[GreenKeys] Various XMission forms

[Dale]

Ralph,


Very interesting.  I imagine AFSK using NBFM would have been legal above 29 MHz, but disastrous on the lower bands.


I've often thought of trying to use the reactance modulator in my AF-67 as a direct FSK driver: just inject +/- FSK voltage directly to pin 1 of the reactance modulator tube and see what it does.


BTW - In the early 1980's I was in college and poor as a church mouse, yet still wanted to get on RTTY.  A friend gave me a Model 15 Teletype (but no cover - man was that loud for the roommates in my apartment!).  I designed and built a solid state terminal unit that detected only the space tone.  I think I set it up for around 1000 Hz.  I used an Elmac PMR-8 receiver.  I had to constantly readjust the frequency using the BFO knob to keep up with the drift.  Interesting that overloading the receiver with too much RF/IF gain never really affected copy.  For transmit I used a shift pot keying circuit tied to the cathode of the VFO tube on my AF-67.  It worked well.


When I graduated from college I moved up to an ST-5 T/U and threw the homebrew away.  Dumb.  But I also moved up to a Drake 2B receiver which was and is still a fantastic RTTY receiver.


73,

Dale

W9DKB





________________________________
From: greenkeys-bounces at mailman.qth.net <greenkeys-bounces at mailman.qth.net> on behalf of Ralph Irish <w8roi at wowway.com>
Sent: Friday, February 16, 2018 7:54 PM
To: Greenkeys
Subject: [GreenKeys] Various XMission forms

A bit back before I eventually got on RTTY, I had a 'brainstorm' about how I might get on
RTTY.  Since most of the literature classified FSK as a 'form of FM', I figured I could put
my AFSK tones into my Multi-Elmac AF-67 in the FM mode and come out with something
resembling (A)FSK.

I ran that idea past the late Keith Petersen, and he cringed when I finished talking.  I guess
that such a signal on HF would have sounded quite bad and most likely very wide.  He gave
me a description of what the modulation would do, etc, and basically said, "NO!!!"
So, I filed that one under 'never do' and moved toward some kind of FSK or AFSK on HF.

People using AFSK on 2m FM get the same type of modulation result.  Just that very few were
using FM on the HF bands.  Elmac and a number of other companies had FM on many HF
transmitters.  It was a permitted mode on most of HF.  Not legal on 160M back then and
possibly some parts of other HF bands.

74,

Ralph - W8ROI


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/greenkeys/attachments/20180218/672632c6/attachment.html>