Message-ID: <4D4E8A68.4060601@freenet.de>
Date: Sun, 06 Feb 2011 12:47:52 +0100
From: wolf_dl4yhf <dl4yhf@freenet.de>
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Subject: Re: LF: Simple PIC based DDS for VLF
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Thanks Andy, nice project.. maybe I should dig out the PIC programmer 
again... !

One suggestion for VLFers: A PIC doesn't cost a fortune. Build two of 
these generators, and clock them with the same source (GPSDO or OCXO). 
For the FSK simply flip between both generators. This has the *big* 
(cannot emphasize this enough..) advantage that if the signal is to weak 
to be seen as DFCW etc, we can still dig it out through a long FFT 
because each of the two carriers remains coherent, and can be coherently 
averaged as long as necessary (much longer than a single DFCW symbol). I 
noticed this on Stefan's signal today : With the very slow settings, all 
you see is a rounded hump in the spectrum because the signal isn't 
coherent. No chance to detect it for "DX" receivers.

Of course flipping the (FSK-) switch may cause a heavy click then 
(depending on the momentary phase shift between the two carriers) but I 
think a robust PA will survive this.

Have a nice sunday,
    Wolf .

Am 05.02.2011 19:57, schrieb Andy Talbot:
> 9kHz OPs may be interested in this DDS suitable for audio/ VLF using 
> just a 16F628 PIC, , R-2R ladder and op-amp filter.   It can generate 
> frequencies up to about 40kHz with typical DDS high resolution / 
> frequency steps, (higher if you overclock the device)  offers two-tone 
> FSK operation by toggling a single input line (ideal for DFCW),  The 
> two frequencies are stored in non-volatile memory and 
> are user-programmable from an RS232 interface using ASCII text based 
> commands.
> See www.g4jnt.com/PIC_DDS.zip <http://www.g4jnt.com/PIC_DDS.zip> 
> for full details.
> Andy
> www.g4jnt.com <http://www.g4jnt.com/>


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    Thanks Andy, nice project.. maybe I should dig out the PIC
    programmer again... !<br>
    <br>
    One suggestion for VLFers: A PIC doesn't cost a fortune. Build two
    of these generators, and clock them with the same source (GPSDO or
    OCXO). For the FSK simply flip between both generators. This has the
    *big* (cannot emphasize this enough..) advantage that if the signal
    is to weak to be seen as DFCW etc, we can still dig it out through a
    long FFT because each of the two carriers remains coherent, and can
    be coherently averaged as long as necessary (much longer than a
    single DFCW symbol). I noticed this on Stefan's signal today : With
    the very slow settings, all you see is a rounded hump in the
    spectrum because the signal isn't coherent. No chance to detect it
    for "DX" receivers.<br>
    <br>
    Of course flipping the (FSK-) switch may cause a heavy click then
    (depending on the momentary phase shift between the two carriers)
    but I think a robust PA will survive this.<br>
    <br>
    Have a nice sunday,<br>
    &nbsp;&nbsp; Wolf .<br>
    <br>
    Am 05.02.2011 19:57, schrieb Andy Talbot:
    <blockquote        cite="mid:AANLkTik1Kvn3TTkfRO3=wiUeW1AJBwFW0yWHB-b3-F7X@mail.gmail.com"        type="cite">
      <div>9kHz OPs may be interested in this DDS suitable for audio/
        VLF using just a 16F628 PIC, , R-2R ladder and op-amp filter.&nbsp;&nbsp;
        It can generate frequencies up to about 40kHz with typical DDS
        high resolution / frequency steps, (higher if you overclock the
        device) &nbsp;offers two-tone FSK operation by toggling a single
        input line&nbsp;(ideal for DFCW),&nbsp; The two&nbsp;frequencies are stored in
        non-volatile memory and are&nbsp;user-programmable&nbsp;from&nbsp;an RS232
        interface&nbsp;using ASCII text based commands.</div>
      <div>&nbsp;</div>
      <div>See <a moz-do-not-send="true"            href="http://www.g4jnt.com/PIC_DDS.zip">www.g4jnt.com/PIC_DDS.zip</a>
        for&nbsp;full details.</div>
      <div>&nbsp;</div>
      <div>Andy</div>
      <div><a moz-do-not-send="true" href="http://www.g4jnt.com/">www.g4jnt.com</a></div>
      <div>&nbsp;</div>
      <div>&nbsp;</div>
    </blockquote>
    <br>
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