[Elecraft] High Current only on 20 Meters

[Jim Brown]

On 3/4/2020 2:56 PM, Adrian wrote:
> I get the same on my KX3 on 12m , When using an antenna analyser the 12m 
> radiation resistance is lower (much less than 50 ohm), 
> with more reactance component than  in the other bands, and when the ATU 
> corrects the reactance component of the load, the current
> tends to be higher (multi-band antenna use with ATU). than the other 
> bands with more radiation resistance values.

I suspect an understanding gap here. What you're describing implies a 
severe mismatch AT THE ANTENNA. A mismatched load (the antenna) is 
transformed by the transmission line to an entirely different impedance 
at every point along the line. The mismatch establishes standing waves 
on the line, and SWR is one measurement of that, BUT -- loss in the line 
causes SWR to gradually get smaller along the line, reaching its lowest 
value at the transmitter.

Computing programs like SimSmith and AC6LA's Excel spreadsheets can take 
measured data from analyzers that are capable of producing suitable 
files, and, if you know the cable's characteristics, can transform a 
measurement made in the shack to the impedance of the antenna itself.

Radiation resistance has meaning ONLY at the antenna feedpoint, and it's 
a characteristic of the antenna itself. It represents power that is 
radiated by the antenna. IF we could connect the analzyer at the 
feedpoint, we would measure its feedpoint impedance, Rs +jXs, but Rs is 
NOT necessarily the radiation resistance.

A study of texts like the ARRL Antenna Book (or equivalent in VK-land) 
are in order. There's a bit of a tutorial in slide show form on my 
website that might get you started on understanding on the transmission 
line part of it. http://k9yc.com/PacificonSmithChart.pdf  The Smith 
Chart is a graphical means of understanding (and computing) what happens 
on a transmission line.

73, Jim K9YC