Reading the responses, this is my basic reason for advocating using a 1:1
current balun for at least 90% of all applications. Yes, the beads over
coax is a very good workable application. For the life of me I don't
understand why tuner manufacturers insist on installing 4:1 baluns in their
boxes as they create more issues than correct solutions.
In general if your antenna is a folded dipole providing some 200 to 300 ohms
impedance at resonance, this is about the only good justification for a 4:1
balun. Other than myself, I run across very few folks using a folded dipole
associated with their stations today.
Most think that if they use 450 ohm line they should make an attempt to
match the line Z. I find this approach to be more incorrect than correct.
Under these conditions, line Z has little to do with the application of a
balun where electrical line length has a greater factor becoming a partial
wavelength matching section.
Likely the cause of the problem at 600 watts is balun failure or an arc
taking place somewhere within the system.
73
Bob, K4TAX
----- Original Message -----
From: "Jim Brown K9YC" <k9yc@audiosystemsgroup.com>
To: <tentec@contesting.com>
Sent: Wednesday, March 18, 2009 10:25 AM
Subject: Re: [TenTec] Problem on 160 meters, Whats up?
On Wed, 18 Mar 2009 08:38:46 -0600, Dr. Gerald N. Johnson wrote:
The higher power is saturating the core of the balun. One of the hazards
of tuning through the balun.
Yes, very likely. There are several very different things called baluns.
The
one in antenna tuners is a transformer, so 100% of the transmitted power
is
in the core. Very likely to saturate with high power, heat, distortion.
Another VERY different thing that is CALLED a balun is really a common
mode
choke. Put a bunch of ferrite cores around coax, or wind a bunch of turns
of
coax through one or more ferrite cores. Those are common mode chokes,
commonly (wrongly) called "current baluns." But when done well (enough
turns
to have a high enough choking impedance), they work VERY well.
73,
Jim Brown K9YC
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