[Elecraft] kpa100 swr bridge

[Don Wilhelm]

Scott,

Have you checked the cable between the KPA100 and your external SWR meter?

You must obtain a good null for the KPA100 bridge before it can be 
expected to indicate anywhere near correct.  If you have problems 
obtaining a null it is usually associated with a T4 problem - check T4 
very carefully for well tinned leads - you should see a little of the 
tinned area above the board.  Make certain the correct color leads are 
in the correct holes.

Once T4 and the balance trimmer cap are correct, you will find that the 
forward and reverse trimpots (R26 and R27) will be close to the correct 
settings if they measure 43k ohms between the center lead and ground - 
set them initially to obtain that value.

You MUST use an insulated tool to adjust the C1 trimmer - both ends are 
above ground and you will not find the correct balance point with a 
conducting screwdriver.  Remove the external wattmeter (SWR meter) and 
attach the dummy load directly with a short coax when doing the balance 
adjustment - it can make a difference.

Also note that an SWR reading of 9.9 is the highest value that the 
wattmeter will indicate, th eactual SWR may be much higher.  Be certain 
the coax you are using is good.

73,
Don W3FPR

Scott McDowell wrote:
> Hello
>
> I just finished building the kpa100 for my k2 and need some help.
> All the test through building went as the manual said they should.
> But I have a problem with the swr bridge null adjustment. With the
> pka100 connected to a 2kw dummy load the k2 shows an swr of 9.9-1
> on all bands. An inline swr meter shows an swr of zero. I went through
> all the adjustments for the bridge but the swr reading on the k2 didn't
> change. Can someone point me in the right direction. I can't find
> anything about this in the manual.
> Thanks
> Scott N5SM
>
>