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Author Topic: Low bands from a truly miniscule plot!  (Read 596 times)

XW0LP

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Low bands from a truly miniscule plot!
« on: December 19, 2019, 11:35:42 PM »

I'm expanding my (very modest) HF station in Laos by replacing my roof-mounted EFHW on 20 metres with a Hustler 4BTV, modified to add 12, 17 and hopefully 30 metre bands (extra wire as per simple modifications published on the web), with resonant radial wires running in the roof space under the antenna. (The house is built of wood and clay roof tiles).

But I also want to erect an antenna for 60 metres and lower bands.  Due to the miniscule plot that my house is on, I have bought two 12 metre, telescopic fibreglass masts from Spiderbeam, and propose to erect an EFHW wire (88 feet), resonant on 60 metres, configured as an upsidedown U shape.

My question was whether I can also use these masts or the 88 feet wire to operate on any other bands?  Is there any way that I could get something resonant on 80 metres?

My plot is slightly larger than my house ==> a 16 x 10 metre rectangular plot.

I do have an FCP balun from Balun Designs, so that might make an antenna for 80 metres possible?

I appreciate any suggestions :)
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K1VSK

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Re: Low bands from a truly miniscule plot!
« Reply #1 on: December 20, 2019, 06:01:57 AM »

There are lots of shortened verticals to which you can add a loading coil with matching network to resonate it on 80. I don’t have any favorites but others may chime in with theirs
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VE1YY

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Re: Low bands from a truly miniscule plot!
« Reply #2 on: December 20, 2019, 08:56:11 AM »

You asked--

"My question was whether I can also use these masts or the 88 feet wire to operate on any other bands?  Is there any way that I could get something resonant on 80 metres?"

One writer mentioned the idea of loaded verticals. You also can make loaded EFHW antennas and loaded centre fed ones.

You might like to consider a Zepp antenna 14m long and then drop the far end down one of your poles by 10m (it keeps the end 2m above persons). You will need an antenna matching unit (AMU) to feed it (or a balun).

You could put your two 12m poles together yielding a  24m mast. Use your wire to make a centre fed inverted V with each leg 13m long. Feed the antenna with open wire or window line. Again, you will need an AMU. The antenna will work on most if bands (160-10).

If you can, get a copy of EZNEC or 4NEC2. Model antennas using the constraints that you have. You will find lots of solutions.

A comment about radials on the roof:  wires in contact with the roof might not resonate but will act more like a ground screen. I have used radials on a roof and they did not resonate. I laid down as many as I could thus making a ground screen. The attached vertical worked well.

73 and GL,
VE1YY

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W1RKW

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Re: Low bands from a truly miniscule plot!
« Reply #3 on: December 20, 2019, 10:39:33 AM »

How about a folded dipole fed with balanced feeders? 

You could build a folded dipole that is less than 20meters in length and have it work on 75m.

http://amfone.net/Amforum/index.php?action=dlattach;topic=18214.0;attach=9681
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KH6AQ

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Re: Low bands from a truly miniscule plot!
« Reply #4 on: December 20, 2019, 12:58:08 PM »

There are many ways to get a functional 160 meter antenna in your situation. One is the 4BTV. Place an RM-80 resonator on top and replace the whip with a ~6 meter wire. The antenna will work on 10, 15, 20, and 160 meters. Note that 40 meter coverage is lost. Being a ground plane it needs at least one resonant 160 meter radial This it can be a wire with a loading coil. In this case the 4BTV should be fed thru a choke balun to ensure that the not-quite-resonant radial intercepts most of the antenna return current. The 3:1 SWR bandwidth will be about 15 kHz.

Another option is to use the two 12 meter masts to configure an inverted-L, or the inverted-U, with a base loading coil for 160 meters.
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KH6AQ

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Re: Low bands from a truly miniscule plot!
« Reply #5 on: December 26, 2019, 12:26:20 PM »

"My question was whether I can also use these masts or the 88 feet wire to operate on any other bands?  Is there any way that I could get something resonant on 80 metres?"

The 4BTV will work on 80 meters using an RM-80 or RM-80S resonator. It will need at least on resonant 80 meter radials. For 3.55 MHz a radial is 20 meters long. Given your smaller than 10 x 16 meter roof the radial (or two radials) can be routed in a U shape. If your 5BTV is mounted in the center of the ~8 x ~14 meter roof two 20 meter radials will fit. Run a radial 4 meters to the roof edge, bend 90 degrees to run 7 meters to another edge, 90 degrees to run 8 meters and bend once more for a total of 20 meters.
« Last Edit: December 26, 2019, 12:39:10 PM by KH6AQ »
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ONAIR

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Re: Low bands from a truly miniscule plot!
« Reply #6 on: December 26, 2019, 08:26:06 PM »

End fed in an inverted L or V configuration.  Could even work as a zig zag!
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AC2RY

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Re: Low bands from a truly miniscule plot!
« Reply #7 on: December 31, 2019, 01:42:32 PM »

I'm expanding my (very modest) HF station in Laos by replacing my roof-mounted EFHW on 20 metres with a Hustler 4BTV, modified to add 12, 17 and hopefully 30 metre bands (extra wire as per simple modifications published on the web), with resonant radial wires running in the roof space under the antenna. (The house is built of wood and clay roof tiles).

But I also want to erect an antenna for 60 metres and lower bands.  Due to the miniscule plot that my house is on, I have bought two 12 metre, telescopic fibreglass masts from Spiderbeam, and propose to erect an EFHW wire (88 feet), resonant on 60 metres, configured as an upsidedown U shape.

My question was whether I can also use these masts or the 88 feet wire to operate on any other bands?  Is there any way that I could get something resonant on 80 metres?

My plot is slightly larger than my house ==> a 16 x 10 metre rectangular plot.

I do have an FCP balun from Balun Designs, so that might make an antenna for 80 metres possible?

I appreciate any suggestions :)

On a small plot you always can raise a vertical. With guy lines you can go up to 20 meters high. Add enough radials and 4 ground rods. That should be sufficient to allow remote tuner like ICOM AH-4 to work on 80 meters. Remote tuner is a must for any short antennas. ICOM makes one of the best ones.
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K0UA

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Re: Low bands from a truly miniscule plot!
« Reply #8 on: January 02, 2020, 01:12:31 PM »

I was very surprised how well my Little Tarheel II mobile antenna works on 80 meters with about 24 foot of extra wire added to the whip. Mobile antennas with their small whips are pretty low efficiency on 80 meters.  Like about 2% or something like that, but if you add some wire, man what a difference. If I had next to no room I would consider  a mobile with some "enhancement" and a good set of radials under it. It is an all band solution and can be tunes.  You would need to have a way to remove the extra long wire for upper band use. but that could be as simple as walking out and removing an alligator clip if you could get to the antenna. As long as the wire you add is still capacitive (in other words the antenna is till shorter than a 1/4 wave whip) then the coil in the screwdriver antenna should be able to tune it.  At least that is what I have found for 80 40 and 20. For 20, I add about 15 feet of extra wire and it tunes up near the end of the coil.  It also has gain over the stock whip, but not quite as dramatic as the gain on 40 and 80.  I can even operate it on 160, a band it is not designed to work on, but I think 100 foot of wire would be more appropriate there.  Just something to consider. Not saying it is the best antenna in the world, but it does beat nothing.  I saw where one fella said he worked 300 confirmed on a mobile antenna in the back yard. I dunno..
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73  James K0UA
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