[Elecraft] PLL Reference Oscillator Range Solved

[G3VVT at aol.com]

In a message dated 31/12/04 04:52:04 GMT Standard Time,  
epalmer at sirisonline.com 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