[Elecraft] K3 SWR Accuracy: Final explanation

[Jack Smith]

Wayne:

There's also an SWR versus output power issue, or is that part of the 
first correction factor? The SWR error increases significantly at lower 
power. I have not had a chance to plot the data because it was not part 
of the original question, but there is a clear power related error seen 
in the raw data, which I assume is tied to the detector diode linearity 
at low voltages.

Jack K8ZOA


Wayne Burdick wrote:
> There are two sources of the reported SWR inaccuracies:
>
> - An SWR calculation scalar that I'll be adjusting in firmware; this  
> is what's causing a 2:1 SWR to read closer to 1.8:1 on some K3s.
>
> - The KAT3 itself, and to a much lesser degree, the KANT3, which is  
> present if the ATU is not installed. Both modules have inherent stray  
> reactance, part of which is due to the 8.2 MHz first-IF trap. These  
> strays slightly alter the impedance seen by the K3's SWR bridge.
>
> Even when the scalar correction is applied, there will still be a  
> small frequency-dependent variation in SWR reading between the K3's  
> bridge and an external instrument. This has no impact on K3 operation.
>
> 73,
> Wayne
> N6KR
>
>
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