[GreenKeys] Diversity

[Richard Knoppow]

----- Original Message ----- 
From: "Jeffrey D Angus" <jdangus at att.net>
To: <greenkeys at mailman.qth.net>
Sent: Sunday, March 24, 2013 10:49 AM
Subject: [GreenKeys] Diversity


> Looking at that converter Larry posted, does anyone
> actually RUN
> diversity on reception these days?
>
> Diversity to me brings up images of a pair of large
> antenna arrays,
> and two Collins R-390As with a complex "voting" system to
> decide
> who's got the best bits to decode.
>
> Which leads to my next question. Is there any "modern"
> diversity
> software out there. Something that can, for example, talk
> to a pair
> of CAT enabled transceivers and a pair of sound cards like
> the USB
> SignaLink series?
>
> Jeff-1.0
> wa6fwi

    It would be interesting to know what's in this box.  I
learned about a much older diversity system, the RCA DR-89,
while restoring an AR-88F, one of the receivers used in it.
The system here is very simple, the three receivers use a
common diode load resistor, which is located in the
combiner. The idea is that whichever diode has the strongest
signal biases off the other two. The system was designed
mostly for CW although it can also work with modulated
signals.  The combiner has a tone generator with a biased
keyer that is adjustable for the level of signal from the
common load resistor that will key a local audio frequency
oscillator.  The output of this is sent via a line to the
register.  The antenna system for this consists of three
antennas spaced ideally at the apexes of an equilateral
triangle and about 1000 feet apart.  RCA used two-bay
"fishbone" antennas in their receiving stations at Riverhead
L.I. and at Pt. Reyes.  However, diversity will work with
much smaller and simpler equipment. In fact, one can get a
substantial diversity effect from a vertical and horizontal
antenna even though closely spaced.
      The diode load coupling evidently has a fairly sharp
transition from one receiver to another as the signal
strength varies but the AVC line can also be used by just
coupling the AVC busses of two or more identical receivers
together. The stronger signal dominates but does not cut off
the weaker signals as in the diode load scheme.  The DR-89
had provisions for adding an adapter for frequency shift
keying but I have no information at about it or even if it
actually existed.  The FS would probably have also been for
Morse rather than RTTY but I suppose could have been either.
These old Morse circuits ran at astonishing speeds, up to
600 wpm per channel although average speeds were probably a
fraction of this.  Diversity can also be used for voice but
I think the RCA set up was probably not used that way, at
least not very often.
     I suspect the more modern diversity converters are more
sophisticated.
     I am not sure if space diversity (there is also
frequency diversity) originated at RCA or Bell Labs but the
references I have to it are all from RCA.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com