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Author Topic: ATAS-120 wire instead of whip, horizontally mounted NVIS?  (Read 2064 times)
KD8PGB
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« on: October 23, 2012, 04:57:41 AM »


 I have been researching NVIS as a truly mobile application for some time and am wondering about using my ATAS-120 horizontally mounted over my truck bed, but instead of the whip, use a wire off the ATAS-120 stretched horizontally over the truck? Would I in theory have an autotuning Mobile NVIS Antenna (if height is correct and wire length correct) ?

Assuming of course that I have some sort of support bracket to support the ATAS as the load on the mount would be prone to breakage if it is mounted horizontally.

So now comes the difficult part, how long of wire to perform NVIS on 40m? It would be nice to have a wire at 6ft so it could be simply over my 8ft truck bed, but I am thinking that would be far too short....or is it?

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N6AJR
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« Reply #1 on: October 23, 2012, 01:11:14 PM »

The ATAS 120 already goes to 40 m, so just mount it horizontally and your are ready to go.  You could also get one of the motorized fold over mounts and run it either vertical or horozontal with the push of a button.
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K0BG
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« Reply #2 on: October 23, 2012, 02:06:40 PM »

Not so fast. Laying over the whip of a mobile antenna, even if you lay it on its side, doesn't produce any viable NVIS capabilities. All one has to do to prove this point, is model the setup.

The other issue is one of frequency. NVIS extends to about 5 MHz, perhaps a bit higher. All of the mythical stuff you read on line about it extending higher is just that!
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AD5TD
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« Reply #3 on: November 10, 2012, 09:02:24 PM »

it is also not advisable to change the length of the whip on the ATAS antenna.  The coil is wound tighter (more turns per inch) inn the band areas for US ham frequencies.  Changing the length of the whip changes that.  It will work with a longer whip (I tried one) but sometimes it won't tune easy. And as Alan said, NVIS is a hit an miss on 5mhz and above that, it just doesn't work.
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