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The Flat Earth Society Meets Amateur Radio

12 May

Just as it looked as though Science was returning to Amateur Radio, along comes another Profit. Some years ago Walt Maxwell dispelled most bad science surrounding SWR. Now, early in our new century we get another pseudo Muse of Science on the scene. I speak of course of a recent presentation by a purported audio engineer in a widely propagated power point presentation concerning common mode chokes and balanced lines. In this document, mention is made of how balanced lines in common mode chokes are bad due to losses in ferrite material. It seems only coax will do.

Sorry mate, your statement is wrong. I have made the measures. I have made balanced line common mode chokes and put them into service in a transmitting environment. I have driven my smallish binocular gherkin sized common mode chokes with upwards of 500 watts and FELT THEM! I have placed a thermocouple on them while transmitting. Even following long intervals of transmitting I was unable to feel temperature rise. Only following extensive key down periods at 500 watts output was I able to measure a 4 degree F increase in bead temperature. This rise in a choke that was sized to be used at 200 watts, not the 500 watt stress level that I have been subjecting it to. On receive, there is no discernible loss of signal. I measured it. It simply does not exist in any meaningful way.

At a time when material costs are rising faster than our paychecks, one would think that the obvious advantages presented the thrifty amateur by balanced lines would be a welcome alternative to pricey, lossy coaxial cables. This presentation purports to remove this option by any thinking amateur. Unfortunately the slides contained on page 10 of the PDF document are false. Which begs the question: if those are wrong, how much of the rest of this presentation is wrong?

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Posted by on May 12, 2008 in Radio

 

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