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Old 1st Oct 2019, 11:53 pm   #112
Radio Wrangler
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Default Re: Antenna recommendation for 40 and 80M bands

Some GDOs have a simple antenna input and allow the oscillator to be switched off. In this way you can use them as a simple absorption wavemeter, or as a modulation monitor into a pair of headphones (AM of course) or as a field strength monitor. Handy if you have no other RF test equipment.

You can put a coupling coil on the antenna feeder and dip that (interpretation can be a bit difficult) to get an idea of antenna resonance.

As far as exhortations to eschew ATUs and have resonant antennae go... I have room for one HF antenna, and it needs to be rather stealthy. It cannot be resonant on all the bands I wish to use, nor can it be any sort of optimum on any of them. Consequently I have a wire antenna as large as fits in my property and I have no choice but to use an ATU. If I'd cut it for one band, I might have got one of the harmonic bands in, but I'd still have needed the ATU for the other bands.

Knowing I'm going to have to use it off-resonance on at least some of the HF bands, I have made sure the feeder is very low loss. Operation away from the Zo of a feeder tends to multiply losses, so start with low loss and the net product of loss is less.

The antenna and feeder are balanced. This nulls stray radiation from the feeder, nulls the ingress of local noise and confers these advantages at all frequencies. This also means that I am not dependent on having a good ground. In fact I want to galvanically isolate my antenna from the house ground because of PME complications.

So I need some sort of balun. Baluns are difficult to make broadband, and are very difficult to make work over a range of impedances. Needing a wide range of impedances AND full HF coverage puts them firmly in the impossible category unless high losses can be tolerated. The solution is to have a balanced resonator in the ATU and to have a coupling coil to give galvanic isolation. The transmitter coupling can be unbalanced, and the antenna coupling can be balanced... so my ATU performs the needed balancing act and at the same time performs the ATU function.

There is plenty of space out at the stables... room to put up rhombics if wanted, but that's miles away from home. The radio club with its tribander on a tower etc is closer. So yes, I could have resonant dipoles If I wished, but doing it at home so I can have a shufti on HF while at home involves compromise. The choice of the right ATU makes that compromise work for me.

If I limited myself to resonant antennae only and no ATU, I would as a consequence be limited in which bands I could use... limited mostly to the bands which are closed through sunspot minima.

George Burt scored over 300 countries with 1W into a tuner with 3dB loss into an open wire feeder and a dipole set by the spacing of two chimney stacks. Proof enough it can work, but I'm not an operator in his league.

But, everyone gets to make their own choice. That's freedom for you!

David
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