[Elecraft] Re: KAT100 with Ladder Line

[Geoffrey Mackenzie-Kennedy]

Hi Peter,

If I may say so I agree with Joe's suggestion to cut off a length of feeder 
and try again if the balun tends to get a little warm. If a balun gets warm 
it means that RF power is being lost to heat the balun, and assuming that 
the balun is not faulty the cause of the power loss is most likely that the 
balun does not like the load presented to it by the transmission line. If 
the transmission line is connected to a load such as an antenna and the 
length of the line is varied, measuring the impedance at the other (open) 
end of the line will show that the value of the resistive component R and 
the reactive component X (which baluns don't like in my experience) will 
change as the length of line is changed, also the sign of the reactive 
component might change (positive to negative or vice versa). The frequency 
(RF) is not changed during these measurements. The actual values of R and X, 
and the sign of X, that appear at the open end of the feeder are primarily 
determined by the feedpoint impedance of the antenna, the characteristic 
impedance of the line (e.g. 600 or 450 ohms), the loss in the line and its 
length. Values change more rapidly as frequency is increased for a given 
change in line length. On a 'flat' line where the VSWR is low, the change in 
R and X is very small.

So if your balun runs warm, cutting off a few feet of feeder as Joe suggests 
could well provide a better load for the balun if the change in reactance is 
in the right direction, worth trying. A problem might arise on other bands 
though, but one solution which Lenny W2BVH reminded me of last night is to 
switch in different lengths of line when changing bands, which I understand 
works very well.

I hope that this helps, and if of interest I could send you off-list an 
illustration of how the values of R and X can vary along a transmission 
line. Please contact me off list if you would like to discuss common mode 
current.

73,
Geoff
GM4ESD

----- Original Message ----- 
From: "Joe-aa4nn" <aa4nn at earthlink.net>
To: "Peter Wollan" <wollan at mayo.edu>; <elecraft at mailman.qth.net>
Sent: Friday, November 16, 2007 3:04 PM
Subject: Re: [Elecraft] Re: KAT100 with Ladder Line


> Hi Peter,
> Try not to worry too much about feeding balanced lines.
> Get the Elecraft BL2 and hook it to the balanced line.
> Connect a 2 or3 foot piece of coax from the BL2 to your rig
<snip>
> ----- Original Message ----- 
> From: "Peter Wollan" <wollan at mayo.edu>
> To: <elecraft at mailman.qth.net>
> Sent: Friday, November 16, 2007 9:50 AM
> Subject: [Elecraft] Re: KAT100 with Ladder Line
>
>
>> Please, I'd like some more discussion of this question.  I've seen 
>> before that baluns on ladder line can be lossy, but I'm not about to  get 
>> a balanced tuner, so it doesn't really help.
<snip>