Posted by
Cookie on
Jul 23, 2010; 12:21pm
URL: http://elecraft.85.s1.nabble.com/Balun-Questions-tp5328810p5329314.html
Brett, I would recommend the Book "Understanding, Building and Using Baluns and
Ununs by the late Jerry Sevick, avaliable from CQ
http://store.cq-amateur-radio.com/Categories.bok?category=Books%3AAntennas&searchpath=1547318&start=10&total=17
With this book, a BS in Physics, 54 years as a ham and 30 years as an EE I
finally understood enough to make a balun or an unun. I don't understand them
well enough to answer your questions correctly. I read all the stuff I could
find on the internet and 50 years of ham magazines before I bought the book and
was still too confused to pick a core and build the unun that I needed. If you
just want a 4:1 balun and don't want a study course, I would recommend that you
buy one. If you really need one that works 160 to 10 buy an expensive one from
a good source, the ones that I tested did not have the advertised bandwidth. I
did not test the Elecraft balun, but what I have seen of Elecraft engineering
would give me confidence to try one.
Willis 'Cookie' Cooke
K5EWJ
________________________________
From: Brett Howard <
[hidden email]>
To: elecraft <
[hidden email]>
Sent: Fri, July 23, 2010 3:53:42 AM
Subject: [Elecraft] Balun Questions
I'll preface this by explaining that I'm a digital guy and I've lately
decided I want to get a little better understanding of magnetics and
RF... Thus why I'm taking on making my own W3NQN band pass filters and
I've also been interested in building a Balun...
So I've looked at a few sites describing how to make a 4:1 balun... One
such solution is to take 2 100 ohm 1:1 baluns and connect them in
parallel on the input side and in series on the output side...
I looked at the Elecraft BL1 manual but I didn't see what material the
core was... However in another article I saw someone post the recommend
getting a FT140-61 and winding 7 to 8 turns on each side to make the two
100 ohm feedlines.
So I ran the numbers and 8 turns on a FT140-61 gives you about 100 ohms
on 160 meters. Thus two 100 ohm points in parallel gives you 50 ohms in
and 200 ohms out. 4:1... Great.
However at say 40 meters... Each feedline is 430 ohms. Thus you've got
a 215ohm input and a 860 ohm output. This just seems like it would make
a mess. Why does it still work?
Finally I'll explain my final goal... I've looked at several ways to
make a 4:1 which involves using two 1:1's. Then there are methods to
take 2 4:1's to make a 6:1 (the feedlines are 125ohm windings to pull
this off). My final goal is to try to make a 6:1 and use it to use
ladder line once I get through the wall with coax. I always just
figured that a 6:1 would be better as it would have a 50 ohm in and a
true 300 ohm out.
However once you get away from the design frequency the feed impedances
go to pot... So is there really much difference in the 6:1 and the 4:1?
I've read of many people doing what I'm talking about with a 4:1 and
just figured that a 6:1 should provide a better match... Am I thinking
right or is the match so terrible anyway that it doesn't so much
matter?
Is it just that the thing balances the currents on the outputs and I'm
just over thinking the matching ability?
Appreciated gentlemen.
~Brett (N7MG)
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