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"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 |
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