[GreenKeys] Space diversity receive antenna

[Brooke Clarke]

Hi Harold:

Yes, diversity is a very good idea on HF RTTY and was the standard for a long time.
Note there are different flavors of diversity, for example two identical antenna systems spaces a wavelength or more 
apart gives you space diversity.  There's also polarization diversity and frequency diversity.  Minimum Shift Keying 
(MSK) has little frequency diversity, but there's some for shifts that are wider than the minimum.  An extreme case of 
frequency diversity is "Chirpcom" where a 40 character message is sent over and over in time while the carrier sweeps 
from 2 to 30 Mhz.
https://prc68.com/I/RCS-5A.shtml#Cc

Time diversity also works.
The MD-1142/UGC is a time diversity modem.
https://prc68.com/I/MD1142.shtml

-- 
Have Fun,

Brooke Clarke
https://www.PRC68.com
axioms:
1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.

-------- Original Message --------
> Date: Sat, 4 Jan 2025 10:29:50 -0700
> From: "Harold Hallikainen"<harold at w6iwi.org>
> To: "Green Keys"<greenkeys at mailman.qth.net>
> Subject: [GreenKeys] Space diversity receive antenna
> Message-ID:
> 	<f45f6025e43820aedf4d2ea03213b318.squirrel at hallikainen.org>
> Content-Type: text/plain;charset=iso-8859-1
>
> I'm really having a problem with QSB. A received signal (20 meters) goes
> from great to down in the noise over several seconds. As an experiment, I
> transmitted both mark and space tones from here in Tucson AZ and received
> them on the KFS SDR in Half Moon Bay CA. I then ran the recorded audio
> into the DSP TU and output the levels of the mark and space filters. The
> results are at
> https://w6iwi.org/script/csvgraph.html?CsvUrl=https%3A%2F%2Fw6iwi.org%2Frtty%2FTuNotes%2Fms220517a.csv
> .
>
> This reminds me of a TV station where I lived in San Luis Obispo CA that
> had a long microwave feed. They put two receive dishes on their tower and
> had a carrier operated relay in the receiver start a slow astable
> multivibrator that switched the receiver input between the two receive
> dishes. The switching would stop when a good signal became present.
>
> So, how about applying this to RTTY? I am using a 30 foot vertical for
> transmit and receive. I could put up a 20 meters dipole about 50 feet
> away. During receive, I could switch between these two antennae.
>
> Is this worth trying? I could use signal strength indicated by the
> receiver. Or I could use something from the terminal unit (such as switch
> during mark hold).
>
> Is anyone using space diversity? Comments?
>
> Thanks!
>
> Harold
> https://w6iwi.org

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/greenkeys/attachments/20250105/abd624d1/attachment.html>