Kelly,
You are quite right to take me to task!
I was addressing more points than you asked - probably because I was
anticipating a wider readership. To try to summarise:
1) The OCFD is particularly prone to CM current because of leg
*reactance*, not directly because of *imbalance*.
2) It does not need a device at the feedpoint to "force" or "drive" CM
current - phrases we often come across in connection with OCFD feedpoint
baluns and ununs - high CM voltages are inherent in the design.
3) I don't what is inside W4THU's DMU. I guess I was addressing the
comment Joe made about it earlier:
"/At one time the Carolina Windom "story" indicated the feedpoint DMU
was designed to force unbalanced current and "force" vertical radiation.
That would be consistent with an autotransformer instead of a voltage
balun/."
However, modelling shows an autotransformer is very little different
from a 4:1 voltage balun in that respect.
73,
Steve G3TXQ
On 26/01/2015 16:21, ve4xt@mymts.net wrote:
Hi Steve,
Thanks for the explanation, but I just want to clarify you're answering my
question, since you appear to be countering points I didn't make.
I didn't say anything about "forcing" CM to the braid. CM is like Forrest
Gump's dog feces: it happens. My point was certain transformers will also choke off CM,
which, if it happens at the feedpoint removes the CM from play on the vertical radiator
of the Carolina Windom.
What is different inside the DMU (W4THU's term) from, say, a 4:1 voltage balun
is never clearly explained, though it's clear he's not trying to choke off CM
at the feedpoint, but at the choke (or line isolator, as he calls it) 24 feet
down the line.
What you appear to be suggesting is W4THU's DMU is just a 4:1 voltage balun. Is
that right?
73, Kelly
ve4xt
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