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Low Noise receiving Loop antenna



 
 
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  #51  
Old November 18th 07, 04:36 PM posted to rec.radio.amateur.antenna
Highland Ham
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Posts: 250
Default Low Noise receiving Loop antenna

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

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

I only built the 80 meter loop not both.

============================
Interesting loop(s) Is there any significance in using RG59 (75 Ohms)
coax, rather than RG58 (50 Ohms) ?

Frank GM0CSZ / KN6WH
  #52  
Old November 18th 07, 06:14 PM posted to rec.radio.amateur.antenna
Richard Clark
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Posts: 2,951
Default Low Noise receiving Loop antenna

On Sat, 17 Nov 2007 23:14:01 -1000, Tony Giacometti
wrote:

No. The main loop will still be tuned to the same frequency, no
matter if direct fed, or with a coupling loop. Many people build BC
loops and use the ferrite bar antennas in the portable radios
themselves to couple to the loop.

how do I calculate the dimensions of the coupling loop?


Hi Tony,

It has 1/5 the diameter and is a single, shorted loop.

Please don't try to make it more elaborate than it should be. One
wire, in a loop, connected to the other side of the feed (i.e. the
wire runs from the center conductor, 'round the circumference, to the
outer conductor).

Of course, this demands that the bigger loop be equally, simply
described. It too is one piece of wire, turned in a circle, each end
connecting to the resonating capacitor. In this case, you want to
optimize for the lowest Ohmic connections and materials. This may
suggest hardline, but, please, don't think of using the inner
conductor for anything at all - that is a waste of time. You could as
easily use copper tubing.

You can put more effort into it, but it will reward you only in the
sense of being the owner of a fine piece of furniture.

73's
Richard Clark, KB7QHC
  #53  
Old November 18th 07, 07:21 PM posted to rec.radio.amateur.antenna
Richard Harrison
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Posts: 588
Default Low Noise receiving Loop antenna

Tony Giacometti wrote:
"How do I calculate the dimensions of the coupling loop?"

You might try to make the radiation pesistance of the loop match the
feedline.

Arnold B. Bailey 0n page 400 of "TV and Other Receiving Antennas" gives
an approximate squation:

R = 197 L to the fourth power for L 0,08 wavelengths.

Best regards, Richard Harrison, KB5WZI

  #54  
Old November 18th 07, 08:25 PM posted to rec.radio.amateur.antenna
external usenet poster
 
Posts: 712
Default Low Noise receiving Loop antenna

On Nov 18, 4:00 am, Tony Giacometti wrote:


I have this feeling I don't know what I am supposed to experience from a
working loop.

Anyone have a mp3 file which can show what happens using a loop?



Here is one I did in 2002 comparing my 16 inch circle loop
vs my T vertical on the BC band.
-----------------------------------------------------------------------------------------------------

I did a few quick comparisons between a 16 inch loop, and my "T"
vertical, which is about 42 ft tall, with a 120 ft long flat top wire.
It's pretty hot on MW. The radio was my ic-706mk2g. I'll let the
recordings speak for themselves.
You can click on the URl for the sound files, and your media player
"should" bring them right up and start playing. Hopefully anyway...

I did three tests, on three different frequencies, at different times
in the evening. I'm in Houston, and used mainly San Antonio as the
"target" city. "good 200 miles away" I recorded each test. I did
compress the audio greatly to save d/l time, but the audio is still
good enough to tell which is best. The files are pretty small and will
d/l quickly. They were huge files in the original sample rate and
format...I will "narrate" each test, so you will know which antenna
was used, and the exact times I switched. You can use the counter in
the media player to keep track of the time.

Test #1 was at about 7:30 PM on 550 kc.
http://home.comcast.net/~nm5k/mwtest1.mpeg
"Time in seconds"
0-13 -----loop
13-26 -----wire
26-38 -----loop
At 38 seconds I nulled the station, so you can hear the null.
46 -----loop, back pointed to the station
57-69 -----wire
69-end -----loop

Test #2 was at about 8:00 PM on 680 kc.
http://home.comcast.net/~nm5k/mwtest2.mpeg
"Time in seconds"
0-11 -----loop
11-23 -----wire
At 37 seconds I nulled the station
46 -----back pointed to the station
55-67 -----wire
67-end -----loop

Test #3 was at about 9:00 PM on 570 kc. Multiple stations on this
freq...
http://home.comcast.net/~nm5k/mwtest3.mpeg
"Time in seconds"
0-10 ----loop
10-23 ----wire
23-37 ----loop
37-48 ----wire
At 62 seconds, I turn the loop 90 degrees to get a totally different
station.
At 74, I turned back to the first station.
85 ----turned back to 2nd station again
91 ----back to the first


Here is another one on the BC where I turn the loop to null the
station.
http://home.comcast.net/~nm5k/mwtest4.mpeg
At first the station is nulled, and you can hear
a Mexican station in the background. At about 12 seconds,
I turn to the desired station. At 20 seconds I switch to
the T vertical. At 30 seconds I go back to the loop.
At 40 seconds, I null the station again.



Right now I am hearing very few stations on the loop amd not a one more than
a S5, with an S1 noise level. I hear a couple stations in the SS contest
from the west coast S5 on the loop no noise to be heard, on the
transmitting antenna S6 noise level and the same west coast station S7

I can hear the stations he is working but not well enough to work either on
the loop or the transmitting antenna. The stations he is working are in the
noise and I know they are there.

Does this sound right?


Probably so. I haven't found the loops to be that great for pulling
out weak stations on 160m. The success will depend on the level
of noise you are able to cut, vs the strength of the desired station.
This is why I'm playing with beverages a bit out in the country.
I'm not sure how this will pan out, as in general changing the
size of the loop should keep an equal s/n ratio, but some claim
better 160m weak signal use if you use the largest loop you
can manage..

I was able to dig up one 160m file, but it's not for nulling
comparisons.
It's just comparing the general noise received comparing
the full size dipole, vs the loop.
http://home.comcast.net/~nm5k/dpvloop.mpeg
This is pretty much all close NVIS type signals..
Starts on the loop, and switches back and forth.
You can tell which is the loop.. Much quieter
background noise. It takes my AGC a second
to adapt..
It's no good for showing nulls, but it does show
the signal level I get from the small 16 inch loop
using no preamp at all.
None of those clips use a preamp. I've never used
a preamp on small loops yet.. I prefer to avoid a
preamp if possible.. :/

I was going to record a current file nulling line
noise, but I don't have any noise at the moment.. :/
I use the loops for BC band use more than
anything. But both do tune 160m, and I use
it for that band when I want to kill some noise.

MK
  #55  
Old November 18th 07, 09:46 PM posted to rec.radio.amateur.antenna
Tony Giacometti
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Posts: 50
Default Low Noise receiving Loop antenna

Owen Duffy wrote:

Tony Giacometti wrote in
news:NNydnfODM_iOB6LanZ2dnUVZ_r6rnZ2d@hawaiiantel. net:

...
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.


Did I miss something. I did see you refer us to a web page that described
the loop using RG59... and now you tell us you used RG6. You might not yet
know it, they are different, and the difference is relevant.

Owen



I looked at the specs for both cables and the difference is very small.
Thats why I used RG-6, I have no source for RG-59 here.
  #56  
Old November 18th 07, 09:53 PM posted to rec.radio.amateur.antenna
Tony Giacometti
external usenet poster
 
Posts: 50
Default Low Noise receiving Loop antenna

Richard Clark wrote:

On Sat, 17 Nov 2007 23:14:01 -1000, Tony Giacometti
wrote:

No. The main loop will still be tuned to the same frequency, no
matter if direct fed, or with a coupling loop. Many people build BC
loops and use the ferrite bar antennas in the portable radios
themselves to couple to the loop.

how do I calculate the dimensions of the coupling loop?


Hi Tony,

It has 1/5 the diameter and is a single, shorted loop.

Please don't try to make it more elaborate than it should be. One
wire, in a loop, connected to the other side of the feed (i.e. the
wire runs from the center conductor, 'round the circumference, to the
outer conductor).

Of course, this demands that the bigger loop be equally, simply
described. It too is one piece of wire, turned in a circle, each end
connecting to the resonating capacitor. In this case, you want to
optimize for the lowest Ohmic connections and materials. This may
suggest hardline, but, please, don't think of using the inner
conductor for anything at all - that is a waste of time. You could as
easily use copper tubing.

You can put more effort into it, but it will reward you only in the
sense of being the owner of a fine piece of furniture.

73's
Richard Clark, KB7QHC


And to think I was just trying to build a simple low noise receiving loop

Lets try this question.....

if I were to start from scratch.......

and I wanted to build a low noise receiving loop......

what style of low noise loop would you suggest I build?

OR is there another solution to my situation on my 1/3 of an acre lot?
  #57  
Old November 18th 07, 10:05 PM posted to rec.radio.amateur.antenna
Owen Duffy
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Posts: 1,169
Default Low Noise receiving Loop antenna

Tony Giacometti wrote in
:

Owen Duffy wrote:

Tony Giacometti wrote in
news:NNydnfODM_iOB6LanZ2dnUVZ_r6rnZ2d@hawaiiantel. net:

...
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.


Did I miss something. I did see you refer us to a web page that
described the loop using RG59... and now you tell us you used RG6.
You might not yet know it, they are different, and the difference is
relevant.

Owen



I looked at the specs for both cables and the difference is very
small. Thats why I used RG-6, I have no source for RG-59 here.


Tony,

You might regard the difference as small, but in the models that I
created the difference in transmission loss, velocity factor, and shield
diameter are relevant.

Anyway, I have built and calibrated a model of the 80m loop described in
the ARRL Antenna Book (19th ed), and I am still checking the model.

Initial results are that it does exhibit a peak in gain at about 300pF of
tuning C, and that peak in gain is just a little less than an untuned
unshielded loop of the same size.

It looks like the gain is about -53dBi (not including feedline). If the
expected noise from a 0dBi antenna in 2kHz was -83dBm, this would give
around -136dBm which is in the region of the quiet noise floor on a good
HF receiver. Of course, if you were in a very noise place, then this
might be sufficient gain to achieve close to max S/N.

I have also modelled the tuned loop with the LHS shield bonded to the
inner conductor at the gap, which removes the lossy s/c stub from the
picture, increasing gain a little. Now this connection will not appeal to
the people with misconceptions about how a shielded loop works, but the
s/c stub formed by the coax on one side of the loop is just another loss
element that can be avoided.

Made of RG6, the gain is about a half dB higher.

I will look at it later in the day and put some notes together.

Owen
  #58  
Old November 18th 07, 10:30 PM posted to rec.radio.amateur.antenna
external usenet poster
 
Posts: 712
Default Low Noise receiving Loop antenna

On Nov 18, 3:14 am, Tony Giacometti wrote:


how do I calculate the dimensions of the coupling loop?


It's really not that critical. But there is a "sweet spot"
where you get the maximum coupling.
The best way is to just test it and see where you get
the strongest level, and nail it down.
I'm looking at my 44 inch per side loop, and the coupling
loop is about 5 inches inside of the main loop windings.
It's a plain single wire.
On my 16 inch loop, it's a circle, and is built on a
plastic humidifier blower housing. The motor mount
acts as the boom to attach to the mast.
When it's on the stand, it almost gives the impression
of some kind of perverted microwave dish at first
look... :/
It's coupling loop is a three turn coax shielded loop
that is appx three inches away from the main coil.
It's also slightly less across, and is about a 12 inch
loop inside the 16 inch loop. Yes, it has a gap in the
shield at the top, which is the center of the total
length of the coax.
I tested various coupling loops on that one, and
got the best level using the three turns, and the
use of a "shielded" coax loop just aids in better
balance. The main coil is plain insulated #12 wire.
As you can tell in the recordings, my nulls are deep.
In most cases with groundwave path signals, I can
make an unwanted station vanish if I want.
That applies to local single source noise too..
My usual culprit is line noise due south or north
or me. But I can kill 95% of it. I'm lucky it seems
to come from one location.
In general, the nulls are not near as good with actual
skywave signals late at night. But they can still
help a bit, as they tend to reject a bit of unwanted
crud vs a larger wire antenna.
If I'm listening to the BC band, I'm always on the loop,
no matter what the time of day. I prefer it even with
skywave signals. But due to the generally lower
signal levels on the weaker 160m band, it's a bit
different animal.
You might have better luck on 160 using say a set
of phased short verticals.
There was a thread talking about those just the other
day. I think W8JI uses those quite a bit, and I
know he often works stuff I don't even hear on the
transmit vertical, or one of my loops.
On 160, I think just being vertical is an advantage
for long haul DX.
Either that or use beverages, which I'm gonna assume
are probably not possible at your QTH...
BTW, one time I hooked the 16 inch loop to a
AC/Delco car radio in a truck.. Worked great.
MK

  #59  
Old November 18th 07, 10:36 PM posted to rec.radio.amateur.antenna
Roy Lewallen
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Posts: 1,374
Default Low Noise receiving Loop antenna

Tony Giacometti wrote:

And to think I was just trying to build a simple low noise receiving loop

Lets try this question.....

if I were to start from scratch.......

and I wanted to build a low noise receiving loop......

what style of low noise loop would you suggest I build?

OR is there another solution to my situation on my 1/3 of an acre lot?


What you should do is realize that there is no such thing as a "low
noise receiving loop". No antenna has any way to tell the difference
between signals and noise, so a "low noise receiving loop" is also just
as much a "low signal receiving loop". All a loop can do that might help
with a noise problem is provide a sharp null in one direction (actually,
two, but it's very unlikely that both will be useful at the same time).
If the noise is coming from a single narrow direction, you can turn the
loop to reduce it. If the noise isn't coming from one narrow direction,
a loop won't be "low noise" and, as I pointed out earlier, might well be
worse than an outside antenna if the noise is being radiated by house
wiring.

From all the descriptions, it sounds like your main problem with the
loop is that the overall gain of your loop + receiver is simply too low
for comfortable listening. What you need in order to provide the
necessary additional gain is either a better impedance match between the
loop and receiver (for which there have been multiple suggestions), an
amplifier either ahead of the receiver (a preamp) or after the receiver
(an audio amplifier), or some combination of those. If you can null out
the noise by turning the loop, then the additional gain will get you
what you're trying to achieve. If not, then a loop isn't the solution,
and the only solution might be to find and eliminate the source of the
noise.

Roy Lewallen, W7EL
  #60  
Old November 18th 07, 10:36 PM posted to rec.radio.amateur.antenna
Tony Giacometti
external usenet poster
 
Posts: 50
Default Low Noise receiving Loop antenna

wrote:

On Nov 18, 4:00 am, Tony Giacometti wrote:


I have this feeling I don't know what I am supposed to experience from a
working loop.

Anyone have a mp3 file which can show what happens using a loop?



Here is one I did in 2002 comparing my 16 inch circle loop
vs my T vertical on the BC band.
-----------------------------------------------------------------------------------------------------

I did a few quick comparisons between a 16 inch loop, and my "T"
vertical, which is about 42 ft tall, with a 120 ft long flat top wire.
It's pretty hot on MW. The radio was my ic-706mk2g. I'll let the
recordings speak for themselves.
You can click on the URl for the sound files, and your media player
"should" bring them right up and start playing. Hopefully anyway...

I did three tests, on three different frequencies, at different times
in the evening. I'm in Houston, and used mainly San Antonio as the
"target" city. "good 200 miles away" I recorded each test. I did
compress the audio greatly to save d/l time, but the audio is still
good enough to tell which is best. The files are pretty small and will
d/l quickly. They were huge files in the original sample rate and
format...I will "narrate" each test, so you will know which antenna
was used, and the exact times I switched. You can use the counter in
the media player to keep track of the time.

Test #1 was at about 7:30 PM on 550 kc.
http://home.comcast.net/~nm5k/mwtest1.mpeg
"Time in seconds"
0-13 -----loop
13-26 -----wire
26-38 -----loop
At 38 seconds I nulled the station, so you can hear the null.
46 -----loop, back pointed to the station
57-69 -----wire
69-end -----loop

Test #2 was at about 8:00 PM on 680 kc.
http://home.comcast.net/~nm5k/mwtest2.mpeg
"Time in seconds"
0-11 -----loop
11-23 -----wire
At 37 seconds I nulled the station
46 -----back pointed to the station
55-67 -----wire
67-end -----loop

Test #3 was at about 9:00 PM on 570 kc. Multiple stations on this
freq...
http://home.comcast.net/~nm5k/mwtest3.mpeg
"Time in seconds"
0-10 ----loop
10-23 ----wire
23-37 ----loop
37-48 ----wire
At 62 seconds, I turn the loop 90 degrees to get a totally different
station.
At 74, I turned back to the first station.
85 ----turned back to 2nd station again
91 ----back to the first


Here is another one on the BC where I turn the loop to null the
station.
http://home.comcast.net/~nm5k/mwtest4.mpeg
At first the station is nulled, and you can hear
a Mexican station in the background. At about 12 seconds,
I turn to the desired station. At 20 seconds I switch to
the T vertical. At 30 seconds I go back to the loop.
At 40 seconds, I null the station again.



Right now I am hearing very few stations on the loop amd not a one more
than a S5, with an S1 noise level. I hear a couple stations in the SS
contest from the west coast S5 on the loop no noise to be heard, on the
transmitting antenna S6 noise level and the same west coast station S7

I can hear the stations he is working but not well enough to work either
on the loop or the transmitting antenna. The stations he is working are
in the noise and I know they are there.

Does this sound right?


Probably so. I haven't found the loops to be that great for pulling
out weak stations on 160m. The success will depend on the level
of noise you are able to cut, vs the strength of the desired station.
This is why I'm playing with beverages a bit out in the country.
I'm not sure how this will pan out, as in general changing the
size of the loop should keep an equal s/n ratio, but some claim
better 160m weak signal use if you use the largest loop you
can manage..

I was able to dig up one 160m file, but it's not for nulling
comparisons.
It's just comparing the general noise received comparing
the full size dipole, vs the loop.
http://home.comcast.net/~nm5k/dpvloop.mpeg
This is pretty much all close NVIS type signals..
Starts on the loop, and switches back and forth.
You can tell which is the loop.. Much quieter
background noise. It takes my AGC a second
to adapt..
It's no good for showing nulls, but it does show
the signal level I get from the small 16 inch loop
using no preamp at all.
None of those clips use a preamp. I've never used
a preamp on small loops yet.. I prefer to avoid a
preamp if possible.. :/

I was going to record a current file nulling line
noise, but I don't have any noise at the moment.. :/
I use the loops for BC band use more than
anything. But both do tune 160m, and I use
it for that band when I want to kill some noise.

MK



Thank you for the audio clips, the loop is really
working for you.

No preamp!!! WOW!!!

Truly Amazing!
 




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