[aprssig] 10 MHz transmitter for APRS

[Robert Bruninga]

Using an Xtal oscillator and only about 6 transistors it is 
possible to make a 300 W transmitter that will fit in a
cigar box.  See the class-E amp in QST about 5 years
or  more back.  I been hoping someone wouild put
it into an APRS TX only rig for mobiles.  It can be
so small because it only  Xmts for 2 secs out of every
10 mintes so dont need a heat sink..

Bob


>>> WA8LMF2 at aol.com 1/13/05 1:24:39 AM >>>
Wes Johnston wrote on 1/12/2005, 8:05 PM:

 > Makes me wonder if PSK31 would be a solution for you....  well the
PSK31
 > transmitter kits from http://smallwonderlabs.com/ .  Use one of
those
 > with a
 > tinytrack in 300baud mode, and you might have a winner.

The Small Wonder PSK transceivers are very low power devices (5 watts
or 
less). PSK31 is effective at very low power levels because: A) It uses

an extremely narrow bandwidth that intercepts very little noise and
QRM, 
and B) not every character has to be received perfectly to understand 
the message.

Standard packet, as used on APRS, requires that EVERY bit of a packet 
burst be received PERFECTLY before ANY data can be recovered from it. 
The 300 baud FSK signal has an effective bandwidth 10s of times wider 
than a PSK signal, and is therefore far more vunerable to noise.

To use HF APRS at all reliably, you will need a decent mobile whip and

50-100 watts TX output.

I have pondered using an FT-817 with a 5-->100 watt CB amp for this 
application.


Stephen H. Smith                wa8lmf (at) aol.com

Home Page:                      http://wa8lmf.com 

New/Updated Symbols for         http://members.aol.com/wa8lmf/ham 
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