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Re: [IRCA] Antenna pattern testing of a MW tuned loop
Brian,
Looks like your getting some pretty nice patterns. Testing outdoors away
from anything metal or "noisy" should give good results.
I did some similar testing in college for a Professor with untuned loops
at HF and have been doing some initial testing on (yet another
iteration) home-brew remote loop for LW/MW. While testing the HF loops
we found that nearby metal more than 1/2 wavelength long can distort the
reception pattern even if it was several wavelengths away which might
explain why the stations above 1MHz are distorted more than the stations
at the low end of the band. Those lines end just past our house and make
a 90* turn less than a block away so they may be too short to effect the
lower MW frequencies. When we took the HF loop out into a pasture we got
very deep nulls compared to doing it in the greenhouse. The best loop
for 3-30MHz was 1M square loop made of welded 3" copper pipe and a
matching network that gave me headaches for a week from doing the Math
:P
One of my locals, KELO 1320, is a 5KW Directional at 6 Miles aimed right
at me that I can see the tower lights of through the trees at night.
What I've found is that stronger signals tend to get "bent" by what I
assume is the power, cable, phone,etc. lines running through the back of
the property. The lines are due East (90*) and the towers are at 150*
but the deepest null is about 10* in the direction of the lines from
line of sight at ~140*.
The next strongest local, KSOO 1140, is at 184* and nulls at close to
180*. More distant signals seem to be skewed less but it's still
measurable and a PITA. WNAX 570 and KFYR 550 seem to be spot on
I've noticed this here before with air and ferrite core loops. The last
trial I did was at 24' AGL on a fiberglass pole about 80' from the lines
and away from the house, etc. I can get a more accurate direction since
I'm using a modified aircraft ADF antenna and indicator. Untuned loop
with a remote tuned preamp/preselector mounted in the unit. Lightning
season and it's not in a waterproof housing as yet so it's only been up
a couple of times for a few hours during the day. "Management" insists
the house get painted before I do any more "fiddling with gizmos". I
suppose she'll want me to paint the pole the same color as the trim :P
Probably best to wait until after lightning season to put it up in the
air anyway.
Tim Hills
Sioux Falls, SD
------ Original Message ------
In preparation for some testing I want to do with a Superloop antenna
once
I can figure out a reasonable way to rotate it, I did some pattern
testing
yesterday on my 6-foot tuned loop. I used my SDR and a simple hiking
compass to take signal strength readings on 4 local and local-ish
stations
in 10 degree increments, plus extra measurements near the two nulls in
the
pattern. I was pretty happy with the results, but there were a few
oddities (the two nulls for each station were considerably different,
the
directional patterns were significantly skewed for my hyper-locals, and
a
few other things). A full writeup is too long for the list and
wouldn't be
complete without the plots, but I've put up a detailed blog post,
including
the pattern plots:
https://azswdxing.wordpress.com/2015/04/27/gear-pattern-test-of-am-bcb-tuned-loop-antenna/
I haven't seen a lot of full pattern testing data on-line, but it's
obviously much more difficult to do for larger antennas. Comments
welcomed
and encouraged.
Brian Rachford - Prescott, AZ
azswdxing@xxxxxxxxx
http://azswdxing.wordpress.com/
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