impedance step down value, since both readings agree pretty well with
the switch vendors ratings, it's very likely that the receiver input
impedance is around 2 ohms.

(And just what sort of detector do
you have that represents a 2 ohm load?)

Cheers,
Tom

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Thu, 27 Oct 2005 12:23:46 -0400, TRABEM wrote:
I'm not sure what the 'abysmal match to the antenna whose Q will be
buried in potter's field' statement is about. With my antenna being in
the 2 ohm impedance range, and the receiver being at 10 ohms (I'll use
your figure), how can the match be abysmal?

Even allowing for the values you offer (they are wrong) you have a 5:1
mismatch. Your actual mismatch is Q times that.

Granted, it's not anywhere
near ideal. Have you assumed I was using a parallel tuned loop?

Tom has already carried the water describing what your antenna Z looks
like. It is orders of magnitude greater by virtue of unloaded Q. You
want to aspire to make your receiver match that as closely as possible
- this design does not. What you have is a heavy, heavy load that all
but wipes out the advantage of Q.

Since power transfer is the goal, and the antenna has a lot of ability
to reject out of band signals,

Not any more.

it was my hope to use the antenna
itself as the only (purposely) tuned circuit in the system. Wouldn't
converting the antenna impedance to a more traditional 50 ohms with a
toroid, and then having a second toroid to convert it back down to 10
ohms also be destructive to the antenna Q and lossy?

2 Ohms, 10 Ohms, 50 Ohms are all still very trivial in comparison to
what the antenna has to offer. At the danger of introducing an
analogy, you have a 1.2 liter high performance race car which needs to
turn 14K RPM for 300 HP and you've put it to hauling a 40 foot fifth
wheel trailer. You are not even going to pull that load a foot before
you burn out the clutch.

Although
ideally, each switch should have it's own 1 ohm variable resistor for
absolute best results...the purpose being to swamp out the dynamic
switch series resistance differences.

You are arguing precision at the wrong end of the scale. Any
additional resistors are burning signal up and any appeal to
technicalities has been lifted from other applications that don't even
come close to this situation. I've been designing with these switches
for 25 years, and for very small signals.

Note the receiver has no rf amp, it isn't needed. The gain is provided
by some low noise op amps, and no rf stage is needed. The QRP2001
receiver is designed for 100 KHz to 30 Mhz, but it is only rated down
to 1.8 MHz. However, it's worst case sensitivity is .4uV for 10 db
sinad.

This is comparing apples and donuts when the menu only offers steak.

First, all these glowing accounts of excellent performance come from
European sources where VLF is far more common, and those services pour
up to a MW into the air. Your fillings would work just as well.
Second, your glowing reports are about HF characteristics with
conventionally sized antennas. When you attempt to extrapolate this
to VLF, you are not carrying the decimal point of inefficiency to the
left as you drop down in frequency.

Again, I think you've assumed it would be fed with a parallel loop
resonant antenna.

You haven't described anything else, and no appeal to series resonant
is going to resolve Q going down the toilet. Loss is loss no matter
what topology. This was the point of discussion with ESR.

And, no active components are needed for outstanding performance.

And yet you were the first to offer some builders have experienced
miserable results. You are about to join that pouting crew. On the
other hand, as I've suggested, you may still get WWVB with all these
problems - even wrist watches do. In that eventuality you have no
real basis of comparison and your only feeling would naturally be one
of wonder and awe. An aw shucks glow in the eyes does not translate
to a marvelous DX receiver.

Again, I think you're trying to match a 2 K parallel tuned loop to the
relatively low impedance of the receiver input. I noticed you said
'follower'. Which, I think means unity gain, but is used for impedance
matching.

Exactly.

Any active component before the audio op amp is STRONGLY
DISCOURAGED in this type of receiver. This includes back to back
diodes as the receiver switches can handle 4v p-p. It also includes
varicap tuning diodes. A front end rf amp should be avoided at all
costs, it can only degrade the performance of this type of receiver.

This only applies in the face of strong signals being applied to such
an amp. Yes, you have guaranteed that with the abysmal match and all
these Cassandra forecasts come true.

The receiver has incredible immunity to strong out of band signals,

This comes only from Q. This is a baseband receiver which means it is
open to all frequencies. Thus the necessity of a hi Q passive front
end (you killed it). What you call immunity is a product of dynamic
range capability and what circuits that follow this detector.

The nature of the beast is that the
quadrature detector cancels them out by (effectively) NOT reinforcing
them.

No, you've gotten very poor instruction on the qualities of this type
of detector. I was designing them 35 years ago and they are used in a
bajillion TVs. Absolutely every one of them has front end
electronics.

The detector neither cancels nor reinforces, it provides a phased
output. The detector also has its points of failure too, but when all
the necessary pre-conditions are met, it has many more features and
immunities. You have described none of these.

What you don't see on the schematic is the
incredible sound of the receiver audio which is clean and crisp...it's
not quantifiable by bench measurements however.

This is simply absurd. The very qualities you describe are measured
every day and are the purpose of this style of detection's use.
However, as you describe them, you still give the appearance of not
knowing what to do with the "I" and "Q" channels. Therein lies the
difference.

I would also offer, that among all your attached references, much less
your own discussion, absolutely nothing is said about the "I" and "Q"
channels. These outputs (why two?) are pushed into a black box, and
one AM signal emerges which begins to argue: what is being detected?
and where? I especially like these ace buster questions because it is
overwhelmingly obvious that no one actually knows what the "I" and "Q"
channels are for. They can be put to work without any more fuss than
amplifying them, but instead they are pushed into equations, software
and black boxes.

What is worse, I have yet to see anyone actually offer what forms of
modulation can be detected - there is a serious gap of research in all
these articles you've offered. For so many that have come here to
breathlessly announce the miracle of the Tayloe mixer, to a person,
they don't even know a fourth of what could be done.

I've put some links to web references of this technology at the end of
the message.

All very nice commercials, and one offers the nuts and bolts of the
practical detector that must have missed your attention as it
contradicts with:
"First, the RF input signal is bandpass filtered and applied to
the two parallel mixer channels."

In fact, and as I've experienced through 30+ years of their design,
there are filters all around.

Your having snubbed the antenna Q violates this first premise. Then
we look at the "I" and "Q" channels, the only way to achieve what you
describe as the marvelous characteristic of
The receiver has incredible immunity to strong out of band signals
is achieved by conventional filtering just like in the superhet. In
fact one of your references employs a nine pole Butterworth. Another
design has cascading filters out to eleven poles. This being a
baseband converter has simply shoved the filtering into the AF band.
Out of band performance only applies for those who cannot hear
dog-whistles. In short, a technological shell game. Effective,
certainly, but not unheard of - direct conversion was the original
form of receiver.

Going further, the QEX article accurately describing the Tayloe
detector describes the purpose of the capacitors in the circuit you
sent me. Problem there is that your lowered RC constants are running
out at 1µS for samples being taken at a much slower rate. Result is a
serious droop is occurring.

schematic I sent you by email.

Didn't get it. My Kill filters barely let your last schematic
through.

73's
Richard Clark, KB7QHC

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Hi Trabem

I've been trying to follow this thread because I like to play with tuned
loop antennas for broadcast band reception.
I missed the part about how much this 20 meters of #2 copper cable with
its support weighs. Your project sounds Serious. That antenna must weigh
close to 500 pounds
The loop antennas I've been building are large diameter coils of smaller
wire. I recognize that the type antenna I build arent acceptable for your
consideration. But, I do have some experience with using a low freq loop
in the city. If you are located near man made noise, it is very likely
that resonating the loop doesnt result in highest Signal/Noise ratio.
Perhaps you already have experience with Low Freq loops and can tell me
about your experiences. I am interested in learning.

Jerry



TRABEM wrote in message ...


You should have the schematic in your mailbox by the time you get this
message.

If I am to translate the annotation correctly (and it is obviously in
error - R10 and R12 are not the pair being changed), then Input Z
somewhere in your frequencies of interest (you've named several) runs
around 10 Ohms with the switch itself attenuating your signal by 6 to
10dB. This, of course, says nothing of the abysmal match to the
antenna whose Q will be buried in potter's field.

Hi Richard,

You are correct, the resistors being changed at R11 and R12, sorry for
the error. To correct the statement on the schematic, consider R11 and
R12 as being changed from 10 ohms to .2 ohms.

I'm not sure what the 'abysmal match to the antenna whose Q will be
buried in potter's field' statement is about. With my antenna being in
the 2 ohm impedance range, and the receiver being at 10 ohms (I'll use
your figure), how can the match be abysmal? Granted, it's not anywhere
near ideal. Have you assumed I was using a parallel tuned loop?

Since power transfer is the goal, and the antenna has a lot of ability
to reject out of band signals, it was my hope to use the antenna
itself as the only (purposely) tuned circuit in the system. Wouldn't
converting the antenna impedance to a more traditional 50 ohms with a
toroid, and then having a second toroid to convert it back down to 10
ohms also be destructive to the antenna Q and lossy?


I gather that the switch operates as a baseband quadrature/synchronous
detector. It looks suspiciously like it will either short the input,
or leave one half dangling, but I trust you got the schematic from a
good source. I won't bother to try to verify the logic.


The logic is good, trust me, the receiver as shown outperforms many
much more expensive ones on the market currently. It is based on the
receiver shown at:

http://www.qrp2001.freeserve.co.uk/qrp2001rf.gif

It's design has been around for awhile, the first prototype was built
in 2000. While I disagree with the use of resistive matching, it
should be ok at VLF as the signals are usually quite large there to
begin with. For a simple receiver, it is the best answer. Although
ideally, each switch should have it's own 1 ohm variable resistor for
absolute best results...the purpose being to swamp out the dynamic
switch series resistance differences.

Note the receiver has no rf amp, it isn't needed. The gain is provided
by some low noise op amps, and no rf stage is needed. The QRP2001
receiver is designed for 100 KHz to 30 Mhz, but it is only rated down
to 1.8 MHz. However, it's worst case sensitivity is .4uV for 10 db
sinad.


The roll-off frequency of the amplifier(s) is at the bottom of the AM
band, it would do better to track the oscillator frequency about one
seventh below so that AM signals are depressed below WWVB instead of
competing with it. Increase the caps from 470pF to 3300pF.


Agreed. Thanks.

The 470 pF value was chosen for a wide band spectral display from DC
to 96 KHz, which is about the best that generic PC sound cards can do
today. If the panoramic view of the surrounding spectrum wasn't
necessary, these caps would be much larger in value. As it sits
however, it's nice to have a panoramic view of the surrounding
spectrum, so the caps might not be changed.

For my purposes, they don't need to be nearly as small as they are,
but the original design was for HF...where a wiew of the surrounding
spectrum was handy.

The reason why you want low front end Input Z is to satisfy the
amplifier topology (the gain will be roughly half what it is probably
specified at). This could have been done better in half a dozen
different ways with the same active parts.

The problem here is some bozo marked the input "antenna" and removed
the necessary follower amplifier that would have been fed by the
antenna which would in turn feed this circuit through the transformer.
This sucker, as drawn, is going to be deaf, deaf, DEAF. If you hear
WWVB it will be by virtue of their strong power, not by any quality of
design here.


WRONG, but I think I understand your error. BTW, the 'bozo' was me::.

Again, I think you've assumed it would be fed with a parallel loop
resonant antenna.

And, no active components are needed for outstanding performance.

It is possible that the antenna circuit might need to be tuned with
passive components, but that possibility needs further evaluation.

To unplug this design's ears and make up for the massive goof, add a
FET follower. Load the FET drain with a 2.2 Ohm resistor and make
sure you couple the signal through a large cap feeding the
transformer. Also, bias the FET on with a hi Z divider so you don't
wipe out the Q of the antenna. I will bet that even the proposed "I"
and "Q" paths are mislabled or missapplied.


OK, this is a fair request...from someone without experience in this
type of receiver. However, in reality, an rf stage of any sort is
unnecessary.

Again, I think you're trying to match a 2 K parallel tuned loop to the
relatively low impedance of the receiver input. I noticed you said
'follower'. Which, I think means unity gain, but is used for impedance
matching.

Any active component before the audio op amp is STRONGLY
DISCOURAGED in this type of receiver. This includes back to back
diodes as the receiver switches can handle 4v p-p. It also includes
varicap tuning diodes. A front end rf amp should be avoided at all
costs, it can only degrade the performance of this type of receiver.

The receiver has incredible immunity to strong out of band signals,
much more than any superhet. The nature of the beast is that the
quadrature detector cancels them out by (effectively) NOT reinforcing
them. The desired signal is however very strongly reinforced. Since we
don't need an rf amp to get good sensitivity, any active component
before the load capacitors is strongly discouraged.

Even at 60 MHz, the performance is only slightly degraded, and that is
due to the inability of the analog switch to enable and disable fast
enough to allow reception there. There is a commercial application
using this technology that implements receive and transmit with analog
switch method and it does not have an RF amp.

Of course, there is a trade off. In order to obtain immunity from
strong adjacent out of band signals, we give up the ability to reject
harmonics. Harmonics are only attenuated 6 db....so a tuned input must
be used if the antenna cannot adequately prevent harmonics of the
receiver frequency from entering the receiver.

In theory, a minimum of 6db enhancement is available because there is
no mixer, so there is no conversion loss!

The susceptibility to harmonics is a small trade off. Remember, a
receiver of this type is wideband, needs no conventional mixers, no
detector diode, no transformers, no crystal filters, no IF amps, has
no conversion loss and no major non-linear components...thus offers
outstanding performance with the cost to build very much reduced
(relative to a superhet). What you don't see on the schematic is the
incredible sound of the receiver audio which is clean and crisp...it's
not quantifiable by bench measurements however.

I've put some links to web references of this technology at the end of
the message.

In the meantime, I'd appreciate comments regarding the issue of how
well the loop will feed the antenna input for the modified receiver
schematic I sent you by email.

Regards,

T

PS:I hope Dave is still with us. Although he probably left when he
assumed I measured the input impedance with an ohm meter:: Dave, are
you able to concede that the input impedance of the receiver might be
around 2 (or 10) ohms now?


-----------------------------------------------------------

If you want read up on this type of receiver, I can recommend the
following:


http://www.qrp2001.freeserve.co.uk/contact.htm

http://www.flex-radio.com/

Flex-Radio makes the quadrature based SDR-1000 transceiver. For a very
detailed explanation (without heavy math) of the detector theory,
check out the QEX article, part 1 at:

http://www.flex-radio.com/articles_files/SDRFMP1.pdf

And, there are independent product reviews for the SDR-1000 at:

http://www.flex-radio.com/articles_files/index.htm

Dan Tayloes NC2030 high performance signle band transceiver is
detailed at:

http://www.qslnet.de/member/df7tv/nc...es_2004_10.pdf

The complete schematics for the NC2030 are at:

http://www.norcalqrp.org/nc2030.htm

Note that the NC2030 uses the same type of detector, but does not use
a sound card and does not rely on a computer at all. It is a stand
alone transceiver.

There is also a 9Y4 who home brewed a complete transceiver, details
at:

http://9y4ar.tripod.com/tayloe_mixer.htm

Although slightly off topic, a low power ssb/cw exciter can be made
just as easily as the receiver using the same analog switch
technology. The process is simply the reverse process of the detector.
To see how simple a high quality transmitter is, try:

http://www.w1tag.com/Phasing.htm


.

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Richard Clark wrote:


This is comparing apples and donuts when the menu only offers steak.

What kinds of steak are on the menu? I haven't had lunch yet and I
could go for a nice Chateaubriand.

By the way, some kinds of donuts have apples in them. Apple fritters I
think they call them. In a way they're both apple AND donut - since you
brought it up.

ac6xg

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

OK Richard,

I like to think I'm not stupid, but reading your last message.......

That being said....

I just went through and reread every single word in this entire thread
including all the replies and I have the following questions:

-------------------------------------

I have a series resonant loop with moderately large conductor wire and
reasonably high Q capacitors. It's tuned to resonate at 60 KHz.

A series tuned circuit is a low impedance circuit, so 60 KHz signals
from the antenna are passed to the receiver and other frequency
signals are attenuated as the X(C) or X(L) on either side of the
resonance frequency attenuates them. Using Reg's rjeloop3 we get 25.4
uH for the loop inductance, and it resonates at 60 KHz with 286,700
pF. It also gives us the X(L), which is 9 ohms and (presumably) the
X(C) is -9 ohms. It estimates Q at 221. The 2 reactances are equal and
opposite, they cancel each other out. This leaving us with the
effective R(ac) for the loop inductance and the effective R(ac) of the
resonating C. The sum of these 2 resistances gives us the net
impedance of the loop. I know that the ESR of the cap is in the
milliohm range and the same for the wire, but I don't know the actual
impedance of loop. For a parallel tuned loop, Reg's program gives me a
value of 2K ohms. I don't really know what the value is for a series
tuned loop such as I will have.

Why does this make my antenna look like 2 K ohms impedance? I was
(admittedly guessing) that it looked more like 2 ohms. Maybe 2 ohms
isn't right, but can the impedance of a series tuned loop made out of
number 2 copper and low ESR caps be 2 K ohms??

-------------------------------------

My receiver measures around 2.5 ohms input impedance, verified by 2
different test methods...maybe that's not absolutely accurate. But,
you said it should have looked like 10 ohms instead. I accepted your
number however, let's say it's a 10 ohm impedance input from now on.

I believe that the antenna and receiver should be designed for maximum
power transfer which means making the antenna and the receiver front
end equal with regard to impedance. Is this correct? Is maximum power
transfer indeed my goal?

-------------------------------------

Regarding the integrating caps C value:

Yes, I understand I've lowered the effective series resistance (by
modifying the input circuit) that charges and discharges the
integrating caps. And, yes, I know different values of caps will be
needed. And, NO, I haven't addressed that issue yet. But, thank you
for pointing it out to me. I had thought these caps should be greater
than 1 uF and possibly larger. At this time, it's not a priority as
Winter is coming here and I have to get the antenna installed and
tuned. Fine tuning the receiver will come in the Winter when VHF
quiets down and the snow is 10 feet deep in the woods. For now, the
priority is making sure the antenna is all set before the snow flies.
Thank you again for reminding me that the integrating caps need to be
a different value. Since I might have to have a different input
circuit, or even an tuned circuit in the front end, I don't want to
address this issue now.

-------------------------------------

So, how do I fix it??

I'd be perfectly happy redoing the input circuit for 50 ohms input
impedance and putting some selectivity back into the front end if
that's what it takes to have the receiver function. My idea of
matching a 2 ohm impedance antenna to a 2 ohm impedance receiver
without any tuning at all (other than the loop antenna) was just that,
an 'idea'. If it doesn't work, then it doesn't work. But, on the
surface, it seems reasonable. It appears the major problem here is
that you think my antenna impedance is 2K and I think it's 2 ohms (or
less). So further discussion is a waste of time and bandwidth (until
this issue is resolved).

-------------------------------------

My primary question is about the impedance of a loop antenna made out
of 20 meters of #2 copper in series with each other using low esr caps
and tuned to resonance at 60 KHz.

-------------------------------------

schematic I sent you by email.

Didn't get it. My Kill filters barely let your last schematic
through.


Not sure what I did to deserve an honored position in your kill file.
I confess to being stubborn and cranky, but I don't think I was
disrespectful or made inappropriate comments. I won't email you
anymore schematics.

Obviously, if I had all the answers, I wouldn't need to ask here. If
you could shed some light on the series tuned antenna impedance and Q,
it would help me to make forward progress and I'd appreciate it. Where
have I gone wrong?

TNX,

T

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On 24 Oct 2005 16:57:07 -0700, "K7ITM" wrote:

I'm puzzled. My copy of rjeloop3 suggests the Q will be about 200 at
60kHz with a 9mm wire diameter, and you'll see about 2kohms when it's
resonated. Are you not taking the output across the ends of the loop
(across the capacitor)?


No, you are describing a parallel tuned loop, aren't you Tom,

That is NOT what I'm trying to build.

I am planning a series tuned loop, which is C in series with L and the
output is taken across the unused loop terminal and the unused cap
terminal.

I think it should be called a series tuned loop, shouldn't it?

I know I suggested a whole bunch of times that your 2K loop impedance
sounded like a parallel tuned loop value and you keep insisting that
my series tuned loop will have an impedance of 2K ohms.

You also told me that "Tom has already carried the water describing
what your antenna Z looks like". I suggested that perhaps Tom and you
thought I was referring to a parallel tuned loop and said several
times that it was a series tuned loop.

Then you ranted on and on or maybe I ranted........

Did Tom and you not hear me when I said it was a series tuned loop or
did I not make it plain enough.

Isn't the impedance of a series tuned circuit LOW at resonance??? It
was when I went to school.

If I've err'd, please let me know how.

Thank you.

T




PS:

And, yes......I expect the Q to be cut in half if I attach a receiver
and a loop with identical impedances to each other. I call it loaded Q
and it's a necessary evil if one doesn't want to resort to electronic
(active component) impedance matching.

Put another way, if my receiver had a 50 ohm input impedance and my
loop had a 50 ohm output impedance (with a Q of 100, unloaded), I'd
expect to have a (net) Q of 50 after the receiver was connected to the
antenna.

Reg's software tells me I have a Q of around 221. I assume that's net
Q for the loop itself (unloaded). If my receiver is made to have the
same Q as the loop, then I expect the loaded Q to be around 110 after
they are connected together.

I know you mentioned an active buffer amp to transform impedances. No
doubt this would help to keep the loaded Q up, but I'd like to avoid
any active antenna preamp/rf stage if possible......as previously
discussed.

And with a skin depth of about 0.01" at 60kHz
in copper, certainly 3" diameter soft copper pipe would have the lower
resistance. You might have some trouble finding soft copper pipe,
though. But even hard copper pipe should have a low RF resistance.
"Reference Data for Radio Engineers" (or "Reference Data for Engineers"
in newer incarnations) has lots of good info for figuring out things
like RF resistance of copper wire. I assume your welding cable doesn't
have strands that are insulated from each other like Litz wire.


I thought about litz, and it probably would have been cheaper than the
copper welding cable I bought. But it's fragile in the outdoors and
breaks easy when the wind blows it especially in long spans like I am
going to have. Rather than encase it in some sort of protected sheath,
I decided to use the welding cable.


Consider that Q is energy stored divided by energy dissipated per
radian (1/2pi of a cycle). Then the net Q will be 1/(1/Q(inductor) +
1/Q(capacitor)). So if the cap and inductor have the same Q, the net Q
will be half that. And if you put a resistive load across the
coil+cap, that will dissipate power and lower the Q further.


I think I understand that now and understood it before you explained
it. But, thank you.

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Thanks Reg,

I'm trying.

But, I wanted to make sure you know that I didn't mean any disrespect
when I commented that you should 'assume nothing'. It was short, but
not in any way to snub you.

I write this only after a comprehensive review of the entire thread.
IN the process oif that review I realized another member thought it
was a hostile comment...so it occurrent to me that you might have
thought so to.

And, in fact, it was not my intention to convey that message when I
wrote it.

If any offense was taken, please accept my apology.

I don't know if you've been following this thread or whether you have
ducked and are laying low.

I'm having a great deal of difficulty understanding how a series tuned
loop can have an impedance of 2K ohms, but Richard has reiterated this
over and over and in fact seemed to take offense when I suggested that
the loop impedance should be much lower.

So, I'm not sure who is right::

Like I said, I'm tryin'

Regards,

T