<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta content="text/html;charset=ISO-8859-1" http-equiv="Content-Type">
</head>
<body bgcolor="#ffffff" text="#000000">
<a class="moz-txt-link-abbreviated" href="mailto:kkotch@earthlink.net">kkotch@earthlink.net</a> wrote:
<blockquote cite="midE1ECHWb-0007Dm-7C@smtpauth06.mail.atl.earthlink.net" type="cite">
<meta http-equiv="Content-Type" content="text/html; ">
<meta name="Generator" content="Microsoft Word 11 (filtered medium)">
<o:SmartTagType namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="PersonName">
<!--[if !mso]><style>st1\:*{behavior:url(#default#ieooui) }</style><![endif]-->
<style>
<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {margin:0in; margin-bottom:.0001pt; font-size:12.0pt; font-family:"Times New Roman";}a:link, span.MsoHyperlink {color:blue; text-decoration:underline;}a:visited, span.MsoHyperlinkFollowed {color:purple; text-decoration:underline;}span.EmailStyle17 {mso-style-type:personal-compose; font-family:Arial; color:windowtext;}@page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in;}div.Section1 {page:Section1;}-->
</style></o:SmartTagType>
<div class="Section1"><br>
<p class="MsoNormal"><font face="Arial" size="2"><span style="font-size: 10pt; font-family: Arial;">Scenario: <st1:PersonName w:st="on">D</st1:PersonName>ual-band
mobile and separate 2m mobile with tnc. <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;">Can a duplexer/diplexer
be built (or is one available) that
would allow both radio systems to be hooked up to one dual-band
antenna? The
dual-band radios with one antenna lead has a built-in duplexer. Is
that where
the problem would occur trying to coordinate another duplexer?<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>
</blockquote>
Unless you implement a "kludge" of mechanical coax relays to
connect/disconnect the various radios, NO !<br>
<br>
The small boxes (so-called "duplexers" that are more correctly called
Diplexers) sold to connect separate VHF and UHF radios to a common
antenna (or built inside dual-band transceivers like a D700) are
merely a low pass filter and a high pass filter in the same box. The
low pass filter (2M port) passes EVERYTHING below about 300 MHz. The
high-pass filter (UHF port) passes EVERYTHING above about 300 MHz.
They have NO SELECTIVITY or ability to discriminate against a specific
frequency WITHIN a band whatsoever. <br>
<br>
By contrast, true duplexers, used by voice repeaters to transmit and
receive simultaneously in the same band, pass or reject a specific
SINGLE FREQUENCY (plus or minus 15-30 KHz or so). Such devices are
typically bulky assembies of multiple resonant "cavities" (4-to-6-inch
diameter cylinders 30-something inches long at VHF connected together
with a coax cable harness ) -- a bit much to put in the trunk of your
car. If you need to transmit on a different frequency, the device
has to be painstakingly retuned, ideally with a sweep generator and
spectrum analyzer. I<br>
<br>
If you are willing to leave the two VHF radios fixed on single channels
and never QSY (presumably at least the APRS radio would meet this
requirement), and you are willing to put up with the bulky cavities,
then you MIGHT pull this off. However since such duplexers can't
adequately isolate frequencies less than about 500 to 600 KHz apart on
VHF, the 2M repeater "sub-band" at 144.5 to 145.5 would be off limits.
The single, fixed, voice channel would HAVE to be above 145.5 or so.
Furthermore this would have to be a SIMPLEX channel since a voice
repeater "channel" is actually two frequencies (one for TX, one for RX)
600 KHz apart. <br>
<br>
I am actually doing this at home. I use an old 4-cavity VHF repeater
duplexer retuned to allow a 144.39 APRS radio and a radio on 146.52
simplex to share a single high-gain Comet colinear base station
antenna. <br>
<br>
<br>
<br>
<br>
Stephen H. Smith wa8lmf (at) aol.com <br>
EchoLink Node: 14400 [Think bottom of the 2M band]<br>
Home Page: <a class="moz-txt-link-freetext" href="http://wa8lmf.com">http://wa8lmf.com</a><br>
<br>
"APRS 101" Explanation of APRS Path Selection & Digipeating <br>
<a class="moz-txt-link-freetext" href="http://webs.lanset.com/wa8lmf/DigiPaths">http://webs.lanset.com/wa8lmf/DigiPaths</a> <br>
<br>
Updated APRS Symbol Chart <br>
<a class="moz-txt-link-freetext" href="http://webs.lanset.com/wa8lmf/miscinfo/APRS_Symbol_Chart.pdf">http://webs.lanset.com/wa8lmf/miscinfo/APRS_Symbol_Chart.pdf</a> <br>
<br>
New/Updated "Rev G" APRS <a class="moz-txt-link-freetext" href="http://webs.lanset.com/wa8lmf/aprs">http://webs.lanset.com/wa8lmf/aprs</a><br>
Symbols Set for UI-View, <br>
UIpoint and APRSplus:<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
</body>
</html>