[aprssig] Need help testing 30m HF APRS in the Northwest

[Stephen H. Smith]

ben at ben.com wrote:
> On Sun, Jul 30, 2006 at 09:18:11PM -0400, Stephen H. Smith wrote:
>   
>> The actual mark and space frequencies for 30M HF APRS are 10.149.2 and 
>> 10.149.4 .
>>     
>
> Yes, I'm doing direct FSK at 10.149.200 and 10.149.400.
>
>   
>> Because of the very narrow receive passband of most TNCs 
>> on 200 Hz shift on HF,  you MUST be within 10-20 Hz absolute of the 
>> correct frequency on transmit.
>>     
>
> Well, the transmitter and receiver have to agree within about 20Hz.
> How do HF gates generally maintain that <2ppm accuracy?
>
> It may be that a mobile HF APRS beacon is impractical.  If so, I'm
> learning it the hard way.
>
>   

It's quite easy for any modern HF transceiver with a TCXO master 
standard for it's synthesizer to maintain +/5 Hz or better indefinitely 
on mid HF freqs.   For old mechanical VFO rigs like TS-820s or early 
synthesized rigs, fugetaboutit !

I have no trouble using my Yaesu FT-100 with the optional hi-stability 
standard as a mobile APRS tracker on 30M.    [The FT-100D has the 
high-stab osc as standard equipment.]    Any recent rig such as an 
IC-702, FT-897, etc with it's high-stab option will have no problem.   

If you are doing direct FSK of a simple crystal osc rig, put the crystal 
in a oven, let it reach a stable temp for a few hours and then calibrate 
it.


In the constant room-temp environment of my house, I am using a Kenwood 
TS-50 with standard osc as an HF monitor/igate. It has stayed on freq, 
as verified against my IFR-1500 service monitor (good to about 1 Hz at 
HF) for almost two years now without tweaking. 





--

Stephen H. Smith    wa8lmf (at) aol.com
EchoLink Node:      14400    [Think bottom of the 2M band]
Home Page:          http://wa8lmf.com


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