[GreenKeys] PERFECT EXAMPLES OF MYSTERY BOXES.

[Wndrrt at cs.com]

Thank You Roy!

Now that was another slam dunk answer for the beginner.  I started my collection of knowledge on terminal units by going to the sites you told me about.  

I am using a ST-5A terminal unit to take the audio signal from my Heathkit SB-101 and feed it to my 19 set.  This I understand was normal for the period because the ST-5A comes with a loop supply.  Since computers and monitors have been around, I would guess that there are several terminal units that do not come with a loop supply which presents a problem to the beginner.  How to tie the, "low level RS-232 and the like" to the loop supply.  So, now I am asking myself are there new systems and companies, say HAL, who build the ST-5A of the year 2005?  How about the computer program MMTTY that I have been using as a learning tool.  Does this program for the most part take the place of many of these 70s and 80s Hals and Dovetrons and others that I have been calling mystery boxes.  Another point:  From what you have told me, it sounds like AFSK was a problem in the past or the hi days of the ST-5A, but now systems have improved to where the audio signal is stable enough to do the job. 

(let me say it like you)
- Jan Bogue, KD6EMW since Oct. 2004 - yes, I am "Keeping 'em Glowing!" Thanks to you detailed help.

Thanks Roy,
Jan 


Roy Morgan <roy.morgan at nist.gov> wrote:

>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!
>7130 Panorama Drive, Derwood MD 20855
>Home: 301-330-8828 Cell 301-928-7794
>Work: Voice: 301-975-3254,  Fax: 301-948-6213
>roy.morgan at nist.gov --
>
>