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K3 (S) Weird Main RX issue

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Udo Langenohl - DK5YA

K3 (S) Weird Main RX issue

Gentleman,

I have a problem with the main receiver on one of my K3s. The main
receiver is between 6 and 8dB worse than the second receiver. The stupid
thing about it: it is not always like that, but the poor sensitivity
comes sometimes creeping or sometimes suddenly. It seems to have
something to do with the transmit / receive switching. I checked this
very carefully with an HP8664A signal generator and a spectrum analyzer.
Sometimes both receivers are exactly the same, then the main receiver
slowly gets worse and worse (within a minute the amplification drops by
6-8dB) sometimes it happens immediately after switching from RX to TX
and back. Then it happens that after switching from RX to TX and back
again, both receivers are the same again. It can also happen that the
main receiver is initially 8dB worse than the second receiver, but
without RX / TX switching the missing 6-8dB are suddenly there again -
in the middle of receiving mode, without switching. So it's intermittent
and it drives me crazy not to find out what's going on. Is that another
bad pin diode somewhere in the main receiver and if so: which one? Maybe
someone has an idea? Help is very much appreciated.

This is a K3 #56xx with all features and all upgrades so its more or
less a K3S rather than an K3.

73 Udo, DK5YA
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Bob Wilson, N6TV

Re: K3 (S) Weird Main RX issue

Does rotating the MAIN RF GAIN knob back and forth make any difference? Or
tapping the ANT or RX ANT buttons a lot to exercise the antenna relays?

I assume both receivers are listening to ANT1, and nothing is connected to
AUX RF or RX ANT.

What happens if you move the coax to ANT2?

73,
Bob, N6TV

On Sat, May 8, 2021 at 1:55 AM Udo Langenohl - DK5YA <[hidden email]> wrote:

> Gentleman,
>
> I have a problem with the main receiver on one of my K3s. The main
> receiver is between 6 and 8dB worse than the second receiver. The stupid
> thing about it: it is not always like that, but the poor sensitivity
> comes sometimes creeping or sometimes suddenly. It seems to have
> something to do with the transmit / receive switching. I checked this
> very carefully with an HP8664A signal generator and a spectrum analyzer.
> Sometimes both receivers are exactly the same, then the main receiver
> slowly gets worse and worse (within a minute the amplification drops by
> 6-8dB) sometimes it happens immediately after switching from RX to TX
> and back. Then it happens that after switching from RX to TX and back
> again, both receivers are the same again. It can also happen that the
> main receiver is initially 8dB worse than the second receiver, but
> without RX / TX switching the missing 6-8dB are suddenly there again -
> in the middle of receiving mode, without switching. So it's intermittent
> and it drives me crazy not to find out what's going on. Is that another
> bad pin diode somewhere in the main receiver and if so: which one? Maybe
> someone has an idea? Help is very much appreciated.
>
> This is a K3 #56xx with all features and all upgrades so its more or
> less a K3S rather than an K3.
>
> 73 Udo, DK5YA
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

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KeithWE6R

Re: K3 (S) Weird Main RX issue DK5YA

Administrator

Hi Udo;
In addition to what N6TV suggested, also click above and below 12Watts.
You will hear the relay on the KPAIO3 riser board click.
Do that when the main RX is down, or click it a bunch to see if you can
force the problem.
If so, replace that relay.
Keith WE6R Elecraft K3/K4 Tech

Does rotating the MAIN RF GAIN knob back and forth make any difference? Or
tapping the ANT or RX ANT buttons a lot to exercise the antenna relays?

I assume both receivers are listening to ANT1, and nothing is connected to
AUX RF or RX ANT.

What happens if you move the coax to ANT2?

73,
Bob, N6TV

On Sat, May 8, 2021 at 1:55 AM Udo Langenohl - DK5YA <dk5ya at dk5ya.de <http://mailman.qth.net/mailman/listinfo/elecraft>> wrote:

>/Gentleman, />//>/I have a problem with the main receiver on one of my K3s. The main />/receiver is between 6 and 8dB worse than the second receiver. The stupid />/thing about it: it is not always like that, but the poor sensitivity />/comes sometimes creeping or sometimes suddenly. It seems to have />/something to do with the transmit / receive switching. I checked this />/very carefully with an HP8664A signal generator and a spectrum analyzer. />/Sometimes both receivers are exactly the same, then the main receiver />/slowly gets worse and worse (within a minute the amplification drops by />/6-8dB) sometimes it happens immediately after switching from RX to TX />/and back. Then it happens that after switching from RX to TX and back />/again, both receivers are the same again. It can also happen that the />/main receiver is initially 8dB worse than the second receiver, but />/without RX / TX switching the missing 6-8dB are suddenly there again - />/in the middle of receivin
g mode, without switching. So it's intermittent />/and it drives me crazy not to find out what's going on. Is that another />/bad pin diode somewhere in the main receiver and if so: which one? Maybe />/someone has an idea? Help is very much appreciated. />//>/This is a K3 #56xx with all features and all upgrades so its more or />/less a K3S rather than an K3. />//>/73 Udo, DK5YA/

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KeithWE6R

Re: K3 (S) Weird Main RX issue DK5YA

Administrator

OK, that info helps.
Does the Sub receiver also suffer when sharing the main?
There is a 3db splitter when you share the main antenna, so you should
see that drop in both receives.
When the sub is on AUX antenna, it is using the coax straight out the
back of the sub receiver to either the Aux BNC or to the ATU where it
would use the OTHER antenna (from the main).

So, when the Sub is using MAIN, is it also down?

The 3db splitter is on the little Sub-In board at the back of the sub
receiver, there could be a bad connection there, the relay or solder on
the little wires to the transformer, or cracked solder joint on
something like the little black choke-coil.

If both suffer when using the main, it could also be D25, just shotgun
replace it.
Look for damaged parts on that little daughter board next to D25, BSF
(Band Stop Filter).
It could also be something on the KXV3 transverter interface, you can
pull and put two jumpers per the silkscreen. If it has the old single
3-legged D5, shotgun replace that.
Keith WE6R Elecraft K3/K4 Tech

On 5/10/2021 9:32 AM, Udo DK5YA wrote:

> Hello Keith,
>
> thanks for your kind answer. I don't think that KPAIO3 is the suspect
> since it also happens at the TVTR RX input. I.e. when I feed exactly
> the same amount of HF to the TVTR input and AUX from the signal
> generator and hit diversity 6-8 DB are missing intermittent at the
> main RX.
>
> 73 Udo DK5YA
>
> 10.05.2021 17:53:49 Keith Trinity WE6R <[hidden email]>:
>
> Hi Udo;
> In addition to what N6TV suggested, also click above and below
> 12Watts.
> You will hear the relay on the KPAIO3 riser board click.
> Do that when the main RX is down, or click it a bunch to see if
> you can force the problem.
> If so, replace that relay.
> Keith WE6R Elecraft K3/K4 Tech
>
> Does rotating the MAIN RF GAIN knob back and forth make any difference? Or
> tapping the ANT or RX ANT buttons a lot to exercise the antenna relays?
>
> I assume both receivers are listening to ANT1, and nothing is connected to
> AUX RF or RX ANT.
>
> What happens if you move the coax to ANT2?
>
> 73,
> Bob, N6TV
>
>
> On Sat, May 8, 2021 at 1:55 AM Udo Langenohl - DK5YA <dk5ya at dk5ya.de <http://mailman.qth.net/mailman/listinfo/elecraft>> wrote:
>
> >/Gentleman, />//>/I have a problem with the main receiver on one of my K3s. The main />/receiver is between 6 and 8dB worse than the second receiver. The
> stupid />/thing about it: it is not always like that, but the poor sensitivity />/comes sometimes creeping or sometimes suddenly. It seems to have />/something to do with the transmit / receive switching. I checked
> this />/very carefully with an HP8664A signal generator and a spectrum
> analyzer. />/Sometimes both receivers are exactly the same, then the main
> receiver />/slowly gets worse and worse (within a minute the amplification
> drops by />/6-8dB) sometimes it happens immediately after switching from RX
> to TX />/and back. Then it happens that after switching from RX to TX and
> back />/again, both receivers are the same again. It can also happen that
> the />/main receiver is initially 8dB worse than the second receiver, but />/without RX / TX switching the missing 6-8dB are suddenly there
> again - />/in the middle of receiving mode, without switching. So it's
> intermittent />/and it drives me crazy not to find out what's going on. Is that
> another />/bad pin diode somewhere in the main receiver and if so: which
> one? Maybe />/someone has an idea? Help is very much appreciated. />//>/This is a K3 #56xx with all features and all upgrades so its more or />/less a K3S rather than an K3. />//>/73 Udo, DK5YA/
>

Udo Langenohl - DK5YA

Re: K3 (S) Weird Main RX issue

In reply to this post by Udo Langenohl - DK5YA

Thanks to all so many who replied, also off list.

I found the K1 relay on the SUBIN board to be faulty. Ordered a new one
and will see what happens after.

73 Udo, DK5YA

hashtag: #cantwaituntilmyK4arrives

Am 08.05.2021 um 10:55 schrieb Udo Langenohl - DK5YA: