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Old November 21st 07, 05:09 PM posted to rec.radio.amateur.antenna
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Default Low Noise receiving Loop antenna

Owen Duffy wrote:

Tony Giacometti wrote in
news:bMednQ1HY8JTVN7anZ2dnUVZ_gGdnZ2d@hawaiiantel. net:
...
sorry, I'm not trying to be an ass here but the diagram I have shows 3
connections to the cap. 2 for the loop and one for the center
conductor of the feedline.

Is my diagram whats confusing the issue?


Here is a diagram of what I suggested:
http://www.vk1od.net/SmallTunedSquareLoop/index.2.gif .

The variable capacitor needs to be 0-400pF. The fixed capacitor should be
at least 1000pF.

If you couldn't arrive at this circuit from the word description, and you
aren't being silly, then it questions whether your intial construction
was based on misinterpretation of the original article.

Here is an even better idea:
http://www.vk1od.net/SmallTunedSquareLoop/index.3.gif .

There is only one change here, the inner conductor is bonded to the outer
conductor at the left hand side of the shield gap. Ask yourself why that
improves things... some will suggest it just halved the loop size, but it
hasn't.



Owen


I understand now, seeing your drawing clears it up for me.
No, I wasn't being difficult or silly, I kept thinking of how I have the
unit wired and I couldn't picture in my mind (senior moment?) the changes.
Anyway now I see what you are asking me to try and I will give this a try.
Hopefully tonite after work.

I will let you know the results. Thank You.
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Old November 21st 07, 08:10 PM posted to rec.radio.amateur.antenna
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Posts: 1,169
Default Low Noise receiving Loop antenna

Tony Giacometti wrote in
news:geadnZCVBcuhxdnanZ2dnUVZ_ojinZ2d@hawaiiantel. net:

Owen Duffy wrote:

Tony Giacometti wrote in
news:bMednQ1HY8JTVN7anZ2dnUVZ_gGdnZ2d@hawaiiantel. net:
...
sorry, I'm not trying to be an ass here but the diagram I have shows
3 connections to the cap. 2 for the loop and one for the center
conductor of the feedline.

Is my diagram whats confusing the issue?


Here is a diagram of what I suggested:
http://www.vk1od.net/SmallTunedSquareLoop/index.2.gif .

The variable capacitor needs to be 0-400pF. The fixed capacitor
should be at least 1000pF.

If you couldn't arrive at this circuit from the word description, and
you aren't being silly, then it questions whether your intial
construction was based on misinterpretation of the original article.

Here is an even better idea:
http://www.vk1od.net/SmallTunedSquareLoop/index.3.gif .

There is only one change here, the inner conductor is bonded to the
outer conductor at the left hand side of the shield gap. Ask yourself
why that improves things... some will suggest it just halved the loop
size, but it hasn't.



Owen


I understand now, seeing your drawing clears it up for me.
No, I wasn't being difficult or silly, I kept thinking of how I have
the unit wired and I couldn't picture in my mind (senior moment?) the
changes. Anyway now I see what you are asking me to try and I will
give this a try. Hopefully tonite after work.

I will let you know the results. Thank You.


Tony,

Keep in mind this scheme improves the impedance match (ie reduces the
mismatch "losses", but it doesn't approach an MPT match unless the fixed
capacitor is very large, and in that case bandwidth would probably be too
narrow for your use. The trick is to improve the system gain enough to be
usable without making the system unusable because it is too narrow. The
suggested fixed capacitor of 1000pF should win you enough system gain, if
it doesn't try larger values (eg 4,700pF).

I will be offline for a few days, I look forward to hearing of the
outcome.

Owen
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Old November 22nd 07, 03:01 AM posted to rec.radio.amateur.antenna
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Posts: 757
Default Low Noise receiving Loop antenna

On Nov 21, 1:10 pm, Owen Duffy wrote:


I understand now, seeing your drawing clears it up for me.
No, I wasn't being difficult or silly, I kept thinking of how I have
the unit wired and I couldn't picture in my mind (senior moment?) the
changes. Anyway now I see what you are asking me to try and I will
give this a try. Hopefully tonite after work.


I will let you know the results. Thank You.


Tony,

Keep in mind this scheme improves the impedance match (ie reduces the
mismatch "losses", but it doesn't approach an MPT match unless the fixed
capacitor is very large, and in that case bandwidth would probably be too
narrow for your use. The trick is to improve the system gain enough to be
usable without making the system unusable because it is too narrow. The
suggested fixed capacitor of 1000pF should win you enough system gain, if
it doesn't try larger values (eg 4,700pF).

I will be offline for a few days, I look forward to hearing of the
outcome.

Owen


I guess it's worth a shot if the level is really that low.
But something seems strange that he would have that
problem. Using even my small 16 inch loop, fed using
the usual cap in parallel method, I have more signal level
than I actually need, even at the upper end of its range.
In general if the background noise level peaks, and there
is a definite difference between the antenna connected,
and unconnected, seems that should be enough
signal level.
On the recordings I made, I was comparing the 16 inch
loop vs full size wire antennas, and the drop in level
is really not that drastic.
IE: the stations still sound "loud" vs the large
wire antennas, and I have pretty decent S meter levels
on the loops.
I'm tuned to 740 kc AM-BC on my big loop right now and
the S meter is reading 40 over 9, and the radio preamp
is off.
I didn't really notice any level problems on the shielded
loops I've tried. But I'm starting to wonder if maybe
he might get a higher level just from using a regular
solenoid loop. It's also possible the radio could
use a tweak.. Which is easy to do on the drake
receivers. All the trimmers are on top of the chassis.
Don't even need any fancy gear. He can tune for the
middle of each band appx, and use the xtal calibrator
as the signal to tweak all the trimmers per each band.
Of course, you would peak each trimmer for max S
meter reading.
On the drakes, he should show a pretty healthy S
meter reading on the calibrator signal if it's working
right.
MK
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Old November 22nd 07, 07:43 PM posted to rec.radio.amateur.antenna
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Posts: 50
Default Low Noise receiving Loop antenna

wrote:

On Nov 21, 1:10 pm, Owen Duffy wrote:


I understand now, seeing your drawing clears it up for me.
No, I wasn't being difficult or silly, I kept thinking of how I have
the unit wired and I couldn't picture in my mind (senior moment?) the
changes. Anyway now I see what you are asking me to try and I will
give this a try. Hopefully tonite after work.


I will let you know the results. Thank You.


Tony,

Keep in mind this scheme improves the impedance match (ie reduces the
mismatch "losses", but it doesn't approach an MPT match unless the fixed
capacitor is very large, and in that case bandwidth would probably be too
narrow for your use. The trick is to improve the system gain enough to be
usable without making the system unusable because it is too narrow. The
suggested fixed capacitor of 1000pF should win you enough system gain, if
it doesn't try larger values (eg 4,700pF).

I will be offline for a few days, I look forward to hearing of the
outcome.

Owen


I guess it's worth a shot if the level is really that low.
But something seems strange that he would have that
problem. Using even my small 16 inch loop, fed using
the usual cap in parallel method, I have more signal level
than I actually need, even at the upper end of its range.
In general if the background noise level peaks, and there
is a definite difference between the antenna connected,
and unconnected, seems that should be enough
signal level.
On the recordings I made, I was comparing the 16 inch
loop vs full size wire antennas, and the drop in level
is really not that drastic.
IE: the stations still sound "loud" vs the large
wire antennas, and I have pretty decent S meter levels
on the loops.
I'm tuned to 740 kc AM-BC on my big loop right now and
the S meter is reading 40 over 9, and the radio preamp
is off.
I didn't really notice any level problems on the shielded
loops I've tried. But I'm starting to wonder if maybe
he might get a higher level just from using a regular
solenoid loop.


What is a solenoid loop?


It's also possible the radio could
use a tweak.. Which is easy to do on the drake
receivers. All the trimmers are on top of the chassis.
Don't even need any fancy gear. He can tune for the
middle of each band appx, and use the xtal calibrator
as the signal to tweak all the trimmers per each band.
Of course, you would peak each trimmer for max S
meter reading.
On the drakes, he should show a pretty healthy S
meter reading on the calibrator signal if it's working
right.
MK



I get 25 over 9 with the calibrator, but I will recheck
some things and make sure everything is ok.
  #75   Report Post  
Old November 22nd 07, 08:37 PM posted to rec.radio.amateur.antenna
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Posts: 50
Default Low Noise receiving Loop antenna

Owen Duffy wrote:

Tony Giacometti wrote in
news:geadnZCVBcuhxdnanZ2dnUVZ_ojinZ2d@hawaiiantel. net:

Owen Duffy wrote:

Tony Giacometti wrote in
news:bMednQ1HY8JTVN7anZ2dnUVZ_gGdnZ2d@hawaiiantel. net:
...
sorry, I'm not trying to be an ass here but the diagram I have shows
3 connections to the cap. 2 for the loop and one for the center
conductor of the feedline.

Is my diagram whats confusing the issue?


Here is a diagram of what I suggested:
http://www.vk1od.net/SmallTunedSquareLoop/index.2.gif .

The variable capacitor needs to be 0-400pF. The fixed capacitor
should be at least 1000pF.

If you couldn't arrive at this circuit from the word description, and
you aren't being silly, then it questions whether your intial
construction was based on misinterpretation of the original article.

Here is an even better idea:
http://www.vk1od.net/SmallTunedSquareLoop/index.3.gif .

There is only one change here, the inner conductor is bonded to the
outer conductor at the left hand side of the shield gap. Ask yourself
why that improves things... some will suggest it just halved the loop
size, but it hasn't.



Owen


I understand now, seeing your drawing clears it up for me.
No, I wasn't being difficult or silly, I kept thinking of how I have
the unit wired and I couldn't picture in my mind (senior moment?) the
changes. Anyway now I see what you are asking me to try and I will
give this a try. Hopefully tonite after work.

I will let you know the results. Thank You.


Tony,

Keep in mind this scheme improves the impedance match (ie reduces the
mismatch "losses", but it doesn't approach an MPT match unless the fixed
capacitor is very large, and in that case bandwidth would probably be too
narrow for your use. The trick is to improve the system gain enough to be
usable without making the system unusable because it is too narrow. The
suggested fixed capacitor of 1000pF should win you enough system gain, if
it doesn't try larger values (eg 4,700pF).

I will be offline for a few days, I look forward to hearing of the
outcome.

Owen



I tried both configurations, both raised the noise level which I am thinking
must be related to the gain you said I would get, I didn't need the preamp
at all. I didn't get the nulls like I get from the original loop - that was
a mild surprise - there was only a 2-3 S unit difference between noise peak
and noise null, The original loop normally has S1-2 99% of the time when
nulled. The current loop has a difference between noise peak and noise null
of 7-9 S units. Now don't misunderstand me, but I like the low noise level.
What concerns me with the other 2 configurations is the gain makes the
noise increase so much that I am not so sure I would be able to hear the
weaker ones.

I think this project as simple as I thought it would be ...... just isn't.
What I would like to accomplish with this loop idea is to have the low noise
and the ability to null out the noise from my neighbors houses. But at the
same time have enough gain to be able to hear the weak signals. Now I don't
have preference for using the preamp or not. Whatever works is what I want
to go with.

Maybe changing the type of loop to a different style of loop would be the
way to achive what I would like to obtain.

Obviously, there is a miriad of designs and configurations. Since I need the
loop only for 75 meters and have a limited amount of real estate this cuts
the pile down to a lesser amount.

What to do...................well, maybe I should start over - why not try
a different type/style of loop. A larger loop might be better for gain but
how big before its not able to null out noise cause I can't rotate it due
to its size?
Does the loop have to be coax? can it be some other type of wire?

Your input is much appreciated.







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Old November 24th 07, 06:45 AM posted to rec.radio.amateur.antenna
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Posts: 1,169
Default Low Noise receiving Loop antenna

Tony Giacometti wrote in
:

Owen Duffy wrote:

....
I will be offline for a few days, I look forward to hearing of the
outcome.

Owen



I tried both configurations, both raised the noise level which I am
thinking must be related to the gain you said I would get, I didn't


I take it that 'raise the noise level' actually means you got more noise
out of the receiver / higher S meter reading on band noise.

need the preamp at all. I didn't get the nulls like I get from the
original loop - that was a mild surprise - there was only a 2-3 S unit


Neither the preamp, nor the tuning changes you made should change the
directivity (ie the pattern, the depth of the nulls) of the antenna.

difference between noise peak and noise null, The original loop
normally has S1-2 99% of the time when nulled. The current loop has a
difference between noise peak and noise null of 7-9 S units. Now don't


I have already told you those measurements don't mean anything to me.

misunderstand me, but I like the low noise level. What concerns me
with the other 2 configurations is the gain makes the noise increase
so much that I am not so sure I would be able to hear the weaker ones.


If you want to improve the depth of the nulls, you have to concentrate on
the balance of the antenna, the symmetry of the loop, its feedline, its
environment etc. I think Roy might have said that earlier.



I think this project as simple as I thought it would be ...... just
isn't. What I would like to accomplish with this loop idea is to have
the low noise and the ability to null out the noise from my neighbors
houses. But at the same time have enough gain to be able to hear the
weak signals. Now I don't have preference for using the preamp or not.
Whatever works is what I want to go with.


It is fairly simple, you might have needed to learn a bit, but you
probably also had to unlearn some stuff.


Maybe changing the type of loop to a different style of loop would be
the way to achive what I would like to obtain.


You have already been told there is no such thing as a low noise antenna.
The loop has the advantage of being able to null out signals from two
opposite directions, which can help if the interference is predominantly
from one (or both) of those directions. You can improve the depth of
those nulls, but pattern or directivity is unrelated to the power
transfer problem.


Obviously, there is a miriad of designs and configurations. Since I
need the loop only for 75 meters and have a limited amount of real
estate this cuts the pile down to a lesser amount.

What to do...................well, maybe I should start over - why not
try a different type/style of loop. A larger loop might be better for
gain but how big before its not able to null out noise cause I can't
rotate it due to its size?
Does the loop have to be coax? can it be some other type of wire?


Remember that symmetry is key to the depth of the null. If it is harder
to build a larger loop with equally good symmetry (including to the
environment), you have more gain, but poorer nulls... and your main
reason for selecting the loop is for rejection of interference using the
nulls. You need adequate gain, and the best balance rather than the other
way round.

Your input is much appreciated.


Thanks

73
Owen
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Old November 25th 07, 07:46 AM posted to rec.radio.amateur.antenna
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Posts: 50
Default Low Noise receiving Loop antenna

Owen Duffy wrote:

Tony Giacometti wrote in
:

Owen Duffy wrote:

...
I will be offline for a few days, I look forward to hearing of the
outcome.

Owen



I tried both configurations, both raised the noise level which I am
thinking must be related to the gain you said I would get, I didn't


I take it that 'raise the noise level' actually means you got more noise
out of the receiver / higher S meter reading on band noise.



yes!



need the preamp at all. I didn't get the nulls like I get from the
original loop - that was a mild surprise - there was only a 2-3 S unit


Neither the preamp, nor the tuning changes you made should change the
directivity (ie the pattern, the depth of the nulls) of the antenna.



I didn't use the preamp for these tests, but the noise level did change and
yes, the nulls were not that deep.

As I wrote this was a mild surprise and I did recheck all connections and
redid the test with the same result.



difference between noise peak and noise null, The original loop
normally has S1-2 99% of the time when nulled. The current loop has a
difference between noise peak and noise null of 7-9 S units. Now don't


I have already told you those measurements don't mean anything to me.

misunderstand me, but I like the low noise level. What concerns me
with the other 2 configurations is the gain makes the noise increase
so much that I am not so sure I would be able to hear the weaker ones.


If you want to improve the depth of the nulls, you have to concentrate on
the balance of the antenna, the symmetry of the loop, its feedline, its
environment etc. I think Roy might have said that earlier.


yes he did, and I am not sure why the depth of the nulls changed.


I think this project as simple as I thought it would be ...... just
isn't. What I would like to accomplish with this loop idea is to have
the low noise and the ability to null out the noise from my neighbors
houses. But at the same time have enough gain to be able to hear the
weak signals. Now I don't have preference for using the preamp or not.
Whatever works is what I want to go with.


It is fairly simple, you might have needed to learn a bit, but you
probably also had to unlearn some stuff.


true, I had to unlearn some things that most likely floated around for
years.



Maybe changing the type of loop to a different style of loop would be
the way to achive what I would like to obtain.


You have already been told there is no such thing as a low noise antenna.
The loop has the advantage of being able to null out signals from two
opposite directions, which can help if the interference is predominantly
from one (or both) of those directions. You can improve the depth of
those nulls, but pattern or directivity is unrelated to the power
transfer problem.


did I misunderstand you, I thought the noise was nullable but at 75 meters
the signals were mostly omnidirectional? Or is this one of the unlearned
things?



Obviously, there is a miriad of designs and configurations. Since I
need the loop only for 75 meters and have a limited amount of real
estate this cuts the pile down to a lesser amount.

What to do...................well, maybe I should start over - why not
try a different type/style of loop. A larger loop might be better for
gain but how big before its not able to null out noise cause I can't
rotate it due to its size?
Does the loop have to be coax? can it be some other type of wire?


Remember that symmetry is key to the depth of the null. If it is harder
to build a larger loop with equally good symmetry (including to the
environment), you have more gain, but poorer nulls... and your main
reason for selecting the loop is for rejection of interference using the
nulls. You need adequate gain, and the best balance rather than the other
way round.

Your input is much appreciated.


Thanks

73
Owen



Ok, I want to build a larger loop to get more gain, if possible deep nulls
for reducing local noise, I would like to try wire instead of coax. I want
to mount it on a PVC pipe frame. Can you give me any ideas as to what shape
and size? Whats a solenoid loop?

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Old November 25th 07, 08:30 AM posted to rec.radio.amateur.antenna
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Posts: 1,169
Default Low Noise receiving Loop antenna

Tony Giacometti wrote in
:

Owen Duffy wrote:

....
You have already been told there is no such thing as a low noise
antenna. The loop has the advantage of being able to null out signals
from two opposite directions, which can help if the interference is
predominantly from one (or both) of those directions. You can improve
the depth of those nulls, but pattern or directivity is unrelated to
the power transfer problem.


did I misunderstand you, I thought the noise was nullable but at 75
meters the signals were mostly omnidirectional? Or is this one of the
unlearned things?


Keep in mind that noise from very close sources can be much stronger than
the aggregated noise from more distant source. If you live in a street
where everyone has the same noisy plasma TV, the noise from your own one
is likely to be much stronger than the aggregate of the others... think
through the propagation mechanism and especially the effects where the
source is in the near field (say within a quarter wave of your antenna).

You can't do much to null the noise from a hundred TVs spread around the
neighborhood, but you can null the noise from a close by dominant source
like your own, or immediate neighbor's. Of course, in nulling the noise
in that direction you also null signals from the same direction.
Fortunately, lots of signals come via an ionospheric path (a higher
angle), and the null of the loop is normally oriented horizontally so it
doesn't knock the ionospheric signals down as much.

If you try something beside a shielded loop, make sure you use an
effective means of isolating the feed line from the loop so that pickup
on the feedline does not feed the receiver.

Perhaps by solenoid loop you mean a multi turn loop. A multiturn loop is
another way of increasing induced voltage, but it increases the source
impedance and you have to solve the impedance matching issue.

....
Ok, I want to build a larger loop to get more gain, if possible deep
nulls for reducing local noise, I would like to try wire instead of
coax. I want to mount it on a PVC pipe frame. Can you give me any
ideas as to what shape and size? Whats a solenoid loop?



You started of with a loop that was too insensitive, so you have improved
that with better matching solving that problem. You can increase the gain
by further improvement of the matching... but you don't need more gain
than sufficient to have the band noise swamp the receiver internal noise.

I know you are convinced that matching also degraded the pattern. If the
matching network was entirely inside an effectively shielded box, it
should not affect the nulls. Make sure that you retained the shielded
loop properly.

Why do you still think that a larger loop has deeper nulls.

Owen
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Old November 25th 07, 08:41 AM posted to rec.radio.amateur.antenna
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Default Low Noise receiving Loop antenna

Owen Duffy wrote:
. . .
If you try something beside a shielded loop, make sure you use an
effective means of isolating the feed line from the loop so that pickup
on the feedline does not feed the receiver.
. . .


In my limited experience, it's extremely difficult or impossible to do a
good job of isolating the feedline from a small loop. The common mode
impedance is just too high.

Roy Lewallen, W7EL
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Old November 25th 07, 09:15 AM posted to rec.radio.amateur.antenna
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Posts: 1,169
Default Low Noise receiving Loop antenna

Roy Lewallen wrote in
:

Owen Duffy wrote:
. . .
If you try something beside a shielded loop, make sure you use an
effective means of isolating the feed line from the loop so that
pickup on the feedline does not feed the receiver.
. . .


In my limited experience, it's extremely difficult or impossible to do
a good job of isolating the feedline from a small loop. The common
mode impedance is just too high.

Roy Lewallen, W7EL


Hello Roy,

I have a small loop with inexpesive voltage balun, and it gives a quite
deep null (though I can't put dB figures on it off hand), and very sharp
null.

I wonder if the reason that Tony perceives that the nulls are shallow is
that he is assessing it on band noise. If so Tony, you should assess the
depth of the nulls on a local (ie low elevation) point source that is
much stronger than band noise. The test signal should dominate the
receiver.

If an antenna with deep nulls doesn't reduce band noise much, it
suggests that the noise is not mainly from a single direction... as
discussed earlier in this thread.

Owen
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