[GreenKeys] Fwd: ST-8000 vs ST-8000A - short form

Fri Jun 5 17:38:48 EDT 2009

Great stuff!

Dave. WD9ITR

On Fri, Jun 5, 2009 at 2:57 PM, Dino Papas<kl0s at cox.net> wrote:
> Bill Henry was kind enough to share the history of the ST-8000 and
> ST-8000A and I thought some of you would be interested in hearing
> about the fascinating development cycle for the two TU's.  Makes me
> appreciate mine all the more!
>
> Thanks to Bill for taking the time to share.
>
> 73 to all.....
>
> Dino KL0S
> ---------------------------------------------
> Begin forwarded message:
>
> From:  ghenry at halcomm.com
> Subject:  Re: [GreenKeys] ST-8000 vs ST-8000A - short form
> Date: June 5, 2009 3:12:37 PM EDT
> To:       kl0s at cox.net
>
> ST-8000:  I designed this modem in 1984-1985.  It has all the bells
> and whistles I had ever wanted in a RTTY demodulator.   The design
> made heavy use of the then-new switched capacitor filters offered by
> Reticon.  The filter center frequencies are set by the switch clock
> frequency. So, there are five frequency synthesizers on the digital
> board - input band-pass filters, Mark filter, space filter, and low
> pass filters.  Each synthesizer is set by the front panel controls.
> And, there is also another synthesizer for the TX audio tones.  Drew
> White, K9CW, designed the synthesizers and the digital control
> circuitry.  I had a lot of fun designing the CRT.  It used a very
> neat rectangular tube made by AEG Telefunken - only cost $35 in
> 1983.  Last time I bought some (1990?) they were $500 and had a 100
> pc minimum order - not available at all, now.  I spent a lot of time
> tweaking the circuits of the ST-8000, playing cassette taped I had
> made of various "nasty signals" over the years.  I did side-by-side
> print outs with the same signal passing through several modems -
> ST-6, MPC-1000, ST-6000, 1280, and the under development ST-8000.  I
> tweaked until the ST-8000 DID work better than the others.  I also
> devised my own HF simulator and tested all modems against it - again
> tweaking to be "the best".  Obviously this is a cut and try approach
> and no doubt there are some conditions I may have missed.  But the
> design has now stood the test of time.  This design also used most
> every part in our inventory and each modem took almost 20 hours to
> build.   It was NOT a cost-efficient design.
>
> The ST-8000A:  This design evolved to meet hard specifications set by
> the government, specifications that were identical to those in the
> 1280A/M manual.  I started with the ST-8000 design but then the
> ST-8000A design developed a life of its own.  At the time, the
> military had a lot of sheltered enclosure RATT set-ups that used the
> 1280A/M and it was therefore an inflexible spec. that whatever modem
> was bid had to be "form, fit, function', and connector"
> interchangeable with the 1280A/M.   That turned out to be a BIG deal,
> but we did it.  The resulting ST-8000A has the basic form of the
> ST-8000 but with many "minor" changes to meet the form, fit,
> function, and connector requirement.  And then there were the
> reliability and host nation requirements.  The reliability has to be
> 25,000 hours MTBF or better.  There is no way to include a CRT tube
> and its HV supply and meet that requirement.  So the scope had to be
> taken out.  Low cost commercial IC's used in the ST-8000 had to be
> replaced with MIL-883B rated components - for example, trading a
> $0.25 dual op-amp for a $17.00 MIL job.  The resulting modem has a
> computed MTBF of 50,000 hours (MIL-HDBK-217, Individual Parts Stress
> Analysis).  Also, the modem had to work in all NATO countries and be
> compatible with their safety and power standards.  Therefore, it is
> designed to work with 115/230VAC, 47 to 440 Hz power sources.  And
> safety standards in other countries are usually much tighter than we
> have with UL approval.  This impacted the design of the transformer
> and all AC components and even the vent hole size in the covers.
> And, the connectors had to be the same round MIL-jobs used on the
> 1280A/M.  Further, the most important connectors (data and audio I/O)
> are NOT standard - the pin inserts are rotated with respect to
> "normal" connectors of that size and pin count.  All this added up to
> a lot of extra cost - and extra labor.  It took 28 hours to make each
> modem and almost that long to do Q/A, testing, and boxing of each
> one.  The resulting modem will withstand a harsh environoment.  But,
> some specifications such as selectivity and sensitivity are slightly
> less than those of the ST-8000 - but still in excess of the 1280A/M
> spec's required by the government.  You can stack any mix of
> ST-8000A's or 1280A/M's in a rack and hook them up and all will work
> the same, even with respect to the Remote Control and diversity
> features.  That was a primary requirement.
>
> 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
>
>
>
> At 06:48 PM 6/4/2009 -0400, Dino Papas wrote:
>
>> Bill -- I wonder if you'd be able to share a little with the RTTY
>> groups of the layman's version of what the ST-8000A was designed and
>> built for vs. the ST-8000 (my favorite as well, and still looking for
>> a TT/L-2!).  I think the guys may be interested.  Obviously it's a
>> winning piece of gear since it's still on the market!
>>
>> 73 -- Dino KL0S
>>
>
> ______________________________________________________________
> GreenKeys mailing list
> Home: http://mailman.qth.net/mailman/listinfo/greenkeys
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:GreenKeys at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>