I always thought the major benefit of using two receivers was to feed each
from a different antenna, preferably one being vertically polarized and the
other horizontal. I can't find the reports just now, but I remember reading
that folks who experimented with this concluded that some of the rapid QSB
we experience comes from shifting polarization on long skip signals. This
wouldn't necessarily be related to phase, though.
The other technique, which is possibly what WB6TZA was referring to, is
summing the signals from two different antennas with a variable phase shift
to partially cancel noise coming from a particular direction. I always
assumed the phase shift was done at RF but maybe it works just as well in
the audio chain. I've never tried it.
I'm pretty sure both techniques require two antennas.
73,
Dave AB7E
----- Original Message -----
From: "Jim Brown" <jim@audiosystemsgroup.com>
To: "topband reflector" <topband@contesting.com>
Sent: Tuesday, April 13, 2004 7:13 AM
Subject: Re: Topband: TRANSCEIVER WITH SEPERATE RECEIVER?
> On Mon, 12 Apr 2004 19:23:07 -0700, wb6tza@socal.rr.com wrote:
>
> >There are boxes
> >to mix and switch the rx audio feeding the headphones... having one
> >rx in phase and one out of phase can bring some startling results,
> >especially with the two receivers are fed from different antennas
>
> VERY important distinction -- what do you mean by "in phase" and "out
> of phase?" Phase is a continuous function having an infinite number of
> values, and is proportional to frequency. Any network that modifies
> the phase of a signal path will do so to a degree that varies with
> frequency. RF phase shift networks and antenna spacing takes advantage
> of these differences to achieve directivity.
>
> Do you really mean that you are inverting the POLARITY of the audio
> signal of one of the receivers and adding it to the audio from the
> other receiver? Polarity is very different from phase -- it has two
> values, + and -, or "normal" and "inverted," and it is NOT a function
> of frequency. This can be done with a gain stage, with a transformer,
> or even by reversing the wiring of balanced I/O. But if it is done
> well, there is NO change to the phase.
>
> Or do you mean that you are inverting the polarity of the RF signal?
>
> Or do you mean that you are shifting the phase of the RF signal to some
> varying degree (as in the ANC-4 noise cancelling unit), then adding the
> phase shifted signal to another signal to null interference?
>
> ALL of these techniques are potentially useful, but they are quite
> different.
>
> Jim
>
>
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