[Elecraft] KAT 500 and open wire

[David Woolley]

Don:

1) made a distinction between feedpoint and load impedance, which led me 
to believe the load was the antenna, and the feedpoint the transmitter end;

2) said that the feedpoint impedance depended on the length of the line 
and the frequency, which further supported that interpretation.

However, considering your definition of feedpoint, and consider balanced 
twin feeder.  Even with a perfect choke at the feedpoint, there will be 
unbalance at the transmitter end, when using designs, like the K series, 
that feed against chassis.  In particular, consider a feeder length of a 
quarter wavelength.  As well as the intended differential mode signal, 
you will also excite the feeder as a quarter wave vertical against the 
chassis and, presumably, ground, if you don't choke at the transmitter end.

My gut feeling is that having a good match to the feeder is an 
oversimplification, but I need to think about that a bit more.

Incidentally, is the 4:1 "current mode" balun configuration really 
purely current mode?  It seems to me that it is behaving as a 
transformer as well as as a choke.


On 07/01/2019 02:12, Jim Brown wrote:
> I think we're confused here about the meaning the words "feedpoint 
> impedance." It is the impedance of THE ANTENNA at the point where the 
> feedline is attached, and it is determined entirely by the antenna, 
> INCLUDING the common mode circuit of the

> I don't know of a way to EFFECTIVELY choke a feedline that is not matched to the antenna.
> a very good choke must be AT THE FEEDPOINT