[Elecraft] K3 SWR Accuracy - reprise

[Jack Smith]

I'm running tests today with the 25 ohm load connected to  the K3/LP-100 
with varying lengths of RG-142B/U coaxial cable, in 24 inch increments 
out to 120 or 144 inches. The result should be a constant SWR, 
neglecting the padding effect of coaxial cable loss, but with the 
impedance varying along the constant  SWR circle if we think in Smith 
chart terms.

I will also measure the R+jX of the load under the same conditions, with 
both the LP-100 and a VNA.

I may have the data analyzed this evening, but more likely tomorrow.

Also added a note confirming that my K3 has the KAT3  tuner, set to 
BYPASS for the tests.

Jack


N8LP wrote:
> That's a good question, Paul. I have a medium power, 150 ohm load laying
> around that I made up a couple years ago for testing purposes. I just
> checked it with my VNA and it has an SWR of 2.92, pure resistive. I did a
> quick test with the K3 at 25W, and it measured between 2.4 and 2.7 depending
> on band. That's about the same percentage error as the 25 ohm load, but it's
> impossible to know if the error is in the same direction. I would think that
> you could calculate the direction using the "tuned" L-network values of a
> KAT3, but I don't have one installed. 
>
> Larry N8LP
>
>
>
> P.B. Christensen wrote:
>   
>>> consistently lower than Jack's, ie. 1.6 on most bands with a 2.0 load.
>>> Not 
>>> a
>>> big deal, but as long as you're in there tweaking the code, can you
>>> verify
>>> that it works with non-KAT3 radios as well?
>>>       
>> I'm curious -- are those who see a smaller indicated VSWR reading on the
>> K3 
>> meter with a 25-ohm load seeing the same discrepancy with a 100-ohm load? 
>> This may partially explain why some owners are seeing varying results
>> under 
>> a 2:1 VSWR since that ratio can be comprised of those two resistance loads 
>> or an infinite set of resistive + reactive conditions -- any of which can 
>> form a load impedance of 25 or 100 ohms.
>>
>> Paul, W9AC
>>
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>
>