> Theoretically, two small loop antennas can have a nicely improved front
lobe
> and, as Tom points, with 180 degree phasing (I prefer about 165 deg.), can
> add nulls in other places to improve overall directivity.
>
> I did several experiments with this configuration three years ago. I
tried
> two K9AY loops inline at 50 and 70 foot spacing. Close spacing (i.e. 1/8
> wavelength or 70 feet on 160M) and near-180 degree phasing are a lossy
> combination; signal levels were down 6-8 dB from the already low levels of
a
> single loop and I decided not to put in further effort.
For over a year now I have been using a rotary, two-loop endfire setup, and
the thing works. Actual gain is about -45 dB, but with a K9AY preamp at the
feedpoint, modified for 20 dB of gain (thanks Gary), and using the MP's
preamp, there is adequate net gain for very low noise reception. Eznec
calculates a 11.10 dB RDF (W8JI unit), which compares to a 1.75 wavelength
Beverage. Turning either side of the antenna to an S-9 W1AW signal, takes
it down into the noise.
The key has been the addition of two large common mode RF chokes, one at the
feedpoint, the other at the receiver jack. The DC block's input must also
be heavily choked, and very importantly....... any other small leaks in the
coax shield /connector system must be repaired. There was initially poor
directional performance, which was found to be caused by a broken "ear" on
the receiver RCA plug. Replacing the plug sharpened the side & back nulls
appreciably, on both 80 & 160m. Balanced, shielded phasing lines are
superior to single coax lines, in this application.
The 30 ft long antenna with two 7'w x 14'h loaded loops, phased 184 degrees,
is much quieter & more directional than the original flag on the same
fiberglass boom.
73, Doug / NX4D
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