[aprssig] HT's for APRS devices

[Robert Bruninga]

I just learned this about the VX-150 5W HT
while building a tracker (floating buoy).

I was surprised that it runs on 7 volts to
14 volts and yet is spec'ed at 5W at any
voltage inbetween.  If it were using a series
regulator it would get hot and waste power
on 12 volts.  It doesnt.

Looking at the shematic, there is a complex
feedback system to the final Amp that uses
feedback to keep a constant power from the
FET PA.  Thus, it is operating efficiently at
any of the voltages.  

The Receiver circuits though, run on a common
series regulator and so are operating at less
and less efficiency with the higher voltage.
Thus, better to operate on an 8V battery 
system if you have to design it yourself.

Probably other HT's do this same kind of power
handling.  Oh, and another thing, the Battery
terminals are connected directly to the same
external 13.8 external power by simply an
isolation diode.  So in this case, I can just
solder the 12v buoy battery system to the
HT's 8v battery connections and not worry about
blowing up the radio.

Saves the potential problmes of dealing with
a rat-shack power connector... in a salty
environment on a throw-away buoy.

Just thought someone might find this useful.

de Wb4APR, Bob