[Elecraft] ladderline and balun question

[Ron D'Eau Claire]

Don: You have standing waves on the coax. That means that there will be
varying levels of RF voltage on the coax that change with frequency and that
are not prevented by a balun at the transition from coax to open wire line.
The 4:1 balun has altered the load impedance and changed the voltage a the
shack. 

You said the original arrangement worked fine. Why not go back to it? 

Personally, I'd take all the baluns out and see if I had any "RF in the
Shack" issues. Any "passive" device like a balun eats RF. Sometimes it's not
enough to care about - sometimes it's a LOT. So I try to keep my
installations a simple as possible. Also, every foot of coax (or any other
transmission line) eats RF. How much depends upon the impedance of the line,
whether it's connected to a load with the same impedance, and the frequency
of operation. Coax is generally the worst type of line to use in an
unmatched system with standing waves due to its rather low impedance, so
keep it as short as possible. 

73, Ron AC7AC 

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

Gents,

I have a ladder line and balun question that I hope someone can guide me 
thru.

I had a good working antenna system with two antennas.  First being an 
Alpha Delta Dipole and the second a 2WL 160m loop antenna at 40 ft in 
the air strung in trees.  So the wire does touch the trees.

Dipole is fed with coax and choked at the feed point and the loop was 
fed with 60 ft of ladder line to a 1:1 current balun then 25ft coax to 
the shack tuner.  Then the amp and radio.   This combination was working 
real well no RF problems in the shack.

I was advised that I would obtain better results for better SWR at 
resonance and easier matching if I removed the 1:1 balun and went to a 
4:1 balun.  I made this change with everything else being the same.  I 
now had RF in the shack again.

I then added an isolation balun to the system by adding 6ft coax from 
the output of the 4:1 to a balun designs 116du which is supposed to have 
4500 ohms of choking impedance on 160m and over 5000 ohms choking 
impedance  on 80 and 40 meters.   This did not eliminate the RF and I am 
still having problems.

So here is the question, is it possible that with the combination of 
length of the ladder line at 60ft plus the 6 ft plus 25 ft of coax I am 
at a feed line length that will be a problem no matter what I do.    I 
keep looking at the internet to try and figure this out but I am 
confused as some information I find says it only applies to 1:1 baluns 
or other factors.

So anyone who can help me understand this feed line question I will be 
greatly appreciative.

Thanks
Don


~73
Don
KD8NNU