Conical, biconical and discone antennae?

[gareth]

As these structures seem to offer a 3:1 bandwidth, is there some
reason why they do not feature largely in amateur service, for
it seems to me that a no-tune antenna covering from 10MHz to
30MHz would give coverage for the whole of the HF bands?

[highlandham]

On 11/05/15 12:24, Jeff wrote:

> A discone will give you more like a 10 to 1 bandwidth, but the reason
> that you don't see them much at hf is down to the size and mechanical
> complexity, and the fact that you don't need continuous coverage, so it
> is easier to have antennas that are cut to specific band(s).
>
> Jeff
===========
Happily Using a 25 MHz - 1.3 GHz Discone antenna for Tx/Rx on 144-146
MHz with a mid-band SWR of 1.6 ..... for local FM phone contacts and
Packet Radio (on 144.850MHz)
Intend to improve the SWR with an adjustable matching box (yet to be built)

Frank , GM0CSZ / KN6WH in IO87AT

[Ralph Mowery]

"highlandham" <highlandh...@rfburns.eu> wrote in message
news:miqcje$vs$1...@dont-email.me...

> ===========
> Happily Using a 25 MHz - 1.3 GHz Discone antenna for Tx/Rx on 144-146 MHz
> with a mid-band SWR of 1.6 ..... for local FM phone contacts and Packet
> Radio (on 144.850MHz)
> Intend to improve the SWR with an adjustable matching box (yet to be
> built)
>
> Frank , GM0CSZ / KN6WH in IO87AT

Is it a true discone at 25 MHz or is it one that has the vertical whip for
the lower portion of the frequency range like many that I have seen ?

Also don't the discones have vertical radiation patern ? Not sure what the
take off angle would be for one of those near the ground for the lower
frequencies.

I have a discone for VHF and above, but not for the lower bands. It seems
to work ok for receiving over a broad range, but I use a differant antenna
for most transmiting.

[Jeff Liebermann]

On Mon, 11 May 2015 11:14:48 +0100, "gareth"
<no....@thank.you.invalid> wrote:

>As these structures seem to offer a 3:1 bandwidth,

At VHF/UHF, 10:1 is possible.

>is there some
>reason why they do not feature largely in amateur service, for
>it seems to me that a no-tune antenna covering from 10MHz to
>30MHz would give coverage for the whole of the HF bands?

Yep, high VSWR, lousy takeoff angle, and size. Here's my model of the
Icom AH7000 (Diamond D-130) discone which is rated for 25 to 1000 MHz:
<http://802.11junk.com/jeffl/antennas/Discone/index.html>
Here's another:
<https://plus.google.com/photos/114032640816757126398/albums/5850933147705167841?banner=pwa>
Scale the models for whatever frequency range you find useful.

Notice the VSWR graphs. In transmit, such an antenna will be a big
problem. You can add an antenna tuner, but that adds loss and fails
the "no-tune" test. Mostly, the discone is receive only.

There are HF discones available. The former MARS station at Ft Ord
(now N6IJ) inherited one from the military.
<https://plus.google.com/photos/105216876940309310015/albums/5404932576445929649>
Note the large size needed to work down to about 3.5 MHz.
More photos:
<https://www.google.com/search?q=hf+discone&tbm=isch>

Discones also have a high takeoff angle. That's not so much a problem
when used at HF, where much of the ionospheric bounce comes from
almost overhead, but is fatal at VHF, where you want to talk to the
horizon, not the birds. You can see the effect here:
<http://802.11junk.com/jeffl/antennas/Discone/takeoff-angle/index.html>
Notice that at 500 MHz, there is no signal at the horizon, with all
the RF going almost straight up.

What the military used discones for is receive frequency hopping all
over their HF bands without any band switching or tuning. LDPA (log
periodic) broadband HF antennas were also used, which incidentally was
also present at N6IJ:
<http://www.n6ij.org/antennas.html>
Neither antenna had much gain, but they sure had the bandwidth.

--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Jeff Liebermann]

On Tue, 12 May 2015 08:33:44 +0100, Jeff <je...@ukra.com> wrote:

>
>> Discones also have a high takeoff angle. That's not so much a problem
>> when used at HF, where much of the ionospheric bounce comes from
>> almost overhead, but is fatal at VHF, where you want to talk to the
>> horizon, not the birds. You can see the effect here:
>> <http://802.11junk.com/jeffl/antennas/Discone/takeoff-angle/index.html>
>> Notice that at 500 MHz, there is no signal at the horizon, with all
>> the RF going almost straight up.
>>
>> What the military used discones for is receive frequency hopping all
>> over their HF bands without any band switching or tuning. LDPA (log
>> periodic) broadband HF antennas were also used, which incidentally was
>> also present at N6IJ:
>> <http://www.n6ij.org/antennas.html>
>> Neither antenna had much gain, but they sure had the bandwidth.

>The take off angle on a discone is no worse that a dipole, your plots
>were done at 6' over a real ground, so virtually any antenna is going to
>have a high take off angle.

The height is 3 meters (actually 120 inches) for all plots, the height
of the mast above a typical tower outrigger or rooftop. At 100 MHz,
that's 1 wavelength and at 1000 MHz, 10 wavelengths. If I scaled the
antenna to HF frequencies, and use an earth ground instead of an
outrigger, that would work out to about 10 times these heights or
somewhere around 30 meters in height, which methinks is quite high
enough to remove much of the ground influences on the take off angles,
at least at the higher HF frequencies.

See:
<http://802.11junk.com/jeffl/antennas/Discone/>
for the original models. If you want to experiment, the NEC deck is
here:
<http://802.11junk.com/jeffl/antennas/Discone/slides/discone.html>
The
SY hgh=120
is the height above ground.

>VNA measurements of my discone show a usable VSWR from 100MHz to over
>500MHz plus 50MHz due to the whip on the top.

Do you transmit into your discone?

>The military also widely use discones for Tx/Rx over the UHF military
>air band 220-400MHz.

Yep. One octave frequency range is easy. One decade is not.

[Jeff Liebermann]

On Wed, 13 May 2015 07:50:13 +0100, Jeff <je...@ukra.com> wrote:

>
>> The height is 3 meters (actually 120 inches) for all plots, the height
>> of the mast above a typical tower outrigger or rooftop. At 100 MHz,
>> that's 1 wavelength and at 1000 MHz, 10 wavelengths. If I scaled the
>> antenna to HF frequencies, and use an earth ground instead of an
>> outrigger, that would work out to about 10 times these heights or
>> somewhere around 30 meters in height, which methinks is quite high
>> enough to remove much of the ground influences on the take off angles,
>> at least at the higher HF frequencies.

>A NEC simulation of a 144MHz dipole over real ground at 3m high shows
>about a 4 degree upward tilt, not so different from your discone
>simulation, so to say that is a reason that discones are no good is
>incorrect. Virtually any vertical antenna at 3m above ground will show
>similar upward tilt.

True. I did that study a while back. Normalized vertical half wave
dipole at various feet point heights in wavelengths above a real
(moderate) ground:
<http://802.11junk.com/jeffl/antennas/vertical-dipole/index.html>
Animated version:
<http://802.11junk.com/jeffl/antennas/vertical-dipole/slides/animated-v-dipole.html>
I misplaced the NEC deck here:
<http://802.11junk.com/jeffl/antennas/vertical-dipole/slides/vertical-dipole-7-0-wavelengths.html>
However, that's at the resonant frequency of the dipole, not something
several octaves higher. The vertical dipole, discone, biconical and
similar antennas all work fairly well near whatever frequency it most
closesly resembles a dipole. It's at the higher frequencies where
things go insane. For example, the Diamond discone at 500 Mhz:
<http://802.11junk.com/jeffl/antennas/Discone/takeoff-angle/slides/500Mhz.html>
Oh, I forgot that I had an animated discone:
<http://802.11junk.com/jeffl/antennas/Discone/slides/discone-animated.html>

>Yes I do transmit on my discone on both 2m and 70cms, the vswr is below
>1.5:1 on both bands, (and also on 6m but that is due to the whip on the
>top and not really part of the discone).
>
>Swept over the range 100Mhz to 500MHz the vswr does not exceed 2:1.

Is that with the VNA, antenna analyzer, or VSWR meter at the antenna,
or with a length of coax cable between the instrument and the antenna?
My rooftop discone also looks rather good with lots of attenuation
between the return loss bridge and the antenna. I would post a screen
grab, but my sweeper needs an electrolytic transplant and is currently
unusable. Actually, I just realized that I have six assorted sweep
generators, none of which are currently functional. Sigh.

Anyway, if you're careful at cutting the element lengths for the ham
bands, and put the dips in the VSWR curver at 146 and 443 MHz, the
VSWR can be made low enough for transmit use. See dips in curve at:
<http://802.11junk.com/jeffl/antennas/Discone/slides/vswr.html>

Incidentally, I used to have a reference vertical biconical antenna on
my roof. I spent some time at an antenna range and with the most
elaborate test equipment I could borrow, characterising the antenna.
Whenever I wanted to know the real gain of an antenna at or near the
horizon, I would compare signals between the test antenna and the
biconical. It was far from perfect mostly due to reflections from
other antennas on the roof, but it was a great sanity check. I also
noticed, but never verified, that I was getting better VHF/UHF
reception with the biconical than with my Radio Shack discone.
Unfortunately, it was destroyed along with most of my other antennas
when a tree fell on my roof in a storm.

[Sal M. O'Nella]

"Jeff Liebermann" wrote in message
news:05n1latsve4knlc3t...@4ax.com...

What the military used discones for is receive frequency hopping all
over their HF bands without any band switching or tuning. LDPA (log
periodic) broadband HF antennas were also used, which incidentally was
also present at N6IJ:

www.n6ij.org/antennas.html>
Neither antenna had much gain, but they sure had the bandwidth.

--
Jeff

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

They were also used for HF transmit on some ships.

Here's a link to an early Navy research paper on the discone/cage
antenna sometimes called a "discage." Unfortunately, only the text
is clear; the pictures are not good.

http://www.navy-radio.com/ant/discage-661464.pdf

Note that a single structure was fed from the top and the bottom by
two separate coax cables.

I had hundreds of inspection and test visits to Navy ships in the 1980s
and 1990s. In practice, I never saw that antenna installed for use
at the extreme low end, as described in the linked paper. There was nearly
always a fan antenna for 2 -6 MHz.

The discone/cage freq ranges were nominally 4 - 12 MHz (cage) and
10- 30 MHz (discone). Both sections were invariably fed through a
multi-transmitter coupler, either four or eight transmitters, depending
on the ship.

I know the fan antennas all had custom matching boxes at the
feed point to bring the SWR within the 3:1 circle. I can't recall if the
sections of the discage also had such matching.

"Sal"
(really KD6VKW)

[Jeff Liebermann]

On Mon, 18 May 2015 12:37:14 -0700, "Sal M. O'Nella"
<salmo...@foodpoisoning.org> wrote:

>They were also used for HF transmit on some ships.
>
>Here's a link to an early Navy research paper on the discone/cage
>antenna sometimes called a "discage." Unfortunately, only the text
>is clear; the pictures are not good.
>
>http://www.navy-radio.com/ant/discage-661464.pdf

Some photos:
<https://www.google.com/search?q=discage+antenna&tbm=isch>

I'm not sure, but some of the discage antennas in the photos are more
like fat "cage dipole" or "cage monopole" antennas. The wire cage
increases the effective diameter of the monopole driven element to
increase it's bandwidth.

I couldn't find a better copy of the 1967 Discage paper. Actually,
I've never heard of a discage antenna. My idea of a cage antenna is
the Viet Nam war era "Elephant Cage" direction finder antenna:
<https://www.google.com/search?tbm=isch&q=elephant+cage+antenna>

>Note that a single structure was fed from the top and the bottom by
>two separate coax cables.

Not so weird. Visualize a biconical antenna fed as two monopoles from
the narrow pointed ends, instead of being fed as a dipole. Now,
reverse the positions of the biconical elements and we have something
that looks like the discage.

>I had hundreds of inspection and test visits to Navy ships in the 1980s
>and 1990s. In practice, I never saw that antenna installed for use
>at the extreme low end, as described in the linked paper. There was nearly
>always a fan antenna for 2 -6 MHz.

I don't have any Navy experience but I can see why a fan antenna was
popular. It's simple, fairly easy to install, and you can cut
elements randomly and still have a working antenna. Best of all, it
doesn't eat deck or turret space.

>The discone/cage freq ranges were nominally 4 - 12 MHz (cage) and
>10- 30 MHz (discone). Both sections were invariably fed through a
>multi-transmitter coupler, either four or eight transmitters, depending
>on the ship.
>
>I know the fan antennas all had custom matching boxes at the
>feed point to bring the SWR within the 3:1 circle. I can't recall if the
>sections of the discage also had such matching.

Despite having a fairly broad bandwidth, it's not a perfect or
constant 50 ohms. Unless the radios can tolerate a moderate VSWR (3:1
perhaps?), some kind of tuner might be useful. However, at <3:1 and
with some kind of VSWR controlled tx power reduction, probably the
impedance matching boxes would be sufficient.

Thanks.

[Sal M. O'Nella]

"Jeff Liebermann" wrote in message

news:vc0lladovb7bphqo3...@4ax.com...

<major snippage>

Despite having a fairly broad bandwidth, it's not a perfect or
constant 50 ohms. Unless the radios can tolerate a moderate VSWR (3:1
perhaps?), some kind of tuner might be useful. However, at <3:1 and
with some kind of VSWR controlled tx power reduction, probably the
impedance matching boxes would be sufficient.

Thanks.

========================================================

This is true. Although automatic systems, called High Frequency Radio
Group, were being introduced about the time I retired, the older, common
transmit multi-couplers always had to be hand-tuned in those by-gone days.
It was a three-step process that I used to do occasionally. I'm assuming
coupler drawers must have had some reactive components inside. I never had
one open or bothered to dig out the schematics for any of them.

"Sal"