[Elecraft] K-2 W.A.O F. NOISE FROM PLL.

[N4ch@aol.com]

Having noticed this problem (synthesizer noise due to 2 signals on almost the 
same frequency in the PLL) on approximately 7183 +/- 2.5 KHz, I decided to 
put the "fix" (part of revision B) in one of my older radios, serial number 
00029.   The fix helped, but not much.....at least that was the case when I 
put in BOTH components that were called for.   The trace connecting pin 16 of 
U-4 to everything else on that node is cut, and bridged with a 100 UH RF 
choke (RFC-15), and then pin 16 is bypassed to ground via a 1000 pF capacitor 
(C-91).   Doing BOTH of these helped only slightly, but I noticed that the 
problem went away COMPLETELY if only RFC-15 was installed (after cutting the 
trace) and C-91 was NOT installed.

I then decided to see if the WAOF problem existed on another K-2 (serial # 
3203, which is Revision B, and already had these changes).   The noise was 
plainly there, but it went away if C-91 was removed, just like # 00029.   I 
then tried something else on both radios.......I put a 68 pF capacitor 
between U-4 pins 12 and 13 (ground).   In BOTH radios, the noise was gone, 
with C-91 there OR not there.

Based on this, it appears that the "best" fix (at least on my sample of 2 
radios that had the problem) is to install RFC-15 (after cutting the circuit 
trace), add the 68 pF cap between pins 12 and 13 of U-4, but DO NOT install 
C-91.

By the way.....I also looked at 2 other radios (serial numbers 00151 and 
01532).   Neither of these had the synthesizer noise at all, and neither had 
any of these changes either.   I decided to leave well enough alone.

73,
Herman, N4CH.


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