[Elecraft] [K2] test problem with VFO and no 7000 kHz signal heard

[Warren Holybee]

Hi, Warren here.

 

I couple years ago I started building a K2. I got it built but was having
issues with the alignment and test, then moved. I just opened the box and
started working on it again.

 

The entire radio is built, but I am still on the Alignment and test part II.
All the tests went well until the VFO Linearization. At first I got a Cal
PLL Info 232, then found that if I increased the VFO to 7180 (which is
outside the 7000-7100 range in the book) that it completes ok. It first I
thought this was fine, but it may be a clue to the other problem I ran into.

 

At the I.F. Amplifier Alignment, I was not able to hear the signal at 7000
kHz. I hear some static that changes in pitch and volume when I adjust AF
gain, RF gain, or L34.

 

I tried a basic signal tracing proceedure on the website (using an antenna
and starting at the cap at the input of the mixer) and got nothing. Several
days of testing later, I jumpered W2 and W3 together and voila, I hear the
internal signal loud and clear right at 7000 kHz.

 

So I'm thinking that either the filter isn't working, or the IF freq. is
off. I am sort of leaning towards the later, given the previous issue with
the Info 232 error. I don't know if it is an issue with the BFO, VFO, or
something else.

 

I don't have a test oscillator, but I do have a spectrum analyzer (8591E)
with a tracking generator. I was thinking of looking at the signal at W2 and
W3 but I don't know what the 50ohm input of the analyzer would do to the
circuit. If it shifts the filter it would be a useless test. 

 

One other thing that I don't think is a big deal. I am working in a cold
space about 50 deg. or so. I found that the VCO voltages don't change (and
are all about 6.5V) until it warms up. Just blowing on that area of the
board with my breath a couple times gets it working. Once it is working the
voltages are solid and don't seem to drift day to day. I'm guessing this is
the Thermistor doing it's job and it just can't deal with the cold temp.

 

My test results are below. Suggestions?

 

Thanks, 

Warren

 

 

PLL Reference Oscillator Range Test

High 12097.64    Low 12084.22     Range 13

 

VCO Voltages

80m       2.26        5.99

40m       1.7          3.30

30m       2.71        3.21

20m       2.35        3.90

17m       3.08        3.27

12m       3.86        4.22

10m       3.25        4.07

 

BFO High              4916.15

BFO Low                              4911.37

Range                   4.78

 

 

BFO set up exactly as described on page 89.

 

VFO Linearization

Cal PLL Info 232

Set VFO to 7180 and it brought VCO in range and performed the calibration.