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" <[email protected]>
To: "Green Keys" <[email protected]>
Subject: [GreenKeys] Space diversity receive antenna
Message-ID:
<[email protected]>
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