[Elecraft] KPA500 switching ideas with a Flex-5000A?

[Edward R. Cole]

First off I was replying to N8NFR's request for "info how to do 
this".   Don't shoot the messenger!

The requirement for simultaneous connection to both antennas adds the 
need for DPDT relays.  Of course a simpler set up could use simpler 
relays.  I have not heard whether the KPA-500 has a bypass RF path 
for running with just low-power.  All this has to be considered.  And 
that is why such switching circuits properly belong outside the amp 
or the tuner (I my opinion).

I would look very careful at all these after-market switching 
boxes.  Check for RF current ratings (you will probably not find 
any).  When loads are resistive math is simple - when SWR is high it 
gets "strange" and many relays will fail.

I just burned up a 1200w rated coax relay that was running into <1.1 
SWR load.  I was running 1200w!  The replacement is rated to 
3kW.  Original relay was a CX600NL.  You get what you pay for.

Open frame relays are fine for 60-Hz AC and DC, but really are a 
cheap way out for RF switching (beware).  Again may run fine at 100w 
into resonant/matched antennas.  RF voltage really spikes when not 
resonant.  This topic is around running the KPA-500 at 500w so be 
careful about power ratings.

Most of my coax switching is manual rotary coax switches or I am just 
connecting the coax manually.  Relays are remote on towers for the 
most part and not used on HF.
---------------
Aside:
Simplest, most reliable, coax matrix has all the antennas terminated 
to panel connectors on big plate panel.  Radios and amplifiers are 
also terminated to connectors.  To connect any radio/amp/tuner to any 
antenna one uses a coax jumper between the appropriate connectors - 
no switches, no logic, KISS!

Of course this is slow so will not satisfy contesters, DXers and 
anyone who is used to "push-the-button" electronics!
Ed - KL7UW
------------------------------

Message: 36
Date: Thu, 14 Jul 2011 07:40:57 -0700
From: "Dick Dievendorff" <dieven at comcast.net>
Subject: Re: [Elecraft] KPA500 switching ideas with a Flex-5000A?
To: <Elecraft at mailman.qth.net>
Message-ID: <003201cc4234$0b696190$223c24b0$@comcast.net>
Content-Type: text/plain;       charset="us-ascii"

This seems awfully expensive.

Array Solutions doesn't spend that much for the relays inside their Six Pak.

Top Ten devices doesn't spend that much for the SPDT relay inside their A/B
station selector.  That unit goes for $77, and that includes a nice box and
the connectors.

The T/R switch within my Ameritron AL-1200 doesn't cost that much.

Wouldn't a sealed or frame relay do the job?  600 watts into a 50 ohm
resistive load is 12 Amps.  20A DPDT frame relays can be acquired for a lot
less than a coaxial relay.

SPST relays cost even less.  KK1L uses relays that are advertised at about
$3.16 each in his 2 x 6 antenna switch.

Is it necessary to operate concurrently on HF and 6 meters?  Wouldn't a
couple of SPST relays suffice for this application?

100 watts into 50 ohms is 2A. You can use a much smaller relay on the 100
watt exciter to amplifier side. I'd use 5A relay.

73 de Dick, K6KR

 > That can be accomplished with three DPDT coaxial relays such as the CX800M

($159/ea from http://www.rfparts.com/coaxial.html ) $477 total

 > It can be done with two coaxial transfer switches but probably cost more

(KC 1420-820 from
http://www.surplussales.com/Relays/rfcoaxialrelays/rfcoax_n.html

are $275/ea. ($550 total)






73, Ed - KL7UW, WD2XSH/45
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