[Elecraft] K3 Antenna static bleed

[Don Wilhelm]

  Fred,

While the K3 has static protective devices that have been mentioned by 
others, I prefer to err on the side of caution.  The UHF connector has 
one problem for antenna/feedline static charge - if the antenna has 
built up a static charge, when the feedline is connected to an SO-239 
jack, the center conductor makes contact first, followed by the shield.  
So the best solution is a DC path provided within the antenna/feedline 
system itself rather than relying on any protection in the K3.

Type N and BNC connectors do it differently, the shield is connected 
prior to the center conductor, thus allowing any charge on the feedline 
to be safely discharged through the radio's protective devices.  With 
UHF connectors, the radio's protective devices may not work because only 
the center conductor of the feedline is connected, and there is no 
return path to the coax shield until the shell is properly tightened.

With UHF connectors, any "antenna disconnection" would best be done 
using an antenna switch rather than a physical disconnection.  The 
disconnect will cause no harm, but the re-connection can do damage 
without warning.  The antenna switch itself is a good place to provide 
that DC return path - either an RF Choke (100 uHy) or a high value 
resistor (500k to 1 megohm) between the center conductor and ground of 
the common connection to the transceiver.  When the transceiver is not 
in use, switching to a dummy load is a prudent thing to do, so if you 
have 5 antennas to switch, a 6 position switch is best with a dummy load 
connected to the 6th position.

Note that this is applicable to any transceiver - I know the question 
was asked about the K3 specifically.

73,
Don W3FPR

On 2/24/2011 10:25 PM, Fred Jensen wrote:
> Forgive me, I'm having a hard time with the schematic:
>
> Does my K3 have an RF choke or a high value resistor across the antenna
> input[s] to bleed the static charge?  For some reason, I'm getting more
> precip static than I usually do.  At N6A in Alpine County for the 2009
> Cal QSO Party, we managed to fry the front ends of two ICOM 756 PRO II's
> from what seemed to be inconsequential snow static.  Don't want that to
> happen to my K3.
>
> 73,
>
> Fred K6DGW
>