[Lowfer] Spatial and time diversity for QRSS

[craig wasson]

I'm trying to see whether weak signal detection can be improved using
various forms of spatial and time diversity.

I seem to recall reading long ago that if you add white noise to white
noise the sum has the same noise level as each of the two sources.  Does
anyone remember their basic electronics enough to know the answer?

I've done some testing and I'm not seeing 1 noise plus 1 noise equaling 1
noise.  But this is not white noise it's atmospheric noise from 2 radios so
maybe the same rules don't apply?

I'm trying 3 kinds of diversity - spatial diversity using 2 receivers and 2
antennas, and time diversity by delaying the signals a few milliseconds to
a few seconds while receiving a QRSS signal.  No solid results yet, but the
theory seems to say this should work.

If time diversity works I'd eventually like to try folding time back on
itself maybe 10 or 20 times by mixing the same signal with itself 10-20
times with each copy some milliseconds apart.  On a QRSS signal my theory
is that this will improve weak signal pickup.

Or maybe it will just be a bunch of noise unless I can get all of the
desired signals to all be in phase.  For a given carrier frequency it
should be possible to phase them right but I'm not sure I have the tools to
adjust the timing that finely...  any advice welcomed!

The third time diversity option I'm testing is to fold in 2 or more copies
of the same QRSS signal from adjacent iterations of the full call being
sent, but I'm not sure of the best way to do this yet.  I suspect this
mixing would need to be at the display level, not the demodulated signal
level.  I have used a program called NDBfinder that does this for NDB
signals but have not been able to get it to work right for QRSS signals.
It does not seem to allow a long enough time window for a QRSS call.  Has
anyone else tried NDBfinder with QRSS?  NDBfinder does not seem to be
actively maintained any longer.

Thanks!

Craig - N6IO