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K9AY works great on medium wave

By Al Merriman - K4GLU
July 4, 1998

In the September 1997 QST on page 43, with a modification in the May 1998 QST on page 73, there is an article by Gary Breed, K9AY on the Terminated Loop.
These looked like they held great promise as Medium Wave DX antennas.
In fact the termination resistance for these antennas is determined by using a BCB station off the end of the loop and adjusting the resistance for minimum signal.
In a word, these things work!

I have a single loop up at the moment oriented roughly N/S.
This antenna is parallel to a pair of slopers that are approximately 135 feet long, 50 feet at the high end and sloping down to 10 feet at the bottom.
These antennas run parallel to each other but are sloped in opposite directions. They are fed at the low end with coax through 4:1 matching transformers.
This pair of slopers have a very good "front to back" ratio when compared to each other. On many frequencies it is possible to swap dominate stations just by switching from one sloper to the other.
Up until now I have considered slopers, and I have a total of 4 oriented roughly N/S/E/W, as being the best wire antennas a Medium Wave DXer could use unless they were fortunate enough to have the room to put up Beverages, rhombics, etc.
That was before I tried a terminated loop!

The loop I have up is a delta, 37 feet on a side for a total of 117 feet.
It is hanging from a tree limb and the bottom is about 3 feet off the ground.
The remote relay box uses a 12 volt relay from Radio Shack and the termination at the moment is a 2K pot.
The transformer I used is 11 trifilar turns of #24 insulated solid telephone wire on a Amidon FT82-75 core.
All performance comparisons are made to the N/S pair of slopers which are parallel to the loop.

Signal levels are down about 8-10db across the entire MW band compared to the slopers.
However, even with this signal loss I am still able to hear the two JFK Airport TIS stations on 1630 and 1700 kHz during the day on the loop. This is not bad for 200 miles and 50 watts or so max even if part of the path is over water.
In addition the loss can easily be made up with a quiet amp.

Front to back is, in a word, impressive. It is no worse than the pair of slopers over the band from 600 kHz up and on many frequencies it is better.
Nulls vary from 5 to over 20 db in a couple of instances and this is during the day. On many frequencies it is possible to swap dominate stations just by reversing the loop feed.

At the moment my terminating resistor is a 2K pot. The ground I am using is only a 3 foot Radio Shack ground rod. This gives a very effective ground when used with one of my slopers but might not be good enough for the loop.
Termination resistance for best nulls varies across the MW band and unless this can be smoothed out with a better ground it is obvious that to get maximum performance a variable resistance is going to be necessary.
This of course brings to mind the Steve Byan system. Since I have a couple of the VTL3A17 Vactrols that Steve uses in his system I will be playing with this in the next few weeks. Stay tuned!
These terminated loops look real interesting. While much more playing around is necessary they hold a lot of promise.
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