[aprssig] HT-220 HT's for APRS
noskosteve at yahoo.com
Fri Jul 20 12:03:13 CDT 2007
OT, but I figured many of you would be interested in this...
I confirm that the normal PTT micro switch is also the T/R switch. The remote mic must have
required a relay; I'm too lazy to dig out a manual and look, but it *must* be so.
I probably have some of those relays. I know I have some relays that are the same size as that
micro switch, and would therefore fit, but memory fades whether they are the exact ones.
It is a 15 V radio. I try to keep my battery charged, but haven't checked it in a while.
I also still have my synthesized HT-220 and it works fine. It is the first synthesided 2M hand
held ever, as far as I know. I did it in 1973.
The synthesizer is inside the extension called the omni housing. The current drain is 6-7ma.
In those days, 2M FM was only 146-148.
To keep drain low, I used a mix down then divide-by-N which was CMOS running from .6 to 1.6 MHz.
Therefore it digitially only does one MHz., so there is a mix-down crystal for each Mhz. and thus
two for Rx and two for Tx (as an Engineer, crystal samples are a cheap ham parts source). This
oscillator, multiplier and harmonic-mixer is three transistors and no tuning. 5Kc steps is done
by diode switching a little cap on all the Mix-down crystal oscillators.
The VCO's are ON FREQ - meaning the Tx VCO needed good shielding. I also used one of the new
Statek tuning fork 10 Kc crystals to eliminate the reference divider. The Ref. oscillator
components are under the Statek TO-5 can.
Interfacing to the radio was rough and it only put out 0.5 W or something like that. I think 2W
A year later I went from the dual BCD DIP switch frequency entry to a keyboard, LED readout
system with some ICs that were ideally suited, however, that board is external !
Dale Heatherington's synthesizer version kit was available in 1976. I also have two of his
Years ago I sent info & pictures to a "HT-220" site, but I don't think he added it. I should
have pix on this computer if anyone wants to see.
I also have a Midland 13-510A on 2M, with a PL board stuffed somewhere....
73, Steve, K9DCI
--- Robert Bruninga <bruninga at usna.edu> wrote:
> Has anyone used the old motorola HT-220 HT's for a simple cheap
> APRS radio? I found a box full of them in my garage.
> I remember doing one years ago, and the only rub was the lack of
> a PTT relay. I think I might just use some diodes and 1/4 wave
> line this time?
> What about XTALS? That can really run up the cost.
> Bob, Wb4aPR
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