Mike,
I don't think anyone here is going to be able to explain to you in a
single
email why the 1:1 balun is better.
However I can show you how to learn about this in a systematic way, using
material from 4 of the experts in this field.
It will probably take you about 10 hours to do this, but then you will
know.
(otherwise, just take our word for it.)
This is a 4 part training course:
PART-1: View GM3SEK's online presentation on common mode current
problems,
especially the first half of it. View all of it but at this point, you
only
need to understand what all can be causing us problems. Ian's
presentation
is a good introduction to that. See:
http://www.ifwtech.co.uk/g3sek/in-prac/
(Note: it is a challenge just to bring the file up. You have to right
click
Ian's link and save the link to your computer. Then double-click the link
on your computer and it brings the PowerPoint file up.)
PART-2: Read W7EL's excellent paper on "Baluns: What They Do and How They
Do It". These 8 pages will give you a good understanding of Baluns (which
Jim rightly called Chokes), and begin to answer your question. See:
http://www.eznec.com/Amateur/Articles/Baluns.pdf
PART-3: View G3TXQ's excellent page on "Tuner Balun Ratios":
http://www.karinya.net/g3txq/tuner_balun/
PART-4: Now that you have a fairly good understanding of all of this,
Read
K9YC's paper, "RFI-Ham". Although this is the most comprehensive paper, I
don't recommend beginning with this one. This is like the graduate
course.
It is 66 pages long, but it has everything in it. See:
http://audiosystemsgroup.com/RFI-Ham.pdf
If you haven't a clue about all of this and view these resources in this
order, you will probably understand most of what Jim wrote, though if
you're
like me, you'll have to read it two or three times.
SHORTCUT for your question, MIKE: Go straight to PART-3.
However I recommend anyone asking this type of question, take the time to
work through all of this. It will be very beneficial.
73
Rick, DJ0IP
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Mike
Bryce
Sent: Friday, July 12, 2013 3:51 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] OCF antennas evolution
I quite aware that open line is generally considered lost less feed line.
What threw me was the use of a 1:1 balun instead of a 4:1.
That's the head scratcher.
Mike wb8vge
Sent from my iPhone
On Jul 11, 2013, at 9:32 PM, k6jek <k6jek@comcast.net> wrote:
Mike,
You're matching the antenna system, the antenna and the feed line. You
just can't separate the two. When the antenna impedance at a particular
frequency is different from the feed line characteristic impedance, the
impedance on the line is different every place on the line. You're
matching
whatever it happens to be at the shack end of the feed line.
Losses are the reason to put the balun near the station instead of near
the antenna. Open wire line has much lower losses than coax under
conditions
of very high SWR. That's the reason we put up with the stuff which is a
royal pain in the arse, just so we can have a ridiculous SWR and not care
about it. And very high SWR is exactly what we have at almost all
frequencies when using a doublet as a multi-band antenna. The only reason
we can get away with such a thing is the low loss of open wire line.
So you
want to run that stuff as far as you can before switching to coax. As
long
as you can is ideally right into a balanced tuner, no balun at all.
Jon
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