Low Noise receiving Loop antenna
 

My neighborhood is loaded with some kind of electrical noise which makes
working 160 & 75 meters difficult. I have tried to locate the source but
have come up empty at this point. It appears to be something other than
power line noise which may mean its coming from someones house.

I was hoping the solution to the problem was to build a low noise receiving
loop antenna.

Well, the noise is mostly gone..........but so are the signals.....even when
I use a preamp.

I have tried an ICE 75 meter preamp and a KD9SV 160/75 meter preamp.

Still the noise is gone but the signals are really weak, if I hear anything
at all.

Not sure what if anything I did is wrong or if I am expecting too much from
this loop or the preamps don't have enough gain to make this work.

Anyone familiar enough with receiving loops to be able to assist me in
figuring out whats wrong here?

TIA

Tony

Low Noise receiving Loop antenna
 

On Sat, 17 Nov 2007 07:36:28 -1000, Tony Giacometti
wrote:

Anyone familiar enough with receiving loops to be able to assist me in
figuring out whats wrong here?

Hi Tony,

There is no such thing as a Low Noise antenna (loop or otherwise).

Given that what you build is deaf, that should be a reality check of
this presumed quality of the antenna.

Well, actually, you built it wrong. However, building it right stands
only a partial chance of lowering noise, and not because the antenna
has some remarkable quality that is not otherwise found in the plug
ordinary dipole. In that sense, the reduction of noise would only
follow turning the dipole (or loop, same thing) until the source of
that noise fell into a null. This is the conventional method of
employing a "Low Noise" antenna.

Let me guess. It is a shielded loop. You forgot to leave a gap in
the shield.

73's
Richard Clark, KB7QHC

Low Noise receiving Loop antenna
 

Richard Clark wrote:

On Sat, 17 Nov 2007 07:36:28 -1000, Tony Giacometti
wrote:

Anyone familiar enough with receiving loops to be able to assist me in
figuring out whats wrong here?

Hi Tony,

There is no such thing as a Low Noise antenna (loop or otherwise).

Given that what you build is deaf, that should be a reality check of
this presumed quality of the antenna.

Well, actually, you built it wrong. However, building it right stands
only a partial chance of lowering noise, and not because the antenna
has some remarkable quality that is not otherwise found in the plug
ordinary dipole. In that sense, the reduction of noise would only
follow turning the dipole (or loop, same thing) until the source of
that noise fell into a null. This is the conventional method of
employing a "Low Noise" antenna.

Let me guess. It is a shielded loop. You forgot to leave a gap in
the shield.

73's
Richard Clark, KB7QHC

it is a shielded loop and no the gap is there, thats why I am wondering why
its not doing what I thought it would do.

Low Noise receiving Loop antenna
 

On Sat, 17 Nov 2007 09:07:58 -1000, Tony Giacometti
wrote:

Let me guess. It is a shielded loop. You forgot to leave a gap in
the shield.

it is a shielded loop and no the gap is there, thats why I am wondering why
its not doing what I thought it would do.

Hi Tony,

It is working perfectly! It is working exactly as it was constructed.

You got your plans from the wrong source (or misread them, or failed
to follow directions).

There are several ways to construct one correctly, so I won't go into
those variations. There is probably a fix to the one you have, but
that is shooting in the dark.

Let's simply investigate the quality you seek. Low Noise comes only
from the antenna's quality of yielding the best dipole performance
possible under the circumstances. As these circumstances often
involve use in the low frequencies, the traditional high elevation
long-wire dipole is usually not an option. Further, if it is, it
rarely allows for rotation. What is usually within the user's skill
or available space renders a dipole that suffers from the proximity of
"things." These "things" disrupt the balance, and hence the
directionality of the dipole; thus noise sensitivity rises (noise
fills in through what should have been nulls in the dipole pattern).
The user still cannot turn the dipole and thus the long-wire in the
garden is a mediocre performer at best, and is usually a
disappointment all around.

Enter the loop.

The traditional loop for low frequency use is in fact quite small. By
being small it suffers less in relation to the proximity of "things."
This, of course, is if you erect it in the same place as that
long-wire disappointment you tugged down. That is, the loop improves
only in comparison; fortunately, it also brings the virtue of being
rotatable. That would be enough, but the snake oil salesmen like to
guild the Lily.

Enter the shielded loop.

The shielded loop solves a problem, certainly. That is the problem of
balance. However, if you use careful crafting of a simple loop, you
don't have any problem to solve.

There are many other details to sort out. That can be left to other
correspondence.

73's
Richard Clark, KB7QHC

Low Noise receiving Loop antenna
 

Richard Clark wrote:

On Sat, 17 Nov 2007 09:07:58 -1000, Tony Giacometti
wrote:

Let me guess. It is a shielded loop. You forgot to leave a gap in
the shield.

it is a shielded loop and no the gap is there, thats why I am wondering
why its not doing what I thought it would do.

Hi Tony,

It is working perfectly! It is working exactly as it was constructed.

You got your plans from the wrong source (or misread them, or failed
to follow directions).

There are several ways to construct one correctly, so I won't go into
those variations. There is probably a fix to the one you have, but
that is shooting in the dark.

Let's simply investigate the quality you seek. Low Noise comes only
from the antenna's quality of yielding the best dipole performance
possible under the circumstances. As these circumstances often
involve use in the low frequencies, the traditional high elevation
long-wire dipole is usually not an option. Further, if it is, it
rarely allows for rotation. What is usually within the user's skill
or available space renders a dipole that suffers from the proximity of
"things." These "things" disrupt the balance, and hence the
directionality of the dipole; thus noise sensitivity rises (noise
fills in through what should have been nulls in the dipole pattern).
The user still cannot turn the dipole and thus the long-wire in the
garden is a mediocre performer at best, and is usually a
disappointment all around.

Enter the loop.

The traditional loop for low frequency use is in fact quite small. By
being small it suffers less in relation to the proximity of "things."
This, of course, is if you erect it in the same place as that
long-wire disappointment you tugged down. That is, the loop improves
only in comparison; fortunately, it also brings the virtue of being
rotatable. That would be enough, but the snake oil salesmen like to
guild the Lily.

Enter the shielded loop.

The shielded loop solves a problem, certainly. That is the problem of
balance. However, if you use careful crafting of a simple loop, you
don't have any problem to solve.

There are many other details to sort out. That can be left to other
correspondence.

73's
Richard Clark, KB7QHC



Richard, I use a vertical antenna, for transmitting its great, does a fine
job, but for receive, with the noise in the neighborhood, its not the best
option. I have tried to use an ANC-4 noise reducer but the noise isn't
reduced enough to hear the weaker signals.

So, what to do, I followed the instructions for building the loop from W2YR
and KN4LF and from this link
http://www.hard-core-dx.com/nordicdx.../coaxloop.html

As I wrote previous I have 2 good preamps but the signals are still very
weak.

Have you ever built one of these?

If so, did you experience the same problem?

I don't have room for a beverage but if I am unable to solve this loop issue
I will probably have to consider a K9AY array which will force me to move
other antennas around on my 1/3rd of an acre.

Low Noise receiving Loop antenna
 

On Sat, 17 Nov 2007 10:30:06 -1000, Tony Giacometti
wrote:

Richard, I use a vertical antenna, for transmitting its great, does a fine
job, but for receive, with the noise in the neighborhood, its not the best
option. I have tried to use an ANC-4 noise reducer but the noise isn't
reduced enough to hear the weaker signals.

Hi Tony,

Leaving that aside for others to comment....

So, what to do, I followed the instructions for building the loop from W2YR
and KN4LF and from this link
http://www.hard-core-dx.com/nordicdx.../coaxloop.html

There is a world of opportunity in making a mistake with this monster.
It goes a long way to do something difficult that could be done vastly
easier.

As I wrote previous I have 2 good preamps but the signals are still very
weak.

You state that there is no gap. The page you supply clearly shows
gaps at the top of the two loops. Anything you hear is a function of
the poor shielding. By your description of your construction, you
shouldn't be able to hear anything at all!

Have you ever built one of these?

No, not one of these (there are too many frogs to kiss them all).

I don't have room for a beverage but if I am unable to solve this loop issue
I will probably have to consider a K9AY array which will force me to move
other antennas around on my 1/3rd of an acre.

A solution is vastly simpler than that - and you can still build a
loop. Google for more designs and submit them here for review (the
one you provided rates low on the sanity scale).

73's
Richard Clark, KB7QHC

Low Noise receiving Loop antenna
 

Tony Giacometti wrote in
news:VvSdnQC_g_Sb0qLanZ2dnUVZ_hKdnZ2d@hawaiiantel. net:

So, what to do, I followed the instructions for building the loop from
W2YR and KN4LF and from this link
http://www.hard-core-dx.com/nordicdx.../coaxloop.html

I think you are describing a scenario where, with the loop+preamp, the
receiver system is limited by internal noise rather than external noise.

So, it is a two band design, and that complicates matters somewhat.

Just concentrating on the 160m loop...

My calcs are that the 160m loop alone, tuned for zero series reactance
(should need ~90pF) and loaded with 50 ohms should have equivalent gain
of around -47dBi.

You would have to consider the preamp NF and gain and receiver NF to
evaluate the system noise floor, and you haven't given those details
(though they may be implied... but I am not familiar with the preamp you
are using).

Without using a preamp, the external noise (based on ITU-R P.372-8
Residiential man made noise) with this loop ought be of about the same
magnitude as the internal noise of a good transceiver, give or take. For
a preamp to improve the situation, it would need a NF significantly
better than the transceiver and sufficient gain to overcome the
transceiver noise.

Owen

Low Noise receiving Loop antenna
 

Tony Giacometti wrote:

it is a shielded loop and no the gap is there, thats why I am wondering why
its not doing what I thought it would do.

What you've done is to build a truly shielded loop. The notion that a
shield somehow blocks the electric field and lets the magnetic field
through is a folk tale -- an intact shield like the one you built blocks
both electric and magnetic fields. (Good thing, too, or else coax cable
wouldn't do its job.) You've just done an experiment that proves it.

The gap in a so-called "shielded loop" provides a path for current
outside the "shield" to get inside. The net result is that the outside
of the "shield" is just an ordinary loop antenna, and the gap acts like
a feedpoint to get the current inside where it can get to the receiver.
It responds to normal electric and magnetic fields exactly like an
unshielded loop. What the "shield" buys you is improved balance, which
helps prevent the feedline from becoming part of the antenna and picking
up local noise which you can null out if balance is good.

Roy Lewallen, W7EL

Low Noise receiving Loop antenna
 

Richard Clark wrote:

On Sat, 17 Nov 2007 10:30:06 -1000, Tony Giacometti
wrote:

Richard, I use a vertical antenna, for transmitting its great, does a fine
job, but for receive, with the noise in the neighborhood, its not the best
option. I have tried to use an ANC-4 noise reducer but the noise isn't
reduced enough to hear the weaker signals.

Hi Tony,

Leaving that aside for others to comment....

So, what to do, I followed the instructions for building the loop from
W2YR and KN4LF and from this link
http://www.hard-core-dx.com/nordicdx.../coaxloop.html

There is a world of opportunity in making a mistake with this monster.
It goes a long way to do something difficult that could be done vastly
easier.

As I wrote previous I have 2 good preamps but the signals are still very
weak.

You state that there is no gap.

sorry, but maybe I wasn't clear enough, there IS a gap - just like the one
in the link.


The page you supply clearly shows
gaps at the top of the two loops. Anything you hear is a function of
the poor shielding. By your description of your construction, you
shouldn't be able to hear anything at all!

Have you ever built one of these?

No, not one of these (there are too many frogs to kiss them all).

I don't have room for a beverage but if I am unable to solve this loop
issue I will probably have to consider a K9AY array which will force me to
move other antennas around on my 1/3rd of an acre.

A solution is vastly simpler than that - and you can still build a
loop. Google for more designs and submit them here for review (the
one you provided rates low on the sanity scale).

I did do a search for loops of this type and basically they are all the
same.

I have been told Wellbrook makes good loops, but I don't like the idea of
spending $300-$500 for one at this point.


73's
Richard Clark, KB7QHC

Low Noise receiving Loop antenna
 

Roy Lewallen wrote in
:

Tony Giacometti wrote:

it is a shielded loop and no the gap is there, thats why I am
wondering why its not doing what I thought it would do.

What you've done is to build a truly shielded loop. The notion that a

I think you guys are reading this the wrong way. Perhaps it should have
been written "it is a shielded loop and no, the gap is there,..."

You know people asking questions don't take much care in expression.

Owen

Low Noise receiving Loop antenna
 

Roy Lewallen wrote:

Tony Giacometti wrote:

it is a shielded loop and no the gap is there, thats why I am wondering
why its not doing what I thought it would do.

What you've done is to build a truly shielded loop. The notion that a
shield somehow blocks the electric field and lets the magnetic field
through is a folk tale -- an intact shield like the one you built blocks
both electric and magnetic fields. (Good thing, too, or else coax cable
wouldn't do its job.) You've just done an experiment that proves it.

The gap in a so-called "shielded loop" provides a path for current
outside the "shield" to get inside. The net result is that the outside
of the "shield" is just an ordinary loop antenna, and the gap acts like
a feedpoint to get the current inside where it can get to the receiver.
It responds to normal electric and magnetic fields exactly like an
unshielded loop. What the "shield" buys you is improved balance, which
helps prevent the feedline from becoming part of the antenna and picking
up local noise which you can null out if balance is good.

Roy Lewallen, W7EL

Roy, I don't fully understand why you made this response to me.
You mentionI built a truly shielded loop. How so? I did exactly what the
directions called for including having a gap.

If these loops are a folk tale, other than using a beverage which I don't
have the room for, how am I going to reduce the noise enough to be able to
woprk 160 and 75 meters effectively?

Low Noise receiving Loop antenna
 

Owen Duffy wrote:

Tony Giacometti wrote in
news:VvSdnQC_g_Sb0qLanZ2dnUVZ_hKdnZ2d@hawaiiantel. net:

So, what to do, I followed the instructions for building the loop from
W2YR and KN4LF and from this link
http://www.hard-core-dx.com/nordicdx.../coaxloop.html

I think you are describing a scenario where, with the loop+preamp, the
receiver system is limited by internal noise rather than external noise.

So, it is a two band design, and that complicates matters somewhat.

Just concentrating on the 160m loop...

My calcs are that the 160m loop alone, tuned for zero series reactance
(should need ~90pF) and loaded with 50 ohms should have equivalent gain
of around -47dBi.

You would have to consider the preamp NF and gain and receiver NF to
evaluate the system noise floor, and you haven't given those details
(though they may be implied... but I am not familiar with the preamp you
are using).

Without using a preamp, the external noise (based on ITU-R P.372-8
Residiential man made noise) with this loop ought be of about the same
magnitude as the internal noise of a good transceiver, give or take. For
a preamp to improve the situation, it would need a NF significantly
better than the transceiver and sufficient gain to overcome the
transceiver noise.

Owen

here are links to the preamps I use

http://www.iceradioproducts.com/reconly.html

http://www.isp.ca/ve3nh/kd9sv.htm

Low Noise receiving Loop antenna
 

Tony Giacometti wrote:

Richard Clark wrote:

On Sat, 17 Nov 2007 07:36:28 -1000, Tony Giacometti
wrote:

Anyone familiar enough with receiving loops to be able to assist me in
figuring out whats wrong here?

Hi Tony,

There is no such thing as a Low Noise antenna (loop or otherwise).

Given that what you build is deaf, that should be a reality check of
this presumed quality of the antenna.

Well, actually, you built it wrong. However, building it right stands
only a partial chance of lowering noise, and not because the antenna
has some remarkable quality that is not otherwise found in the plug
ordinary dipole. In that sense, the reduction of noise would only
follow turning the dipole (or loop, same thing) until the source of
that noise fell into a null. This is the conventional method of
employing a "Low Noise" antenna.

Let me guess. It is a shielded loop. You forgot to leave a gap in
the shield.

73's
Richard Clark, KB7QHC

it is a shielded loop and no, the gap is there, thats why I am wondering
why its not doing what I thought it would do.


I have corrected my statement! Sorry!

Low Noise receiving Loop antenna
 

On Sat, 17 Nov 2007 12:02:35 -1000, Tony Giacometti
wrote:

I did do a search for loops of this type and basically they are all the
same.

Hi Tony,

If the link you supplied is an indication of sameness, they are
equally complex and problem magnets.

No, loops are not all the same. There is quite a variety (you
supplied one poor variant to a simple turn of wire in the sky).

I have been told Wellbrook makes good loops, but I don't like the idea of
spending $300-$500 for one at this point.

More than $20 spent is only buying custom designed furniture.

73's
Richard Clark, KB7QHC

Low Noise receiving Loop antenna
 

On Sat, 17 Nov 2007 12:15:11 -1000, Tony Giacometti
wrote:

Tony Giacometti wrote:
it is a shielded loop and no, the gap is there, thats why I am wondering
why its not doing what I thought it would do.


I have corrected my statement! Sorry!

Hi Tony,

No, as Owen pointed out, a poor reading on my part. Sorry.

73's
Richard Clark, KB7QHC

Low Noise receiving Loop antenna
 

Tony Giacometti wrote in news:CpKdnabH6fWF-
:

here are links to the preamps I use

http://www.iceradioproducts.com/reconly.html

NF=1.8dB and Gain=18dB


http://www.isp.ca/ve3nh/kd9sv.htm

Ok, I can't work with specs like "Noise figure is quite low and the
design appears to have no vices." I am not saying it is bad, it just
doesn't say anything meaninful... well to me anyway.

Still no info on the transceiver, but lets guess it has a NF=8dB.

Transceiver + preamp has a NF of 2dB, which suggests an equivalent noise
floor of about -139dBm (2kHz bandwidth).... provided that the preamp
doesn't generate internal noise due to IMD and which would not be
captured in the 1.8dB spec NF.

ITU-R P.372-8 suggests ambient noise on 1.8MHz in Residential locality
should be about -75dBm+AvgAntGain or about -122dBm, so you should get
noticeably more noise (~17dB) from the loop than from a dummy load. That
would mean the configuration should deliver almost as good a S/N ratio as
possible... even though the S meter reading might be shy.

Again, I am talking about the 160m loop alone. You can't diagnose this
easily with the two loops in parallel.

Owen

Low Noise receiving Loop antenna
 

Richard Clark wrote:

On Sat, 17 Nov 2007 12:02:35 -1000, Tony Giacometti
wrote:

I did do a search for loops of this type and basically they are all the
same.

Hi Tony,

If the link you supplied is an indication of sameness, they are
equally complex and problem magnets.

No, loops are not all the same. There is quite a variety (you
supplied one poor variant to a simple turn of wire in the sky).

I have been told Wellbrook makes good loops, but I don't like the idea of
spending $300-$500 for one at this point.

More than $20 spent is only buying custom designed furniture.

73's
Richard Clark, KB7QHC


OK, other than leveling all existing structures within 2,500 ft of my house
and burying the power lines, how do I solve this problem?

also, if these loops don't work then why do these designs exist?

Low Noise receiving Loop antenna
 

Owen Duffy wrote:

Tony Giacometti wrote in news:CpKdnabH6fWF-
:

here are links to the preamps I use

http://www.iceradioproducts.com/reconly.html

NF=1.8dB and Gain=18dB


http://www.isp.ca/ve3nh/kd9sv.htm

Ok, I can't work with specs like "Noise figure is quite low and the
design appears to have no vices." I am not saying it is bad, it just
doesn't say anything meaninful... well to me anyway.

Still no info on the transceiver, but lets guess it has a NF=8dB.

Transceiver + preamp has a NF of 2dB, which suggests an equivalent noise
floor of about -139dBm (2kHz bandwidth).... provided that the preamp
doesn't generate internal noise due to IMD and which would not be
captured in the 1.8dB spec NF.

ITU-R P.372-8 suggests ambient noise on 1.8MHz in Residential locality
should be about -75dBm+AvgAntGain or about -122dBm, so you should get
noticeably more noise (~17dB) from the loop than from a dummy load. That
would mean the configuration should deliver almost as good a S/N ratio as
possible... even though the S meter reading might be shy.

Again, I am talking about the 160m loop alone. You can't diagnose this
easily with the two loops in parallel.

Owen


I am using a heavily modified Drake R-4c receiver. Sherwood mods.
And I at this point I only built the 80 meter loop as I wanted to make sure
it worked on 80 before I went and built one for 160.

I don't think ITU-R P.372-8 had my neighborhood in mind when it was
composed.

S-9 on this receiver is about the minimum on 160 and S-7 is the minimum on
75.

Much of the time its higher and a royal pain in the arse.

Low Noise receiving Loop antenna
 

Tony Giacometti wrote in
news:suednRqSYJd58aLanZ2dnUVZ_uDinZ2d@hawaiiantel. net:

also, if these loops don't work then why do these designs exist?

Tony,

A few questions:

1. With a 50 load on the preamp input, when tuned to a quiet spot in the
band, RF gain full, preamps on, telephony bandwidth, does the S meter
deflect at all?

2. If no s meter deflection, note the receiver audio output voltage.

3. With the loop connected on the preamp input, when tuned to a quiet
spot in the band, RF gain full, preamps on, telephony bandwidth, does the
S meter deflect at all?

4. If no s meter deflection, note the receiver audio output voltage.

5. What is the ratio of the voltage at 4 to the voltage at 3? If it is
more than about 3:1, you have achieved nearly as good a S/N ratio as is
possible.

Owen

Low Noise receiving Loop antenna
 

On Sat, 17 Nov 2007 12:38:11 -1000, Tony Giacometti
wrote:

OK, other than leveling all existing structures within 2,500 ft of my house
and burying the power lines, how do I solve this problem?

also, if these loops don't work then why do these designs exist?

-sigh-

Tony, if "loops don't work" is the only message you've gotten to this
point, it is the wrong message.

Certainly your loop doesn't work - or at least I have to take your
word for it. That is a far different issue.

Loops do work if you follow standard practices.

The real question is:
"Is a loop my solution?"
and with that comes the $64,000 prize.

In other correspondence you describe noise levels pushing the S-Meter
to S9. If that noise is coming from one direction, a dipole or loop
can solve it. If it is general (meaning that your neighbor's fish
tank heater is bathing you in noise), then you don't stand a chance.

You don't need an antenna, yet. You need to find the source of noise.

73's
Richard Clark, KB7QHC

Low Noise receiving Loop antenna
 

Tony Giacometti wrote in
news:bcSdnVU4bZ7W86LanZ2dnUVZ_vShnZ2d@hawaiiantel. net:


I am using a heavily modified Drake R-4c receiver. Sherwood mods.
And I at this point I only built the 80 meter loop as I wanted to make
sure it worked on 80 before I went and built one for 160.

I obviously misunderstood you when you provided a link to a two band
antenna... or did you forget to tell us that?

I will let you rework the calcs for your scenario.


I don't think ITU-R P.372-8 had my neighborhood in mind when it was
composed.

S-9 on this receiver is about the minimum on 160 and S-7 is the
minimum on 75.

S meter readings are pretty meaningless, but using the convention of 50uV
for S 9, 6dB/SPoint, ITU-R P.372-8 does indeed suggest median noise at
~S7 for a 2kHz bandwidth and Residential locale.

As to whether your receiver indicates S7 accurately, that is another
matter.

People who brag about S1 noise level on 80m have a lossy antenna and/or
(and) an innaccurate S meter.


Much of the time its higher and a royal pain in the arse.


Something many of us experience.

Owen

Low Noise receiving Loop antenna
 

Owen Duffy wrote:

Tony Giacometti wrote in
news:suednRqSYJd58aLanZ2dnUVZ_uDinZ2d@hawaiiantel. net:

also, if these loops don't work then why do these designs exist?

Tony,

A few questions:

1. With a 50 load on the preamp input, when tuned to a quiet spot in the
band, RF gain full, preamps on, telephony bandwidth, does the S meter
deflect at all?


not noticeable



2. If no s meter deflection, note the receiver audio output voltage.

125mv


3. With the loop connected on the preamp input, when tuned to a quiet
spot in the band, RF gain full, preamps on, telephony bandwidth, does the
S meter deflect at all?


not noticeable



4. If no s meter deflection, note the receiver audio output voltage.

150mv


5. What is the ratio of the voltage at 4 to the voltage at 3? If it is
more than about 3:1, you have achieved nearly as good a S/N ratio as is
possible.

Owen

Low Noise receiving Loop antenna
 

Owen Duffy wrote:

Tony Giacometti wrote in
news:bcSdnVU4bZ7W86LanZ2dnUVZ_vShnZ2d@hawaiiantel. net:


I am using a heavily modified Drake R-4c receiver. Sherwood mods.
And I at this point I only built the 80 meter loop as I wanted to make
sure it worked on 80 before I went and built one for 160.

I obviously misunderstood you when you provided a link to a two band
antenna... or did you forget to tell us that?

I used the design for the 80 meter loop - I would think they are mostly
independent of each other.



I will let you rework the calcs for your scenario.

????



I don't think ITU-R P.372-8 had my neighborhood in mind when it was
composed.

S-9 on this receiver is about the minimum on 160 and S-7 is the
minimum on 75.

S meter readings are pretty meaningless, but using the convention of 50uV
for S 9, 6dB/SPoint, ITU-R P.372-8 does indeed suggest median noise at
~S7 for a 2kHz bandwidth and Residential locale.

As to whether your receiver indicates S7 accurately, that is another
matter.

S-9 is 50 uv on this receiver on 40meters - can't be sure its exactly the
same on 80, but the calibration voltage for S9 is very very close on 80.




People who brag about S1 noise level on 80m have a lossy antenna and/or
(and) an innaccurate S meter.

or they are lying........



Much of the time its higher and a royal pain in the arse.


Something many of us experience.

Owen

Low Noise receiving Loop antenna
 

Tony Giacometti wrote in
news:A5SdnQdv8vz466LanZ2dnUVZ_t2inZ2d@hawaiiantel. net:

Owen Duffy wrote:

Tony Giacometti wrote in
news:suednRqSYJd58aLanZ2dnUVZ_uDinZ2d@hawaiiantel. net:

also, if these loops don't work then why do these designs exist?

Tony,

A few questions:

1. With a 50 load on the preamp input, when tuned to a quiet spot in
the band, RF gain full, preamps on, telephony bandwidth, does the S
meter deflect at all?


not noticeable



2. If no s meter deflection, note the receiver audio output voltage.

125mv


3. With the loop connected on the preamp input, when tuned to a quiet
spot in the band, RF gain full, preamps on, telephony bandwidth, does
the S meter deflect at all?


not noticeable



4. If no s meter deflection, note the receiver audio output voltage.

150mv


5. What is the ratio of the voltage at 4 to the voltage at 3? If it
is more than about 3:1, you have achieved nearly as good a S/N ratio
as is possible.

So, the ratio is 1.2.

Two thirds (actually 1/1.2^2) of your total noise is from the receiver
internal noise. That is not a good situation, S/N on signals will be
degraded by relatively excessive contribution from the receiver, actually
caused by inadequate antenna gain.

Expected ambient noise level from a lossless antenna in 2kHz at 3.6MHz
should be around -82.9+33dBm or -49.9dBm. The 80m loop gain is about -
47dBi, so expected receive level would be -97dBm which is some 40dB above
your receiver noise floor.

Things aren't working like they should, so you need to localise the
problem.

I have no idea of the sensitivity or bandwidth of your receiver, but a
good (not outstanding, just good) (bare) receiver with a noise floor of -
130dBm should see a large increase in noise moving from dummy load to the
loop. (Ambient at -97dBm would be equivalent to S5 if your S meter was
accurate.)

Just for verification, I performed the same test you did, but with a
600mm a side untuned loop and an ICR20 receiver, and I got a 10 fold
increase in noise from the loop compared to the dummy load. Your loop is
larger and tuned, so it should be a 10dB more sensitive.

BTW, I didn't state it, but those noise measurements MUST be made in SSB
mode.

Owen

Low Noise receiving Loop antenna
 

On Nov 17, 9:36 am, Tony Giacometti wrote:
My neighborhood is loaded with some kind of electrical noise which makes
working 160 & 75 meters difficult. I have tried to locate the source but
have come up empty at this point. It appears to be something other than
power line noise which may mean its coming from someones house.

I was hoping the solution to the problem was to build a low noise receiving
loop antenna.

Well, the noise is mostly gone..........but so are the signals.....even when
I use a preamp.

I have tried an ICE 75 meter preamp and a KD9SV 160/75 meter preamp.

Still the noise is gone but the signals are really weak, if I hear anything
at all.

Not sure what if anything I did is wrong or if I am expecting too much from
this loop or the preamps don't have enough gain to make this work.

Anyone familiar enough with receiving loops to be able to assist me in
figuring out whats wrong here?

TIA

Tony

Hi Tony,

I haven't bothered to wade through ALL the responses so far, but I am
left wondering just what you did build. Could you explain it in more
detail? Diameter, number of turns, how you're feeding it, how it's
"shielded," exactly where the gap is, ... All the details.

A loop can be effective in decreasing noise in two ways. If the noise
is electromagnetic radiation it can only work if that radiation is
coming from one direction, and in that case, you orient the loop to
reject radiation from that direction. You better not want to be
receiving a signal from the same direction, of course. The second way
it can help is by rejecting locally generated electric field noise--
where you are in the near field of the source, and the electric field
is considerably stronger in relationship to the magnetic field than it
is in electromagnetic radiation. But the electric and magnetic fields
fall off with distance rather quickly, so this only works if the noise
source is on the order of a wavelength or less away.

In order to build a loop that's effective in not responding to an
electric-only field, it must be small compared with a wavelength. I'd
think you'd want something around a foot in diameter for 80 meters,
possibly slightly larger. You won't pick up much signal, but more
importantly, it will be a high Q loop that you need to tune, and the
resulting bandwidth will not be great. I have a suspicion that's
where your problem lies. Reg Edwards supplied us with a very decent
loop analysis program that might give you some insights. Look for
rjeloop3.exe under http://www.we0h.us/G4FGQ-index.html.

Cheers,
Tom

Low Noise receiving Loop antenna
 

Owen Duffy wrote:

Tony Giacometti wrote in
news:A5SdnQdv8vz466LanZ2dnUVZ_t2inZ2d@hawaiiantel. net:

Owen Duffy wrote:

Tony Giacometti wrote in
news:suednRqSYJd58aLanZ2dnUVZ_uDinZ2d@hawaiiantel. net:

also, if these loops don't work then why do these designs exist?

Tony,

A few questions:

1. With a 50 load on the preamp input, when tuned to a quiet spot in
the band, RF gain full, preamps on, telephony bandwidth, does the S
meter deflect at all?


not noticeable



2. If no s meter deflection, note the receiver audio output voltage.

125mv


3. With the loop connected on the preamp input, when tuned to a quiet
spot in the band, RF gain full, preamps on, telephony bandwidth, does
the S meter deflect at all?


not noticeable



4. If no s meter deflection, note the receiver audio output voltage.

150mv


5. What is the ratio of the voltage at 4 to the voltage at 3? If it
is more than about 3:1, you have achieved nearly as good a S/N ratio
as is possible.

So, the ratio is 1.2.

Two thirds (actually 1/1.2^2) of your total noise is from the receiver
internal noise. That is not a good situation, S/N on signals will be
degraded by relatively excessive contribution from the receiver, actually
caused by inadequate antenna gain.

Expected ambient noise level from a lossless antenna in 2kHz at 3.6MHz
should be around -82.9+33dBm or -49.9dBm. The 80m loop gain is about -
47dBi, so expected receive level would be -97dBm which is some 40dB above
your receiver noise floor.

Things aren't working like they should, so you need to localise the
problem.

I have no idea of the sensitivity or bandwidth of your receiver, but a
good (not outstanding, just good) (bare) receiver with a noise floor of -
130dBm should see a large increase in noise moving from dummy load to the
loop. (Ambient at -97dBm would be equivalent to S5 if your S meter was
accurate.)

Just for verification, I performed the same test you did, but with a
600mm a side untuned loop and an ICR20 receiver, and I got a 10 fold
increase in noise from the loop compared to the dummy load. Your loop is
larger and tuned, so it should be a 10dB more sensitive.

BTW, I didn't state it, but those noise measurements MUST be made in SSB
mode.

Owen


I did the measurements in the SSB mode.

This receiver is very quiet with no antenna connected.
When I tune the preselector for a peak in noise the noise jumps up
noticeably.

What about the AGC setting?

Low Noise receiving Loop antenna
 

Tony Giacometti wrote:
Roy Lewallen wrote:

Tony Giacometti wrote:
it is a shielded loop and no the gap is there, thats why I am wondering
why its not doing what I thought it would do.

Roy, I don't fully understand why you made this response to me.
You mentionI built a truly shielded loop. How so? I did exactly what the
directions called for including having a gap.

My apology. I too-quickly and incorrectly read your "and no the gap is
there" as "no gap is there". My statement about your creating a truly
shielded loop was wrong. The loop with the gap should work as intended.

If these loops are a folk tale, other than using a beverage which I don't
have the room for, how am I going to reduce the noise enough to be able to
woprk 160 and 75 meters effectively?

"Shielded" loops aren't a folk tale, they work fine. They have a broad
pattern with, if constructed properly, narrow and deep nulls. It's a
mistaken idea about how they work that's the folk tale.

Roy Lewallen, W7EL

Low Noise receiving Loop antenna
 

Owen Duffy wrote:
Roy Lewallen wrote in
:

Tony Giacometti wrote:
it is a shielded loop and no the gap is there, thats why I am
wondering why its not doing what I thought it would do.
What you've done is to build a truly shielded loop. The notion that a

I think you guys are reading this the wrong way. Perhaps it should have
been written "it is a shielded loop and no, the gap is there,..."

You know people asking questions don't take much care in expression.

I'm sorry to say, all too often I don't take proper care in reading
postings. Although lack of punctuation does tend to exacerbate
misunderstanding, the fault was mine. I'm trying to do better, but still
slip up as I did this time.

Roy Lewallen, W7EL

Low Noise receiving Loop antenna
 

Roy Lewallen wrote:

Tony Giacometti wrote:
Roy Lewallen wrote:

Tony Giacometti wrote:
it is a shielded loop and no the gap is there, thats why I am wondering
why its not doing what I thought it would do.

Roy, I don't fully understand why you made this response to me.
You mentionI built a truly shielded loop. How so? I did exactly what the
directions called for including having a gap.

My apology. I too-quickly and incorrectly read your "and no the gap is
there" as "no gap is there". My statement about your creating a truly
shielded loop was wrong. The loop with the gap should work as intended.

If these loops are a folk tale, other than using a beverage which I don't
have the room for, how am I going to reduce the noise enough to be able
to woprk 160 and 75 meters effectively?

"Shielded" loops aren't a folk tale, they work fine. They have a broad
pattern with, if constructed properly, narrow and deep nulls. It's a
mistaken idea about how they work that's the folk tale.

Roy Lewallen, W7EL

Roy, you scared the daylights out of me for a minute,

By the way, any idea why this loop might be under performing?

Low Noise receiving Loop antenna
 

K7ITM wrote:

On Nov 17, 9:36 am, Tony Giacometti wrote:
My neighborhood is loaded with some kind of electrical noise which makes
working 160 & 75 meters difficult. I have tried to locate the source but
have come up empty at this point. It appears to be something other than
power line noise which may mean its coming from someones house.

I was hoping the solution to the problem was to build a low noise
receiving loop antenna.

Well, the noise is mostly gone..........but so are the signals.....even
when I use a preamp.

I have tried an ICE 75 meter preamp and a KD9SV 160/75 meter preamp.

Still the noise is gone but the signals are really weak, if I hear
anything at all.

Not sure what if anything I did is wrong or if I am expecting too much
from this loop or the preamps don't have enough gain to make this work.

Anyone familiar enough with receiving loops to be able to assist me in
figuring out whats wrong here?

TIA

Tony

Hi Tony,

I haven't bothered to wade through ALL the responses so far, but I am
left wondering just what you did build. Could you explain it in more
detail? Diameter, number of turns, how you're feeding it, how it's
"shielded," exactly where the gap is, ... All the details.

A loop can be effective in decreasing noise in two ways. If the noise
is electromagnetic radiation it can only work if that radiation is
coming from one direction, and in that case, you orient the loop to
reject radiation from that direction. You better not want to be
receiving a signal from the same direction, of course. The second way
it can help is by rejecting locally generated electric field noise--
where you are in the near field of the source, and the electric field
is considerably stronger in relationship to the magnetic field than it
is in electromagnetic radiation. But the electric and magnetic fields
fall off with distance rather quickly, so this only works if the noise
source is on the order of a wavelength or less away.

In order to build a loop that's effective in not responding to an
electric-only field, it must be small compared with a wavelength. I'd
think you'd want something around a foot in diameter for 80 meters,
possibly slightly larger. You won't pick up much signal, but more
importantly, it will be a high Q loop that you need to tune, and the
resulting bandwidth will not be great. I have a suspicion that's
where your problem lies. Reg Edwards supplied us with a very decent
loop analysis program that might give you some insights. Look for
rjeloop3.exe under http://www.we0h.us/G4FGQ-index.html.

Cheers,
Tom

Hi Tom, heres the link to the loop I built.

http://www.qsl.net/kc2tx/

I only built the 80 meter loop not both.

Low Noise receiving Loop antenna
 

Owen Duffy wrote in
:

I just went and re-examined the article, and it is not series tuned as I
first thought, it is parallel tuned.

My calcs of your loop were all on the basis of series tuned loop, and are
not applicable to the parallel tuned circuit.

It is questionable whether the parallel tuned circuit is an efficient
coupling method for a low Z receiver.

Owen

Low Noise receiving Loop antenna
 

On Nov 17, 11:36 am, Tony Giacometti wrote:


Anyone familiar enough with receiving loops to be able to assist me in
figuring out whats wrong here?

TIA

Tony


I use a lot of solenoid loops. You should not need a preamp
with a decent size loop using an R4C in most cases.
I'm wondering if you are actually tuning the loop to resonance.
Do you notice a sharp, fairly high Q peak of noise and signals
at the point where you think it is tuned?
There will be no mistake hearing this peak if it's working
correctly.
400 pf seems kind of low to me...
IE: lets take a regular solenoid loop, being calculated by
Reg Edwards loop program rjeloop3.exe..
It's fairly accurate.
I set up a one turn loop using a 20 mm wire, each side
of the loop 5 ft, or 1525mm. I set 1900kc as the
desired frequency, which is the middle of the band.
It shows a stray capacitance of appx 9 pf, and requires
appx 1350 pf to tune to 1900 kc.
See my problem with your meager 400 pf?
Of course, you using coax instead of plain wire may
be effecting the results..
I'm just not sure if you are actually tuned.
I have two solenoid loops that I often use. One is a
16 inch circle, and the other is a diamond loop
44 inches per side.
The 16 inch loop uses appx 12 turns. The larger
loop, 5 turns. I still use fairly large values of caps
to drop down low in frequency. IE: a dual 365pf BC
radio cap, with both gangs tied together is usually
needed to cover the whole BC band.
On my large loop, the various gangs of the cap
add up to a good bit more than 730 pf..
More like 1000+ pf or so.. So I get a wider tuning
range, and can switch gangs out to get small
values for the higher bands.
Anyway, when building small loops, you usually must
build the loop around the cap at hand, rather than
try to match the cap to a set number of wires.
You would think a "planned" loop would work though..
Anyway, the first thing I would need to know is
do you hear a sharp noise peak when "tuned"?
You should. And you really should have enough
signal to not need a preamp in most cases.
As an example, the loss in comparing the 5 ft
per side loop vs a 1/4 wave monopole is appx
-21 db according to the program. "1900 kc"
That should not be enough to kill you on the lower
bands.
I run both of my loops straight to my IC-706mk2g
most of the time, and need no preamp at all on
160m or BC. And I don't have to enable the radio
preamp either.
It's possible you could have a problem with the
preamp. :/
If you want to try a solenoid loop, here is the program.
http://home.comcast.net/~nm5k/Rjeloop3.exe
I put it on my server, as I forgot where the archive
of all his files are..
A simple way to make a PVC frame is here..
http://home.comcast.net/~nm5k/loop5.jpg
The loop you have should work ok once tuned, but
there seems to be a problem of some kind.
Is your feed line ground shield making a connection
to the loop on the other side of the cap from the
center pin connection?
I use separate coupling loops on mine and the coax
feeds that loop. The variable cap is connected in parallel
across the main loop connections.
I get better balance and cleaner nulls if I use a
coupling loop vs feeding directly at the cap/loop
connection. But of course, I'm not using a "shielded"
loop to aid in balance. But in the end, I get just
as clean nulls as the shielded loop.
MK

Low Noise receiving Loop antenna
 

Tony Giacometti wrote in
:


I did the measurements in the SSB mode.

This receiver is very quiet with no antenna connected.

I know it is popular to make measurements with no antenna connected
(meaning the antenna jack is left o/c). The measurements are meaningless.

Measurements with a matched load are meaningful, the noise output power
of the receiver is due to the equivalent receiver noise power + the noise
in a matched load.

You will also see discussion of whether receiver noise increases or
decreases when a matched load is disconnected... it varies from receiver
to receiver and it highlights the useless nature of the o/c measurment.

When I tune the preselector for a peak in noise the noise jumps up
noticeably.

What about the AGC setting?


To make a meaningful comparison, the receiver gain must not change
between measurements, so no change in AGC, no change in RF or AF gain,
safest if there is no S meter reading for both measurements.

Turning AGC off doesn't necessarily extend the range of the SSB receiver
where audio output is linearly related to RF input, don't depend on it
unless you have measured its performance.

Owen

Low Noise receiving Loop antenna
 

On Nov 17, 6:16 pm, wrote:
On Nov 17, 11:36 am, Tony Giacometti wrote:



Anyone familiar enough with receiving loops to be able to assist me in
figuring out whats wrong here?

TIA

Tony

I use a lot of solenoid loops. You should not need a preamp
with a decent size loop using an R4C in most cases.
I'm wondering if you are actually tuning the loop to resonance.
Do you notice a sharp, fairly high Q peak of noise and signals
at the point where you think it is tuned?
There will be no mistake hearing this peak if it's working
correctly.
400 pf seems kind of low to me...
IE: lets take a regular solenoid loop, being calculated by
Reg Edwards loop program rjeloop3.exe..
It's fairly accurate.
I set up a one turn loop using a 20 mm wire, each side
of the loop 5 ft, or 1525mm. I set 1900kc as the
desired frequency, which is the middle of the band.
It shows a stray capacitance of appx 9 pf, and requires
appx 1350 pf to tune to 1900 kc.
See my problem with your meager 400 pf?

Hummm, I see you say you have only used it on 80m.
According to the program, using a 2.5 ft per side loop,
you would need appx 850-860 pf to tune 3700 kc.
I guess the capacitance of the coax is making up
the rest.. ??? IE: I think RG-58 and RG-8 is good for about
28-29 pf per foot or so. Even if you added that say extra
290 pf, you still come up a bit short from the 850+ pf
needed for a plain wire loop.
I think I would disconnect the preamp, at least for
testing, and see if you can determine a noise peak
into the receiver. You need to find out of the loop
is actually tuning to resonance. Make sure both
conductors of the feedline are connected to each
connection of the loop, with the variable cap in
parallel across those connections.
If it's tuning, you should hear a distinct noise peak,
and I really doubt you would need the preamp to
hear it into a R4C. Once you get that going, it should
be downhill from there.
I have a R4C, along with an old original R4 too, so I know
they should have enough sensitivity to hear the noise
peak with no preamp. Well, unless it's broke.. :(
MK

Low Noise receiving Loop antenna
 

Tony Giacometti wrote:

Roy, you scared the daylights out of me for a minute,

By the way, any idea why this loop might be under performing?

Well, first of all, I think the problem might be your expectations. A
small loop has a very broad pattern, with a couple of very narrow and
deep nulls. If you have noise coming from a very narrow angular region,
you can use a loop to null it out. But if it's coming from the wiring in
a neighbor's house, is getting on the power lines, or otherwise comes
from a range of angles, the loop won't help. If the noise is getting
into your house via the mains wiring, then the loop will probably make
things worse compared to an outside antenna, since it's closer to at
least one source of the noise.

And this does seem to be the case. Although you didn't say in so many
words, it sounds like the signal/noise ratio is worse when using the
loop than when using the outside antenna. If so, then the last couple of
sentences in the above paragraph apply.

In a recent posting you say the noise level comes up substantially when
you connect the loop, so you can quit worrying about your receiver noise
figure in my opinion -- and with it, the AGC operation, S-meter
calibration, and so forth. It means that external noise is considerably
louder than receiver noise. You can also quit worrying about how many
turns. A preamp, or even an audio amplifier connected to the receiver
output, will make both signals and noise louder, in the same ratio, if
they're not loud enough to hear.

So the only thing which can be wrong with the loop that you can't fix
with a little amplification is that maybe it's poorly balanced so the
nulls aren't what they should be. The only way I know of to test for
this is to rotate the loop when listening to a distant station or a
small battery powered signal source -- something coming from only one
direction. You should be able to null it out pretty effectively. If you
can't, the problem might be loop construction or it might be proximity
of other conductors warping the pattern. If you can successfully null
out point-source signals, then the loop is performing as it should. And
if that's not good enough, then a loop isn't the solution to your problem.

Roy Lewallen, W7EL

Low Noise receiving Loop antenna
 

Owen Duffy wrote:

Owen Duffy wrote in
:

I just went and re-examined the article, and it is not series tuned as I
first thought, it is parallel tuned.

My calcs of your loop were all on the basis of series tuned loop, and are
not applicable to the parallel tuned circuit.

It is questionable whether the parallel tuned circuit is an efficient
coupling method for a low Z receiver.

Owen


I am able to get a noise peak tuning the capacitor and the preamps I use are
supposed to be a match from approx 25 ohms to about 125 ohms.

I believe this should work, but for some reason not like I thought it would.

Low Noise receiving Loop antenna
 

Owen Duffy wrote:

Tony Giacometti wrote in
:


I did the measurements in the SSB mode.

This receiver is very quiet with no antenna connected.

I know it is popular to make measurements with no antenna connected
(meaning the antenna jack is left o/c). The measurements are meaningless.

I did put a matched load on the receiver for these tests.


Measurements with a matched load are meaningful, the noise output power
of the receiver is due to the equivalent receiver noise power + the noise
in a matched load.

You will also see discussion of whether receiver noise increases or
decreases when a matched load is disconnected... it varies from receiver
to receiver and it highlights the useless nature of the o/c measurment.

When I tune the preselector for a peak in noise the noise jumps up
noticeably.

What about the AGC setting?


To make a meaningful comparison, the receiver gain must not change
between measurements, so no change in AGC, no change in RF or AF gain,
safest if there is no S meter reading for both measurements.

Turning AGC off doesn't necessarily extend the range of the SSB receiver
where audio output is linearly related to RF input, don't depend on it
unless you have measured its performance.

Owen

I am thinking I should take another look at the receiver and make sure it
does'nt have something strange going on.

I do appreciate your input.

Low Noise receiving Loop antenna
 

Tony Giacometti wrote in
news:sO2dnUZbkeShCaLanZ2dnUVZ_v2pnZ2d@hawaiiantel. net:

I believe this should work, but for some reason not like I thought it
would.


Tony, I have described a simple untuned loop for field strength
measurement. The article is at
http://www.vk1od.net/SmallUntunedSquareLoop/index.htm . The sensitivity
of the loop is sufficient that external noise on 3.6MHz is much greater
than the receiver internal noise, ie S/N of signals on the band will be
about as good as they can be, a higher gain antenna will increase the S
meter reading, but not improve S/N ignoring the effects of noise blankers
and noise reduction. The predicted performance has been confirmed by
comparison to a calibrated EMC measurement loop.

The purpose of tuning a loop is preselection and / or better impedance
matching to improve gain (by reducing loss).

The purpose of shielding a loop is for better balance to achieve deeper
nulls, but shielding isn't the only way, nor the best way necessarily.
Roy mentioned that.

Try a simple untuned loop, the balun is REAL important (for deep nulls),
see how it works then see if you can get the improved version to work. It
is questionable whether the shielded loop construction is a real
improvement, it brings some loss elements (the s/c stub loss, the line
loss in the other half the loop) to the design, losses that be worse than
a balun.

Owen

Low Noise receiving Loop antenna
 

wrote:

On Nov 17, 11:36 am, Tony Giacometti wrote:


Anyone familiar enough with receiving loops to be able to assist me in
figuring out whats wrong here?

TIA

Tony


I use a lot of solenoid loops. You should not need a preamp
with a decent size loop using an R4C in most cases.
I'm wondering if you are actually tuning the loop to resonance.
Do you notice a sharp, fairly high Q peak of noise and signals
at the point where you think it is tuned?
There will be no mistake hearing this peak if it's working
correctly.
400 pf seems kind of low to me...
IE: lets take a regular solenoid loop, being calculated by
Reg Edwards loop program rjeloop3.exe..
It's fairly accurate.
I set up a one turn loop using a 20 mm wire, each side
of the loop 5 ft, or 1525mm. I set 1900kc as the
desired frequency, which is the middle of the band.
It shows a stray capacitance of appx 9 pf, and requires
appx 1350 pf to tune to 1900 kc.
See my problem with your meager 400 pf?
Of course, you using coax instead of plain wire may
be effecting the results..
I'm just not sure if you are actually tuned.
I have two solenoid loops that I often use. One is a
16 inch circle, and the other is a diamond loop
44 inches per side.
The 16 inch loop uses appx 12 turns. The larger
loop, 5 turns. I still use fairly large values of caps
to drop down low in frequency. IE: a dual 365pf BC
radio cap, with both gangs tied together is usually
needed to cover the whole BC band.
On my large loop, the various gangs of the cap
add up to a good bit more than 730 pf..
More like 1000+ pf or so.. So I get a wider tuning
range, and can switch gangs out to get small
values for the higher bands.
Anyway, when building small loops, you usually must
build the loop around the cap at hand, rather than
try to match the cap to a set number of wires.
You would think a "planned" loop would work though..
Anyway, the first thing I would need to know is
do you hear a sharp noise peak when "tuned"?
You should. And you really should have enough
signal to not need a preamp in most cases.
As an example, the loss in comparing the 5 ft
per side loop vs a 1/4 wave monopole is appx
-21 db according to the program. "1900 kc"
That should not be enough to kill you on the lower
bands.
I run both of my loops straight to my IC-706mk2g
most of the time, and need no preamp at all on
160m or BC. And I don't have to enable the radio
preamp either.
It's possible you could have a problem with the
preamp. :/
If you want to try a solenoid loop, here is the program.
http://home.comcast.net/~nm5k/Rjeloop3.exe
I put it on my server, as I forgot where the archive
of all his files are..
A simple way to make a PVC frame is here..
http://home.comcast.net/~nm5k/loop5.jpg
The loop you have should work ok once tuned, but
there seems to be a problem of some kind.
Is your feed line ground shield making a connection
to the loop on the other side of the cap from the
center pin connection?
I use separate coupling loops on mine and the coax
feeds that loop. The variable cap is connected in parallel
across the main loop connections.
I get better balance and cleaner nulls if I use a
coupling loop vs feeding directly at the cap/loop
connection. But of course, I'm not using a "shielded"
loop to aid in balance. But in the end, I get just
as clean nulls as the shielded loop.
MK


Lots of good info, thanks!

This link was the guide I used to build the loop, I am only using the 80
meter loop.

http://www.qsl.net/kc2tx/

Without the preamp I do get a noise spike when I tune the cap.
Its very noticeable also.

I would have thought that the signals I have heard would be much louder
especially using the preamp.

I have 2 different types of preamps and they both behave the same way.

For what its worth, I have never considered just plain wire for the loop.
I do use coax RG-6 - its all I can get, no RG-59 around here.
Another ham mentioned to me that using 75 ohm hardline would be the best.
None of that stuff here either.

I am beginning to think my feedline could be a problem. I can replace that
stuff rather easily.

I like your idea of a separate coupling loop.

Any idea what the loop would need to be electrically and physically?
Do I need to change my tuning cap if I change to a coupling loop?

Anyway, thanks for your input - great stuff.

Low Noise receiving Loop antenna
 

On Nov 17, 7:31 pm, Tony Giacometti wrote:


I am thinking I should take another look at the receiver and make sure it
does'nt have something strange going on.

I do appreciate your input.

You are getting a peak so the loop is tuned.. I doubt the
receiver is the problem, or you wouldn't hear the noise
peak. So it's down to pretty much what Roy just said at this
point. You need to check the nulls. And if the noise
is multiple sources, it can only do one at a time, unless
two are in the same exact direction, or exactly 180 apart.
So it might, or might not do what you want.
The null should be very sharp. Just a slight movement
can cause quite a change in the depth of the null
on a local noise source, so the aim has to be near
perfect for best results.
MK