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Re: [linrad] Using Linrad as a Diversity Receiver?
- Subject: Re: [linrad] Using Linrad as a Diversity Receiver?
- From: Stan <stan@xxxxxxxxxxxxxxx
- Date: Sun, 31 Aug 2003 13:37:57 +0000
Diversity systems have their place, from HF thru microwaves.
frequency diversity using multiple frequencies
space diversity as in a tropospheric scatter system using at least 2
separate "scattering" volumes
polarization diversity as in using a separate V and H polarization
A fourth diversity is time diversity were 2 identical signals are time
delayed by a constant amount and transmitted.
These were available to the ham market maybe 30 years ago. application
was HF to counter the QSB and
frequency selective fading.
In one quad diversity tropo scatter system I played with, we used 2
common (scatter) volumes and 2 different linear polarizations.
2 big 30' dishes fed 4 identical front ends, IF's and demodulators. The
strongest signal was selected post detection and fed to the
data decoders. Later, pre detection combiners were used to eliminate 3
detectors, about 3 racks of equipment.
For space diversity a decent physical separation between antennas is
needed, like multiple wavelengths.
I am planning a 23 cm eme system with LINRAD, using 2 polarizations on
RX, RHCP and LHCP and 1 polarization on TX.
OK1DFC feed, 8' (2.4M) solid dish, and az/el drive are on hand and
pondering installation details.
Stan, WA1ECF FN41sr Cape Cod
A thread on another reflector prompted me to consider using Linrad as a diversity
receiver (after all, the Dual Polarity receive is just a special case of diversity
receiving) , by feeding one receiver into one input channel and the other receiver
into the other input channel, just as one would do with H and V elements for 144 MHz
EME, for example.
I first tried this with 2 receivers with two different 432 MHZ antennas [one a
circular satellite antenna, the other a vertical stack of 4 Hpol yagis] listening to
a 432 MHZ CW beacon about 45 miles away. Using Linrad for diversity reception in
this fashion seems to work pretty well, but I wonder if the time constant of the best
linear combination machine [that is likely a misnomer given my math and recall
abilities] is a bit too slow for non-polarity-related diversity reception. Is there
a way to change this time constant? How does it relate to the setting of the 'usual'
I also noted that hitting "X+Y" in the baseband window with polarity fixed and at
zero does not send one input channel to one ear and the other input channel to the
other ear as I expected it to.
I plan to put up another HF antenna to try diversity reception with 2 HF receivers
and 2 antennas and Linrad.
Has anyone else tried this?
Has it been discussed before? I think it has, or at least Leif mentioned it
somewhere, I think, but I couldn't find any references to it tonight.
Thanks in advance.
PS I didn't detect MGS but it was fun to try ;)