[Elecraft] Load Impedance (was Re: Measuring SWR

[Don Wilhelm]

Richard,

More specifics are needed for a good answer.
The easy way to do it is to measure the impedance at the shack end of 
the feedline with an antenna analyzer.
Yes, you moved the feedpoint away from center (but did not say by how 
much) and the voltages will be higher and the current will be lower at 
the frequency where the radiator is resonant, but it is an unknown at 
other frequencies.
The quarter wave feedline -- at what frequency is it a 1/4 wave?
It will certainly act as a matching transormer, but more detail is needed.

As I indicated, measure it with an antenna analyzer to see what the real 
situation is on 60 meters.

The theoretical loss will because of currents through the inductors will 
increase, but the practical consideration for the KXAT3 will be minimal 
as long as the SWR does not exceed 10:1.

73,
Don W3FPR


On 4/11/2019 9:37 AM, Richard Corfield wrote:
> I'm experimenting with portable antennas at the moment for my KX3 and,
> rather than cut the 80m legs of my link dipole to get an antenna that
> resonates on 60m, I've experimented with running it off centre. I've found
> what looks like resonance at the right frequency range, based on low return
> loss.
> 
> http://m0rjc.me.uk/screenshot_20190411-132334/
> 
> The problem is, that impedance is low. I guess it's being transformed down
> by the 10m of feed line, as normal wisdom for an off-centre feed is high
> impedance due to the lower currents and higher voltages towards the ends of
> a half wave antenna. Considering a velocity factor of 0.66 that feed line
> is about 1/4 wavelength long!
> 
> Presumably the KXAT-3 will tune this, but do I lose efficiency by having
> what would be higher currents in its circuitry?