<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML xmlns:o = "urn:schemas-microsoft-com:office:office" xmlns:w =
"urn:schemas-microsoft-com:office:word"><HEAD>
<META http-equiv=Content-Type content="text/html; charset=iso-8859-1">
<META content="MSHTML 6.00.2900.3157" name=GENERATOR></HEAD>
<BODY lang=EN-US vLink=purple link=blue bgColor=#ffffff>
<DIV><FONT face=Arial size=2>Hi Ken,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>great going!</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Actually, it occurs to me that you might be able to
appeal to a much wider audience (and make kitting really worth your while) if
you can adjust it such that besides using frequency info from the back plane,
you use the same info through CAT commands. The PIC code could be set up to
regularly poll the radio and respond to its commands (much as a SteppIR control
box does to retune its antenna every 50kHz). Enable user selection of
various radio types to account for the different flavors of CAT commands and
you're good to go.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Just a thought.</FONT></DIV>
<DIV>73 de Joe - AB1DO</DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=kenklein@austin.rr.com href="mailto:kenklein@austin.rr.com">Ken
Klein</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=hpsdr@hpsdr.org
href="mailto:hpsdr@hpsdr.org">hpsdr@hpsdr.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Wednesday, September 19, 2007
22:42</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [hpsdr] Small Loop Antenna</DIV>
<DIV><BR></DIV>***** High Performance Software Defined Radio Discussion List
*****<BR><BR>
<P>
<HR>
<P></P>
<META content="Microsoft Word 11 (filtered medium)" name=Generator>
<STYLE>@page Section1 {size: 8.5in 11.0in; margin: 1.0in 1.25in 1.0in 1.25in; }
P.MsoNormal {
FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman"
}
LI.MsoNormal {
FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman"
}
DIV.MsoNormal {
FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New Roman"
}
A:link {
COLOR: blue; TEXT-DECORATION: underline
}
SPAN.MsoHyperlink {
COLOR: blue; TEXT-DECORATION: underline
}
A:visited {
COLOR: purple; TEXT-DECORATION: underline
}
SPAN.MsoHyperlinkFollowed {
COLOR: purple; TEXT-DECORATION: underline
}
SPAN.EmailStyle17 {
COLOR: windowtext; FONT-FAMILY: Arial; mso-style-type: personal
}
SPAN.EmailStyle18 {
COLOR: navy; FONT-FAMILY: Arial; mso-style-type: personal-reply
}
DIV.Section1 {
page: Section1
}
</STYLE>
<DIV class=Section1>
<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></DIV>
<P>
<HR>
<P></P>_______________________________________________<BR>HPSDR Discussion
List<BR>To post msg: hpsdr@hpsdr.org<BR>Subscription help:
http://lists.hpsdr.org/listinfo.cgi/hpsdr-hpsdr.org<BR>HPSDR web page:
http://hpsdr.org<BR>Archives:
http://lists.hpsdr.org/pipermail/hpsdr-hpsdr.org/<BR></BLOCKQUOTE></BODY></HTML>