K2: VFO clicks/pops in the presence of strong signals

[Linden, Mike (BRC-Hes)]

  I have just completed "Test and Alignment, Stage II" of K2 #4137.
Everything seems to have gone very well -- all Voltages were in range and it
seemed that everything worked as it should. However, I've now run across a
strange problem.

  I find that clicks/pops occur when I tune the VFO in the presence of
strong signals. For instance, if I set the XG1 for 50uV and tune the VFO up
and down from the XG1's frequency of 7040kHz, I hear clicks/pops (about
S-5/6) when the VFO transitions the following boundaries:

7015.79/80 (click/pop getting very weak here)
7020.79/80
7025.79/80
7030.79/80
7035.79/80
7040.79/80 (XG1's signal is theoretically centered at 7040.00)
7045.79/80
7050.79/80
7055.79/80 (clock/pop getting very weak here)

  The clicks/pops occur when I roll the VFO's last two digits
back-and-fourth across the .79/.80 boundary. The clicks/pops do not occur
when I turn off the XG1.

  I have also noticed that I can hear these clicks/pops when I get up around
7300 and strong broadcast stations are present.

  While I've seen a few mentions of this (or similar problems) in the
archives, I've never really seen any explanation or cure. Any ideas?

  Thanks, Michael N9BDF
          K2 #4137


PS  The "Amateur Radio Emergency Communications Consistency Act" (HR 1478)
and the "Amateur Radio Spectrum Protection Act" (HR 713 & S. 537) are in
Congress. Please contact your Congressmen to ask for their support of these
bills! See the following ARRL link for details:
http://www.arrl.org/govrelations/ <http://www.arrl.org/govrelations/>

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[Sverre Holm]

>  I hear clicks/pops (about
> S-5/6) when the VFO transitions the following boundaries:
>
> 7015.79/80 (click/pop getting very weak here)
> 7020.79/80
> 7025.79/80
> 7030.79/80
> 7035.79/80

Such clicks about every 5 kHz is normal and is part of the construction
of the PLL/VFO-system of the K2. Let me see if I can explain it. The
reference oscillator of the PLL is based on a 12 and something MHz
crystal, with a variable division ratio following it. However, these
steps would be way too course, and therefore the crystal is pulled by
varicaps over about 5 kHz between every change of division ratio. The
pops you hear is when you are the end of the pulling range, and the
divisor changes and the varicap voltage goes to the other end of the
pulling range.

--
73,
Sverre

------------------
Sverre Holm, LA3ZA
www.qsl.net/la3za

 

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[Mychael Morohovich]

Chuck is a friend from a morning CW net. NA-137 is Maine West and is on the
IOTA Directory's  Most Wanted List. Condx not the best today, but I just
managed to work Chuck from my QTH in Western PA.

Mychael


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[Don Wilhelm-2]

Mike,

You are hearing the PLL reference transitions (Sverre explained it nicely),
but they should be at a low level and not very noticable unless you listen
closely.

If you happened to run CAL PLL without the bottom cover in place, those
clicks will be louder than normal - so re-run it with the cover on.

You may be able to reduce the intensity of the clicks/pops by moving the PLL
reference voltages a bit - be certain 80/75 meters is entirely within the
specified range.  Of course, re-run CAL PLL after shifting the PLL range.

73,
Don W3FPR

----- Original Message -----

>   I have just completed "Test and Alignment, Stage II" of K2 #4137.
> Everything seems to have gone very well -- all Voltages were in range and
it
> seemed that everything worked as it should. However, I've now run across a
> strange problem.
>
>   I find that clicks/pops occur when I tune the VFO in the presence of
> strong signals. For instance, if I set the XG1 for 50uV and tune the VFO
up

> and down from the XG1's frequency of 7040kHz, I hear clicks/pops (about
> S-5/6) when the VFO transitions the following boundaries:
>
> 7015.79/80 (click/pop getting very weak here)
> 7020.79/80
> 7025.79/80
> 7030.79/80
> 7035.79/80
> 7040.79/80 (XG1's signal is theoretically centered at 7040.00)
> 7045.79/80
> 7050.79/80
> 7055.79/80 (clock/pop getting very weak here)
>
>   The clicks/pops occur when I roll the VFO's last two digits
> back-and-fourth across the .79/.80 boundary. The clicks/pops do not occur
> when I turn off the XG1.
>
>   I have also noticed that I can hear these clicks/pops when I get up

around
> 7300 and strong broadcast stations are present.
>


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[Mychael Morohovich]

Also alternating between SSB on 14.260 MHz.

Mychael
K2#1025


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