[aprssig] DTMF on HF?

Erv Heimbuck erv at heimbuck.com
Fri Jan 10 18:04:48 EST 2014

The airlines use tgone signaling on HF for the over water runs.  In order to
make that work they use AM for the signaling but switch to USB for the voice
communications.  Primarily because the accuracy of the frequency in order
for the tones to decode was much more critical than what they could maintain
carrier frequency.  The tones depend on tuning on sideband but on AM
frequency changes do not change the frequency bveing transmitted.  I
occasionally listen to Aircraft HF  and always wondered.  One of our ham
club members designed the decoders used by the airlines for this so I asked
him and that was his answer.  I then would switch to AM when they annouceed
a selcal test and sure enough the tones are crystal clear in that mode.

For what it is worth.





From: aprssig-bounces at tapr.org [mailto:aprssig-bounces at tapr.org] On Behalf
Of Robert Bruninga
Sent: Friday, January 10, 2014 10:10
To: aprssig at tapr.org
Cc: amsat-bb at amsat.org
Subject: [aprssig] DTMF on HF?


Has anyone had any experience with any success at DTMF working on HF for
some rudimentary commands?


I know tuning is critical as well as inter-tone noise must be way down.


Just thought maybe someone has experimented with it.


Bob, WB4aPR


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