Several of you have shown interest in the loop antenna. I have updated
my web page to show more details. If you have it cached, you may have
to refresh it. The URL is:
http://tomthompson.com/radio/ReceivingLoop/loop.html
Let me know if some of it is unclear.
Tom W0IVJ
On 3/28/2014 1:53 PM, Tom Thompson wrote:
Hi Ken,
One thing to keep in mind when you choose a loop is the antenna
factor. I believe your RFI is mainly on 80m. A small (10") loop
that is not tuned will have a terrible antenna factor on 80 m. You may
not even hear the noise from your house. Also, your receiver probably
does not have a very good attenuator in the front end. When you get
close to the noise, you can detune the loop and get some attenuation.
You need to keep the signal right at the noise level in the null for
the AGC NOT to work if the S-meter is not very good. When the AGC is
NOT working, you can listen to the strength of the signal through the
speaker. Again, remember the null is looking through the loop with
the feed at the bottom. Also, I always put a choke balun right at the
loop so I don't get false readings from picking up signals on the coax
when the signal gets strong.
When you start your hunt, find the direction of the noise by nulling
the loop. You now have an ambiguity in direction. Peak the noise by
turning the loop edgewise and walk in one direction. Keep rotating the
loop back and forth looking for the peak signal to get stronger. If
the peak is getting weaker, walk in the other direction. When you get
very close to the RFI, use the null feature of the loop and attenuate
the signal by switching in an attenuator or detuning the loop.
I have been able to trace a grow light almost to the room in the house
by not getting on the residential property. Once I find the house and
if the RFI is on a timer, I will position myself in front of the house
and wait for the noise to appear to make sure I have the right house.
If you get this far, email me and I'll tell you how I approach the
grower. That is sometimes tricky and could be dangerous so I do not
want to generalize here.
Tom W0IVJ
On 3/28/2014 1:17 PM, Kenneth G. Gordon wrote:
"The unshielded loop will...respond to electrostatically induced noise."
While:
"The shielded loop , on the other hand, is almost insensitive to
electrostatically induced noise."
In other words, the shielded loop is NOT a good choice to DF the
types of
noise we are most often bothered by, while the un-shielded loop is
specifically sensitive to such noise.
So, my use of my NM-20B, with its shielded loop, was counter-productive.
Kenneth G. Gordon W7EKB
"Courage is being scared to death but saddling up anyway."--- John
Wayne
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