[Elecraft] K2 unadvertised feature ?

[Steve Kavanagh]

Thanks for taking the time to consider my problem, Don.  Here's a few more observations.....

> If the 8R line in the K2 goes low, it is because the K2 has
> entered the transmit state.

You'd think so, but since the display does not show a frequency change between the receive state and the anomalous state when the RIT is on (and offset) this is not entirely the case.
 
> As a
> further thought, the driver for VRFDET on the K60XV is a
> tri-state driver and must have an enable input to drive the
> VRFDET line.
> 
> if you do not
> have a transverter band selected on the K2, the input should
> be grounded by the K2 relay on the K60XV option.
> 
> If you *do* have the K2 set to a transverter band and the
> low power output is selected, then yes, the RF input on the
> output line could be coupled back into the K2 bandpass
> filter - the obvious result should be receiver overload, but
> not changing into transmit state.

I am thinking of the VRFDET detector in the K60XV, not the one on the K2 RF board, as the source of my problem.  Its enable signal is the 6LP power supply to Q2/U2, which is on in both receive and transmit states.  The VRFDET output from Q2 (P1-pin7) is about 0.4 V in receive and goes up to over 2 V when I transmit on 6m, so there is certainly RF being detected.  In any case, when I switch to a transverter band which does not use the low power output (thus turning off the 6LP voltage), the problem goes away completely.

I tried connecting the cliplead "antenna" to many points on the K60XV (with the cover off the K2), including XVTR IN, all 3 pins of Q1, P1-pin1 (currently fitted with an extra 4.7nF bypass to pin2), and the junction of D1 & D2.  The only one which resulted in the anomalous state was XVTR OUT.  I'm thinking I should try the VRFDET detector diode on the K2 RF board, though.
 
> I would suggest that you work to reduce the stray RF energy
> in the shack, and if that is not possible, 

It really isn't practical in my apartment station or in the rover vehicle.  Space limitations force operation close to the antennas.

> try ferrite cores
> on all inputs to the K2 including the power connection.

In this simplified K2-only test configuration the only connections to the K2 are the pickup antenna to the XVTR OUT and the power connection, and the power lead does in fact have a clip-on ferrite choke in use for this testing, which ought to do something at 50 MHz.

> Try running the K2 and the 6 meter transmitter from different
> power supplies, 

The power supplies (at the home station) both plug into the same AC power bar, but otherwise the 6m setup is completely separate. 

> and/or try bonding the other transmitter to
> the K2 to see if there is any difference.  Often slight
> ground potential differences can cause "strange happenings".

Agreed.  I have tried various different ground connections, and different sensitivities to the RF fields result, presumably due to different RF potentials on the K2 case compared to that on the XVTR OUT jack. But there was no magic cure, so far. And this situation will be completely different in the car, anyway...I need to find a more robust solution.  I am thinking of perhaps some sort of bandpass or low pass filter in the TX IF line, though the design is complicated by the fact that the terminating impedances aren't all 50 ohms.

73,
Steve VE3SMA


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