[Elecraft] K3 Receive De-sense Problem

[Guy Olinger K2AV]

>From your description, the problem is most likely NOT desense. It would be
intermittent center conductor connection with capacitive pass-through.
Desense would follow some external transmission pattern. Yours sounds more
like a mechanical or corrosion based intermittent.

If you own a K3, blame it dead last after you have triple-checked all other
possible sources. The odds are way against the K3 being the problem. If the
K3 is at fault you should be able to see it with only a wire connected to
the chassis connector as a signal source.

Coax patch cables are a long-time, NOTORIOUS source of problems. From the
long experience of many, there is nothing redemptive about patch cables
that should give them a free pass looking for trouble. Hams will use an old
one because they don't want to make a new one.

Also problematic are non-Amphenol coax elbow adapters which have a spring
internally to go around the bend.

The spring contact becomes corroded if QRO has EVER been used on them or
they have EVER gotten damp. Amphenol's have the male pin internally
threaded to screw into the line from the female end. This process makes it
more expensive to manufacture, hence the more common cheep-cheep versions
with the spring. They work ok OUT OF THE WEATHER with CB and RX only, and
probably OK with 100w. But getting damp or running QRO will corrode the
female-spring-male center conductor connection.

Hams should THROW AWAY any spring-based elbow adapter, and only purchase
Amphenol elbows. If there is a non-Amphenol in the shack, you will likely
use it and forget that you did until it goes bad. You can go around a
hamfest and pick up a dozen Amphenol elbows inexpensively. The Amphenol's
are good forever.

Older PL259's had a longer shell, and some manufacturers of new equipment
have gone to mounting the SO239 chassis connectors with the flange INSIDE
the chassis/case. Then the longer shells then cannot firmly force the pin
and spline to mate, and you will have intermittent connection. THROW AWAY
any PL259 with the longer shell or with anything other than teflon as a
center insulator. Replace them on any patch cord.

A K3 is almost never the source of intermittents.

73, Guy.

On Friday, March 13, 2015, Hank Garretson <w6sx at arrl.net> wrote:

> For the past few months, I have had intermittent receive de-sense with my
> K3/100-F, Serial 1523. Firmware 5.14, 2.13, 1.19 installed this week, but
> de-sense was there with previous firmware.
>
> Intermittently receive sensitivity will drop about ten dB. Usually happens
> after transmitting, but sometimes happens spontaneously with no
> transmitting. A dit usually restores sensitivity. If I don't dit,
> sensitivity randomly restores itself.
>
> CW, SSB, RTTY. All contest bands. (Don't do WARC.)
>
> I have one-by-one eliminated my BCD antenna-switches, my ACOM amplifier,
> and my antenna/dummy load switch. With these items in or out of line, I
> still get intermittent de-sense.
>
> Which leads me to believe the problem is with the K3 itself. (It could be
> one of my coax patch cables, but I suspect not.)
>
> KXV3 installed, but use ANT1.
>
> SUB installed. Intermittent de-sense with and without SUB engaged.
>
> Suggestions?
>
> 73,
>
> Hank, W6SX
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