[Elecraft] K3 with xmit and receive antennas - advice needed

[Dick Dievendorff]

John:

You don't have a lot of time before this Field Day, but in the longer term,
there's a better way.

For this Field Day, I'd look for a manual switch from MFJ or Alpha-Delta or
something along those lines.

The K3 (and most other radios of recent vintage) provide back-panel "band
change" or "band level" lines that can be used for this purpose.  The K3
uses a 4-line (plus ground) BCD encoding on the back-panel accessory
connector to indicate the band. Yaesu uses the same scheme.  Band decoders
for this 4-line BCD encoding that are advertised for Yaesu products work
well with the K3.

ICOM uses a different scheme, but the idea is the same.

Available band decoders for the K3 / Yaesu 4-wire BCD protocol include:

Elecraft KRC2 http://www.elecraft.com/KRC2/krc2.htm, 

Unified Microsystems BCD-10  http://www.unifiedmicro.com/decoder.html  See
the link at the bottom for a more complete description of a simple switching
system. http://www.unifiedmicro.com/BBCD10_BLK.pdf

Top Ten Devices http://www.qth.com/topten/bdecoder.htm 

Array Solutions
http://www.arraysolutions.com/Products/bandmaster.htm#top%20of%20page

and microHAM http://www.microham-usa.com/Products/band%20decoder.html

The capabilities (and prices) of these devices varies considerably.  Some of
them have many more functions than just band decoding.

These all help to automate the antenna selection process. You change the
frequency from the radio front panel (or your logging program on your
computer), the radio provides signals to the band decoder, the band decoder
provides +12V to an appropriate set of relays, and the relays select the
appropriate antenna.  Some antenna relay boxes can switch two radios to N
antennas, and isolation becomes a very important issue.   

There are antenna relay boxes available from some of the same sources. I've
seen any number of construction articles in QST and NCJ about this.  It's a
popular station automation topic for contesting stations.  In a contest,
particularly with guest operators, it's ideal if you can just change the
radio's frequency and start transmitting, everything else is automated. Some
of my current antennas require an ATU, and I have to tune my amplifier, but
I'm hoping someday to automate all that, too.  The really competitive
stations have all this automated.

You could ask this question on the TowerTalk or CQ-Contes reflector and get
lots of advice...

73 de Dick, K6KR


-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of John Watkins
Sent: Wednesday, June 09, 2010 3:33 PM
To: Elecraft Reflector
Subject: [Elecraft] K3 with xmit and receive antennas - advice needed

All,

My K3 does not have the option that provides for the third antenna input
(KXV3).  Would the following method allow me use dual antennas for Field
Day.  Use the switched 12 volt out to drive an antenna relay to make the
changeover.

Will this work?  Is there a better approach?

Thanks, John N0EVH
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