[Elecraft] [K2] K2 Adding a Gas Discharge Tube a Benefit?

[W B Reese]

I'd like to recommend to others my solution.

An Alpha Delta Model TT3G50

While it may not be as inexpensive as winding your own chokes etc, it 
is a whole lot easier.  I have a double male connector on the back of 
the K2/100/AT100 and it feeds the amplifier or antenna.  I never move 
it.  BTW I have a coax fed dipole and on 80 meters I deal with 
substantial SWR's when I get up to the fone band.  Sometimes as high 
as 5:1 because my antenna is tuned on 3530 KHz.  My amplifier, an 
Ameritron 811H doesn't like that, so I have a tuner, a MFJ 989B - 
this is the one to have, the coil is on a ceramic form and doesn't 
come "un-sprong" as other models do.  Anyway, it has a switch in it 
to put your rig on a dummy load when not on the air.  Between the 
two, it provides (I believe) an excellent measure of protection.

TR, WB6TMY
____________

At 04:46 AM 11/14/2009 -0500, Don W3FPR wrote:
>While that RF Choke is well and good from the standpoint of static
>discharge, I strongly suggest you move it outboard of the KPA100.
>With the original KPA100 design, there was a 100 uH choke located at the
>antenna jack.  That choke was removed along with the improved T/R switch
>design. - The reason - that choke could (and in some cases did) couple
>with circuits in the base K2 and cause a parasitic oscillation to occur,
>especially when operating on 40 meters.
>So while I do encourage you to use such a choke, I also encourage you to
>mount it somewhere in your antenna system outside the K2/100 enclosure.
>If you have an antenna switch, open it and install the choke at the
>'input' jack.  If you have an amplifier that is always in line, install
>it at the amplifier input.  Worst case, if you have no convenient place
>to mount it in the shack end of your antenna system is to use a small
>die cast box with a male chassis mount UHF connector on one side and a
>female UHF jack on the other, place the choke in the enclosure, wire the
>connector centers together, and mount the box directly on the KPA100
>SO-239 jack.
>
>As for the gas discharge tube, that may do a good job, but do calculate
>the gas tube voltage rating assuming a 3:1 SWR at the 100 watt level -
>it should not fire with that peak RF voltage.  By my quick calculations,
>a 200 volt breakdown gas discharge tube would be about right.
>Mount the gas discharge tube at the same place as the RF Choke.
>
>For the best protection, disconnect the antennas when the K1, K2, K3,
>KX1 are not in use - or even better use an antenna switch to switch in a
>dummy load instead of the antenna.
>
>73,
>Don W3FPR

Tel: . . . 707-832-4304