[Elecraft] K2 unadvertised feature ?

[Don Wilhelm]

Steve,

But I don't think a transverter should normally pump RF back into the K2 
transverter output.  Are you trying to simulate RF pickup on the coax 
between the K2 transverter output and the transverter input?  If that is 
what you are trying to simulate, I would feel more comfortable having 
the high RF field present on the coax shield (with the coax terminated 
at the far end), and no signal pumped backwards into the K2.

You are correct - if both TX and RX are off, both 8T and 8R will be at 
zero volts (no power to the early stages of the K2 transmitter and no 
power to many parts of the receiver.

You are also correct that noise as I suggested on the PTT/DOT line would 
cause the K2 to go into transmit - it is not, it is just going 'out of 
receive'.

You will probably have to poke around with an RF Probe or an adequate 
oscilloscope to determine which lines have RF on them in order to 
determine what circuits in the K2 (or on the K60XV) are hot with RF.
With the information I have received thus far, I would be more 
suspicious of the AUXBUS signal line, because that is a signal the 
communicates directly between the various processors in the K2, and 
clearly the microprocessor is doing 'strange and unusual things'.  It 
may take a K2 firmware expert (Wayne) to figure out what is happening in 
the microprocessor to cause RX to drop.

73,
Don W3FPR

Steve Kavanagh wrote:
> Don:
>
> Thanks for the quick reply ! 
>
> I'd reply off list with the nitty gritty details but I did have a request from another interested ham to make the results public.
>
> I have now put together a much more controlled test setup for the K2 that doesn't involve high levels of RF all over the shack !  I now have a low power crystal oscillator/multiplier source at about 146 MHz (which puts about 0.5 mW into a 50 ohm load) connected to the XVTR OUT jack connected in parallel with a 50 ohm load using a BNC Tee just behind the rear panel.  This reliably reproduced the observed effects (KEY OUT going to ground, receiver quiet and S-meter to maximum), and simulates the loading effect of having a transverter connected.
>
>   
>> Check the gate of Q4 to see if the voltage there drops -
>> that causes 8R to drop.
>>     
>
> Yes it does drop when I key the 146 MHz test source, and the collector of Q2 (8R) does too.
>
>   
>> Also check the state of the TX signal from the
>> microprocessor (gate of Q3) 
>>     
>
> That voltage remains unchanged at approximately zero volts, as does the collector of Q1 (8T).
>
> So clearly the K2 is switching into an odd state.
>
>   
>> My guess that the PTT
>> input may be the culprit is only a guess, but it is possible
>> for severe noise (high RF levels) on the PTT line to cause
>> the microprocessor to become 'mixed up'.
>>     
>
> If the K2 is in CW mode it does not start sending dots, so the PTT line is not going low.  Which doesn't mean it doesn't have RF on it, but we are now talking about a pretty low level (500 microwatts) of generally shielded RF so I would be surprised if stray coupling to the PTT line would be the culprit.
>
> Back to head scratching.....
>
> 73,
> Steve VE3SMA
>   
>