> With SSB and CW, which use a heterodyne detector that mixes the signal
> with a local oscillator, the phase of the audio output at the detector
> is a direct function of the phase of the rf signal at the antenna. If
> you try to combine the audio from the two receivers, there will be
> phase cancellations, so that adjustment of rf phase becomes extremely
> critical, much like adjusting the phases of the noise and signal
> antennas on the MFJ or similar noise canceller. Has anyone figured
> out a way around this difficulty?
That's an excellent understanding and description of the problem Don.
I'm not sure how that would be satisfied using two separate VCO's
that are "dial locked", as happens in the FT1000 when one VFO dial
adjusts two totally different synthesizers by using the same digital
"word". Phase problems would also be compounded when the filters are
not exactly identical.
I track my R4C's (that are driven from common oscillators for carrier
and injection) by looking at them on a spectrum display and
overlapping the passbands. Of course I hand-select filters that are
as similar as possible in shape and phase delays.
The saving grace in systems where little attention is paid to phase
detail is that our ears, listening in stereo, really don't detect
phase well (if at all). While it is better to have everything the
same, we can get away with some surprisingly large phase
In my own experience, which certainly does not mean it applies to
everyone, I find exact phase and identical passband phase
distribution are clearly worth it on noise floor signals. The effect
I hear is that noise has an unusual hollow resonance, and a musical
difference in that hollow rushing sound is a very weak signal. It is
very interesting to listen to the effect with smooth rushing band
noise in winter as I switch from close spaced to wide spaced
antennas. Close spaced (under two wavelengths or so) antennas do not
help me any significant amount in stereo.
Of course they can help if I combine them in mono. Unfortunately
combining them in mono means I have to ride a receiver phase
control constantly, to make up for phase shift in the signal at both
It is an odd effect to be able to totally null a signal out while
adjusting the receiver filter tracking only the smallest amount, and
add 1/4 wl of transmission line in an antenna feedline and have it
73, Tom W8JI