Ok,
tnx for information, as always very helpfull . No braid breaker gives me 25 dB
F/B at 500 m (1500 ft) RX site . I use my minivna generator to have a TX
signal on my 2 el endfire array .
Next question is were to put the null on the back so I can determine the lenght
of the delayline
73
Luc
ON4IA
On Sunday, June 8, 2014 1:53 PM, Tom W8JI <w8ji@w8ji.com> wrote:
I think that idea of transformer balun or transformer unun isolation is
generally a bad idea in a phased system, and not necessary in almost any
system except very special cases.
I would generally just forget that system for a number of reasons.
Attenuation of common mode, and everyone forgets this, is attenuation is a
function of shunt impedances (or common mode impedances) to the added series
impedance. It is like the system forms an attenuator pad.
If you cannot accomplish adequate isolation with a simple choke of
reasonable impedance, it is best to look at the system and correct it.
With a very short cable and reasonable "grounds" on each end, just a few
dozen ohms of choke impedance makes a large change in attenuation. With very
poor grounds, or the wrong cable lengths, almost no impedance will be
adequate. People pick poor solutions because they fail to logically look at
the system. Because they do not consider the system, the invent magic things
to create unnecessary ridiculous impedances.
I would use a shield breaker for feeding an electrically very short dipole,
because common mode impedance is always extremely high. It has no ground at
all. I would never use it on any type of Marconi (even with a poor a small
element ground).
I might use it on a video system or a 60Hz - 20kHz system where a reasonable
choke is difficult. Not on 2 MHz except very special cases. It is generally
a misguided idea for most things at HF and higher.
<<<<<<
I made a braid breaker by using a binocular core 73-202 with 2 turns
primairy and 2 turns on
secondary . The term braid breaker comes from John s latest edition of low
band DX ing
I found that it is difficult to get signal levels identical on both elements
when using it, so maybe better to use a good common mode choke at the
feedpoint .>>>>>>
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