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Sudden loss of K3 RX sensitivity

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N4ZR

Sudden loss of K3 RX sensitivity

Yesterday afternoon, I thought the bottom had dropped out of the bands,
because everything was puny weak, yet I was still working people with
about the usual success rate. After I finished the contest, I dug out
my XG3, and checked the sensitivity on each band - in all cases, 160-10,
the K3 S-meter was reading about S6, on the -73 dBm output setting.
Previously it has read S-9 as intended. Transmit is completely normal.
Subjectively, my long-present line noise to the west is no longer audible

I've checked for inadvertent mis-setting of various controls, thinking
that it might be operator error, but haven't found anything. Is it
likely that something has died in the receive path? Should I get on the
phone to Elecraft Support? Of course, I'll box it up and send it to
them if that is indicated, but would hope to avoid a month or more off
the air.

TIA

--
73, Pete N4ZR
Check out the new Reverse Beacon Network
web server at <http://beta.reversebeacon.net>.
For spots, please use your favorite
"retail" DX cluster.

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Mike K8CN

Re: Sudden loss of K3 RX sensitivity

Pete,

There was a similar report on the forum last year from Per-Tore, LA7NO. In
an extended email conversation we deduced his problems were caused by failed
PIN diodes in one of the T/R switches, which ultimately proved to be the
case. His K3 also lost TX power, unlike your situation, so you may have
lost only the PIN diode in the RX path. There were many other possible
causes suggested by others on the forum around that time (late July 2020) -
you might read that thread and try the simple fixes first (e.g., twist and
re-seat the TMP connectors) before delving into circuit/component failure
possibilities. The old thread is here:

http://elecraft.365791.n2.nabble.com/Elecraft-K3-problem-td7663573.html#a7663581

73,
Mike, K8CN

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DC-3

Re: Sudden loss of K3 RX sensitivity

Plus one on the TMP connectors. It has happened to me a couple of
times over the years. A little dab of Deoxit and move it around a bit
when re-installing seems to do the trick.

Richard

K6VV

On 2/23/2021 5:40 AM, Mike K8CN wrote:

> Pete,
>
> There was a similar report on the forum last year from Per-Tore, LA7NO. In
> an extended email conversation we deduced his problems were caused by failed
> PIN diodes in one of the T/R switches, which ultimately proved to be the
> case. His K3 also lost TX power, unlike your situation, so you may have
> lost only the PIN diode in the RX path. There were many other possible
> causes suggested by others on the forum around that time (late July 2020) -
> you might read that thread and try the simple fixes first (e.g., twist and
> re-seat the TMP connectors) before delving into circuit/component failure
> possibilities. The old thread is here:
>
> http://elecraft.365791.n2.nabble.com/Elecraft-K3-problem-td7663573.html#a7663581
>
> 73,
> Mike, K8CN
>
>
>
>
> --
> Sent from: http://elecraft.365791.n2.nabble.com/
> ______________________________________________________________
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Buck

Re: Sudden loss of K3 RX sensitivity

In reply to this post by Mike K8CN

I have had a similar loss of RX on my K3S. It is cured by turning the
RF control down and then back up. I don't know what causes this and
whether it is hardware or software related. A twist of the knob is all
it takes to fix so I live with it.

Buck, k4ia
Honor Roll
8BDXCC
EasyWayHamBooks.com

On 2/23/2021 8:40 AM, Mike K8CN wrote:

KeithWE6R

Re: Sudden loss of K3 RX sensitivity

Administrator

In reply to this post by N4ZR

Hi Pete;
RF gain up?
Adjust width to click thru all filters.
Does ATT/Pre change the sensitivity? (if not, it could be something in
that circuit).
Try the RX antenna BNC input (if KXV3 equipped).
Try Ant 2 (if KAT3 equipped).
If good at RX ant, then most likely D26 or 27 on RF board.
If bad at RX ant too, then could be D5 on older KXV3 or D25 on RF board.
Email me, I have a flow-chart picture I can send you to help.
keith at elecraft.com WE6R K3 Tech.
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Elecraft mailing list

Re: Sudden loss of K3 RX sensitivity

Pete;

Always do what the master says. Keith knowns more about the K3 than almost anyone.

That 3db figure stands out for me, though. For a component failure or a misadjustment I would expect something else. This sounds more like the antenna is being split, going to another place along with the main RX input. Is it possible you are feeding the same antenna input to both main and sub RX?

It will be interesting to see what you and Keith come up with.

73!
Jack, W6FB

> On Feb 23, 2021, at 12:00 PM, Keith Trinity WE6R <[hidden email]> wrote:
>
> Hi Pete;
> RF gain up?
> Adjust width to click thru all filters.
> Does ATT/Pre change the sensitivity? (if not, it could be something in that circuit).
> Try the RX antenna BNC input (if KXV3 equipped).
> Try Ant 2 (if KAT3 equipped).
> If good at RX ant, then most likely D26 or 27 on RF board.
> If bad at RX ant too, then could be D5 on older KXV3 or D25 on RF board.
> Email me, I have a flow-chart picture I can send you to help.
> keith at elecraft.com WE6R K3 Tech.
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Mike K8CN

Re: Sudden loss of K3 RX sensitivity

I must correct my earlier post on Pete's question - faulty memory on my part
regarding the actual failed part in LA7NO's K3 T/R switch. It was NOT the
PIN diode D25, but was instead the RF choke (RFC30) that provides
the DC path to ground that enables the 7T or 7R control voltages to select
the signal path through D25. That choke failed open.

Mea culpa, and 73,

Mike, K8CN

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