KAT2 C55 adjustment - jumping 099-000

[ub5_073_oleg]

Folks,

yet another KAT2 SWR bridge null adjustment question.

I can reach 003 mV in ATU CALn mode. But after exiting and
entering CALn again, K2 displays 097, 098, 099, 000, 001 and
so on till it reaches a steady state around 003.

What could it mean? Looks to me like a display value overrun
at 100...

Pin 1 of LM358 has 0V on RX and 3.1V on TUNE.


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[ub5_073_oleg]

I think I found it. Making 1-turn loop through T1, I made
the wire jumper about 1/4" shorter as suggested in manual.

After replacing it with "correct" 1-1/4" one, I am able to
reach 007 mV with C55 adjustment. (thanks to
http://www.qsl.net/ve3mcf/elecraft_reflect/KAT2_Setup_C55.txt)

Now the next problem: after CALp, competed with RF-probe and
DMM, SWR reading is still very inaccurate. E.g. 1.4:1 at 25
Ohm instead of 2:1.

Have I to go for 2 dummy loads method (25 and 100 Ohm) or
can I investigate something before?


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[ub5_073_oleg]

Don, thanks for quick answer!

With "calibrate the SWR", do you mean simply adjusting REFL
R2 until SWR reading is correct, without touching C55 and
FWD R1 any more?

Oleg


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[Don Wilhelm-4]

The KAT2 does indeed have trouble indicating SWR at the correct level -
it is typically too low.
Since you have calibrated SWR=2 loads (hopefully used with VERY short
connecting coax), you can do the null calibration and then the forward
power calibration and after that attempt to calibrate the SWR - if you
cannot adjust the Reflected pot high enough, just set it at maximum.

Since the KAT2 tuning algorithm tunes for the minimum SWR point, tuning
will not be affected even though the numerical SWR report may be on the
low side of correctness.

73,
Don W3FPR

ub5_073_oleg wrote:

> I think I found it. Making 1-turn loop through T1, I made
> the wire jumper about 1/4" shorter as suggested in manual.
>
> After replacing it with "correct" 1-1/4" one, I am able to
> reach 007 mV with C55 adjustment. (thanks to
> http://www.qsl.net/ve3mcf/elecraft_reflect/KAT2_Setup_C55.txt)
>
> Now the next problem: after CALp, competed with RF-probe and
> DMM, SWR reading is still very inaccurate. E.g. 1.4:1 at 25
> Ohm instead of 2:1.
>
> Have I to go for 2 dummy loads method (25 and 100 Ohm) or
> can I investigate something before?
>
>  

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[Don Wilhelm-4]

Yes, that is exactly correct - do that as the last step.

73,
Don W3FPR

ub5_073_oleg wrote:
> Don, thanks for quick answer!
>
> With "calibrate the SWR", do you mean simply adjusting REFL
> R2 until SWR reading is correct, without touching C55 and
> FWD R1 any more?
>
>
>  
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