Kevin,
It is normal to see a higher response touching a random, wire to C6
compared to touching the same wire to W6. The C6 location is a high
impedance point while the W6 and D6 locations are low impedance - the
capacitive dividers (C7,8 and C4,5) reduce the impedance.
The end of a random wire is a high impedance and matches better at C6.
If you were connecting the center conductor and ground the shield of a
properly matched feedline close to the test point, you would likely find
a better response at W6 than at C6.
That is why that testing technique is called Cheap and Dirty - it does
have some eccentricities that the user needs to be aware of (like this
one), but overall is a quick troubleshooting aid.
If you are getting about the same response at D6 and W6, then the
bandpass filter is probably OK.
73,
Don W3FPR
Kevin Cozens wrote:
Greetings.
I have barely used my K2 going on about two years now. It seemed to work
well when I first got it off the person who had assembled it. I got
occasional comments about good audio when operating on SSB. I then
started applying the mods to bring it in line with the post 3000 serial
number units, applied the PLL stability mode, and replaced the crystals
with a more closely matching set, and completely re-aligned the radio.
Since then, the radio seems to have become slightly deaf, and I also
have some issues with transmit audio. I've considered selling it to
someone who could fix it and starting over. Having acquired a good
digital storage oscilloscope some months back, I'm going to have another
shot at trying to fix the problems. I'll start by working on the receive
issues.
I'm planning to get one of the Elecraft signal generator kits to help
with tracking down the receiver issues. Since I don't currently have
one, I'm starting with the cheap and dirty signal tracing notes from
Tom, N0SS. I pulled out the KSB2 and disconnected the KAT2 to eliminate
them as a source of problem. I have noticed one odd thing when using a
random length of wire and touching one end of it to the indicated test
points.
Touching the wire to either side of C6 (RF Board page 3), the S meter
reading on the front panel goes up by about 2 LED's. What is odd is that
if I touch W6, or either end of D6 (the previous and next points in the
signal chain) I don't see this level of increase in signal level.
This isn't making sense to me right now. I would think I would get the
same signal level increase at either W6, or D6, but not at neither point
compared to both sides of C6. Could this indicate bad, or wrong value
caps, for C5 and/or C7? Any other thoughts about this rather odd
behaviour? Seems to be pointing towards something to investigate further
but I hope I don't have to removed that bottom rear panel as its more of
a pain to remove.
__
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