[Elecraft] Garbled K2 SSB Signals

[Matt Zilmer]

Hi Don,

Electrical tape is slightly resistive, at least the ones I've used. At
Idealab (Pasadena, CA - tech incubator), we used electrical tape to
"lightly ground" sections of a proto RF PCBA we were developing. Doing
this snubbed out some parasitic oscillation that we never really
understood.  One of our grad student techs found this by accident.

Murphy acts in strange ways, sometimes.

73,
matt W6NIA

On Sun, 04 May 2014 09:35:32 -0400, you wrote:

>Dale,
>
>That is an old problem often referred to as WAOF (Weird At One Frequency).
>That frequency region is where the PLL frequency and the VFO frequencies 
>cross.  Those two signals can couple together producing the condition 
>that you observe.  The fix is to reduce the opportunity for those 
>signals to couple together.
>
>Make certain that C88 on the bottom of the RF board soldered between 
>pins 12 and 13 of U4 is on the correct pins and has the shortest 
>possible leads.  Also the length of the leads for RFC15 and C91 should 
>be as short as possible at the connection point with U4 pin 16.
>
>If that does not take care of it, flush cut all pins and component leads 
>in the vicinity of U4 and U6 including the R-paks to eliminate anything 
>that could act as an antenna.  Also above the board make certain the 
>varactors and capacitors in the VFO and PLL area are seated completely 
>down on the board - long leads will cause the signals to couple together.
>
>The last gentleman who had this problem reported that the above efforts 
>did not stop it entirely, but when he covered the U4 area with 
>electrical tape, the problem went away.  Now, I can't explain why the 
>electrical tape would have that effect, but give it a try.
>
>73,
>Don W3FPR
>
>
>On 5/4/2014 9:11 AM, dale at k4eq.net wrote:
>> I completed my K2 earlier this week and everything seems to be working
>> great. However, I have discovered one problem. Received SSB signals from
>> 7180 to 7185 kHz are garbled even with the NB and preamp off. Thus far I
>> haven't observed this problem on any other frequency. Any ideas what may be
>> causing this?
>>
>
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Matt Zilmer, W6NIA
www.elecraft.com
831-763-4211  x129