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[aprssig] APRS on all Radios!!!!

Steve Grantham aa5sg-2 at sera.org
Sun Aug 17 16:27:15 UTC 2008


Wouldn't the 120-Hz subcarrier still be problematic for phase modulated 
rigs?  And, wouldn't this type data interfere with the CTCSS or DCS signals 
used with many repeaters in service today?

Why not simply use something like MIC-E?   With the use of properly 
implemented CTCSS, repeater users would not hear the MIC-E packets.  Perhaps 
the goal here is simultaneous voice and data transmission?

What about using the other end of the audio spectrum?  Use PSK-31 with 
something like a 4-kHz subcarrier that might be just outside the audio 
passband of the audio frequency (AF) receiver section.  PM transmitters 
could handle that AF easily.  (Not too high a subcarrier frequency though as 
system deviation and channel bandwidths would need to be preserved.)  Pick 
it up before the receiver AF section and send it to the demodulator.  If 
necessary, add a series op-amp filter to  notch out any excess PSK tone 
prior to audio injection to the receiver speaker amp or repeater audio 
coupler.  If that didn't work, then maybe we could move away from PM or FM 
to something like GMSK and explore other data transmission scenarios?

How about using MIC-E on the uplink and modulating PSK-31 at the FM repeater 
transmitter for the downlink?  This would make it easier to implement at the 
user's rig and let the repeater trustee be the one responsible for dealing 
with the PSK-31 deviation at the repeater.  (Hmmm... Someone could possibly 
build and market a kit for the end user MIC-E/PSK-31 gadget?)  What could be 
easier?

Steve, AA5SG


----- Original Message ----- 
From: "Bob Bruninga " <bruninga at usna.edu>
To: "'TAPR APRS Mailing List'" <aprssig at lists.tapr.org>
Sent: Sunday, August 17, 2008 9:28 AM
Subject: Re: [aprssig] APRS on all Radios!!!!



<snip>

>> Needs careful thought/design.
>> This is a problem for Phase modulated rigs
>> because of ... low freq components...
>
> Could it simply be PSK-31 encoded? What is the lowest carrier tone that 
> can carrry PSK-31? Some APRS dongles already are starting to decode 
> PSK-31.  And with say a 120 Hz carrier, it would seem that it would remain 
> sub-audible?  We would of course add CRC checks to make each info packet 
> complete.
>

<snip>

> Bob, WB4APR
>






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