[Elecraft] TxMon and K3 (tuner bypassed) SWR missmatch

[Don Wilhelm]

David,

You are trying to compare apples and oranges and expecting them to be 
the same.

The K3 SWR indication is at the *input* to the KAT3, and the TX Monitor 
is indicating the SWR at the *output* of the KAT3.
That is no reason that they should match.

The TX Monitor will always give you the unmatched SWR of your antenna, 
while the K3 will always indicate the match obtained after the antenna 
is tuned.

If you could place the TX Monitor sensor between the K3 PA stage and the 
KAT3, you could expect them to agree, but that connection location is 
impossible without seriously modifying your K3.

Even with the KAT3 in bypass, there is still some residual reactance 
which will make the readings different.
With the K3S, and its KAT3A, there is a relay that will truly bypass the 
L/C portion of the KAT3A and the readings should be closer, but still 
not exact.

With wattmeters as they are, expect a 10% difference in readings without 
alarm - wattmeters are not usually precision instruments unless you get 
into lab instrumentation which costs many, many dollars.

73,
Don W3FPR

On 11/4/2016 6:59 PM, dmoes at nexicom.net wrote:
>
> I recently installed the TX monitor in my P3 and have a discrepancy with
> the SWR reading between it and the K3
>
> with a dummy load connected the P3 and K3 read 1.12 and 1.0
> respectively   a level of error that is to me quite acceptable.
>
> however  when connected to an antenna  I will see the SWR on the K3
> often close to 1:1   when the P3 will show up to a 1:2.   as the SWR
> climbs above 1:2 on the P3  the K3 reading will track it fairly closely
> but about a level of 1 below.  example
> K3 1:1  P3 1:2,
> K3 1:1.5  P3 1:2.5
> K3 1:2   P3 1:3   and so on
>