On Thu, 27 Oct 2005 20:52:45 -0400, TRABEM wrote:


That being said....

....


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

Is that to mean the loop circuit consists of an inductor (including
its radiation resistance and copper losses) of about j10 ohms and a
capacitor (including its losses) of about -j10 ohms and a load
resistance (being the 2 to 10 ohms receiver input Z) in series
(ignoring transmission line for the moment)?

You quote a Q figure and talk about expected bandwidth earlier in the
thread. Wary of making any unwarranted assumptions, is it safe to
assume that you know that it is the loaded Q that will determine the
bandwidth of the circuit in operation?

If you insert the rx input Z in series in the loop as described above,
you don't need a calculator to see that the loaded Q cannot be 200+,
and you might be lucky if it is better than 5 if the numbers you have
quoted are correct. This circuit is not likely to give you much front
end selectivity, is it?

Perhaps you need to consult a textbook to review your understanding of
unloaded Q, loaded Q, efficiency, and bandwidth, and where to apply
which Q value.

Owen
--

On Thu, 27 Oct 2005 14:55:32 -0400, "Fred W4JLE"
wrote:

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

Sure, it's a fair question.

I have a simple receiver with a low impedance input that is few with a
toroid transformer and a tuned circuit to match the impedances and to
keep out of band signals out.

I want to convert the receiver from HF to VLF (60 KHz) and to use a
series tuned loop of high Q as an antenna. In order to simplify the
receiver input, I have mentioned as an option to eliminate the 50 ohm
matching transformer and the tuned circuit in the front end of the
receiver....and to feed it directly with my low impedance loop. In
this way, the loops high Q would serve as the only means of preventing
out of band signals from getting into the receiver.

In order to make sure that actually happens, I suggested making the
loop Q as high as possible.

Hence my 'almost fanatical adherence to Q'

Not sure if it will work, but wanted to run it past the group.

Regards,

T

On Thu, 27 Oct 2005 20:52:45 -0400, TRABEM wrote:

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 resonant loop. First, this is a contradiction in terms and
as your interpretations hinge upon this reading, it bears examination.

A series tuned circuit is a low impedance circuit, so 60 KHz signals
from the antenna are passed to the receiver

To be in series, you have to describe the source and its common, you
simply describe the loop. With this, you neglect the coupling between
the actual source of power, a remote transmitter, and the antenna's
Radiation Resistance. This value appears no where in your analysis
and yet it is largely responsible for the atrocious efficiency of this
breed of antenna.

I've thrown together a quick model of your 5M on a side loop using
(and being generous) #1 wire. The bottom of the loop is 10M above
ground. In terms of performance relative to an isotropic antenna it
is down 60dB. It displays an impedance of:
Impedance = 0.05849 + J 10.37 ohms
An addition of a 0.2555µF capacitor draws this down to:
Impedance = 0.05851 + J 0.006073 ohms

Please note that the capacitor is perfect, no ESR whatever. In a
system with Zc = 0.0585, this antenna presents a 1.11 SWR. The half
power points of its resonance are only 600 Hz apart. Hence a Q of
100.

This is without any extraneous detector circuitry whatever. We will
see where its addition leads.

By simply inserting your 2 Ohms (I know full well where my 10 Ohms
will take us) - in series - (again, your thesis) and re-assigning the
system Zc to that same 2 Ohms, this antenna presents a 1.077 SWR.

Sounds hunky-dory, right? Except when you look at the Q which has
plunged to 2.9 and the antenna loss now compares to -75dB compared to
an isotropic.

Your receiver, in series with the loop, has just killed 15dB of gain
and wiped out the Q by 95%. Not bad for a day's work.

I will forgo the remainder of your questions to allow you to digest
the material above. You can validate these readings by using EZNEC
which in its free version is perfectly suitable to this question.

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

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.

This is not the kill file of unsophisticates simply ignoring by
posting name. Agent has much more flexibility to read headers and
judge what is spam. Works great and eliminates that source by - well
I cannot guess the amount simply because I don't count the kills, and
none survive the trash can except those at a lower level of sifting.

I'm getting a lot of correspondence right now helping designers out.
About half a dozen posts a day. Seems to be peak season and their
mail lands in my inbox without incident.

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.

I simply pointed out I've only receive one of your emails, and the
kill files put it in the trashcan - that is one step above absolutely
erasing it. The presumption from the several kill-rules is that your
headers appear to be spoofed. Now, tell me that you aren't doing
something out of the ordinary like passing mail through an open relay.
;-)

73's
Richard Clark, KB7QHC

Hi Owen,

Hi Owen,

I am using large copper cable and relatively low loss capacitors. I
expect the 9 ohms of inductive reactance to cancel out the -9 ohms of
capacitive reactance leaving only the sum of the AC (or RF) resistance
of the copper and the ac resistance of caps to give me my net
impedance. Am I correct up to this point??

I'm trying to take this step by step so I can understand where I've
gone wrong.....clearly I must have made an error somewhere.

I don't know what the actual ac resistance of the caps is, but I do
know the ac resistance of 20 meters of #2/0 copper welding cable is
pretty damn low.

Yes, the loop is series tuned, so the output is taken on the
unconnected capacitor terminal and the unconnected wire end.

Rjeloop3 gives estimates my Q at 221 even though it thinks I'm
building a parallel tuned loop. But, I think Q is Q, and the Q of both
types of loops is the same provided the same materials have been used
in both loops.

I am (for now) not considering the effects of hooking it to a receiver
and/or the transmission line. I confess I have not tried to quantify
the actual values of the ac resistance of the copper and have only
rough estimates of what the esr of the caps is. I'd be pretty
surprised if the dc resistance of the cable is much more than .1 ohms
though, so the ac resistance should be a little higher at 60 KHz.

Can you estimate what the unloaded Q of the loop is (in round
numbers), and if so, can you agree that it might be around 221 (as
Reg's software predicts)? Can you estimate what the impedance of the
loop is (in round numbers)? Again, do not factor in the receiver input
impedance as we aren't sure whether I'll keep it as is or match it's
impedance with a preamp and/or toroidal transformer. For the moment,
assume the receiver is mounted at the loop (which is a very real
possibility since it's fairly small).

Thanks for jumping in.

T

On Thu, 27 Oct 2005 22:38:47 -0400, TRABEM wrote:

Hi Owen,

Hi Owen,

I am using large copper cable and relatively low loss capacitors. I
expect the 9 ohms of inductive reactance to cancel out the -9 ohms of
capacitive reactance leaving only the sum of the AC (or RF) resistance
of the copper and the ac resistance of caps to give me my net
impedance. Am I correct up to this point??

I'm trying to take this step by step so I can understand where I've
gone wrong.....clearly I must have made an error somewhere.

I don't know what the actual ac resistance of the caps is, but I do
know the ac resistance of 20 meters of #2/0 copper welding cable is
pretty damn low.

Yes, the loop is series tuned, so the output is taken on the
unconnected capacitor terminal and the unconnected wire end.

Rjeloop3 gives estimates my Q at 221 even though it thinks I'm
building a parallel tuned loop. But, I think Q is Q, and the Q of both
types of loops is the same provided the same materials have been used
in both loops.


Forget Rjeloop3 for the moment and think about what you have.

You focus on how low the resistance of the loop inductance is, and
whether or not the capacitor ESR is significant... neither is when you
jam a 2 ohms receiver in series with it all (ignoring the transmission
line).

You seem to be analysing your series circuit with part of it (the rx)
replaced with a s/c.


I am (for now) not considering the effects of hooking it to a receiver
and/or the transmission line. I confess I have not tried to quantify

Well, what good is it to know what the loop L and C do when not
connected to the receiver?

the actual values of the ac resistance of the copper and have only
rough estimates of what the esr of the caps is. I'd be pretty
surprised if the dc resistance of the cable is much more than .1 ohms
though, so the ac resistance should be a little higher at 60 KHz.

Can you estimate what the unloaded Q of the loop is (in round
numbers), and if so, can you agree that it might be around 221 (as
Reg's software predicts)? Can you estimate what the impedance of the
loop is (in round numbers)? Again, do not factor in the receiver input
impedance as we aren't sure whether I'll keep it as is or match it's
impedance with a preamp and/or toroidal transformer. For the moment,
assume the receiver is mounted at the loop (which is a very real
possibility since it's fairly small).

Read Richard's response, though it is more detailed and no doubt more
accuracy.

I think you will understand the problem when you analyse a three
component series circuit (your topology), the Loop L, the Loop C and
the Rx input z. (You can ignore radiation resistance, loop loss,
capacitor loss, they are all much less than rx input z so the loops
loss is dominated by the rx input z in your circuit.)

The place this will end up is that you will come to realise that
knowing how the L and C of the loop behave unloaded, and dwelling on
that behaviour ignoring the effect of loading is probably why you are
where you are (an assumption I know).

When you have worked that out, you may understand why others are
asking how you are going to couple to the loop. Your proposal to
insert the 2 ohms (or whatever) rx input in series with the loop
components isn't delivering what you wanted, and it won't matter how
thick the loop conductor is, or how low the ESR of the capacitor is.

Owen
--

In a series resonant circuit, at resonance it is equivalent to a dead short
(disregarding the R of the circuit). Series resonant circuits are usually
used as traps. To develop a voltage one needs a parallel resonant circuit at
the resonant frequency, The Q will simply determine how quickly the voltage
falls off each side of resonance.

Next there are two types of Q, first the calculated unloaded Q and second
the in circuit or loaded Q.

I think you are heading down the wrong path with the series circuit as your
fighting a loosing battle. Assuming a perfect coil and capacitor you create
an infinite Q circuit. Now you hook it up in your circuit. First there has
to be enough resistance to develop the voltage , and here is the rub, as you
increase the resistance to develop a voltage you decrease the Q. Yuk!

Go with a parallel circuit like the rest of the world uses and you will be
going in the right direction.

TRABEM wrote in message ...
On Thu, 27 Oct 2005 14:55:32 -0400, "Fred W4JLE"
wrote:

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

Sure, it's a fair question.

I have a simple receiver with a low impedance input that is few with a
toroid transformer and a tuned circuit to match the impedances and to
keep out of band signals out.

I want to convert the receiver from HF to VLF (60 KHz) and to use a
series tuned loop of high Q as an antenna. In order to simplify the
receiver input, I have mentioned as an option to eliminate the 50 ohm
matching transformer and the tuned circuit in the front end of the
receiver....and to feed it directly with my low impedance loop. In
this way, the loops high Q would serve as the only means of preventing
out of band signals from getting into the receiver.

In order to make sure that actually happens, I suggested making the
loop Q as high as possible.

Hence my 'almost fanatical adherence to Q'

Not sure if it will work, but wanted to run it past the group.

Regards,

T

I have a series resonant loop ......

A series resonant loop. First, this is a contradiction in terms and
as your interpretations hinge upon this reading, it bears examination.


OK, now we're making progress. I knew there had to be an explanation
for your insistence that the antenna presented a 2K impedance to the
feedline! I absolutely knew it could not be correct and you were
equally determined::

Let me describe exactly what I hope to build, and you can enlighten me
regarding what the proper term is. Thanks for hanging in there, the
road was a little bumpy....

I'm thinking feedline attached to one end of the wire. The other end
of the wire is attached to the capacitor bank. The other side of the
capacitor bank is attached to the other feedline terminal. Or, stated
another way, the cap is in series with the wire and the 2 transmission
line terminals are connected to the left over cap and the unused wire
end.


A series tuned circuit is a low impedance circuit, so 60 KHz signals
from the antenna are passed to the receiver

To be in series, you have to describe the source and its common, you
simply describe the loop. With this, you neglect the coupling between
the actual source of power, a remote transmitter, and the antenna's
Radiation Resistance. This value appears no where in your analysis
and yet it is largely responsible for the atrocious efficiency of this
breed of antenna.

OK, but I hadn't thought this entered into the calculations of the
loop.....it is what it is and we all know it's too damn short and too
damn close to the ground to be efficient. At 60 Khz, there is so
little difference between 5 feet off the ground and 50 feet off the
ground, that I guess I never thought it mattered much...and, so tended
to skip over these details. Any antenna that I can build with my
budget will never be efficient:: Is this a fatal error, or do I
really need to look at this issue to proceed?

I understand these types of shortened antenna are often less than .001
percent efficient because they are so short relative to the wavelength
being transmitted or received.


I've thrown together a quick model of your 5M on a side loop using
(and being generous) #1 wire. The bottom of the loop is 10M above
ground. In terms of performance relative to an isotropic antenna it
is down 60dB. It displays an impedance of:
Impedance = 0.05849 + J 10.37 ohms
An addition of a 0.2555µF capacitor draws this down to:
Impedance = 0.05851 + J 0.006073 ohms

Please note that the capacitor is perfect, no ESR whatever. In a
system with Zc = 0.0585, this antenna presents a 1.11 SWR. The half
power points of its resonance are only 600 Hz apart. Hence a Q of
100.


OK, are you telling me my receiver would need to have an (impossibly
low) input impedance of .06 ohms to work well with the antenna I've
planned?

This is without any extraneous detector circuitry whatever. We will
see where its addition leads.

By simply inserting your 2 Ohms (I know full well where my 10 Ohms
will take us) - in series - (again, your thesis) and re-assigning the
system Zc to that same 2 Ohms, this antenna presents a 1.077 SWR.


OK, I'm not completely understanding the last paragraph. Have we
abandoned the .06 + j10 real loop impedance and/or are we talking only
about feeding a 2 ohm impedance loop into a 2 ohm impedance receiver
(which seems to be a match made in heaven at first glance)?

If we aren't considering the .06 j10 anymore, are you trying to
impress upon me that even a perfectly matched 2 ohm antenna connected
to a 2 ohm impedance receiver knocks the Hell out of the Q by that
large of a factor?? If so, I can understand the need for the buffer
follower you suggested earlier!!

Send me a sign, I sense an incoming lightening bolt::

Another user just suggested I think of Q as stored energy and that
anything that consumed that energy severely lowers the Q. I can
understand that since the goal of the impedance matching is to
transfer as much of the stored energy as possible. Further, if this is
the case, it seems an active antenna matching buffer amp (impedance
shifter) is necessary when using a loop of the type I planned. Not
sure whether I am getting it or going off on another tangent....like I
said above, send me a sign::


Sounds hunky-dory, right? Except when you look at the Q which has
plunged to 2.9 and the antenna loss now compares to -75dB compared to
an isotropic.

Your receiver, in series with the loop, has just killed 15dB of gain
and wiped out the Q by 95%. Not bad for a day's work.

I will forgo the remainder of your questions to allow you to digest
the material above.

Yes, please do forgo, for the moment anyway...... Please specify
whether you are explaining a 2 ohm impedance loop hooked to a 2 ohm
impedance front end (in the preceding paragraph). Then, we can proceed
I think..... I'm trying to assume NOTHING. Please forgive me if I seem
to need a lot of clarification.


Not sure what I did to deserve an honored position in your kill file.

This is not the kill file of unsophisticates simply ignoring by
posting name. Agent has much more flexibility to read headers and
judge what is spam.................

OK, understand. When you made the original comment, I thought you were
saying I had done something purposely inappropriate. I use Eudora in
order to avoid the Bill Gates problem, so I understand the difference
between sorting to the trash and sorting to the junk mailbox! Trash is
trash, gets emptied forever when I close the program. Junk is possibly
trash, but doesn't fit all the criteria, so it's saved (just in case
it really isn't garbage).

Got yah.


your
headers appear to be spoofed. Now, tell me that you aren't doing
something out of the ordinary like passing mail through an open relay.


Well, I'm not sure how and what happens after I hit the send button.
To the best of my knowledge, I am not doing anything of that nature.
It's (my email) a paid service, so it should be on the up and up. Is
it possible it might be a DSL issue, where the IP address is masked to
some extent?

Thanks for hangin in there.

T

I think you are heading down the wrong path with the series circuit as your
fighting a loosing battle. Assuming a perfect coil and capacitor you create
an infinite Q circuit. Now you hook it up in your circuit. First there has
to be enough resistance to develop the voltage , and here is the rub, as you
increase the resistance to develop a voltage you decrease the Q. Yuk!

Go with a parallel circuit like the rest of the world uses and you will be
going in the right direction.


I think I'm starting to get it. Am I cutting off my foot to spite my
face::

Comments made by you and a few others have nudged mein the right
direction.....

The higher I make the series resonant Q, the lower the impedance goes,
hence it's almost impossible to get a lot of voltage out of it??

Not sure why it matters that much. But, I was under the impression
that a perfectly matched antenna and front end would only decrease the
Q by a factor of 2.

Follow along with Richard's comments if you like and add your comments
as I check here often and read everything, sometimes many mant y
times::

Regards,

T

PS:I had begun thinking that the higher imedance presented by a
parallel loop was harder to match with a balun, which is why I started
thinking of a series loop. I'm gettin there, thansk again.

I've been trying to follow this thread because I like to play with tuned
loop antennas for broadcast band reception.

I'm not sure you missed that much, I'm possibly on the right track
though.

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

No, not all. It's a little heavy, but we have big tall hard wood
forest here and my main concern is not weight, it's the ice that
happens in Winter. So, lighter wire would never survive.


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.

I understand this. But, I live quite a distance from any city and the
distances to my neighbors is measured in hundreds of feet. It's quite
rural. If I suspect there is a source of noise in the house, I have
access to the high voltage (pole mounted disconnect) and can shut the
power off to my house from a switch 900 feet from the house. If the
noise persists, it isn't a local noise source::


Perhaps you already have experience with Low Freq loops and can tell me
about your experiences. I am interested in learning.


I'm still learning too......and look forward to getting the big loop
up. It's starting to look like i need to go back to the books though.
Right now, Richard is trying to get me back on track as I've
apparently led myself astray. I'm definitely still learning::


T

On Fri, 28 Oct 2005 03:00:00 GMT, Owen Duffy wrote:


I think you will understand the problem when you analyse a three
component series circuit (your topology), the Loop L, the Loop C and
the Rx input z. (You can ignore radiation resistance, loop loss,
capacitor loss, they are all much less than rx input z so the loops
loss is dominated by the rx input z in your circuit.)

So... if you did this, and you want the loop to give you front end
selectivity, and you want the bandwidth to be xxx which led you to
want the LOADED Q to be 100 or more (whatever), you now know that the
load introduced by the receiver into the series loop you have dictated
needs to be better than () XL/Qloaded or 0.1 ohms (not twenty or
more times that value).

How can you deliver a load impedance to the loop derived from the rx
input circuit and its transmission line that is efficient and less
than 100 milliohms (at the loop)?

Is your single turn series loop idea practical at 60KHz?

Owen
--