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Pattern reversal on any kind of terminated loop (SuperLoop, Flag, DKAZ, Kaz
Delta, Ewe, et al.) is fairly straightforward.
At each end of the antenna, install a step-down transformer. This would be
16:1 if coaxial cable is used or 9:1 if you employ balanced speaker wire, zip
cord, or twisted pair such as CAT-5.
Construction of such transformers is fairly easy if you use inexpensive
binocular cores (Fair-Rite 2873000202 or Amidon BN-73-202). On these cores a
16:1 would be 12 turns: 3 turns and a 9:1 is 12 turns: 4 turns. You can also
use toroids, preferably "J" or "75" material. Impedance ratio is the square of
the turns ratio.
Route the "shack" end of the two feedlines to a four-pole double-throw switch
so that one feedline goes to a 250 ohm or 500 ohm pot (for in-shack termination
adjustment) and the other feedline to a transformer (1:1 = 4 turns: 4 turns if
coax.; 2:1 = 7 turns: 5 turns if 100-ohm balanced) en route to the receiver's
input or a 50-ohm in / out amp (e.g. RPA-1) ahead of the receiver.
Though written for the DKAZ, the information about pattern reversal in the
article below applies to any terminated loop:
http://www.durenberger.com/documents/DKAZREPORT.pdf
In the case of an east-west antenna, the switch (page 13 of above article) can
be put in one position to get east / null west or the other position for get
west / null east. Same principal applies for antennas configured for any other
pair of opposing directions.
With longer runs of feedline, the efficacy of in-shack termination may go down.
Vactrol or motor drive schemes might be the only ways to manage termination
remotely. In such cases, the reversal capability goes away so maybe at that
point you need a second antenna.
As Mark D. mentioned, if you still want to use the FLG amp, you can have it the
shack with a step-up transformer off the feedline that would be the same ratio
(backwards) as the step-down out at the antenna.
Very few medium-wave set-ups get much of a real life signal-to-noise
improvement by having the amplifier outdoors. But if you feel that you do, you
could have an FLG amp at both sides of the antenna. The amplifier should
provide termination close enough to what you want so you will notice the
opposing nulls when you swap feedlines ahead of your receiver.
The outputs of the two feedlines can be presented to the inputs of a phaser
such as the Quantum Phaser. Then you can adjust for super-deep nulls of
specific pests although that would not typically hold up on frequencies much
more than 50 kHz either side of the frequency being worked.
The feedlines of each end can also be brought to two separate same / similar
receivers and the audios brought out to a stereo recorder for interesting
results.
Here are some demo files made at my former QTH in Billerica, MA:
http://chowdanet.com/markc/WEB2005A/dx_wesx-wneb-1230.mp3
http://chowdanet.com/markc/WEB2005A/dx_wmrc-wccm-1490.mp3
http://chowdanet.com/markc/WEB2005A/dx_wnri-wmyf-1380.mp3
Mark Connelly, WA1ION
South Yarmouth, MA
<<
Greetings,
I finally got a 47' x 22' corner fed super loop back up and operational. It is
in use with a FLG 100ln. The antenna is directed at ~304 deg. I wonder if I can
make it reversible a la reversible DKAZ antennas I have read about. The other
end would be directed at ~124 deg, nigh perfect for Latin America. I was
thinking about another FLG 100ln on the other end. Any insights would be
welcome.
Thanks!
Craig Barnes
Drake R8A, Eton E1
ALA 1530ln
47 x 22 super loop at 304 deg
>>
<<
Hi Donald. Reversing should be doable. DX Monitor Vol 53, #35 has
suggestions on reversing; of course YMMV.
Depending on your lead-in situation, you may be able to get by with a single
RF amplifier at the 'shack.' If you use an FLG100 to try this, use an
appropriate step-up transformer from the lead-in to the amp input. (If coax
lead-in, use 1:18; if twisted-pair use 1:9). This gets you "free' RF gain.
Regards,
Mark Durenberger, CPBE
>>
<<
Precisely! When the termination is the same value as the opposite end (the
radio feed) you will find your deepest null; best directionality.
A good place to start if you don't want to screw around all day is to use an
800 to 900 ohm resistor as the null.
BUT since I'm not a SuperLoop user these resistance values may not be the
best; if so, someone else will chime in.
Regards,
Mark Durenberger
>>
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