[Elecraft] KAT500: Tuning on 6m

[Ignacy]

Jim Brown-10 wrote
> If I put KAT500 in BYP,  the K3 often shows SWR's of 2 to 3. 
> 
> If left in AUTO, the mismatch is apparent in received audio. 
> 
> Without the KAT500, the antenna itself exhibits a 1.3 SWR consistently . 

Many tuners add SWR even in bypass because the path through is not 50 Ohm.
It is easy to check. Set a tuner in bypass, add a dummy load, and scan SWR.
Usually SWR increases rapidly with frequency. Like 1.1 on 20m, 1.5 on 10m
and 2.0 on 6m. This causes unnecessary matching when in automatic mode. 

The best way around this is to add a cap on the tuner input.  Find that
value that minimizes SWR on 6m. Usually it is 10-30pF. The cap needs to be
big enough to handle power but not too big since the voltages are pretty low
at low SWR (< 200V at 500W level). 

Ignacy, NO9E 





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