[Elecraft] K2 unadvertised feature ?

[Don Wilhelm]

Steve,

While something is happening, I don't think it is happening the way you 
surmise.

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

As far as I know, the presence of voltage on the VRFDET line will not 
cause the K2 to enter transmit state.  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.

I do not doubt that something is happening in your K2 due to the RF 
input to the low power TX line, but 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.

If your RF field is strong enough, it could cause the K2 to do 'strange 
things', and going into transmit state could be one of those 'strange 
things', but I doubt the mechanism is through the VRFDET signal - that 
line only controls the power output, it does not place the K2 in 
transmit state by itself - there is another cause. Without measurement, 
I can only speculate about it, but I would suspect something is creating 
confusion on the AUXBUS signaling line which causes the K2 
microprocessor to enter the transmit state.

I would suggest that you work to reduce the stray RF energy in the 
shack, and if that is not possible, try ferrite cores on all inputs to 
the K2 including the power connection.  Try running the K2 and the 6 
meter transmitter from different power supplies, 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".

73,
Don W3FPR

Steve Kavanagh wrote:
> Does the K2 have a feature where a sufficiently high V RFDET voltage causes the 8R line to go low, thus switching the PIN (1N4007) diodes and protecting the receiver from damage if high power is applied to the antenna socket while receiving ?
>
> If so this would explain the behaviour I have been getting due to RF getting into the K60XV, which I posted at
>
> http://mailman.qth.net/pipermail/elecraft/2009-January/104241.html .
>
> I've done some more measurements with everything disconnected from the K2 except for 12v power and an alligator clip lead used as an antenna connected to the transverter out socket.  Transmitting on another rig on 6m still causes the transverter key out line to be keyed, and I have confiirmed that the 8R line in the K2 is going low.  It seems to take around 100 microwatts to make this happen.  The only explanation that seems to make sense is that this power is detected (V RFDET) and the K2 microprocessor reacts to this by setting 8R low.
>
> Does this theory make sense ?
>
> 73,
> Steve VE3SMA
>
>
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