[OZAPRS] HF frequency drift reports ...?

[Gerard Hill]

On 30/06/2011 7:31 PM, OE3MZC Mike wrote:
> However it would be much easier for mobiles if more I-Gates would have
> 800Hz"wide band" receive capabilities...10times better.
> I think there is not just the SCS DSP-TNC that can do this, but also some
> software for soundcard from G4hyg
> http://www.crosscountrywireless.net/aprs_messenger.htm
> but I am not sure...

After becoming interested in QRP APRS on HF I started running the APRS 
Messenger software. It allows operation using some more efficient modes 
than regular HF APRS. It also provides a variety of different speeds 
from 63 bits/s to 250 bits/s. The receiver is frequency agile and 
decodes all 8 supported modes simultaneously within a range of ± 100 Hz. 
The actual mode only needs to be set for transmit - I normally use 
GMSK250. GMSK is Gaussian Minimum-Shift Keying - the mode used in GSM 
mobile phones. It works at a much lower signal to noise ratio than 
frequency-shift keying. There is also PSK and QPSK. Anyone who has tried 
PSK31 will know how well it works with weak signals. Now apply that to 
packet radio...

There are IGates operating on 10.1497 MHz and 7.0347 MHz (carrier), very 
close to the FSK300 frequencies. In fact the same transceiver can be 
used to service FSK and GMSK/PSK/QPSK. Unfortunately Mike, the beaut 
decoder in APRS Messenger does not decode FSK300 packet as one of the 8 
modes.

Just about any PC can be used to run APRS Messenger, even a Netbook. A 
regular sound card is used to connect to the transceiver. It talks 
directly to the APRS-IS and can interface to UI-View or APRSISCE 
software if you need it to. There is not yet a TinyTrak or OpenTracker 
implementation, so for mobile use the only option at the moment is to 
run it on a small PC.

APRS Messenger provides some exciting new modes that have not seen a lot 
of activity yet so look out for the stations using -63 and give it a go!
http://aprs.fi/info/?call=*-63

There are some options for frequency agile FSK300 packet decoders (apart 
from the Tracker DSP TNC). I haven't tried any of these and they aren't 
necessarily free. They have been mentioned on the Cross Country Wireless 
mailing list.
- TrueTTY  http://www.dxsoft.com/en/products/truetty
- APRS-SCS http://www.tapr.org/~kb2scs/scs01.html

Cheers ... Gerard, VK2IO