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<div class="moz-cite-prefix">On 12/5/2012 12:12 AM, Bob Poortinga
wrote:<br>
</div>
<blockquote
cite="mid:CAEEMhL6uX3+EqR_ssJHJsOczdWPXYOdbNoNDEm9jJ+OPY8qoKA@mail.gmail.com"
type="cite">
<pre wrap="">Lynn KJ4ERJ writes:
</pre>
<blockquote type="cite">
<pre wrap="">If anyone knows of a cheap SSB HF 30m transmitter, or better yet
transceiver, I'm interested!
</pre>
</blockquote>
<pre wrap="">
I wonder if a Norcal 40A can be adapted to 30M.
<a class="moz-txt-link-rfc2396E" href="http://www.fix.net/~jparker/wilderness/nc40a.htm"><http://www.fix.net/~jparker/wilderness/nc40a.htm></a>
73 de
</pre>
</blockquote>
<br>
<font face="Arial">I've just been carrying on an off-list discussion
on this very issue. After playing around with the various APRS
Messenger digimodes on 30 meters, I think there is a way to do
this easily. You don't need a full-blown 30M SSB transmitter with
a separate TNC converting data to audio tones. <br>
<br>
Classic AX.25 packet, GMSK and MFSK16 are all
single-tone-at-a-time FSK modes. Two throughts I had were to
either have a DSP chip directly generate the RF signal at 10 MHz,
given that DSPs can operate on signals at 50 MHz and beyond. <br>
<br>
These three modes are constant-power FSK (i.e. like key-down CW)
between two RF frequencies 200 Hz apart in the case of FSK,
several tones in the case of GMSK, or between 16 discrete RF freqs
at only a 2-3 Hz rate over a spread of about 500 Hz in the case of
MFSK16. <br>
<br>
Since they are not a complex two-tone simultaneous signal like
PSK63: <br>
<br>
a) you aren't concerned with the shape of the waveform, just it's
frequency. It shouldn't be much of a challenge for a DSP to
directly synthesize a simple sine wave (or reasonable
approximation thereof) at 10 Mhz. <br>
<br>
b) with a single tone at a time involved, there is no issue with
amplifier linearity or intermodulation distortion. You stick a
couple of MOSFET power amp stages directly onto the output pin of
the DSP to jack the output up to half a watt or a watt or so.
Saturate them and drive them into highly-efficient class-C
operation. <br>
<br>
After my experiences on multiple cross-country road trips running
both classic AX.25 300-baud FSK and the APRS Messenger
PSK63-GMSK-MFSK16 modes, I would vote for MFSK16. Any of the
digimodes is vastly superior to classic 300-baud FSK for weak
signal work, especially in the presence of multipath and noise,
thanks to their low symbol rates, but MFSK16 is waaay beyond any
of the others in the signal-to-noise ratio required to work
successfully. It will provide solid copy on signals so weak, you
can't even hear them in the speaker. <br>
<br>
MKSK16 has about a 10 dB advantage over PSK63 in t;erms of the
minimum SNR required. You can cut the transmit power in half
(losing 3 dB on TX) and still be 5-6 dB ahead at the RX end. And
the TX can use a saturated efficient class-C PA which PSK63
can't! <br>
<br>
<br>
<br>
An alternative approsch we discussed would be to hang a varactor
diode across a simple crystal oscillator running directly at
10.149.70 MHz. I.e the basic crystal-controlled "rockhound"-type
1-watt QRP CW transmitter. <br>
<br>
A single-chip low-end microcontroller could easily output a 0/5
volt DC logic-level waveform to apply across the varactor (rather
than audio tones) to directly FSK the crystal on classic AX.25.
Or an output voltage at 16 stepped values could be generated by
the on-chip a-to-d to modulate the varactor for MFSK16 operation.
One could even use a table to generate 16 UNevenly spaced voltages
to compensate for the non-linearity of voltage vs freq in the
varactor/crystal system. Such a device would have the cheap,
essentially-disposable, minimalism of a TinyTrack III.<br>
<br>
The microcontroller and QRP crystal transmitter could be combined
on one small board to yield the 30-meter equivalent of a
MicroTrack AIO. <br>
<br>
</font>
<hr width="100%" size="2"><font face="Arial"><br>
--<br>
<br>
Stephen H. Smith wa8lmf (at) aol.com <br>
Skype: WA8LMF<br>
Home Page: <a class="moz-txt-link-freetext" href="http://wa8lmf.net">http://wa8lmf.net</a><br>
<br>
High Performance Sound Systems for Soundcard Apps<br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/ham/imic.htm">http://wa8lmf.net/ham/imic.htm</a><br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/ham/uca202.htm">http://wa8lmf.net/ham/uca202.htm</a><br>
<br>
Vista & Win7 Install Issues for UI-View and Precision Mapping<br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/aprs/UIview_Notes.htm#VistaWin7">http://wa8lmf.net/aprs/UIview_Notes.htm#VistaWin7</a><br>
<br>
"APRS 101" Explanation of APRS Path Selection & Digipeating <br>
<a class="moz-txt-link-freetext" href="http://wa8lmf.net/DigiPaths">http://wa8lmf.net/DigiPaths</a> <br>
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