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Author Topic: ATU And Fan Dipole Question...  (Read 802 times)
MM0IMC
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Posts: 66




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« on: October 05, 2017, 07:12:08 AM »

Hi folks,

This is probably one of those rhetorical questions, but...

I have a fan dipole for 40m and 20m with elements for each band. I also occasionally put a separate dipole for 60m, as I find there is too much interaction between the other bands. My question is, can I leave the 60m dipole up and buy a decent QRO ATU and use the 60m dipole on higher bands like 40m and 20m?
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W1VT
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Posts: 2485




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« Reply #1 on: October 05, 2017, 07:52:56 AM »

Yes you can.  How useful it is depends on your location, the height of the antenna, and the line loss on the bands you need to use the ATU.  It is a good idea to model and calculate the predicted losses.  A few dB isn't too bad, but a lot of common scenarios end up with 10 or 20 dB loss.  Line loss can be reduced significantly by locating your tuner close to the antenna or by using a really low loss feeder like open wire between the tuner and the antenna.  In a way it is a lot like taxes, in which it really does make a difference if you can intelligently choose the numbers.

Zack W1VT
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WB6BYU
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Posts: 17053




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« Reply #2 on: October 05, 2017, 07:54:24 AM »

The 60m dipole will work on the other bands, but the issue is the feedline loss.

20m might not be too bad, as it is close to the third harmonic of 60m (though
they don't actually line up very well, with the 3rd harmonic of 60m in the
15 - 16 MHz range).  On 40m the higher SWR will increase the losses in the
coax:  you can reduce that by using a larger (lower loss) coax.  Not that you
won't be able to make contacts, but you might only radiate half as much power.

The traditional approach is to use twinlead or ladder line, which has lower
losses at high SWR and should give you a fairly efficient multi-band antenna.
(It might be usable on 80m as well in that case.)
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