[Elecraft] K1 KAT1 SWR Adjustment

[Don Wilhelm]

Carl,

Yes, I may have been the one to suggest those resistors for a dummy load 
- if you used the 50 ohm ones, they should be flat up to 200 MHz or more 
depending on your physical implementation - short leads and such.

Yes, adjust R2 to indicate the correct SWR - no smoke will happen - but 
do that as the last step.
The C9 adjustment must be done first, and once that is correct, do not 
touch it again or you will have to do everything all over.

If you want to use your 25 ohm and 100 ohm resistors to indicate a 
better setting for C9, then connect them alternately (use *short* leads) 
to the antenna jack - you are looking for the SWR indication to be the 
*same* for both (ignore the actual SWR amount, just adjust C9 slightly 
until they both read the same).  After that, go back to the 50 ohm load 
and set the trimmer resistor for forward power, and lastly use either 
your 25 or 100 ohm load and set the SWR = 2.0, then call it done.  On 
the KAT2 and KAT1, it is not uncommon for the final adjustment of the 
reflected trimmer resistor to be quite different than the setting for 
the FWD trimmer - it just happens to be that way.  As I indicated in my 
previous note, the actual SWR means nothing to the tuner itself, it 
merrily searches for the minimum SWR - and minimum SWR is a better 
indication of correct tuning than any actual SWR value.

73,
Don W3FPR

Strode, Carl R wrote:
>  Don, thanks so much for the reply.
>
> My dummy load is one I cooked up for my K2 SWR adjustment.  It consists of some 50 ohm precision film type resistors bolted to an aluminum heat sink.  I can't recall who gave me the idea, and suggested the actual resistors to use, but it may have been you.
>
> I have four of them all presently connected in a series parallel arrangement for a load very very close to 50 ohms.  My antenna analyzer says it's essentially flat.
>
>
> I do have one question.  You say the third step is to adjust the "trimpot" with the known SWR dummy loads.  Are you referring to R2, or C9?
>
> If it is R2 that you are talking about, I've given that a shot already.  I ended up returning it to the setting as specified in the KAT1 manual.
>
> I was worried that smoke and flames might come shooting out.
>
> When I adjusted it for a better SWR indication it was about 180-degrees out of rotation (i.e. the manual says to adjust R1, and visually set R2 to match the rotation of R1).
>
>
> Carl Strode
> WA7CS
>
> carl_r_strode at rl.gov
>
> -----Original Message-----
> From: Don Wilhelm [mailto:w3fpr at embarqmail.com]
> Sent: Tuesday, January 29, 2008 12:02 PM
> To: Strode, Carl R
> Cc: 'Elecraft at mailman.qth.net'
> Subject: Re: [Elecraft] K1 KAT1 SWR Adjustment
>
> Carl,
>
> The main reason for the reflected circuitry in the KAT1 is to monitor for the lowest SWR during a TUNE operation.  For that purpose, it is not necessary that the indication is accurate.
>
> If you wish to calibrate the SWR indication, check the C9 balance setting first - connect a known good 50 ohm non-reactive load (the Elecraft DL1 is good)  If you do not know for certain about your dummy load, measure it with an antenna analyzer.  If it is anything other than a pure 50 ohms resistive, you may still achieve a null, but the bridge will be balanced at the impedance of your actual load and not necessarily 50 ohms resistive.
> Next, calibrate the forward power, and lastly, calibrate the SWR indication (by adjusting only the trimpot) using a resistive load which produces a known SWR, such as a 100 ohm (SWR=2.0) or a 75 ohm load (SWR=1.5).
>
> The power level is not critical to any of these adjustments, but it may be easier to see the null at 5 watts than at 1.5 watts.  If you want to do it at 5 watts, adjust first at lower power and then make quick, but small, adjustments at the higher power.
>
> 73,
> Don W3FPR
>
> Strode, Carl R wrote:
>   
>> My new K1 is working great!
>>
>> However, the SWR indications appear to be a bit low.
>>
>> For example, I have a ground mounted vertical antenna (Hy-Gain 18-HT Hy-Tower) with lots of radials.  The SWR as indicated by the K1 is 1.0:1, which does not appear to be correct.  My trusty MFJ 249 tells me the SWR on this antenna is closer to 1.5:1, as I would expect.
>>
>> If I connect a non-inductive dummy load of 100 or 25 ohms, the indicated SWR is closer to 1.5:1 instead of the expected 2.0:1.
>>
>> When adjusting C9 for the lowest possible voltage, the instructions tell me to set the power out to 5.0 watts, however the manual does not tell me to increase power from the 1.5 watts nominal tuning output level to the full 5.0 watts.
>>
>> Should I enter TUNE mode, then tap to increase output power to 5.0 watts as I make the C9 adjustment?
>>
>>
>>
>>     
>
>
>