"Owen Duffy" wrote in message
news
On Sun, 25 Jun 2006 15:26:13 GMT, "Frank"
wrote:


The antenna pattern is highly predictable using modeling software.
The transmission line losses are probably not as high as Owen predicts
since we do not know the value of the attenuator inside the balun.

That implies there is an attenuator inside the balun. I don't believe
we actually have any information with which to better understand the
balun.

Frank, in the absence of information on the balun, I did model it as
ideal, and that the load at the load end of the coax was 4200 ohms.
That is probably a reasonable assumption.

A real balun would not perfectly isolate the transmission line from
drive so influencing feed point impedance , and would probably
transform the real feed point impedance to something different to 4200
ohms, and so the line losses could be different (better or worse).

If the balun was built with substantial loss, it would tend to reduce
line losses, and yes, 3dB of loss (which would affect performance on
all bands), would improve the performance on 7MHz (though that balun
doesn't look like it contains a 200W dissipater).

All in all, the configuration, although used widely, can be expected
to perform poorly. IMHO was right in being
suspicious of the product claims.

Owen

I am inclined to agree with you Owen. I was being a little facetious
about the load. I also noticed there is not a single specification on the
web site, except for power ratings. (Including the irritating term
"RMS power"). Incidentally 750 W into 4200 ohms represents
2.5 kV peak. If the balun is a real transformer it must be well
insulated.

Frank