If you're not interested in using the spectrum legally then so be it, but equally don't expect too much help to do so.
As others have said, there is nothing sacred about using DTMF on LF, HF, VHF or anywhere else, nor in any analogue mode that supports a standard 3kHz voice channel, AM, FM, PM etc. However it's not likely to be used on an SSB channel, you might want to think why that might be. The only reason it became ubiquitous on VHF and UHF narrowband FM was through increasingly common usage.
I am interested in using it legally. Have I expressed otherwise?
More the reason why I may not be.. which appears so far that I just have to move the frequency.
But that doesn’t explain AM/FM kits that broadcast right of top of AM/FM commercial broadcast bands.
I’m not trying to express any poor attitude, I just don’t do vague well.
In the old days,such things were strictly forbidden,but various people pointed out that such prohibitions didn't apply to Signal Generators,or Oscillators that someone might build up for some other purpose.
They argued that very low power from tiny AM or FM transmitters would not cause any significant interference
to Broadcasting,& besides,it was permitted in the USA,so it must be a great idea!
After all,that approach worked well with getting CB legalised!
They also followed CB's lead,in "just doing it,anyway".
Various Electronics mags started publishing "RF bugs",& the whole silly idea took off.
From all I've heard,they are still not really legal,but "slip through the cracks"---if nobody complains,ACMA doesn't do anything about it.
DTMF SSB modulated? I imagine the bandwidth would be there. SSTV is expected to work
at least locally.
Hum.. to think about it… For any real HF work it would be unreliable,
Both clocks would have to be clocked fairly accurately. Doppler shift,
ionospheric movement, and just about any other natural effect like tunnelling would be undesirable.
There is no critical clock with DTMF--the decoder at the other end recognises the tone frequencies & does whatever they mean.
HF radios quite commonly use Selcall which is similar,Hams use RTTY,as did OTC & the old PMG on SSB.
You don’t have too many HF repeaters or such equipment wanting to be controlled by
domestic amateur radio.
It might also be an issue that a multi frequency wave doesn’t have vertical symmetry.
10 metre repeaters often are controlled by CTCSS,which uses low frequency tones,so is a little different.
Why do you say a multi frequency wave doesn't have vertical symmetry?
They are just audio tones.
Not that it matters ------TV video certainly lacks vertical symmetry,& is transmitted perfectly well on VSB.
Tesla coils & such are pretty much regarded as "unintentional radiators".
This,plus the fact that they are in intermittent use lets them "slip through the cracks" lust like the other low power devices.
Once you modulate them,the radiation is no longer unintentional,so you can get in strife.
Think of it from the point of view of a Narrowcast station:
There they are,with all sorts of restrictions on how much power they can use,restricted bandwidth,plus the same stabilility & spurious specs as the big guys on the "real" Broadcast Band.
Suddenly up you come,drifting back & forth across their allocation,pumping out DTMF tones at a similar power level to them.
They well may become quite hostile after a few listener complaints.
ACMA is called in,you are told to "cease & desist" & maybe fined.
Worse,you have now "drawn the crabs" & in the worst case,there will be a general crackdown on "Tesla coils." & similar devices.
Ironically,if you had been down in the AM Broadcast Band proper,your signal would probably have been comfortably overridden by the 10kW to 50 KW stations.
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