[hpsdr] External T/R switch for PureSignal

[John Ackermann N8UR]

If you're interested in a kit to provide external T/R switching
optimized for PureSignal setups, read on.

If you've experimented with PureSignal, you know that the ANAN T/R
switching isn't up to the task because (a) it shorts the receiver input
to ground during TX, and (b) there is a lot of crosstalk within the
switch/filter board.  The combination means that you can't get a useful
sampler signal into the radio without some sort of modification.

Thanks to much help from KC9XG, I found that it's easy on the ANAN-10 to
bypass the internal T/R by just removing the RX coax between the Hermes
board and the amp board.  Then, you can use the Hermes SMA RX connector
and get TX from the ANT1 BNC connector.  After that, all you need is an
external switch.  No new holes are required.  (I don't own an ANAN-100
but as long as you can route the RX signal directly to the Hermes
receive input, the same setup should work.)

The external switch needs two relays: one to switch the antenna between
TX and RX, and the second to switch the receiver path between antenna on
RX and a signal sampler on TX.  It needs good isolation for PureSignal
(which is where my perfboard prototype with junkbox relays fell short).

So, I've laid out a 3 inch (wide) by 1 inch (deep) circuit board with
two BNC connectors (ANT and TX) and two SMA connectors (RX and SAMPLE).
 It uses the same relays as the Alex boards, and theoretically should
have more than enough isolation for PureSignal.  It should handle 100W.
 It takes 12V input and has a transistor switch for keying.

This is early stage, and I'm just ordering Rev. A boards now.  But I'm
trying to see if there's enough interest to do a TAPR kit (all
through-hole parts!) that would probably be in the $50 range.

If you'd be interested, please drop a note off-list to jra at febo.com.

73,
John