Harold,

In the heyday of RTTY (1940s-1980s?) space diversity was standard for long distance/ intercontinental HF RTTY, like RCA Global & military.  Most systems combined the two receivers in real-time rather than trying to switch them.  The Navy even used triple diversity with three antennas and three receivers. The Army CV-116 and the Navy URA-8 & -17 are good examples of military units.  Collins made a diversity FSK converter for commercial service. I believe that the Dovetron MPC-1000 series were set up for paring two units for diversity operation.

Most (if not all) of the receivers at KPH/KFS would have been set up for diversity.

There seems to still be some frequency diversity RTTY on the HF bands.  You can often hear what sounds like the same digital signal being sent a few hundred KHz apart.  (Frequency diversity makes more sense shipboard, where you don't have a lot of room for antennas.)

have fun,

Duncan
K2OEQ



On 1/4/2025 12:29 PM, Harold Hallikainen via GreenKeys wrote:
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