[GreenKeys] PERFECT EXAMPLES OF MYSTERY BOXES.

[Roy Morgan]

At 11:58 PM 12/15/2004, you wrote:
>I went by ebay today and saw more mystery boxes: ... and Dovetron Tempest 
>MPC-1000T II RTTY Terminal Unit.

Jan,

The Dovetron (that particular model) does not have a loop supply in it. The 
inputs and outputs are low level RS-232 and the like.

Some time ago here on this list, a number were made available (I have one 
of them), so a number of guys here are or will be familiar with them.  You 
can get a manual for this model at:
<http://www.qsl.net/w6ger/pdfdocs/docs.html>

>  I have heard the
>name HAL before.  Is this a famous name in RTTY?

Yes. HAL Communications is still in business, can supply manuals (as far as 
I know) for older equipment, and has a web site at:
http://www.halcomm.com/


>   Dovetron Tempest sound impressive I think, but what does MPC stand for.

Multi-Path Correction (I think.)  Tempest is a collection of engeineering 
methods and mechanical/electronic features intended to reduce 
electromagnetic radiation from the unit to reduce the possibility of 
clandestine detection of the signals being processed.  You don't need that, 
but the Tempest Dovetron is a very fine unit (if you can solve the problem 
of driving and detecting normal loop current/voltage separately.)

>  Do some have loop supplies?

Yes some do.

>  Do some only receive and others only send?

Few only send..and that would be called an FSK keyer or exciter*.  Some 
both receive and "send": sending can be either keying of a loop or creation 
of audio frequency shifted tones for input to an SSB transmitter.

*  The terms "Keyer" and "exciter" have been applied to two kinds of units:

1) Generation of audio tones for driving the audio input of SSB 
transmitters (and AM transmitters for use at VHF and UHF.)  Normally, the 
tones are at 2175 and 2295 Hz (850 hz shift), but commercial units often 
times allow varying the shift amount and the center frequency.

2) Generation of RF signals that are frequency shifted. In this category, 
two subdivisions exist: those whose output is between 2 and 4 mc and 
is  mulitplied in the transmitter, and those whose output is at the desired 
transmit frequency, no matter where in the HF spectrum it 
falls.  (Examples, respectively, are the Northern Radio Company Model 105 
or 115? and the Technical materiel Corporation XFK.)

Note: in the Byron Kretzman paper and other literature of the time, "FSK" 
meant shifting the RF carrier, usually at the VFO or Crystal, and "AFSK" 
meant applying shifted audio tones to the mike input of an AM transmitter, 
or later to an SSB transmitter. Kretzman's cautions about not using AFSK on 
the low bands were based on the poor spectral performance of available 
equipment. Then, professional equipment did a fine job, and now solly state 
circuits are likely to do just fine, too.  That includes the personal 
computer with software to generate the audio tones using the sound card.

Roy



- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
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