Quick DTMFOUT Question


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  1. #1
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    Default Quick DTMFOUT Question

    With the DTMFOUT command: the suggested clock frequencies are 20 & 40 MHz. Does this mean that frequencies between these 2 (eg 24MHz) aren't suitable?

    Thanks,

    Troy

  2. #2
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    Default Re: Quick DTMFOUT Question

    Troy, 20Mhz. is about the minimum you can run to produce good results. The sky is the limit....
    Dave Purola,
    N8NTA
    EN82fn

  3. #3
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    Default Re: Quick DTMFOUT Question

    Dave,
    that's the answer I was hoping for - although I tried the tones on 24MHz and 40MHz clock speeds last night and they worked fine on 40, but didn't on 24 (ie. were audible but not detected by my DTMF receiver). Might have more of a play over the weekend.

    Regards,

    Troy

  4. #4
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    Default Re: Quick DTMFOUT Question

    You also have to put the digital representation of the tones thru a lowpass filter. Look in the manual for an example. I have used this command for generating tones for our 2 meter repeater and it works just fine...
    Dave Purola,
    N8NTA
    EN82fn

  5. #5
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    Default Re: Quick DTMFOUT Question

    Quote Originally Posted by Dave View Post
    You also have to put the digital representation of the tones thru a lowpass filter. Look in the manual for an example. I have used this command for generating tones for our 2 meter repeater and it works just fine...
    Yes Dave, I knew this. I've read over that page 20 times, it would be nice for the wording to be clearer on the suitable clock speeds for it though. I've implemented that lowpass filter as suggested and it seems to work "ok", but analyzing the tones on my iphone "iAnalyzer" app suggests that the correct dual frequencies of each DTMF tone produced are more often than not the 2nd and 3rd most prominent frequency outputted unlike a proper specific purpose DTMF device, but they appear to work on 40MHz anyway, so... so long as it's reliable (which is critical to my application).

    Thanks,

    Troy

  6. #6
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    Default Re: Quick DTMFOUT Question

    Ok, to answer my own question (I've recently revisited this) you can't use the DTMF command for any oscillator frequencies between 20 and 40MHz. If say I'm using a 32MHz osc and declare that with a suitable DEFINE, PBP appears to assume I'm using a 20MHz osc to base its frequencies around. So, you can still create DTMF tones with say a 32MHz osc, but you need to do it with the FREQOUT command and you need to multiply your chosen frequency parameters/arguments by (20MHz/32Mhz) or 0.625.

    Also, I noticed that the frequencies produced from a dual tone creation have non-trivial shadow frequencies in some upper bands even utilising the dual low pass filter suggested in the manual. This doesn't appear to occur with single tones, only with dual tones.

    Regards,

    Troy

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