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I once had an occasion where the bottom of a coil did get warm, while the top did not. Yet my RF ammeters showed the same current on both ends. What was going on? What was he measuring, where was the coil? W9UCW used 100 mA at the bottom, I doubt that this would "cook" the coil. You see the pictures, they are good quality coils and he use two meters and flippped the coil to eliminate possible error as described here. I ultimately determined that the soldered connection from the coil to the lower antenna mast (for experimentation, it was copper) was adding some undesireable resistance. Solder is not a particularly good conductor of electricity. I copper-plated over the solder joint. Not only did the bottom section of the coil no longer get warm, but the two RF ammeters both showed about 20% more current flowing in the antenna. And my far-field instruments showed a 1.5dB increase in field strength. Again, put on the fricken Hustler 80m resonator, feed it 100W and feel it! No meters, no hokus pokus, just "naked" antenna. This is one example of being fooled....If you took coil temp at face value, you would think the current taper was quite steep, judging from the temp's of the windings. But nope...A resistive connection seemed to be the culprit. Note that his meters showed the same current on both ends. :/ You can see why I'm afraid of that "hook" that usually is lurking ready to bite at a moments notice. Don't worry, if you are right, it will come out in the end. But that hook...Ouch.. MK One insufficiently described measurement is enough to throw rest out of the window? W9UCW has shown data from various measurements and positions of the coil (pictures how it was done) and W5DXP backed it up with explanation of reflected wave and simulation and comparison with loading stub. It came out, this is the ned. If you choose not to believe, its a free country :-) Yuri |
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