[Elecraft] k2 KPA100/KPA100 schottky diodes

[Jim Wiley]

John -


A 1N5711 is pretty much the same from any manufacturer, but instead of 
addressing the repair, let's address the actual problem, which is 
static  buildup on the antenna itself. 


You might try a RF choke, perhaps somewhere between 1 and 5 
milli-henries (mH), from the antenna base (coax center conductor) to 
ground.  The exact value is not important, as long as the inductance is 
not too low.   The RF choke is will bleed off static charges, but won't 
help all that much for fast rise items like nearby lightning strokes.   
Lightning arresters are better for that purpose.  Of course nothing will 
protect against a direct hit, so  disconnecting cables  when a storm is 
expected is always  a good idea.  


If you don't have an RF choke handy,  you can make one easily enough by 
putting 20 to 30 turns of 20 to 24 gauge enamel insulated wire on a 
FERRITE core, such as an FT-80 or a  FT-200  (or anything else that is 
handy.  The same type wire as is used to wind the toroids in your 
Elecraft radio is what you want.   If you don't have some wire handy,  
any electric motor repair shop can help you out, and if you ask nicely, 
they might just give it to you for free.   You will need about 3 to 6 
feet, depending on how many turns you put  on the core. Smaller gauge 
wire is easier to wind, and power rating is not an issue here.   A 
larger core is better, in that it will be easier to wind and have more 
room for the wire). 


Lacking a handy toroid core, then a resistor rated between 2000  and 
10,000 Ohms at  1 or 2 watts might do, but the resistor could cause 
problems if you are feeding the antenna on multiple bands, as I suspect 
you are.  On some frequencies, the feed-point  impedance of the antenna 
could be several hundred to even a couple of thousand ohms, and the 
resistor would then be absorbing a large portion of your outgoing signal 
- which is why the RF choke is a better solution.  However, this is one 
instance where a  wire-wound resistor is OK for use around RF, so if you 
happen to have a 5 to 50 watt  wire-wound power resistor handy, it  will 
work just fine.


The overall idea is to drain off the static charge before it has a 
chance to build to potentials that can arc across something or damage 
your set.    Back in the vacuum tube days, we didn't have to worry so 
much about such things,  but that was then, this is now.


- Jim,  KL7CC



Jferg977 at aol.com wrote:
> Is there any reason to choose one specification over another for the  
> 1N5711's which are found in the KPA100 and KAT100?  The ones currently  being shipped 
> appear to be GTE's vs whatever the kits came with in 2006.
>  
> I had thought that the frequent frying of these diodes on my k2 was due to  
> lightning strikes but it looks more like the product of static discharges via 
> my  23 foot vertical - you can hear the snaps as the potential arcs across the 
> coax  connection at my Balun.  I had thought that this only happened in storms 
>  but it turns out to start as the storm is coming.  Clearly the answer is to  
> disconnect the radio from the antenna unless I'm using it.  It's also been  
> suggested that I put an inductor shunt between the lead in and ground, but  I'm 
> at a loss to size it.
>  
> It also occurred to me to bring a wire up from the grounding system to  about 
> the height of the antenna and put one of those wirebrush static wicks on  it. 
>  
> Is what I'm considering crazy?  If you think so, it will be ok to tell  me.
>  
>  
> 73   AI4TO       john  ferguson    M/V Arcadian
>
>
>
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