[Elecraft] SWR Measurement with KAT3

[Ron D'Eau Claire]

Vic is quite right! 

I'll add a couple of points:

1) The power display of the K3 is quite good, from a few milliwatts to 100
watts. It can be calibrated even further if you have a known, calibrated
meter to use with an external dummy load.

2) If you are interested in measuring the SWR on the feeder itself for the
purposes of evaluating your feed line losses, the place to measure it is at
the antenna end, not the rig end. We normally put the SWR meter at the rig
only because we're interested in the load the final amplifiers are "seeing",
but with the internal wattmeter that's taken care of internally, as Vic
said. When the display reports a low SWR after the ATU tunes up, it means
the K3's finals are seeing the load they need to work efficiently regardless
of what's going on outside the rig. To evaluate the SWR of the feeder
itself, the meter needs to go to the load (antenna) end of the feed line for
accurate measurement. That becomes more important as the feeder losses and
SWR increase. After all, an infinitely lossy 50 ohm feed line will show a
1:1 SWR at the rig no matter what the SWR might be at the far end. In the
real world, you might measure an SWR of 4:1 at the rig and use that to
determine that for the length of line and frequency, you consider the losses
acceptable, but the antenna end might show an actual SWR of 10:1 or greater.
That's the number you really need to evaluate the feed line losses. 

Ron AC7AC



-----Original Message-----

Dick Roth wrote:
> I've been reading the mail for a while, but am not sure this has been 
> covered.  I scanned the K3 Manual, but couldn't find what I was 
> looking
> for...this:  with the KAT3 tuner installed in the K3, where does one
> hang an SWR/Power meter?

You can read SWR and power as seen by the K3's final amp on the K3's 
display.

If you connect an external meter it will tell you the SWR on the 
feedline after the KAT3, which is interesting, but not what the K3's 
final is seeing. Power readings will possibly be wrong, because many 
meters don't read power accurately when SWR is high.
-- 
73,
Vic, K2VCO
Fresno CA