HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Hi Richard,

I feel SO MUCH better now!!!!!!!!

Just read and replied to Reg's latest comments a few minutes ago and
it seems I am on the right track-my major error was not realizing that
my series loop impedance as originally suggested was very much lower
than I thought it to be ...and I've finally realized that it COULD NOT
POSSIBLY be matched to a receiver that had 2 (or 10) ohms input Z.

Now that I've realized my originals series loop antenna had an
impedance in the milliohm region, the other explanations that you gave
made perfect sense.

At least, I feel like I made it to the first level::

I'm a little hesitant to make this suggestion, but let me ask the
question(s) at the risk of taking to large a step forward and
stumbeling::

If you would, just give me a yes or no answer to these questions so I
can make sure I don't have seriously flawed remnants of the old
thinking.....

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

With the current model of parallel loop...

If my receiver was 2K input impedance (whether tuned input or not),
could I connect it to my loop with a piece of 2000 ohm open wire line
and expect the net (or loaded) Q to be around 100 (assuming a 2K
impedance open wire line could be built and that my unloaded antenna Q
was 200 to start with).

Yes or No?

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

With the current model of parallel loop...

If I elected to use a buffer amp with megohms of input impedance,
would I preserve the unloaded Q and end up with a net Q of about 200
because I haven't loaded the loop?

Yes or No?

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

I believe my receiver is microvolt sensitive and that the loop will
deliver a relatively good signal to the receiver even though the loop
isn't terribly efficient. If I build selectivity into the front end of
the receiver, do I really need high Q (200)??

I think the answer is NO.....

Since my receiver is quite sensitive (characterized at uV before I
convert it to VLF), I think I could save a lot of money by sacrificing
some antenna Q and building modest selectivity into the front end.

Or, I could elect to use the antenna as planned (impedance matched,
but no front end tuned circuit) and instead convert the receiver to an
untuned input (allowing the antenna Q to be the sole form of tuning).

Is this reasoning basically correct or seriously flawed?

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


However, one of the fascinating characteristics of this style of
detector is that you can feed each channel to the earpieces of a
stereo headset. "I" for one, "Q" for the other earpiece. This gives
you the chance to use your wet-ware instead of someone's software and
hardware.

The brain does all the necessary fourier analysis automatically and in
real time. The upshot of it is that when listening to a CW signal,
and hearing the field of signals around it, you perceive those signals
in a mind-space.

OK, I am an avid cw operator, often operating as a hired gun at m/m HF
contest efforts. So, I completely understand the concept of having the
brain do the processing. The brain is a very seriously viable filter
that is adaptive with regard to the audio spectrum sent to it by a
conventional receiver.

I haven't tried actual binaural operation, but have heard others talk
about it. The users claim it is a different world from the very first
second of listening to it and are constantly amazed at the effect and
improvement.

I have a friend who isn't quite local...but we chat from time to time
although we don't see each other that often. He has a high frequency
hearing loss in one ear and has a great deal of difficulty with cw. He
built a binaural project from a QST article and was stunned to hear
the results. He was sold ont he idea in short order!

But I never though much about hooking up a stereo headphone to the i/q
audio streams.

The difference is that your binaural perception with its phase
separation capability could be brought to bear to ignore the field of
noise to concentrate on your partner. When you hear the mono
recording, the phase information is lost and your partner's
conversation merges with the background noise.


OK, I am with you with respect to the brain filtering out unwanted
conversations to let you focus on your conversational partners distant
voice. But, I thought traditional binaural receiver meant that the
frequencies higher than a certain point went to one ear and that the
all the frequencies lower than the same frequency went to the other
ear. In this manner the listener has a feeling of 'depth' or
'richness' that isn't present in a mono setup.

This is interesting though.

But, I never thought that the brain could process the I and Q to
provide opposite (unwanted) sideband rejection...which is why I
thought the primary function of the I/Q precessing was about (whether
it be hardware or software based).

Are you suggesting that the brain can also process the I/Q output
streams and provide opposite sideband rejection as well as selective
frequency and adaptive filtering?

I have also
played with bucket-brigade delay lines to create this effect. At one
time Paul McCartney was using it with his music. Aural phase
relationships have a strong psychological information content that is
taken for granted.


I'll investigate this over the Winter season, which is long and hard
here. Thanks for planting a bug in my ear (no pun intended) about
this. I probably would not have thought of it otherwise.

Regards,

T

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

Trabem,

Without wishing to detract you in any way from your objective of a
matched series tuned loop I would like to describe how I would do a
similar job with the usual parallel tuned, multiturn loop.

I do not understand the type of receiver you propose and I am not
seriously interested. But I should say the theoretical working
bandwidth of my proposal is about 1/2 of yours.

Actual bandwidth of both your and my proposals is indeterminate
because of the uncertainty of ground proximity and nearby
environmental loss. The working bandwidths could be very similar.

Using similar size loop dimensions to yours, ie., 5.3 metres square -
Frequency = 60 Khz.
5 turns of close wound 2mm diameter enamelled wire.
Inductance = 710 micro-henrys.
Tuning capacitor = 0.01 uF approx.
Reactance of L and C = 268 ohms.
Conductor resistance loss = 2.5 ohms.
Intrinsic coil Q = 107
Matched working Q =53
3dB working bandwidth = 1.12 KHz.

Impedance match to 50-ohm receiver obtained via small coupling loop,
in the same plane, about 1 metre square. Working Q = 53 or less
depending on height above ground.

The working Q may not be high enough for your particular application.
I describe the antenna for you to see what is possible in comparison
with your series-tuned proposals.
----
Reg, G4FGQ.

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

By the way, I consider the most sensible and understandable
contributions to this thread have been the questions asked by the
originator, Trabem.


I think that's a high compliment, considering how totally messed up I
was at the start of this.

I am now half-way down a bottle of South African red plonk. It's
supposed to be good for the arteries.

If a little is good, is more better?

And a very BIG + THANKS from me. Thanks for hangin' in there.

Regards,

T

PS:Read your previous example, which closely parallels some existing
real life loops I found on the Internet last evening. Thanks for the
example as well and I think it's time to start soldering.

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Fri, 28 Oct 2005 09:02:14 -0700, Richard Clark
wrote:



That is the point of my questions. They are veiled implications, not
tests of knowledge. No one in your list of links, much less those
I've read over the years knows the PRACTICAL implication of the "I"
and "Q" channels. So, I may as well drop the other shoe.


Didn't Don Stoner describe a synchronous detector way back. I think I
remember reading an article in the mid sixties in "The Sideband
Handbook" or similar.

I was about 15 then, so a detector that had something like 17 bottles
in it seemed overkill when I was copying CW and SSB on an AM receiver
(ie diode detector) with BFO.

The appeal being an all-mode detector (including DSBSC), but
synchrounous detectors didn't seem to catch on in comms receivers,
well not until DSP detection... well I don't recall coming across them
anyway.

Owen
--

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Fri, 28 Oct 2005 14:19:14 -0400, TRABEM wrote:
With the current model of parallel loop...

If my receiver was 2K input impedance (whether tuned input or not),
could I connect it to my loop with a piece of 2000 ohm open wire line
and expect the net (or loaded) Q to be around 100 (assuming a 2K
impedance open wire line could be built and that my unloaded antenna Q
was 200 to start with).

Yes or No?

You have too many suppositions to give a straight answer. First,
there is no such thing as a 2000 Ohm open wire line. As for the gist
of the question:
Yes.

With the current model of parallel loop...

If I elected to use a buffer amp with megohms of input impedance,
would I preserve the unloaded Q and end up with a net Q of about 200
because I haven't loaded the loop?

Yes or No?

Yes.

However, as Tom has pointed out separately, this may not be the
optimal solution.

I believe my receiver is microvolt sensitive and that the loop will
deliver a relatively good signal to the receiver even though the loop
isn't terribly efficient. If I build selectivity into the front end of
the receiver, do I really need high Q (200)??

I think the answer is NO.....

Well, this is a good opportunity to examine that tumble down the slope
to the Q = 2 (caused by the severe loading of your proposed design).

The correlative to this is, how much selectivity do you need in a
field where stateside VLF is relatively rare? Further, by the action
of the strong filtering that usual attends the "I" and "Q" channel
processing, you could easily repair any shortfall.

However, back to that Q = 2. That still offers respectable (not
fantastic) selectivity against signals out at the bottom of the AM
band which is 10f (one decade) away.

OK, I am with you with respect to the brain filtering out unwanted
conversations to let you focus on your conversational partners distant
voice. But, I thought traditional binaural receiver meant that the
frequencies higher than a certain point went to one ear and that the
all the frequencies lower than the same frequency went to the other
ear. In this manner the listener has a feeling of 'depth' or
'richness' that isn't present in a mono setup.

Binaural is what the fellows in white coats mean by listening with two
ears.

This is interesting though.

And rarely reported for this style of detection. What a pity.

Are you suggesting that the brain can also process the I/Q output
streams and provide opposite sideband rejection as well as selective
frequency and adaptive filtering?

The rejection is psychological, not actual. It is what I meant by
"mind-space." The vectors do not add up to zero, the mind simply
ignores the off-band content like you would at a party listening to
that cute office temp's whispers when your wife is yelling across the
room at you.

Listen to a recording of that same scenario in mono and you WILL hear
your wife!

The brain reassembles all delay/phase information content at the party
to sort out what to pay attention to. When that same information is
passed through a monaural channel, the phase information is lost and
everything competes equally lousy given the S/N ratio.

73's
Richard Clark, KB7QHC

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On 28 Oct 2005 09:44:00 -0700, "K7ITM" wrote:



OK, maybe you're beginning to understand. Q can be calculated as
reactance (at resonance) divided by the effective series resistance, or
as effective parallel resistance divided by reactance at resonance.
For a loop where you know the series resistance, it's easiest to use
that first relationship. If you put your 10 ohm receiver input in
series with your 10 ohm reactance loop, you've ruined all that effort
to get to a very low loop conductor resistance and obviated the need
for high-Q capacitors. And we're all having a very hard time seeing
how you will couple your 10-ohm receiver input to EITHER the
parallel-tuned loop OR the series tuned loop, without having nasty
consequences for your holy-grail Q.


It appears to me that a 10 ohm receiver input impedance is dead center
with regard to any loop configuration I could come up with...it
doesn't work with anything! It's easy to see now::

You might think it's best to impedance match ("conjugate match") to
your load, so you transfer the most power to the load. However, that
may not be optimum from a system design standpoint. If you already
have enough signal (along with atmospheric noise) that the receiver
doesn't contribute significantly to the overall SNR, then you may be
better off by intentionally mismatching so that the Q remains high, if
that's important to you. (I personally think you've overrated it, but
that's up to you to decide.) But even if you're wanting to get the
lowest noise contribution from your electronics, the appropriate match
is generally not the conjugate impedance match that results in highest
power transfer. For example, an MMBT2222 NPN transistor running at
about 100uA collector current in a common-emitter configuration with no
feedback will have a low-frequency (e.g. 60kHz) input resistance around
50kohms, but the optimal source resistance from a noise standpoint--the
source resistance which will yield the lowest noise figure for the
amplifier--will be about 2kohms. At optimal source resistance, you can
get a noise figure well below 1dB from an MMBT2222--and from many other
bipolars.


Is the MMBT2222 the same as a 2N2222, which I already have in my junk
box? Also have 3904's, maybe they are just as suitable?

Should I tune the output, or rely on a modest input tuned filter in
the front end and just do a no tune in and out common emitter?

Assuming a 50 ohm receiver input impedance, is it ok to take the
output across a 50 ohm emitter resistor?


One reason that people like to use FET amplifiers across their
"parallel-tuned" loops is that the amplifier input resistance is quite
high, but (using appropriate FETs) the noise contribution of the
amplifier is negligible. And with proper design, the distortion
contribution can be considerably lower than the distortion of your
detector. For high source impedances, JFETs can give noise figures
that are a small fraction of a dB.


JFET's sound good too.

Richard, which type of buffer amp has a lower distortion and better
linearity in the presence of (potentially) large out of band signals?
If I do use a buffer to preserve the Q, it has to be 'clean' in order
to preserve the performance of the QSD receiver. Appreciate any
enlightenment along these lines.

I'm not opposed to using an op amp IF it provides cleaner output
signals and if the power consumption is manageable.

I must say it seems much cheaper (and probably more practical) to use
a buffer to preserve the existing Q than it is to build higher Q into
the loop...only to have it cut in half by the addition of a receiver
front end.

Regards,

T

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Fri, 28 Oct 2005 20:12:48 GMT, Owen Duffy wrote:

Didn't Don Stoner describe a synchronous detector way back. I think I
remember reading an article in the mid sixties in "The Sideband
Handbook" or similar.

I was about 15 then, so a detector that had something like 17 bottles
in it seemed overkill when I was copying CW and SSB on an AM receiver
(ie diode detector) with BFO.

The appeal being an all-mode detector (including DSBSC), but
synchrounous detectors didn't seem to catch on in comms receivers,
well not until DSP detection... well I don't recall coming across them
anyway.

Hi Owen,

17 bottles indeed. That seems to strike a resonant chord in the
ganglia because my construction was on a utility box of about 3" x 9"
x 15" (not counting power supply requirements). We were working from
a printed article certainly; and to confirm your recollection, there
was a list of modes that could be detected that was long.

My perception of the resurgence of interest in synchronous detection
(it seems to have many names) is that a considerable body of knowledge
evaporated in the 70s and 80s to leave only fragments of what this
detector was useful at.

73's
Richard Clark, KB7QHC

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Fri, 28 Oct 2005 13:35:19 -0700, Richard Clark
wrote:

The rejection is psychological, not actual. It is what I meant by
"mind-space." The vectors do not add up to zero, the mind simply
ignores the off-band content like you would at a party listening to
that cute office temp's whispers when your wife is yelling across the
room at you.

Listen to a recording of that same scenario in mono and you WILL hear
your wife!


I understand the Bell Labs explored this effect (which they referred
to as the "cocktail party effect") when exploring the nature of
conversation for the purposes of novel approaches to telephony
multiplexing.

I don't think they developed a technology solution to exploit the
cocktail party effect, but they did incorporate their knowledge of the
statistical / syllabic / sentence characteristics in their Time
Assignment Speech Interpolation (TASI) equipments, and TASI was quite
successful.

I think the term we would use for the cocktail party effect on a phone
channel is "a crossed line", and you may be right in that the loss of
spatial information because of the mono channel may have been the
reason it didn't work.
--

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

On Fri, 28 Oct 2005 21:10:04 GMT, Owen Duffy wrote:

I don't think they developed a technology solution to exploit the
cocktail party effect, but they did incorporate their knowledge of the
statistical / syllabic / sentence characteristics in their Time
Assignment Speech Interpolation (TASI) equipments, and TASI was quite
successful.

Hi Owen,

This mimics Paul McCartney's use of phase mixing in his music in the
late 70s. Earlier, I was using Reticon bucket-brigade chips to
develop a frequency independent delay line such that I could mix input
and output (much like the FIR/IIR topology of today's DSP technology,
except I was doing it in analog rather than digital) to obtain a
variable phase. I still have the breadbox sitting on the shelf. I
was anticipating using this device to place "voices" in the
stereo-space of program content that I was mixing for. The concept
was much too cerebral for the producer who simply wanted matched
levels.

73's
Richard Clark, KB7QHC

HIGH Q CAPS FOR VLF LOOP ANTENNA?
 

I believe my receiver is microvolt sensitive and that the loop will
deliver a relatively good signal to the receiver even though the loop
isn't terribly efficient. If I build selectivity into the front end of
the receiver, do I really need high Q (200)??

I think the answer is NO.....

Well, this is a good opportunity to examine that tumble down the slope
to the Q = 2 (caused by the severe loading of your proposed design).

The correlative to this is, how much selectivity do you need in a
field where stateside VLF is relatively rare? Further, by the action
of the strong filtering that usual attends the "I" and "Q" channel
processing, you could easily repair any shortfall.

However, back to that Q = 2. That still offers respectable (not
fantastic) selectivity against signals out at the bottom of the AM
band which is 10f (one decade) away.



OK, I'm not sure how we got back to the Q=2 scenario. I think my
proposed design is the old series tuned loop, which I have firmly
rejected.

With no tuning in the front end, the Q of the receiver would approach
1.......Yes, I understand that.

I understand the answer you gave initially, which was 'I think the
answer is NO....'.

I understand the degree of protection against signals in the bottom of
the bc band.

When you said "Well, this is a good opportunity to examine
that tumble down the slope to the Q = 2 (caused by the severe
loading of your proposed design)"...................did you mean
to say or to infer '(caused by the severe loading of your old (now
defunct) series resonant loop design"???

All is in agreement above EXCEPT in not sure why the reference to the
old design.

Thanks again.

T