Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Old November 17th 07, 10:04 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Dec 2006
Posts: 1,169
Default 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
  #2   Report Post  
Old November 18th 07, 12:01 AM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jun 2006
Posts: 1,374
Default 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
  #3   Report Post  
Old November 17th 07, 10:15 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Oct 2007
Posts: 50
Default 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!
  #4   Report Post  
Old November 17th 07, 10:25 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 2,951
Default 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
  #5   Report Post  
Old November 17th 07, 11:56 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 644
Default 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


  #6   Report Post  
Old November 18th 07, 12:08 AM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Oct 2007
Posts: 50
Default 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.
  #7   Report Post  
Old November 18th 07, 03:36 PM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
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
  #8   Report Post  
Old November 18th 07, 12:16 AM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 757
Default 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
  #9   Report Post  
Old November 18th 07, 01:15 AM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Jul 2006
Posts: 757
Default 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

  #10   Report Post  
Old November 18th 07, 01:51 AM posted to rec.radio.amateur.antenna
external usenet poster
 
First recorded activity by RadioBanter: Oct 2007
Posts: 50
Default 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.




Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Low Noise Receiving antennas Tony Giacometti Antenna 21 October 14th 07 07:18 AM
Receiving Loop John Antenna 5 August 13th 06 06:16 PM
Receiving loop antenna design Owen Antenna 36 June 25th 05 01:34 AM
Random Legth Receiving Only Ant.; Close Into A Loop ? Robert11 Antenna 2 September 26th 04 03:26 AM
Technical question for receiving TV signals by a loop Antenna David Kao Antenna 0 January 20th 04 01:14 AM


All times are GMT +1. The time now is 10:19 AM.

Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
Copyright ©2004-2025 RadioBanter.
The comments are property of their posters.
 

About Us

"It's about Radio"

 

Copyright © 2017