[aprssig] HT-220 HT's for APRS

Steve Noskowicz noskosteve at yahoo.com
Fri Jul 20 13:03:13 EDT 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
was normal.
  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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