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Noisy RF gain pot?

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G3XAQ

Noisy RF gain pot?

I have just (again) acquired a K2/100. It shows exactly the symptom
below as described in 2009

---
If I move (even very slightly) the rf gain control the audio silences
and the S
meter shows full deflection. After about three seconds or so the receiver
recovers and the s meter returns to normal. This happens wherever teh
rf gain
control is positioned about it's axis.

Any suggestions ?

73 de Vic GW4JUN
-----

It was suggested the RF Gain pot might be noisy but the OP never
followed up. Is this most likely root cause? If so, can someone point me
towards a replacement 5K LIN pot that will fit, ideally sourced from
Newark (Farnell in the UK)?

Thanks a lot,

Alan G3XAQ
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Don Wilhelm-4

Re: Noisy RF gain pot?

Alan,

If the RF gain pot is worn it will behave that way.
If this is a fairly new K2 I would say SN above 4000, the pot should
not be worn out yet unless the operator used it excessively - so in that
case, look for an unsoldered connection between the RF gain control and
the path to the K2 Control Board.

73,
Don W3FPR

On 2/17/2015 12:44 PM, Alan Ibbetson wrote:

> I have just (again) acquired a K2/100. It shows exactly the symptom
> below as described in 2009
>
> ---
> If I move (even very slightly) the rf gain control the audio silences
> and the S
> meter shows full deflection. After about three seconds or so the receiver
> recovers and the s meter returns to normal. This happens wherever teh
> rf gain
> control is positioned about it's axis.
>
> Any suggestions ?
>
> 73 de Vic GW4JUN
> -----
>
> It was suggested the RF Gain pot might be noisy but the OP never
> followed up. Is this most likely root cause? If so, can someone point
> me towards a replacement 5K LIN pot that will fit, ideally sourced
> from Newark (Farnell in the UK)?
>
> Thanks a lot,
>
> Alan G3XAQ

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G3XAQ

Re: Noisy RF gain pot?

Thanks Don. It's an early K2, serial number 997. Is there anything
unusual about the pot or is it just a standard sized miniature 5K linear?

73, Alan G3XAQ

On 17/02/2015 18:02, Don Wilhelm wrote:

> Alan,
>
> If the RF gain pot is worn it will behave that way.
> If this is a fairly new K2 I would say SN above 4000, the pot should
> not be worn out yet unless the operator used it excessively - so in that
> case, look for an unsoldered connection between the RF gain control and
> the path to the K2 Control Board.
>
> 73,
> Don W3FPR
>
> On 2/17/2015 12:44 PM, Alan Ibbetson wrote:
>> I have just (again) acquired a K2/100. It shows exactly the symptom
>> below as described in 2009
>>
>> ---
>> If I move (even very slightly) the rf gain control the audio silences
>> and the S
>> meter shows full deflection. After about three seconds or so the receiver
>> recovers and the s meter returns to normal. This happens wherever teh
>> rf gain
>> control is positioned about it's axis.
>>
>> Any suggestions ?
>>
>> 73 de Vic GW4JUN
>> -----
>>
>> It was suggested the RF Gain pot might be noisy but the OP never
>> followed up. Is this most likely root cause? If so, can someone point
>> me towards a replacement 5K LIN pot that will fit, ideally sourced
>> from Newark (Farnell in the UK)?
>>
>> Thanks a lot,
>>
>> Alan G3XAQ
>
>

--

Alan Ibbetson
[hidden email]
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Don Wilhelm-4

Re: Noisy RF gain pot?

Alan,

With that serial number, there could be a lot of wear on the pot if the
prior operator used the RF Gain a lot.
It is one of the standard size pot 5K linear, but there are pots with
different form factors. I would suggest you get the proper one from
Elecraft PN E520004 to be certain it fits.

73,
Don W3FPR

On 2/17/2015 1:15 PM, Alan Ibbetson wrote:

> Thanks Don. It's an early K2, serial number 997. Is there anything
> unusual about the pot or is it just a standard sized miniature 5K linear?
>
> 73, Alan G3XAQ
>
> On 17/02/2015 18:02, Don Wilhelm wrote:
>> Alan,
>>
>> If the RF gain pot is worn it will behave that way.
>> If this is a fairly new K2 I would say SN above 4000, the pot should
>> not be worn out yet unless the operator used it excessively - so in that
>> case, look for an unsoldered connection between the RF gain control and
>> the path to the K2 Control Board.

Stephen G4SJP

Re: Noisy RF gain pot?

Alan,

Don is right. I thought I had done the right thing some years ago,
ordering what I thought was the same pot from a UK supplier. I still have
it in my drawer of bits somewhere - it didn't fit. I then ordered from
Elecraft, not stupidly expensive although the shipping always bites it
seems to me, and all was well. (Wish I'd never sold the K2 but I had to at
the time to part fund the K3, which I still have :-)

73 Stephen G4SJP

On 17 February 2015 at 19:25, Don Wilhelm <[hidden email]> wrote:

> Alan,
>
> With that serial number, there could be a lot of wear on the pot if the
> prior operator used the RF Gain a lot.
> It is one of the standard size pot 5K linear, but there are pots with
> different form factors. I would suggest you get the proper one from
> Elecraft PN E520004 to be certain it fits.
>
> 73,
> Don W3FPR
>
> On 2/17/2015 1:15 PM, Alan Ibbetson wrote:
>
>> Thanks Don. It's an early K2, serial number 997. Is there anything
>> unusual about the pot or is it just a standard sized miniature 5K linear?
>>
>> 73, Alan G3XAQ
>>
>> On 17/02/2015 18:02, Don Wilhelm wrote:
>>
>>> Alan,
>>>
>>> If the RF gain pot is worn it will behave that way.
>>> If this is a fairly new K2 I would say SN above 4000, the pot should
>>> not be worn out yet unless the operator used it excessively - so in that
>>> case, look for an unsoldered connection between the RF gain control and
>>> the path to the K2 Control Board.
>>>
>>
> ______________________________________________________________
> Elecraft mailing list
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>
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>

G3XAQ

Re: Noisy RF gain pot?

OK, thanks everyone. I'll order a replacement pot. 73, Alan G3XAQ

On 17/02/2015 19:32, Stephen Prior wrote:

> Alan,
>
> Don is right. I thought I had done the right thing some years ago,
> ordering what I thought was the same pot from a UK supplier. I still
> have it in my drawer of bits somewhere - it didn't fit. I then ordered
> from Elecraft, not stupidly expensive although the shipping always bites
> it seems to me, and all was well. (Wish I'd never sold the K2 but I had
> to at the time to part fund the K3, which I still have :-)
>
> 73 Stephen G4SJP
>
> On 17 February 2015 at 19:25, Don Wilhelm <[hidden email]
> <mailto:[hidden email]>> wrote:
>
> Alan,
>
> With that serial number, there could be a lot of wear on the pot if
> the prior operator used the RF Gain a lot.
> It is one of the standard size pot 5K linear, but there are pots
> with different form factors. I would suggest you get the proper one
> from Elecraft PN E520004 to be certain it fits.
>
> 73,
> Don W3FPR
>
> On 2/17/2015 1:15 PM, Alan Ibbetson wrote:
>
> Thanks Don. It's an early K2, serial number 997. Is there
> anything unusual about the pot or is it just a standard sized
> miniature 5K linear?
>
> 73, Alan G3XAQ
>
> On 17/02/2015 18:02, Don Wilhelm wrote:
>
> Alan,
>
> If the RF gain pot is worn it will behave that way.
> If this is a fairly new K2 I would say SN above 4000, the
> pot should
> not be worn out yet unless the operator used it excessively
> - so in that
> case, look for an unsoldered connection between the RF gain
> control and
> the path to the K2 Control Board.
>
>
> __________________________________________________________________
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> <http://mailman.qth.net/mailman/listinfo/elecraft>
> Help: http://mailman.qth.net/mmfaq.__htm
> <http://mailman.qth.net/mmfaq.htm>
> Post: mailto:[hidden email].__net
> <mailto:[hidden email]>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
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> <mailto:[hidden email]>
>
>

G3XAQ

K3 receiver noise figure with KRX3 option

I want to parallel the receivers on my recently-acquired K2 with my K3.
I have the KXV3A RX ANT option on my K3 and K160RX option on my K2. The
"obvious" way to couple the two is with a 3dB hybrid but that will cost
me 3dB degradation in noise figure on both receivers.

The KRX3 option in the K3 has to address the same problem and I'm
wondering if there are any clever tricks I can copy. I am finding the
schematics hard to follow but I can see a 3dB hybrid splitting the
signal path in two. Where I'm struggling is in finding where the signal
goes after leaving the hybrid. Is there a super low noise amplifier that
I can't find on the diagrams to make up for the hybrid when the KXR3 is
fitted? Or maybe perhaps the hybrid is there all the time whether the
sub receiver option is installed or not and the design absorbs the loss
into the overall noise figure?

Or is it all a lot cleverer than that?

Thanks,

Alan G3XAQ
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Joe Subich, W4TV-4

Re: K3 receiver noise figure with KRX3 option

> The "obvious" way to couple the two is with a 3dB hybrid but that
> will cost me 3dB degradation in noise figure on both receivers.

Yes, that's correct. However, in general one does not care so much
about the noise figure of the receivers since the "antenna noise" is
significantly higher than the receiver noise floor. The only time
it might be an issue is on a very quiet band with an inefficient
antenna (3 element yagi/vertical on 6M in a rural area ... dipole
or vertical on 10 M in a rural area, etc.).

> Is there a super low noise amplifier that I can't find on the
> diagrams to make up for the hybrid when the KXR3 is fitted?

No. There is no amplifier to make up for the -3dB loss when the
hybrid is activated (when the Sub RX is enabled and uses the main
antenna). The loss is certainly noticeable with signals at the
receiver noise floor - e.g. weak signals on 6 or 10 meters.

> Where I'm struggling is in finding where the signal goes after
> leaving the hybrid.

One output of the hybrid goes to the sub RX input via P2 Pin 3 of
the SUB IN module. the other output returns to the main RX input
via K1A and P1, Pin 9 (connects to J1 on the main board).

73,

... Joe, W4TV

On 2015-02-18 4:11 PM, Alan Ibbetson wrote:

> I want to parallel the receivers on my recently-acquired K2 with my K3.
> I have the KXV3A RX ANT option on my K3 and K160RX option on my K2. The
> "obvious" way to couple the two is with a 3dB hybrid but that will cost
> me 3dB degradation in noise figure on both receivers.
>
> The KRX3 option in the K3 has to address the same problem and I'm
> wondering if there are any clever tricks I can copy. I am finding the
> schematics hard to follow but I can see a 3dB hybrid splitting the
> signal path in two. Where I'm struggling is in finding where the signal
> goes after leaving the hybrid. Is there a super low noise amplifier that
> I can't find on the diagrams to make up for the hybrid when the KXR3 is
> fitted? Or maybe perhaps the hybrid is there all the time whether the
> sub receiver option is installed or not and the design absorbs the loss
> into the overall noise figure?
>
> Or is it all a lot cleverer than that?
>
> Thanks,
>
> Alan G3XAQ
> ______________________________________________________________
> 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]
>