[Elecraft] I'm Stuck!

Tue Jan 7 00:42:01 2003

Hello Roy,
I had a comparable result here (K2, Rev. B).
After replacing C173 by 330pF and C174 by 120pF I got the following 
readouts:

BFO High Freq. 4916.75kHz
BFO Low Freq. 4912.90kHz
Range (High-Low) 3.85kHz

Although the range is sufficient the BFO Low Freq. still is higher than it 
should be (<=4912.7kHz).

So I thought it would be a good idea to compress 
the winding of L33 a bit to get a higher inductivity  but after desoldering 
the 5.1MOhm resistor across L33 it turned out that the windings are glued 
to the core. Taking into account the thin diameter of the winding I decided 
not to do as I planned. But when I pressed the 5.1MOhm resistor back onto 
L33 I obeyed about 100Hz shift of 
BFO Low Freq. to lower frequencies, which I think results of increased 
capacity. So I decided to try with adding some capacitance at another 
location.
I added about 4pF (in fact its a small Murata SMD Trim cap TZC03 6,0pF) 
from X4 to ground. This is easily done on the bottom side of the RF board 
using the PIN of X4 which is next to its ground wire pad and the ground 
wire pad itself. At this time I have some pictures of my K2 assembly at 
http://www.qsl.net/df7tv/k2_3105.html just look for the last picture on 
this page and there you'll see the blue trim cap just below L33. 
This cap will shift mainly BFO Low. Freq..

Although this solution may have disadvantages the result was as I wanted it 
to be:

BFO High Freq. 4916.72kHz
BFO Low Freq. 4912.35kHz
Range (High-Low) 4.37kHz

Use of a trim cap allowed me to arrange the available BFO range such that 
it is now symmetrical to the given boundaries (4916.3/4912.7 kHz).

[When doing measurements always place the bottom cover back to the case -- 
this may shift the BFO Low Freq. by about 100Hz down.]

73
Thomas

Von:            	"Roy Vickers" <[email protected]>
An:             	<[email protected]>
Betreff:        	[Elecraft] I'm Stuck!
Datum:   	Mon, 6 Jan 2003 06:16:52 -0600

> Hi,
> I am in the process of building my k2, sn 2884 and have reached the final
> alignment and test. I decided it was a good time to install the stability
> mod so that's what I did. After doing so, I ran the CAL FCTR and that's
> where I ran into problems. Before mod: 4916.94 - 49.26 = 4.48; after mod
> 4917.12 - 4913.73 = 3.39. I added an 82pf cap across c174 and the result was
> 4917.08 - 4913.35 = 3.73,not much improvement. I added a 200pf (max size
> recommended) and I get
> 4917.00 - 4913.27 = 3.73. I calibrated the internal counter to WWV and am
> confident
> that it's right on. I've rechecked the component values and they're correct
> and I marked the old xtals when I removed them so I know they're not back in
> the circuit. Any ideas guys??? Could I take my old L33 toroid and wind a
> higher inductance coil?
> thx
> Roy Vickers
> 
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-- 
Thomas Martin, Stuttgart, Germany
http://www.qsl.net/df7tv