Fw: [Elecraft] KAT100 null

[Bill Carpenter]

I just checked my analyzer with a good known 50 Ohm load and it read 60 ohms 
so I'm sure my dummy load is fine - the analyzer reads 10 ohms high I guess. 
I have checked all connections/solder joints and yes the input wire goes 
through T1 lol.  I do get a null but at around 2 volts, not near zero as it 
should be.  When I attempt power calibration at 20 watts I can't get near 
the 2.7 volts specified -I can only get to around 2 volts with full 
clockwise on R4.  Since that is the same as the null could U5 be bad?  Just 
occurred to me.
 Ackkkkkk!

----- Original Message ----- 
From: "Bill Carpenter" <nz0t at cox.net>
To: <w3fpr at arrl.net>
Sent: Saturday, December 08, 2007 1:54 PM
Subject: Re: [Elecraft] KAT100 null


> Hi Don,
> I'm using my old Heath dry dummy load/wattmeter which shows 60 ohms pure 
> resistive on my MFJ analyzer (who knows how accurate that is) and I'm 
> using a good, very short jumper. All connections look fine and yes, the 
> input jack wire goes through T1 lol.  I do get a null but it's at around 
> 1.9 to 2 volts on my DMM.
> This is driving me crazy - it has to be something simple I'm missing!
> ----- Original Message ----- 
> From: "Don Wilhelm" <w3fpr at embarqmail.com>
> To: "Bill Carpenter" <nz0t at cox.net>
> Cc: "elecraft list" <elecraft at mailman.qth.net>
> Sent: Saturday, December 08, 2007 1:04 PM
> Subject: Re: [Elecraft] KAT100 null
>
>
>> Bill,
>>
>> That indicates something is wrong.  Are you using a good dummy load with 
>> a very short connecting cable?  If you have any doubts about the dummy 
>> load, check it (and the cable too) with an antenna analyzer - anything 
>> other than a 50 ohm resistive load can cause problems with obtaining a 
>> good null.
>>
>> The other thing that can cause difficulty with the null is any reactance 
>> in the tuner - there is a small amount of residual, but not enough to 
>> change the null drastically.  Look the tuner over carefully for 
>> unsoldered connections in the relays and inductor and capacitor parts of 
>> the tuner.
>>
>> As for 'dumb' things, make certain the wire to the input jack goes 
>> through the center of the toroid.
>>
>> 73,
>> Don W3FPR
>>
>> Bill Carpenter wrote:
>>> Everything has gone fine with my new KAT100 until I got to the SWR 
>>> bridge null adjustment.  The best null I can get is about 1.9 to 2.0 
>>> volts. I checked T1 and even took it out and rewound it with new wire. 
>>> The 4 leads of T1 are in the correct holes and continuity checks fine. 
>>> Everything else in the bridge circuit looks fine to me and the coax 
>>> jumpers I'm using are fine. I have the KPA100 so I'm attempting the 
>>> adjustment at 20 watts.  U5 is installed correctly.
>>>
>>> Very frustrating!  Any help is GREATLY appreciated!!
>>>
>>> 73,
>>>
>>> Bill NZ0T
>>>
>>
>