[Elecraft] Hang-up on Relay Using QSK

[Guy Olinger K2AV]

Hi, Lee,

K3 does not have a T/R relay in the RX path. It uses PIN diodes, which are
just peachy fine at 100 watt power levels. Amplifiers are another separate
problem. QSK is a strain on any amplifier running 1500 watts. This is
because affordable PIN diodes for the usual circumstances sort of disappear
beyond 500 watts or so. Ask anyone that has owned an Alpha 89, which came
out with PIN diodes for T/R switching. They never did that again. The pin
diodes will hold as long as you NEVER, EVER do anything like transmit into
an open or very high SWR.

One of the most common QSK caused problems in amplifiers is insufficient
delay setting in the transceiver (ANY brand or model) to allow amplifier's
t/r relays to close AND settle before RF is applied to the amplifier. This
is sometimes called "hot-switching".

The outcome of hot-switching is burned contacts at minimum producing the
problem you describe and others. At worst if allowed to continue, this can
produce burned a burned bandswitch with irreparable damage, ruined
transmitting capacitors, arc paths in various places, or damaged internal
coax runs. For certain kinds of transmitting tubes, the tubes can be
damaged by non-engineered states present during an arc-fault.

Many amplifiers will NOT t/r switch and settle in the K3's 8 ms minimum
delay, and some require MORE delay than advertised.

There are aftermarket t/r boards which drive vacuum relays such as Jennings
RJ-1A to quicker closures by a very short burst of higher than normal
actuation voltage. These produce measured switch delays in the 2-5 ms
range. But hard QSK use does wear down the vacuum relay after a while and
they need to be routinely replaced to avoid issues.

BEFORE you tear apart your K3 or send it back to Big E, PROVE beyond a
shadow of a doubt that it is NOT the t/r relay circuitry in your 87A. The
FIRST reason to do this is to make sure that the inevitable amplifier
damage caused by a bad relay in the 87 is headed off. If the relay is not
contacting properly at times, TAKE THE AMP OUT OF SERVICE and get the relay
fixed, or a quicker circuit installed. You could easily save your self a
$1000 repair bill on the 87.

The 87 will switch to transmit by grounding the relay jack. The next time
that the receive goes weak, unplug the cable from the 87's relay jack. Then
see if you can make the RX come back by repeatedly grounding the 87's relay
jack while the K3 sits unkeyed in RX mode.

If you can make the RX come back up that way, the problem is in the 87A,
and it's time to take it out of service.

This also is just another example of our strange predilection to always
blame the K3 first, which after noting what actually was found, is most
often just dead wrong.

73, and Good Luck
Guy K2AV

On Tuesday, December 1, 2015, KY7M <ars-ky7m at cox.net> wrote:

> Towards the end of CQWW CW, I was having issues with the K3 not getting
> back
> to receive when I stopped transmitting.  This was an intermittent problem -
> if I keyed the radio again with a dit or two, I could get back to full
> receive.  I could still hear signals, but greatly attenuated when the relay
> would hang up.  I was using QSK with the K3 and my Alpha 87A.  I am not
> seeing any fault indication on the 87A and I am trying to figure out if the
> problem is in the K3.  I also have a KPA500 but have not used it in a
> contest lately to know if the problem would repeat with another amplifier
> or
> barefoot.  It seems to happen only after heavy use.  I think I experienced
> it a week earlier in the WAE RTTY contest as well, but did not do as much
> operating as in CQWW.
>
>
>
> 73,
>
>
>
> Lee, KY7M
>
>
>
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