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Hi Ken,<br>
<br>
Congratulations!!! Sounds like a fun add-on to the HPSDR!<br>
<br>
Dpending on the interest, you might consider another strategy:<br>
- Put the source code of the PIC on a website (HPSDR)<br>
- Design your PCB with the Express-pcb and put the design-file on the
website<br>
(There are other similar possibillities, e.g. posting the PCB in
gerber-format....)<br>
<br>
Just a thought...<br>
<br>
Furthermore: Would it be possible to miniaturize the loop to, let say
e.g. 1 foot? This would make a nice in-house antenna :-)<br>
<br>
Good luck, 73 Jeroen PE1RGE<br>
<br>
Ken Klein wrote:
<blockquote
cite="mid200709200242.l8K2gDEp024718@ms-smtp-05.texas.rr.com"
type="cite">
<pre wrap="">***** High Performance Software Defined Radio Discussion List *****
</pre>
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<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Hi all;<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">A few months ago, I
published to the list a proposal for a
small transmitting loop antenna which would be automatically tuned by
snooping
the SDR for frequency information and tuning a resonating capacitor on
the antenna
using a PIC processor and servo motor. <o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">At the time, it was just
a proposal and as a proposal,
interest wasn’t terribly high. However, I continued to work on the
project and now have some success to report.<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">To quickly recap the
project, a PIC18F4321 takes frequency
information from the Atlas backplane that is encoded in 39-bit binary
in I2S
format. Once received from the bus, the frequency is decoded to form
an
index into a 2K-entry lookup table which translates the frequency
information
into a motor position. The PIC drives a stepper motor coupled to a
22-turn vacuum capacitor to a pre-calibrated position which resonates
the
antenna at the DDS frequency of the SDR. Voila ! A small loop
antenna that always stays in tune with the SDR.<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">To do the project, I had
to learn PIC assembly programming
and the IDE. (In retrospect, I wish I had forked over the do-re-mi for
a
C compiler and done it in C, but the code is stable and operational, so
it’s going to stay in assembly. (But a word to the wise for any
future projects, do it in C, for gosh sakes!!!)<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Last night, using a
3-foot diameter loop made from
5/8” copper plumbing tubing and a 100pf vacuum cap, I was able to
calibrate across the entire 20-meter band and load the antenna with an
SWR of
1.1:1 or less. After calibrating, I was able to tune across the band
with
the SDR, while the antenna followed the SDR frequency perfectly,
staying always
in resonance. (The SDR antenna tuner was disabled.) Needless to say,
I’m delighted with the results. <o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">I’m at the point now of
wanting to lay out the final
PWB for the project, and thought that I would ping the group and see if
there
is enough interest in making this a full-fledged project. If so,
I’ll be glad to document the design, code, PWB layout, mechanicals,
parts
list, part sources, cost, operation, programming, and anything else
interesting
about this project. I would also consider handling a group buy for the
PWBs or even a kit.<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">I’ve tried to make the
project as generic as possible,
so that someone could duplicate it with their own antenna without
having to
code from scratch or redesign the mechanicals. I think the design
could
easily be adapted to any antenna at all that could be tuned with a
stepper
motor and variable cap or variable inductor. <o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">I understand that future
projects using the Atlas bus will
also continue to transmit frequency information on the backplane in
this same
format. No changes will have to be made to interface future HPSDR
receivers and transmitters. <o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">So let me know if you
guys want me to take this project to
the next stage and lay it all out for you. Personally, it’s been a
really exciting process and I’d be anxious to find others that want to
try the same thing. I am certainly open for suggestions and solicit
comments and ideas.<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Very 73,<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Ken WR5H<o:p></o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;"><o:p> </o:p></span></font></p>
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</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Ing. Jeroen Bastemeijer
Delft University of Technology
Department of Electrical Engineering
Electronic Instrumentation Laboratory
Mekelweg 4, Room 13.090
2628 CD Delft
The Netherlands
Phone: +31.15.27.86542
Fax: +31.15.27.85755
E-mail: <a
class="moz-txt-link-abbreviated" href="mailto:J.Bastemeijer@TUDelft.nl">J.Bastemeijer@TUDelft.nl</a>
GPS: Lat N52.00002 Lon E4.37157 Alt 46.2m</pre>
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