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

[Don Wilhelm]

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

va2gu wrote:
> My K2 is S/N 5879 with RX ANT, KPA100, EXT ANT TUNER options. 
>
> Have had damage from snow static discharge, to the diodes (5711) in the SWR
> bridge of the TUNER, the cap C114 on the K2, just inside the RX ANT option
> and on a MOSFET inside the home brewed TR switch.
> That was in 2007.
> Talked with Gary at Elecraft for recommendations. 
> The K3 has gas disch. components for protection and i tried to order them
> then, but they didn't have stock.
> After some thoughts, i decided to prevent the static buildup which would
> occur with a simple gas discharge element; this would build to the
> ionization voltage and short the static, causing a pop if you're on the
> radio.
>
> So i have wound several chokes and placed them on all points going to
> outside (antennas).
> It is a 60uh which costs pennies; use the plastic housing of a ball point
> pen (abt 7/16" dia) and cut it to 5/8" long.after you
> have wound 110 turns of 26ga enamel cu. wire on it. Just make sure that you
> do not finish the windings at the same end
> as the start of windings. 
> Then put liquid tape on it and wind a few turns of black tape over the
> ass'y.
> Install inside the apparatus, where the antenna comes in.
>
> At 2mhz, it gives 1200 ohms. The choke will draw about 300 ma at 100watts
> out. If you dont like loosing 40mw for 50 ohms antenna Z, just put more
> turns on your ball point pen housing.
>
> This has been in use since Nov. 2007 and still works. And i do get strong
> snow buildup on the 1/2 wave 160m dipole up here.
>
> Also get yourself a few 1N5711; they're cheap, but very expensive (time
> wise) if you dont have 'em and they're blown up!!
>
> 73's
> va2gu
>
>
>
> k7hbg wrote:
>   
>> Hi all you K2 owners;
>>  In the ongoing effort to preserve and protect our SWR and Power bridge
>> diodes,
>> would the installation of a gas discharge tube between the antenna
>> connector
>> and ground as in the K3 be of any help in this battle?
>> Regards, Bob K7HBG
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