[Elecraft] #3062 Part II BFO test problem

Mon Jan 27 10:57:01 2003

*** That happened to me also and Gary at Elecraft responded with: ***

We know the last batch of BFO crystals have higher Lm or motional
inductance, and do not move as far. I tested over 200 of them last month
and found that to be the case.
The current recommendation is to add 47pF to C174, and 120pF to C173 on
the bottom of the PCB if the BFO range is too small. Tests I did for
Wayne shows this usually solves the problem. As long as you can reach
4913.0 at the low end, and 4916.5 at the high end - you should be fine.
Wayne posted some info about this on the Elecraft reflector last month.

Be sure and ground the cans of the crystals before concluding what the
range is, since it can make a 200-300 Hz difference at the lower freq.
It does not change the higher freq. as much, maybe 20-50Hz.
>
If your BFO range is too small, then add the caps. If you do not have
them, email [email protected] and Scott will send you two caps as
mentioned above.

If you wish, we can send a new set of the BFO crystals with a wider
range and/or lower freq. But adding the caps, or just changing C173,
C174 to larger single cap values of 330pF for C173 and 120pF for C174
would be easier in my opinion. Wayne came up with this change for the
kits with slightly low BFO range, and I verified it works well.

 C173:  220 + 120 = 340, round down to 330 pF.

 C174:  82 + 47 = 129, round down to 120 pF

 All of us are aware of the narrower range of the last batch of BFO
 crystals. One good thing about them, is that they should have less drift
 with temperature changes. Some of the previous batches had so much range
 (5-6kHz, and too much in fact), that they could increase the drift of
 the BFO.

 You can also connect a 3.3pF to 4.7pF across the PCB pad of X3 or X4
 that connects to L33,  and to ground. Use the either of the pair of
 ground pads near the crystals that is used to ground the crystal can.
 This alone can make a 1-2kHz drop in the low BFO frequency without
 affecting the BFO high frequency.

*** I had Elecraft send me new xtals but that didn't fix. As of this
writing, I put my old 39mh L33 back in, which is not a option if you have
sn3000+. I'm still conversing with Gary on this issue and several others are
experiencing the same problem.

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Ron Schuster
Sent: Monday, January 27, 2003 8:46 AM
To: [email protected]
Subject: [Elecraft] #3062 Part II BFO test problem

My frequency measurement results are:  high freq is 4917.0,  low freq is
4913.5

The low frequency spec is less than 4912.  The range spec is 3.6.  It fails
both
of these.

I have checked all components and soldering.   Verified X3, X4, D37, D38,
L33, C169, C173, C174

Any ideas??

<>-< <>-< <>-< <>-< <>-<<>-<<>-<<>-<<><-<
Ron Schuster  (N9RC)
Cincinnati, OH
[email protected]
Outbound eMail scanned by Norton AntiVirus
<>-< <>-< <>-< <>-< <>-< <>-<<>-<<>-<<>-<

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