[GreenKeys] Space diversity receive antenna

[Richard Knoppow]

    RCA made a triple diversity receiver, the DR-89. Its handbook is on 
line. This consisted of three AR-88 type receivers with minor 
modification with a combiner and other accessories. Switching was by 
means of the strongest signal dominating the detector output. The 
antennas are the key, they are large and spaced a few wavelengths apart. 
These were CW although a frequency shift accessory was available.
     RCA built more elaborate receiver systems for its own use at its 
major transoceanic stations.
     RCA also had a unique multiplex printer system used in its own 
stations.
     The point to point receivers at Bolinas would have been diversity 
but I am not so sure of KPH, which was a maritime station, same with 
KFS. MacKay/ITT also had fixed point to point stations.

On 1/4/2025 9:50 AM, Duncan Brown wrote:
> 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
>>
>>
>>
>>
>>
> 
> 
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-- 
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998