[Elecraft] K2 signal tracing...

[Ian Liston-Smith]

Hi all,

In a quest to get to the bottom of my K2 not having enough volume (after ascertaining the audio section is ok) I started upon the Signal Tracing section of the manual, made up the Elecraft RF probe and even made the 10.000 MHz xtal oscillator - appendix E page 9. (Note: My K2 is not insensitive, just barely adequate in volume. An extra audio amp would probably sort it out, but at about $700 for the basic kit I shouldn't need to; in fact most users DON'T need to so I guess there's something not quite right with my kit.)

First 'issue': The RF probe doesn't come close to providing RMS readings on my DMM. Three volts p-p of the 10MHz oscillator measured with 100MHz scope (measured when connected to the K2 antenna input) input should give an RMS of about 1.06 volts by my reckoning. DDM 'RMS' using probe reads 200 mV, confirmed by connecting probe to DC-coupled scope. No good for recording the 'actual' against the 'expected' measurements in the manual. Am I missing something here?

I decided to ditch the probe and use the scope and derive the RMS from the peak-to-peak measurements.

Mixer, IF Amplifiers and crystal Filter section Appendix E page 11

Most readings were near enough to those in the manual until I got to "8: IF saturated output" measurements. I could only get close to the figures with RF max and AGC off otherwise no output at U11. Is AGC off for this test is correct or do have I a fault? (Such a fault would surely make the K2 worse than mine is...?) 2nd crystal filter output seemed ok, but product detector saturated output (with oscillator output at max or set to give 0.15 Vrms as in para 8?) had no significant gain. 

AGC tests also App E, page 11

This was ok but I couldn't get the U2 pin 1 volts above 4.8V even after peaking the tuning. It should be 6.9V but at what oscillator input level?

Either I'm not interpreting the instructions here correctly (they seem a bit vague regarding AGC on or off settings), my K2 is within the spread of voltage tolerances or I have a fault, although seemingly not a serious one - I don't know.

I'm not going to do any more checks is case I am already 'barking up he wrong tree'! So perhaps someone could clarify some of the tests or suggest other checks. 

Thanks and regards,

Ian, G4JQT