Topband: Polarity and Phase

[Tom Rauch]

> Rather than get into a mathematical discussion about it let me just
> mention the old HP 8405 Vector Voltmeter.  This measures the relative
> phase of two signals from about 1 MHz to 1000 MHz by down-converting
> the two signals that you want to measure for their phase relationship
> to an IF of 20 KHz.   The actual phase measurement is then made
> at 20 Khz.

I was going to use that as an example also John, but the post was so long I
deleted it! I only want to add a couple observations.

I notice if the phase relationship between incoming channels is not
maintained, a noticeable amount of "good effects" are lost.

While the FT1000 uses separate conversion schemes (different LO frequencies)
and different signal processing, it works OK in stereo diversity. It is not
as good as my other receivers, but still it is OK. The oscillators all run
from one time-base, and there is no difference in frequency.

You can check this by combining the outputs and listening for a beat when
both receivers tune in the same carrier while locked. When you hit A=B, the
sub and the main are on exactly the same frequency even if not in a specific
phase relationship.

I find the largest improvement when both channels are exactly on the same
frequency even though it might be in any phase relationship, and the least
improvement when they are not. I can't tell you what the frequency
difference limit is, but I know more than a fraction of a Hz difference
starts to bother me. I also find it best if both channels are identical in
as many characteristics as possible.

I don't find that close spacing between antennas does anything worthwhile.
Wide spacing is the key, at least from what I can tell. That's what makes
the noise sound really hollow and the signal stand out.

73 Tom