K2 - frequency control

[Nick G3RWF]

I have just started to notice a click and a very small jump in frequency every 5 kHz on my K2. For example I find it on 30M:
10105.78
10110.78
10115.78
10120.87 (etc)

on 40M it appears:
7034.3
7029.93
7024.93 (etc)

Is this something that has always been there which I have just noticed ? I can work round it but would prefer not to. As usual I run the risk here of exposing my ignorance so please be kind if the answer is obvious!
73 Nick G3RWF
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[David Woolley (E.L)]

Nick Henwood wrote:
> I have just started to notice a click and a very small jump in
> frequency every 5 kHz on my K2. For example I find it on 30M:

That would suggest an error in your CAL PLL data.  I'd suggest
re-calibrating the 4MHz oscillator then doing CAL PLL.  It may be
advisable to recalibrate the filters, as your 4MHz may have been wrong.
  Normally you only need to move them up one notch and then back down,
so that the firmware senses a change and re-reads the frequency.

--
David Woolley
"The Elecraft list is a forum for the discussion of topics related to
Elecraft products and more general topics related ham radio"
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[Geoffrey Mackenzie-Kennedy]

David Woolley (E.L) wrote on Sunday, June 08, 2008 at 10:59 AM

> That would suggest an error in your CAL PLL data.  I'd suggest
> re-calibrating the 4MHz oscillator then doing CAL PLL.  It may be
> advisable to recalibrate the filters, as your 4MHz may have been wrong.
> Normally you only need to move them up one notch and then back down, so
> that the firmware senses a change and re-reads the frequency.

David,

I believe that your suggestion is a correct explanation for one cause of the
clicks, but a situation also exists where the clicks disappear in the
absence of strong signals. In case it might be of interest to the List, here
follows a comment which I made to Nick this morning.


The clicks are very noticeable with my K2 when tuning between 7160 and 7195
kHz (roughly) if the strength of the BC stations in that part of the band is
much over S9, and they can reach S9 + 70db as measured by the S meter of my
homebrewed receiver, which is calibrated in dbm, also by my Spectrum
Analyser. I have not really checked other parts of 40m and am interested
that you find clicks on 30m as well. However the clicks disappear when the
BC stations become weaker.

>From tests made with a sig gen and Spectrum Analyser I am pretty sure that
the root cause of the problem is the lack of shielding and proper bypassing
in the K2, also pcb layout. It would appear that a strong signal entering
the antenna connector leaks into the VCO and PLL Reference area of the RF
board, and after a process of mixing with one or more of the K2's
oscillators appears as a signal whose fequency is about the same as that of
the PLL Reference. If this rogue signal is strong enough it attempts to take
over control of the VCO loop from the PLL Reference, and the clicks are
caused by these attempts. If the incoming signal is strong enough I have
found that the K2 will lock onto the signal and won't let go until the
receiver has been tuned a Khz or more away, and then lets go with a 'whoop'.
The small jump in frequency that you notice is an example of this 'lock'
behaviour.

73,
Geoff
GM4ESD

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[Don Wilhelm-4]

Nick,

First, check RFC15 on the bottom of the RF Board to see if it is open -
check it with an ohmmeter, the voltage will read 5 volts on both sides
of the inductor even if it is open.

Once you have determined that RFC15 is not the problem, do CAL PLL again
- be certain the bottom cover is in place during the process.  After a
CAL PLL, the clicks should be substantially reduced.

Note that such clicks are rarely possible to eliminate completely, but
if the PLL is working and tracking properly, the level should be so low
that they are not noticeable under normal circumstances.  The 5 kHz
intervals are where the PLL range switches from high to low, so when the
PLL DAC values in the EEPROM are correct, tracking willl be very close
and the clicks almost not audible.

Since you are near high power broadcast stations, you may find that
radiation from those stations will sometimes pull the PLL and the clicks
may be more difficult to eliminate, especially on the high end of 40 meters.

73,
Don W3FPR

Nick Henwood wrote:

> I have just started to notice a click and a very small jump in frequency every 5 kHz on my K2. For example I find it on 30M:
> 10105.78
> 10110.78
> 10115.78
> 10120.87 (etc)
>
> on 40M it appears:
> 7034.3
> 7029.93
> 7024.93 (etc)
>
> Is this something that has always been there which I have just noticed ? I can work round it but would prefer not to. As usual I run the risk here of exposing my ignorance so please be kind if the answer is obvious!
> 73 Nick G3RWF
>  

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