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K3 Receive De-sense Problem

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Hank Garretson

K3 Receive De-sense Problem

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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Vic Rosenthal

Re: K3 Receive De-sense Problem

Hank, check the grounding of the SO239's. I believe the path is through
some hardware. Also don't absolve the patch cables too quickly.

On 13 Mar 2015 06:30, Hank Garretson 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

--
73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/
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Frankie Hunt K4TEN

Re: K3 Receive De-sense Problem

In reply to this post by Hank Garretson

I had those exact symptoms, except with a different radio and band. (IC746 on 2 meters).
The problem was a coax / coax connection. I replace the defective piece of coax.
I no longer trust "finger tight" connections. I use a small pair of ignition pliers to gently snug things up.

Frankie
K4TEN

Chester Alderman

Re: K3 Receive De-sense Problem

I also had these symptoms with my K3. Fortunately my troubleshooting was
very easy because my K3 would 'de-sense' every time I would switch from my
tri-bander to my 40m yagi. Poor weather proofing at my antenna switch at the
TOP of the tower was the culprit. Thus...NEVER put an antenna switch at the
top of your tower plus weather your connections once and then go back and do
it again!
73,
Tom - W4BQF

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of
Frankie Hunt K4TEN
Sent: Friday, March 13, 2015 8:36 AM
To: [hidden email]
Subject: Re: [Elecraft] K3 Receive De-sense Problem

I had those exact symptoms, except with a different radio and band. (IC746
on
2 meters).
The problem was a coax / coax connection. I replace the defective piece of
coax.
I no longer trust "finger tight" connections. I use a small pair of
ignition pliers to gently snug things up.

Frankie
K4TEN

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Richard Fjeld-2

Re: K3 Receive De-sense Problem

In reply to this post by Frankie Hunt K4TEN

I have found the center conductor on certain PL-259 plugs is slightly smaller than others. They make a marginal contact with the SO-239 socket. Sometimes intermittent. The trouble it causes can be hard to identify.

I test for light friction/rubbing when I insert a PL-259 plug. If doubtful, I put a spot of solder on the tip, and file it down until it rubs without force going in.

Dick, n0ce

> Date: Fri, 13 Mar 2015 05:35:39 -0700
> From: [hidden email]
> To: [hidden email]
> Subject: Re: [Elecraft] K3 Receive De-sense Problem
>
> I had those exact symptoms, except with a different radio and band. (IC746 on
> 2 meters).
> The problem was a coax / coax connection. I replace the defective piece of
> coax.
> I no longer trust "finger tight" connections. I use a small pair of
> ignition pliers to gently snug things up.
>
> Frankie
> K4TEN
>
>

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Guy Olinger K2AV

Re: K3 Receive De-sense Problem

In reply to this post by Hank Garretson

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 <[hidden email]> wrote:

Jim Brown-10

Re: K3 Receive De-sense Problem

In reply to this post by Richard Fjeld-2

On Fri,3/13/2015 10:45 AM, Richard Fjeld wrote:
> I have found the center conductor on certain PL-259 plugs is slightly smaller than others. They make a marginal contact with the SO-239 socket. Sometimes intermittent. The trouble it causes can be hard to identify.

Junk connectors are a VERY common cause of problems. If the connector
doesn't say Amphenol, it's almost certainly junk. An exception are the
vintage connectors with MIL-spec numbers stamped into them. Amphenol's
best solder-on PL-259 is 83-1SP.

73, Jim K9YC
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Hank Garretson

Re: K3 Receive De-sense Problem

In reply to this post by Hank Garretson

Thanks to everyone who responded, both to the group and privately.

Still unresolved is whether it is the K3 or my cabling.

Before tackling the daunting task or checking the cables or tearing into
the K3, I'm going to borrow another transceiver and see if the problem is
still there.

If no, then it's the K3. If not, then it's cables.

Stay tuned.

Thanks again for all the suggestions. Very much appreciated.

73,

Hank, W6SX
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Joe Subich, W4TV-4

Re: K3 Receive De-sense Problem

> If no, then it's the K3. If not, then it's cables.

Don't count on it. If no, it could be the cable connected to
the K3.

73,

... Joe, W4TV

On 2015-03-14 10:07 PM, Hank Garretson wrote:

> Thanks to everyone who responded, both to the group and privately.
>
> Still unresolved is whether it is the K3 or my cabling.
>
> Before tackling the daunting task or checking the cables or tearing into
> the K3, I'm going to borrow another transceiver and see if the problem is
> still there.
>
> If no, then it's the K3. If not, then it's cables.
>
> Stay tuned.
>
> Thanks again for all the suggestions. Very much appreciated.
>
> 73,
>
> Hank, W6SX
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
> This list hosted by: http://www.qsl.net
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>