[Elecraft] extreme signals

[Ron D'Eau Claire]

Hi, Fred:

The K2 is sufficiently robust that you don't need to put diodes back to
back at the antenna input. That can lead to problems RFI and intermod
interference should there be enough r-f to make them conduct. 

The HF Pack experience is a lot like you are describing. It is a
situation in which rigs may be on the same frequency within only a few
feet of each other. In that EXTREME case, enough r-f might appear at the
i-f amplifier to cause a "howling" effect due to extreme overload of the
amplifier. The howl is avoided by putting the diodes in as Wayne
recommends to hold down the signal levels as needed. They will never
conduct except in that very extreme condition. Putting them at the i-f
amp avoids the problems of putting back-to-back diodes at the antenna
input - and I'm not at all sure they would hold the signal level down
low enough to avoid the howling problem. After all a pair of silicon
diodes will still allow a signal of 1.2 volts peak-to-peak to appear at
the antenna terminal! (2 x 0.6 volts, typically). 

The "mod" came up because the Elecraft guys (or the ARRL in their Labs)
never tested rigs operating on the same frequency AND within a few feet
of each other.  From what I've read the diodes did the trick. I don't
work HF Pack, so I don't have personal experience of the issue.

Ron AC7AC
K2 # 1289


-----Original Message-----
Just found Wayne's recent mod for extreme signal strength, back to back
diodes in the IF amp.

Coupla questions:

1)  What's "HF Pack" the circumstance that reportedly uncovered the
problem?

2)  When a kid we used to put back to back diodes just like this across
the receiver antenna input.  Purpose was to protect the front-end from
overload, particularly static discharge.

3)  Is there a spot in the receiver front end where back to back diodes
like this might be used to limit nasty static on the antenna and perhaps
further protect the whole receiver from extremely strong signals
introuced by a second K2 in the same tent perhaps on the same band?

TNX for collective wisdom,

Fred
kt5x / w5ya/qrp