PLL Reference Oscillator Range Solved

[N0EHQ]

Good evening all.

 Just an update on K2 #4595 regarding the PLL reference oscillator range problem I was experiencing. I contacted Gary at Elecraft via e-mail a few days before the holiday.

Gary suggested that perhaps the crystal X1 in the PLL was the culprit. I received in the mail today a different crystal along with a 12 mH inductor and new diodes for D16 and D17. I replaced the crystal only and it by itself brought the PLL reference oscillator range up to 10Khz from the previous 8 Khz. Should I even bother with the different inductor?  I also believe the diodes are probably doing the job as well.

Now to find out why the BFO range is too low. The BFO high frequency comes in above the expected minimum of >=4916.3 at 4918.2 The BFO low frequency comes in above the expected maximum of <=4912.7 at 4914.8 with a resulting range of 3.4 compared to the expected minimum range of >=3.6. D37 and D38 are of correct values as are X3 and X4.

Building this K2 this last couple of weeks has been shall I say, an enlightening if not humbling experience. It's time for bed.

73, Ed N0EHQ

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[G3VVT]

 
In a message dated 31/12/04 04:52:04 GMT Standard Time,  
[hidden email] writes:

Now to  find out why the BFO range is too low. The BFO high frequency comes
in above  the expected minimum of >=4916.3 at 4918.2 The BFO low frequency
comes in  above the expected maximum of <=4912.7 at 4914.8 with a resulting range
of  3.4 compared to the expected minimum range of >=3.6. D37 and D38 are of  
correct values as are X3 and X4


>From the schematic the usual suspects would be L33, X3, X4, D37, D38, C173,  
C174 and posssibly C169 with the gate circuit of Q24.
 
However first a check on the of voltage range on the V BFO rail at  U10D-14
on the K2 Control Board may be helpful. According to the K2 manual  this should
range between 0 to 8V and with varicap diodes the maximum capacity  which
would determine the lowest frequency of the BFO is with minimum applied  voltage.
If the voltage does not swing low enough this would inhibit the ability  of
the BFO to reach it's minimum frequency.
 
The crystals may be a bad batch which may occasionally happen pushing the  
frequency in this case too high. The varicap diodes D37/38 type 1SV149 can  be
damaged by excessive heat during installation. When checked on a  capacitance
meter recently a new diode came out at about 890pF. One that had  been fried
that I tested was nearer 820pF. Are the capacitors noted the correct  values,
place correctly and soldered?
 
Bob, G3VVT
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