[GreenKeys] Diversity with two ST-8000A's

[Ron Ott]

A couple of the ST-8000As sold on eBay had Option 1 installed, per the item description.




________________________________
From: Roy Morgan <k1lky at earthlink.net>
To: Michael M. Raskin <rask1553 at bellsouth.net>
Cc: GreenKeys at mailman.qth.net
Sent: Tuesday, October 20, 2009 8:32:46 PM
Subject: Re: [GreenKeys] Diversity with two ST-8000A's


On Oct 20, 2009, at 11:19 PM, Michael M. Raskin wrote:

> Has anyone done this?  I have two 8000A's and would like to try it.  
> Can someone give me some pointers and/or some references to read on  
> this.

Mike,

Do you have a manual?  It mentions that the Diversity function is  
operative only with "Option 1" or some such installed.  I understand  
that this is a different EPROM chip that must be installed in the  
unit.  You can, of course, get that from HAL.  I suspect  you'd need  
two.

Here is some authoritative info written by the ST-8000A designer at  
HAL, Bill Henry, posted to the list by Dino Papas in June ;09:
(The "1230A/M is the unit made by the other company with which the  
8000A is completely compatible.)

...
Diversity:  The ST-8000A will even work diversity with a 1280A/M (or
with another '8000A, of course).  But, the diversity systems in the
ST-8000 and ST-8000A are very different.  The ST-8000 uses "Selection
Diversity", the best of two RTTY signals is chosen based on S/N.  The
data output to the printer is switched to the modem that has the best
signal.  The ST-8000A and 1280A/M use "Combination Diversity". In
this case the Mark outputs and Space outputs of each modem are
paralleled and the resulting vector-sum Mark and Space audio signals
are detected and used to drive the data output.  In theory,
Combination Diversity will produce copy even through short fades of
Mark or Space signals (selective fading).  But, if you have any
interference in either Mark or Space channels of either modem, the
interference may dominate the detector and what might have been an
otherwise good copy may be trashed by the interference.  Selection
diversity shines when completely different antennas and different
receiving frequencies can be used.  Combination works best on just
one frequency and with similar antennas.  The Dovetron MPC-1000 also
used combination diversity.  Hank and I lost a lot of sleep arguing
this issue in the wee hours at the RTTY Journal Hospitality Suite at
Dayton for several years in a row.  There probably is "no best
solution" - but I'd never admitted that to him!

That's more than the "short form" - but my fingers wouldn't stop.

Bill, K9GWT
>

Roy Morgan
k1lky at earthlink.net
529 Cobb St.
Groton NY, 13073
Home: 607-898-3607
Cell: 301-928-7794



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