[Elecraft] KAT2: C55 Adjustment

[Don Wilhelm]

Don and all,

This is exactly the method I have been using on all the Elecraft 
wattmeters that I have worked on for several years now.  I believe you 
mentioned it first, so I do have to give you all the credit for this 
great idea.

It does result in a more accurate setting of the trimmer capacitor than 
just observing the null, but you have to just nudge the trimmer setting 
a bit at a time.   As you stated, the 'manual' adjustment done first 
will get things close, and these loads can be used to refine the adjustment.

With the KAT2 (and KAT100), I connect each load to the two antenna jacks 
and use the ANT 1/2 button to switch between the loads - with the KPA100 
it is harder because I have to connect and disconnect the loads for each 
comparison.  I could devise a switch, but that would introduce an 
unknown SWR element.

I have a set of 25 and 100 ohm loads constructed from 30 watt thick film 
power resistors ( 50 ohm 1% resistors), so they will handle up to 60 
watts continuous, and I like to do a final check at higher power with 
the KPA100 and KAT100.  If you choose this route, be certain to keep the 
connections to them VERY short - connecting to these (non 50 ohm) loads 
with even a short piece of 50 ohm coax will alter the SWR due to 
transmission line effects.  I use male to male connectors.

73,
Don W3FPR

DolfinDon at msn.com wrote:
> Hi
>
> I have a method that works well for me to adjust the power/SWR bridge.
>
> You will need to make up two additional dummy loads besides your 50 ohm. 
> These need to be 25 ohms and 100 ohms. I used 2 50 ohm 2 watt MOS resistors 
> mounted inside a PL239 connector wired in series for the 100 ohm and in 
> parallel for the 25 ohm. For the kAT2 you will also need UHF to BNC 
> adapters.
>
> After you do the procedure below from the manual set the forward power pot 
> per the manual. Set the reverse power pot to about the same position as the 
> forward pot. Now using about 2-3 watts with the 25 ohm load note the SWR 
> reading. Now install the 100 ohm load and adjust the null in very small 
> amounts until you get the same reading with both the 25 and 100 load. It 
> does not matter what the reading is yet, just so it is the same. Once that 
> is done adjust the reverse pot so the K2 displays 2.0:1 with either load. 
> Now go back and check the power and SWR with the 50 ohm load. The SWR should 
> be 1.0:1. If the power is off adjust the forward power pot to correct it and 
> recheck the reverse again with the 25 and 100 ohm loads to make sure you 
> still get 2.0:1. All of this will interact a little so you may need to go 
> through it several times.
>
> Hope this helps
>
> Thanks
>
> Don Brown
> KD5NDB
>   
>