2 baluns on doublet feedline to overcome impedance changes?
 

hi, everybody;

i am interested in constructing a choke balun for balancing a doublet
75 metres long, centre-fed with 30 metres of ladder line, an l-match
between the rig and the feeder;

i have read around a bit, including roy lewallen's splendid article
below; it seems that a balun maintains balance best when its inductive
reactance outweighs the line impedance by a factor of at least 4;

at about 2 mhz, the impedance at the bottom of my feeder will be high,
resulting in considerable imbalance on the line (more so that the
frequency is low, where the balun's inductive reactance is lower); i
have two questions;

1) would a balun at the antenna end of the line (where the impedance
is much lower) maintain balance in both antenna and line?
2) and then how about another balun at the l-match end of the line,
for frequencies where the antenna-end impedance is high?

your assistance would be appreciated; best wishes

--
http://eznec.com/Amateur/Articles/Baluns.pdf

2 baluns on doublet feedline to overcome impedance changes?
 

wrote:
1) would a balun at the antenna end of the line (where the impedance
is much lower) maintain balance in both antenna and line?

The antenna is balanced. The feedline is balanced. What you
would need is a BALBAL, not a Balun. I haven't seen any
BALBALs advertised lately.

2) and then how about another balun at the l-match end of the line,
for frequencies where the antenna-end impedance is high?

When I ran into the same problem, I decided to adjust my
ladder-line length per band so the balun would always be
looking into an impedance between 35 ohms and 85 ohms.

http://www.w5dxp.com/notuner.htm

No tuner equals no tuner losses.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

2 baluns on doublet feedline to overcome impedance changes?
 

On 6 July, 14:41, Cecil Moore wrote:
The antenna is balanced. The feedline is balanced. What you
would need is a BALBAL, not a Balun. I haven't seen any
BALBALs advertised lately.

one thing i neglected to mention is that the rig is grounded;
according to the roy lewallen document i referred to, the ground
connection causes imbalance, regardless of the ladder line;

When I ran into the same problem, I decided to adjust my
ladder-line length per band so the balun would always be
looking into an impedance between 35 ohms and 85 ohms.

http://www.w5dxp.com/notuner.htm

i used that link in a posting just the other day; i always liked your
design; but i'm not interested in it here;

i'm also aware of the link-coupled transmatch;

73

2 baluns on doublet feedline to overcome impedance changes?
 

another clarification; my lower-case typing back there caused a
counter-intuitive reproduction of the phrase `L-match'; the match
between the feeder and the rig is an L-match; it does not isolate the
ladder line from earth

2 baluns on doublet feedline to overcome impedance changes?
 

wrote:
one thing i neglected to mention is that the rig is grounded;
according to the roy lewallen document i referred to, the ground
connection causes imbalance, regardless of the ladder line;

A grounded rig doesn't necessarily cause imbalance
in balanced systems. For instance, a primary/secondary
isolated transformer will cancel the common-mode
components at the transformer secondary windings.
(Such a transformer works best when optimized for
a single band.)

i'm also aware of the link-coupled transmatch;

Unfortunately, the secondary winding in the Johnson
Matchbox is referenced to ground through the loading
capacitors. It appears the Johnson designers didn't
consider common-mode problems.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

2 baluns on doublet feedline to overcome impedance changes?