[Elecraft] Re: k3 SWR readings seem generous

[wayne burdick]

Michael E Fox (N6MEF) wrote:

> My factory-assembled K3 is reading 1.0 SWR while my LP-100A and tuner 
> both agree on about 1.4-1.5.

The KAT3's stray impedance (in bypass mode) may impact the SWR as seen 
by the K3's bridge, since this bridge is between the ATU and the LPFs. 
This effect would be more pronounced on the highest bands. Your 
external bridge is between the KAT3 and the antenna, so it may read 
differently from the K3 if any strays are present.

The "bypassed" state of the KAT3 is actually a per-band combination of 
L and C intended to cancel out the ATU's own strays. But compensation 
accuracy will vary from one KAT3 to the next due to the 5% tolerance on 
the components. So on some bands, the SWR in bypass mode might actually 
look closer to 1.0:1 with a load Z that is not quite perfect.

Still, all of these effects should be small, and I'll do some tests to 
see if I can duplicate an SWR discrepancy between the K3 and an 
external instrument.

73,
Wayne
N6KR

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