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Old 2nd Oct 2019, 10:43 pm   #121
Radio Wrangler
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Location: Fife, Scotland, UK.
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Default Re: Antenna recommendation for 40 and 80M bands

Quote:
Originally Posted by Bazz4CQJ View Post
I have never used an end-fed antenna for transmitting, but I assume that to use a GDO or any kind of antenna analyser you would have to inductively couple it in to a circuit with a ground or a counterpoise.
That's true. But leaves you the quandary of are you using the counterpoise to help measure the antenna or are you using the antenna to measure the counterpoise?

Because you can't do a perfect counterpoise, or produce a perfect ground up by the feedpoint of your antenna, the answer has to be 'a bit of both' and it's hard to decide what the proportions are.

The elegant way to evade the problem is to duplicate your antenna in the opposite direction and measure between them. You can logick that each of the two antennae must have the same impedance, so the impedance of one alone must be half of the impedance your measurement gives. Simple, elegant and effective!

It's a general problem-solving technique. Make two identical things and measure one against the other.... you can blame half of the total impairment, value or whatever on each.

It's common to make two identical crystal oscillators and to mix them together to measure their noise characteristics. You get to measure at low frequencies and you can assume half the noise comes from each.

We all started out knowing nothing. Some people merely started learning earlier, but that's all. They have an advantage for only a while if those who come along later are faster and can catch up. There is no progress if the pupil cannot overtake the teacher. Don't worry about it, you're making good progress and you have an interest in the area. Look at athletics. The amateurs run fastest. By the time they turn professional they are getting older and slowing down. An amateur also has the freedom to investigate things that take his fancy. The professional is limited to working in areas the accountants think profitable. Enjoy the freedom!

David
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