[amsat-bb] Re: DTMF on HF?

[Rick Walter]

I sometimes listen to the HF ATC station from New York Center talking to the planes going to the Caribbean while working on the laptop in the shack. They transmit selcall to the planes to make sure they can be alerted. The selcall code is always 4 letters. They send two "tones" I always thought the 4 letters meant two tones together and another two together just like DTMF but I must be wrong. 

Rick WB3CSY
Sent from Rick's iPad2

> On Jan 10, 2014, at 4:45 PM, Jim Wright <wrightjrjr at verizon.net> wrote:
> 
> 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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