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Old November 18th 07, 08:25 PM posted to rec.radio.amateur.antenna
[email protected] nm5k@wt.net is offline
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First recorded activity by RadioBanter: Jul 2006
Posts: 757
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