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Author Topic: Home-made backyard discone antenna for HF  (Read 3522 times)
N8DV
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« on: September 03, 2009, 11:39:32 AM »

I was wondering if there is anyone in the vast multitude of ham radio that has made or attempted to make, a discone antenna for the low bands? I have done a simple preliminary search and couldn't find any plans for a backyard discone antenna. 73
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AC8ZX
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« Reply #1 on: September 03, 2009, 12:19:26 PM »

If you go to the Green Valley ARC you will see articles and pictures of an HF discone antenna. Look under Explore Titan and you will see discone ant. SWR charts. You will need a very big back yard.

http://www.gvarc.us/index.html

73 Bob
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WA3SKN
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« Reply #2 on: September 03, 2009, 12:25:00 PM »

Sure it's been done!  And it was in the earlier antenna handbooks too.
It was not that popular because it takes a lot of wire and has no gain to speak of... not very useful for HF work.  The big plus was a large bandwidth... useful at VHF/UHF.  For HF there were better antennas.
73s.

-Mike.
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K3GM
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« Reply #3 on: September 03, 2009, 12:51:44 PM »

"If you go to the Green Valley ARC you will see articles and pictures of an HF discone antenna. Look under Explore Titan and you will see discone ant......"

Back in the 1960's the Naval Air Develpoment Center in Warminster, PA had one of these on top of the main building along with a BIG!, LPDA.  This was 20 years before I got my ticket, but I thought that immense discone was a sweet looking conglomeration of aluminum and wire.
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KA5IPF
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« Reply #4 on: September 03, 2009, 12:56:09 PM »

A friend had the best description of the performance of a discone I have ever heard;

"It equally attenuates all design frequencies"

Clif
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WB6BYU
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Posts: 13580




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« Reply #5 on: September 03, 2009, 01:04:16 PM »

There have been a number of articles over the years,
including (IIRC) a photo on the front of QST that showed
a roof-mounted discone covering 20 - 6m, and a design
for a backyard version for 40 - 10m.

The July 1975 QST article by John Belrose VE2CV might be
a good place to start, though the one I remembered was
older than that.  There is also an article in the October
1974 QST that shows some possible simplifications.
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K1DA
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« Reply #6 on: September 03, 2009, 01:39:03 PM »

The Navy had a transmitter site at the south end of
the island where we live which featured a number of Inverted Discones held up buy  circles of 60 foot telephone poles.  They worked from 4 to 20 or so.  
What was not visible 'till the Navy left was the 120 radial system under each one and a oil filled balun
about the size of an NC 300.  We tried one after the Navy just walked away from them in the '70s and it wasn't that good.  Of course they ran at least 10kw judging from the firehose fitting on the input.
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W5AOX
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« Reply #7 on: September 03, 2009, 02:00:04 PM »

As others have mentioned, there was an HF discone project in the ARRL Antenna Manual for several issues.
We built one at Los Alamos for use as a broadband tracking antenna for sounding the ionosphere for current Maximum Usable Frequency.  It actually worked quite well.  Those who decry its "lack of gain" might consider it's got about the same gain as a dipole, but a dipole is a rather narrow frequency antenna.  Being able to use it for most any frequency without "antenna tuners" was pretty cool, and being able to use it for VHF too was a plus, though it of course is lossy at those frequencies.
It DOES require a lot of wire;  I'd try making one using just 4 wires in the skirt and top hat if I had time to play with antennas any more.
I am underwhelmed by those who denounce something they haven't tried themselves.... which constitutes most of the responses you get on such queries.
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N3OX
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« Reply #8 on: September 03, 2009, 03:06:54 PM »

"Those who decry its "lack of gain" might consider it's got about the same gain as a dipole, but a dipole is a rather narrow frequency antenna"

But the ham bands are actually a rather narrow set of bands ...

I don't know about anyone else, but I don't have much need for an efficient transmit antenna that accepts power over the whole 1.8-30MHz spectrum.

Personally, I think a homemade discone seems like a lot of work to avoid to make a multiply-tuned antenna of some other sort... trap vertical or parallel verticals or base tuned or whatever.

But just because I don't want to build one doesn't mean someone else shouldn't ;-)  It's just the thing that it's built for is continuous bandwidth, not anything that's actually useful to folks like us who have to stuff our transmissions into little narrow bands.

There's some utility to having a wideband transmitting antenna on 80m and 160m but wouldn't some sort of cage vertical be easier to build than a discone?

73
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
N3OX
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« Reply #9 on: September 03, 2009, 03:39:44 PM »

"I am underwhelmed by those who denounce something they haven't tried themselves.... which constitutes most of the responses you get on such queries."

I think that it's not absurd to tell people you don't understand what advantages some particular antenna design has even if you've never built one.  If someone posted here asking "has anyone built that antenna N3OX described in his article?"

http://www.eham.net/articles/20174

I wouldn't think it was the least bit inappropriate if someone came in and said "No, I haven't built that.  What would be the point of that?"

An experimenter shouldn't get too discouraged when other people already "know" what the results of that experiment are and tell you so.  If they're right and you think they're wrong, you learn something.  If they're wrong and you think they're wrong, you feel vindicated.  If they're wrong and you think they're right, you get a surprise...  It's hard for the experiment to have a downside as long as you have the time to do it and don't go engage in bad methodology just to make sure you get the opposite result than that which your detractors expect.

So if you're an experimenter who likes experimenting for the sake of experimenting, by all means, ignore everyone who questions your motives in an internet forum, do the experiment,  and come to your own conclusion.  



73
Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W1ITT
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« Reply #10 on: September 03, 2009, 05:31:57 PM »

The discone uses a lot of material for a given amount of gain, and a wire HF discone can be a rat's nest to erect if not handled carefully.  However, for experimenting with Automatic Link Establishment  (ALE) it certainly has merit, and the "no gain" complaint fades when compared to the resistively loaded wideband antennas that some use.  It's also a good general purpose SWL antenna.
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WB6BYU
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Posts: 13580




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« Reply #11 on: September 03, 2009, 06:18:27 PM »

Actually since the addition of the WARC bands it may not
be a bad choice for 20 - 10m, with 5 bands in an octave
range, with the possible addition of 30 or 40 on the low
side or 6m on the high end, depending on construction.
(Though 6m probably would justify a separate antenna for
serious work.)  Given a suitable support, it isn't that
hard to run wires for the cone, and even the disk needn't
be too difficult if the size is kept reasonable.

Sounds like a good experiment to me.
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KQ6Q
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Posts: 993




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« Reply #12 on: September 03, 2009, 10:03:44 PM »

I was a crew commander at Davis-Monthan in the 1970's and my primary site was across the valley, at the entrance to Madera Canyon. The Orange balls may still be on the power lines for Helo avoidance. I used to take my TenTec Century 21 out there, with some coax and an N-adapter to use the big discone on the ham bands. I had a 100 mile horizon, and it was absolutely fabulous. I did a lot on 80 meters, where that antenna had an alternate feedpoint, and was used as a diamond-shaped folded cage monopole. 599 Into Washington State, Alaska, and Japan. It was also nice on the upper bands - worked into Europe a few times on 15 meters, but the only hours I could spare time to operate were at night, and 80 meters absolutely rocked.
If the discone were ever blown away, we had a retractable vertical, under an armored cover, that could be raised to be a 1/4 wave at any frequence from about 3 to 30Mhz. That was an amazing piece of machinery. Wonder if they just buried it in place when they demolished the sites? The one at 571-6, the green valley site, might still be there. It did require periodic maintenance of the mechanical hardware tho... might be seized up by now.
Fred Wagner
MCCC crew R-152, 571st SMS, Dec 1974 - Feb 1979
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AB7E
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« Reply #13 on: September 04, 2009, 12:57:43 AM »

KA5IPF: "A friend had the best description of the performance of a discone I have ever heard;

"It equally attenuates all design frequencies"


Neither you nor your friend know much about a discone, then.  It doesn't "attenuate" at all, and in fact has roughly the same performance as a well-built 1/4 wave vertical antenna ... which is a couple of dbi gain.  The problem with an HF discone, as others have mentioned here, is simply that it involves way more metal than necessary to get the job done on the ham bands.  It's also much more visually obtrusive than the alternatives.

Dave   AB7E
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K8GU
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« Reply #14 on: September 04, 2009, 05:03:36 AM »

There is also an HF discone article in the Fifth ARRL Antenna Compendium.  As Dan says, unless you need the continuous bandwidth, it's a relatively complicated antenna.  The ham bands aren't wide enough or close enough together to warrant building one unless you just want to try it.  ALE is probably the best use, although a lot of ALE systems use LPDAs because they are only interested in one direction.  Unless it's an oblique sounder (which I suspect is the case for the LANL system described by W5AOX), discones aren't particularly useful ionosondes since they don't have significant vertical radiation.
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