from K3UK's HF-APRS YahooGroup.
-- Forwarded message --
From: oe3mzc mailto:oe3mzc%40oevsv.at[EMAIL PROTECTED]
Date: Dec 18, 2007 4:22 AM
Subject: [HF-APRS] Frequency accurracy tolerance tnc? main problem for
HF-APRS shortwave ?
To: mailto:HF-APRS%40yahoogroups.com[EMAIL PROTECTED]
many tncs for 300baud FSk packet radio used for APRS on hf only
decode within a very narrow frequency window of abt. +-30Hz.
(KAM, MixW, AGWPE, PK232,SCS PTC-2,TNC-2 etc..)
This is very difficult to adjust and represents the main reason for
failure in decoding hf-aprs signals.
To my knowledge there is only one hardware that could cope with
frequency drift in a much better way: a DSP-TNC from SCS
see:
http://www.scs-ptc.com/datasheets/scs_datasheet_tracker_english.pdfhttp://www.scs-ptc.com/datasheets/scs_datasheet_tracker_english.pdf
This DSP modem can simultaneously decode multiple signals in a
bandwith of up to plus/minus 400Hz around an adjustable center
frequency, e.g. all signals with a 800Hz bandpass will be decoded.
When connected in AX25 to two stations at same time, the tnc will
even adjust its own transmitted qrgs according to the two partners
and their individual offset automatically.
The most helpful feature however is the frequency readout.
the comand ESC %M enter will display a Mheard list with offset
frequencies. This can be used to for tuning.
example from 30m APRS channel in Europe:
* %m
*
DIRECTLY RECEIVED HF-PR STATIONS:
WIDE3 -15 Hz, DM5LW +25 Hz, OE3MZC-9 -25 Hz, OE3XMU -25 Hz
DF5WXF-2 +25 Hz, F4CKT +25 Hz, F6KPH-4 +18 Hz, DF4FO -25 Hz
DF4FO-3 -25 Hz, SR3NWY -25 Hz, DB0CHV +0 Hz, SL5ZL -25 Hz
F5ZQC-4 +25 Hz, WIDE5 -25 Hz, G0JXN-10 -3 Hz, RA3IM -6 Hz
F5LEB +0 Hz, TRACE3 +0 Hz, F6KCF-10 +0 Hz, TRACE2 +0 Hz
EA6XQ -6 Hz, EA6XQ-5 +25 Hz, RELAY -6 Hz, UA1WCF -28 Hz
HB9CGH-4 +0 Hz, UA1WCF-2 -25 Hz, WIDE7 +25 Hz, F5KCN-3 +25 Hz
WIDE2 +0 Hz, G7EOB-7 +0 Hz, G0IQK-10 -25 Hz, MB7UJ +0 Hz *
AA1XD -25 Hz, W1JMC -50 Hz *OZ4DX -43 Hz, W1ON -6 Hz,
EA6AFM +0 Hz, OK2PEN -28 Hz, EC2A-1 +25 Hz, EB2EMZ-8 +25 Hz,
73 de Mike, OE3MZC
I use this very same TNC to transmit my 30 metre HF APRS signals via
an Icom 703, from my motorcycle mobile.
Have found no trouble for Igates to receive my signals and most of
them are using older TNCs. The real good part of this TNC is it can
transmit in SCS Robust Packet mode, which is better than ordinary 300
baud HF Packet. The other things with this TNC are, it only has a USB
interface, which limits connectivity for many Packet programs. There
is NO on board mailbox either, like TNCs of old.
I have been looking for software that has inbuilt Mail box facilities
that works with the USB of this TNC.
As Mike points out in his post, the freq tracking of this TNC is
awesome and its a good product, just needs a few design changes to
make it more appealing ;-)
73s
Jack VK4JRC
