[amsat-bb] Re: DTMF on HF?

[Jim Wright]

In days past, the telephone companies ran an analog carrier system of 24 
SSB channels with what was called a pilot tone at a reduced level.  The 
pilot was indeed a carrier reference that was PLL to the office master 
clock.
These 0-4 Khz channels could get off on the receiving end, but a 
"satellite doppler" type tracking circuit PPL to the incoming pilot tone 
kept everything in the pass band of the specific crystal filters for 
each channel.  Bear in mind we expected pilot error in the CPS range, 
rather than 10s or 100s of cycles.

I would think one can design this to work with today's digital 
components rather than use the "rock solid" crystal filters this L 
Multiplex phone equipment did back in the day.
Connect the pilot tone receive PLL to control the receive RF 
oscillator.  I suspect it would work if the barn door was not too wide 
for the PLL to lock on.  May get expensive if you have to use the 
crystals from yesteryear.

73
Jim WA4IVM




On 1/10/2014 2:28 PM, Kevin Muenzler, WB5RUE wrote:
> I doubt that it would be useful because the tolerances are extremely high in
> DTMF so if you are only a few Hz off the tones won't lock.  FM might be ok
> but certainly not SSB.  FM itself has its own problems on HF so that might
> not be useable either.
>
> Kevin Muenzler, WB5RUE
> Grid-EL09uf
> Eagle Creek Observatory
> http://www.eaglecreekobservatory.org
> I'd be unstoppable if it weren't for law enforcement and physics
>
>
> -----Original Message-----
> From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
> Behalf Of Robert Bruninga
> Sent: Friday, January 10, 2014 11:10 AM
> To: aprssig at tapr.org
> Cc: amsat-bb at amsat.org
> Subject: [amsat-bb] 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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