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1-10 of 13 messages
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Homemade multiband HF vertical antenna opinions
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by VY1JON on November 19, 2008
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Hi folks!
If i were to put a length of approximately 20ft of wire inside a vertical PVC pipe, fed against a metal roof (additional radials could be used), with a antenna tuner right at the bottom of it (in a waterproof box). Would it be efficient? Is it something that could work or would i simply be wasting my time? Would i be able to transmit from 80m to 10m with a decent swr?
In the previous topics, i was suggested to use a 5/8 silver rod, or something like it and rip the coil out of it, but i couldn't find any and i can't see myself buying a new one just so i can use the radiator. And also, using two lengths of electrical conduit, or copper pipe soldered together (20ft or so) would be a bit flimsy in the wind.
Thanks for your opinions, greatly appreciated 73's!
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RE: Homemade multiband HF vertical antenna opinion
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by VA7CPC on November 20, 2008
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My answers, for what they're worth:
> If i were to put a length of approximately 20ft of
> wire inside a vertical PVC pipe, fed against a metal
> roof (additional radials could be used), with a
> antenna tuner right at the bottom of it (in a
> waterproof box). Would it be efficient?
It would be fine on 20m and higher frequencies, OK on 30m, workable on 40m, and poor on 80m. That's assuming that the roof and radials are large enough to act as a groundplane at the lower frequencies -- say, 30x30 feet for 40m.
> Is it something that could work or would i simply be
> wasting my time?
Not a waste of time.
> Would i be able to transmit from 80m to 10m with a
> decent swr?
Sure -- the antenna tuner (if it has enough range) ensures the rig sees 50 ohms. But that's the wrong question. The right question is:
. . . Would I have decent efficiency ?
Watch out for tuner losses on the lower-frequency bands. There's free software that (I think) will compute losses in T-network tuners. Driving a 20' wire on 80m will generate high voltages, high currents, and large losses.
On the SGC website, you'll find some long "white papers" on short verticals with autotuners --
www.sgcworld.com
Take a look at the "HF User's Guide" and the SG-230 or SG-237 User's Manual.
Excerpt from the SG-237 manual:
-------
Flagpole: If a flagpole is made of PVC pipe, it is easy to tape a large gauge wire to the inside of
the pipe and use a good counterpoise. Typical flagpoles are 25 to 35 feet in height, which offers
excellent performance on all bands. Note the ground radials that are necessary with any long
wire or vertical antenna.
--------
A copy of the ARRL Antenna Book will explain how this all hangs together.
Charles
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RE: Homemade multiband HF vertical antenna opinion
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by W8JI on November 20, 2008
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80 meters would be the problem. 40 meter and above would be OK with the possible exception of 15, 12, and 10 meters.
One thing that would help would be a much thicker element than a piece of wire. What the wire is made from doen't matter much, but the diameter of the conductor has a profound impact on impedance and tuner losses on bands where the wire is not resonant and also around 1/2 wave long.
73 Tom
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RE: Homemade multiband HF vertical antenna opinion
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by WA3SKN on November 20, 2008
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It all depends on the counterpoise!
The metal roof might get a little small for 80 or 160 meters, but should be great for 20 meters and above. 40 and 30 meters all depends on the size of the roof.
This assumes you do not live in a warehouse!
73s.
-Mike.
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RE: Homemade multiband HF vertical antenna opinion
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by W5DXP on November 20, 2008
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> VY1JON wrote: If i were to put a length of approximately 20ft of wire inside a vertical PVC pipe, fed against a metal roof ... Would i be able to transmit from 80m to 10m with a decent swr? <
I have used a 22ft vertical with four elevated radials slanting down at 45 degrees from a 22ft height. It worked well 40m-10m driven by an SG-230 at the base. 22 feet is a compromise length between a 40m 3/16WL monopole and a 10m 5/8WL monopole. It didn't work worth a darn for 75m SSB. However, it did work well enough for some CW and PACTOR2 contacts on 80m.
The SG-230 provided SWR<2:1 on the coax on all bands. (Not saying anything about efficiency)
Here are the gain@TOA for my antenna as reported by EZNEC.
40m, 0.53@22; 30m, 0.94@19; 20m, 1.47@16; 17m, 1.91@14; 15m, 2.47@12; 12m, 3.4@13; 10m, 4.21@11.
Of course, those values do not include tuner losses but take a look at that omni-gain on 10m.
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RE: Homemade multiband HF vertical antenna opinion
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by N5LRZ on November 20, 2008
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Lets see.... A quarter wave length for 80 is about 65 feet or so. A quarter wave for 160 is about twice that length or 125 feet or so.
SO a mere 20 feet of wire would pretty well much suck pond scum on 80 as a transmitter even if you could transmatch it. On 160 it would be far far worse.
In theory a 6 inch piece of wire if fed with the proper coil and cap could be made to have a 50 ohm imp point BUT 6 inches would still transmit like ONLY 6 inches.
And dummy loads do not transmit worth a damn even if they have a low SWR.
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RE: Homemade multiband HF vertical antenna opinion
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by W5DXP on November 20, 2008
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> N5LRZ wrote: SO a mere 20 feet of wire would pretty well much suck pond scum on 80 as a transmitter even if you could transmatch it.
Yet, consider a base-loaded 8.5' whip is a fairly decent 80m mobile antenna, ~3 dB down from standard screwdrivers, and ~6dB better than an 80m hamstick. An autotuner at the base is akin to base loading a 20 foot whip. If one likes CW, it would probably do an adequate job and extending it to 22 feet raises the 80m radiation resistance by about 25%.
--
73, Cecil, w5dxp.com
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RE: Homemade multiband HF vertical antenna opinion
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by N5LRZ on November 20, 2008
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Re above poster...
COMPARED to a full sized half wave dipole and or a full wave length loop antenna.
Screwdrivers pretty well much suck as well watt for watt of applied power.
Screwdriver antennas are nothing more than than a tricked out dummy load antenna.
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RE: Homemade multiband HF vertical antenna opinion
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by N5LRZ on November 20, 2008
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PS Hamsticks are nothing but a joke of an antenna.
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RE: Homemade multiband HF vertical antenna opinion
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by W5DXP on November 20, 2008
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> N5LRZ wrote: Screwdriver antennas are nothing more than than a tricked out dummy load antenna. <
Halitosis is better than no breath at all.
Here's mine: http://www.w5dxp.com/shootout.htm
What can I do to make it more effective and still be legal? What does your 75m mobile antenna look like?
--
73, Cecil, w5dxp.com
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