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, d...@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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