Topband: Receiving on Directional Antenna

[Gary Breed]

W8JI:

> 1.) If the signals are in phase and have nearly-equal S/N ratios and
> mixed to mono from widely separated antennas, I get substantial
> S/N improvement in the sum. But it is impossible to hold the signal
> in-phase for long and QSB makes the levels vary rapidly also.
>
> 2.) If I listen in stereo I get slightly less enhancement but QSB,
> phase and levels have less effect so the enhancement is more
> reliable.
>
> 3.) If I listen in two different directions, either in stereo or mono, it
> decreases S/N ratio a quite noticable amount. The change is about
> the same as just using a poorer receiving antenna.

Tom is right about combining antennas or radios at RF and audio. Phase
and amplitude effects will cause cancellations that negate the benefit
much of the time. But my experience is different than his observations
in points 2 and 3.

I am quite enthusiastic about diversity reception in "stereo". In both
the CQWW160 CW test and on 40M in ARRL DX CW, I extensively used two
radios with different antennas in each ear. I worked many stations that
were copiable in one ear and undetectable in the other.

With this arrangement, there is no inherent S/N degradation -- each ear
is presented with the full S/N performance of its associated antenna. The
"net" S/N will vary with each operator's ability to deal with the two
sensory inputs. And you can always switch to a single RX/antenna to dig
out a weak signal.

73, Gary
K9AY




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