On Thu, 20 Mar 2014 00:06:50 -0700, Jon Danniken
wrote:

Hi all, I'm cooking up a discone antenna for receiving,

I don't want to discourage you, but if you're building something from
scratch, may I suggest you build an antenna that works better than a
discone. There was a discussion in this newsgroups recently that
drifted over to discones. To illustrate some of the problems, I ran
simulations of a Diamond D-130 discone (without the low frequency
vertical section) to illustrate how the antenna pattern is less than
ideal at the higher frequencies. See:
http://802.11junk.com/jeffl/antennas/Discone/index.html
An animated slide show is at:
http://802.11junk.com/jeffl/antennas/Discone/slides/discone-animated.html
The frequency is shown in the upper left. The gain in the lower
right. Note that the gain is still there, but at higher frequencies
is mostly pointing almost straight up.

Unless you're interested in listening to satellites and aircraft, I
recommend a biconcial instead. It's very much like the common "fan
dipole" used for multiband HF operation without requiring traps.

Unfortunately, my only biconical model that might be suitable seems to
have a problem. (I don't recall where I found the model). There are
some nasty nulls at several frequencies between 50 to 1000 MHz that
need to be fixed. I'll play with it some more when I have time.
http://802.11junk.com/jeffl/antennas/biconical/
I set the characteristic impedance to 75 ohms, which seems to work the
best. However, anything between 50 and 200 ohms should work. For 75
ohms, a 1:1 broadband balun (i.e. a transformer) is necessary. I'll
create an animated GIF file for the patterns at various frequencies
when I have more time.



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

On Thu, 20 Mar 2014 21:12:57 -0700, Jeff Liebermann
wrote:

http://802.11junk.com/jeffl/antennas/Discone/
http://802.11junk.com/jeffl/antennas/biconical/
I did some more tinkering with these two. Looks like the biquad also
has holes in the gain plot, but shows more gain at more frequencies
than the discone. I changed the characteristic impedance of the
biquad to 150 ohms to get a better looking VSWR. Real ground and
animated GIF's of the biconical antenna when I have more time.

Diamond D-130 discone antenna model borrowed from:
http://www.qsl.net/kp4md/modeling.htm
I don't recall where I found the biconical.

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

On 03/20/2014 10:58 PM, Jeff Liebermann wrote:
On Thu, 20 Mar 2014 21:12:57 -0700, Jeff Liebermann
wrote:

http://802.11junk.com/jeffl/antennas/Discone/
http://802.11junk.com/jeffl/antennas/biconical/
I did some more tinkering with these two. Looks like the biquad also
has holes in the gain plot, but shows more gain at more frequencies
than the discone. I changed the characteristic impedance of the
biquad to 150 ohms to get a better looking VSWR. Real ground and
animated GIF's of the biconical antenna when I have more time.

Diamond D-130 discone antenna model borrowed from:
http://www.qsl.net/kp4md/modeling.htm
I don't recall where I found the biconical.

Neat, thanks. I've read that the discone is really a ground hugger, and
your ground plots show that perfectly.

Jon

On 03/20/2014 09:12 PM, Jeff Liebermann wrote:
On Thu, 20 Mar 2014 00:06:50 -0700, Jon Danniken
wrote:

Hi all, I'm cooking up a discone antenna for receiving,

I don't want to discourage you, but if you're building something from
scratch, may I suggest you build an antenna that works better than a
discone. There was a discussion in this newsgroups recently that
drifted over to discones. To illustrate some of the problems, I ran
simulations of a Diamond D-130 discone (without the low frequency
vertical section) to illustrate how the antenna pattern is less than
ideal at the higher frequencies. See:
http://802.11junk.com/jeffl/antennas/Discone/index.html
An animated slide show is at:
http://802.11junk.com/jeffl/antennas/Discone/slides/discone-animated.html
The frequency is shown in the upper left. The gain in the lower
right. Note that the gain is still there, but at higher frequencies
is mostly pointing almost straight up.

Thanks Jeff, I had not considered a biconical, but it looks interesting.
The discone I am building is of a "spoke" variety, with the cone built
separate from the disk, so it would be simple to duplicate another cone
and invert it on top of the other cone.

Unless you're interested in listening to satellites and aircraft, I
recommend a biconcial instead. It's very much like the common "fan
dipole" used for multiband HF operation without requiring traps.

I do like aircraft, although I am starting to think that I might be
better off with a dedicated airband antenna (looking at j-poles right
now) along with a wideband antenna for general scanning.

Speaking of multiple antennas, I know that some antennas use multiple
elements tuned to different bands, but can you connect two antennas to
the same feedline? Like, say, a discone/biconical and a j-pole?

Unfortunately, my only biconical model that might be suitable seems to
have a problem. (I don't recall where I found the model). There are
some nasty nulls at several frequencies between 50 to 1000 MHz that
need to be fixed. I'll play with it some more when I have time.
http://802.11junk.com/jeffl/antennas/biconical/
I set the characteristic impedance to 75 ohms, which seems to work the
best. However, anything between 50 and 200 ohms should work. For 75
ohms, a 1:1 broadband balun (i.e. a transformer) is necessary. I'll
create an animated GIF file for the patterns at various frequencies
when I have more time.

I'll look forward to that, thanks!

Jon

On Fri, 21 Mar 2014 08:14:01 -0700, Jon Danniken
wrote:

Thanks Jeff, I had not considered a biconical, but it looks interesting.
The discone I am building is of a "spoke" variety, with the cone built
separate from the disk, so it would be simple to duplicate another cone
and invert it on top of the other cone.

If you want to be cheap and sloppy (like me), consider that a bowtie
antenna, commonly found on broadband TV antennas, is nothing more than
a flattened biconcial antenna. While it is directional, it's
functions much the same way as a biconcical and is much easier to
build (out of aluminum roof flashing).

I do like aircraft, although I am starting to think that I might be
better off with a dedicated airband antenna (looking at j-poles right
now) along with a wideband antenna for general scanning.

I don't have any professional experience with aircraft antennas.
However, I have done some ADS-B 1090 MHz designs and tests. The basic
idea is that the antenna should have the most gain at the horizon and
somewhat above the horizon to get the most range. Commercial jets fly
at about 5 miles altitude maximum, so gain in the upwards direction is
less critical. That's quite opposite of what the discone and
biconical will do.

Speaking of multiple antennas, I know that some antennas use multiple
elements tuned to different bands, but can you connect two antennas to
the same feedline? Like, say, a discone/biconical and a j-pole?

No. The best you can do is insert a diplexer at the feedpoint
junction, and separate the operating frequencies. Putting two
antennas in parallel doesn't work. If both antennas received the same
signal, the antenna pattern would be a conglomeration of both
antennas, which could just as easily result in a null as it could a
peak (also known as a mess).

I have such an arrangement at a site. 120ft of very expensive 2"(?)
Heliax going between the tower and the building. One triplexer and
three antennas, each on a different band, on top of the tower. Another
triplexer and 3 radios at the other end. Works so-so as intermod and
desense are a problem on some frequencies due to insufficient
triplexer isolation.

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

Jeff Liebermann wrote:
Jon Danniken wrote:

Thanks Jeff, I had not considered a biconical, but it looks interesting.
The discone I am building is of a "spoke" variety, with the cone built
separate from the disk, so it would be simple to duplicate another cone
and invert it on top of the other cone.

If you want to be cheap and sloppy (like me), consider that a bowtie
antenna, commonly found on broadband TV antennas, is nothing more than
a flattened biconcial antenna. While it is directional, it's
functions much the same way as a biconcical and is much easier to
build (out of aluminum roof flashing).

I do like aircraft, although I am starting to think that I might be
better off with a dedicated airband antenna (looking at j-poles right
now) along with a wideband antenna for general scanning.

I don't have any professional experience with aircraft antennas.
However, I have done some ADS-B 1090 MHz designs and tests. The basic
idea is that the antenna should have the most gain at the horizon and
somewhat above the horizon to get the most range. Commercial jets fly
at about 5 miles altitude maximum, so gain in the upwards direction is
less critical. That's quite opposite of what the discone and
biconical will do.

I thought the discone/biconicals were more of a horizon-looking antenna,
at least from what I have read on them?

Speaking of multiple antennas, I know that some antennas use multiple
elements tuned to different bands, but can you connect two antennas to
the same feedline? Like, say, a discone/biconical and a j-pole?

No. The best you can do is insert a diplexer at the feedpoint
junction, and separate the operating frequencies. Putting two
antennas in parallel doesn't work. If both antennas received the same
signal, the antenna pattern would be a conglomeration of both
antennas, which could just as easily result in a null as it could a
peak (also known as a mess).

I have such an arrangement at a site. 120ft of very expensive 2"(?)
Heliax going between the tower and the building. One triplexer and
three antennas, each on a different band, on top of the tower. Another
triplexer and 3 radios at the other end. Works so-so as intermod and
desense are a problem on some frequencies due to insufficient
triplexer isolation.

Maybe I'll look at a switcher of some sort eventually, and plan on just
manually doing it for now, thanks.

Jon

On Sat, 22 Mar 2014 08:47:56 -0700, Jon Danniken
wrote:

I don't have any professional experience with aircraft antennas.
However, I have done some ADS-B 1090 MHz designs and tests. The basic
idea is that the antenna should have the most gain at the horizon and
somewhat above the horizon to get the most range. Commercial jets fly
at about 5 miles altitude maximum, so gain in the upwards direction is
less critical. That's quite opposite of what the discone and
biconical will do.

I thought the discone/biconicals were more of a horizon-looking antenna,
at least from what I have read on them?

After I ran the NEC2 models, that seems true for the low end of the
frequency range. They are suppose to look something like a broadband
version of a vertical dipole. However, as the frequency goes up,
additional lobes appear until at the top of the frequency range, most
of the RF is going straight up. A Biconical is somewhat better than a
discone at retaining a sane looking pattern and reasonable gain, but
not much better.

My point about listening to aircraft is that there's little difficulty
hearing aircraft that are overhead, and plenty of difficulty hearing
aircraft near the horizon. Therefore, the antenna should have most of
its gain towards the horizon, and less gain above the horizon to near
overhead. At low frequencies, the discone does that. At the high end
of the range, it's quite the opposite.

Maybe I'll look at a switcher of some sort eventually, and plan on just
manually doing it for now, thanks.

Ummm... climbing the tower to rotate a manual switch doesn't sound
like a good idea.



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

Jeff Liebermann wrote:
Jon Danniken wrote:


I thought the discone/biconicals were more of a horizon-looking antenna,
at least from what I have read on them?

After I ran the NEC2 models, that seems true for the low end of the
frequency range. They are suppose to look something like a broadband
version of a vertical dipole. However, as the frequency goes up,
additional lobes appear until at the top of the frequency range, most
of the RF is going straight up. A Biconical is somewhat better than a
discone at retaining a sane looking pattern and reasonable gain, but
not much better.

My point about listening to aircraft is that there's little difficulty
hearing aircraft that are overhead, and plenty of difficulty hearing
aircraft near the horizon. Therefore, the antenna should have most of
its gain towards the horizon, and less gain above the horizon to near
overhead. At low frequencies, the discone does that. At the high end
of the range, it's quite the opposite.

Aha, okay I got you now, thanks for that. I still need to figure out
how to read the "lobe pattern" charts.

Maybe I'll look at a switcher of some sort eventually, and plan on just
manually doing it for now, thanks.

Ummm... climbing the tower to rotate a manual switch doesn't sound
like a good idea.

Hehe, indeed it doesn't. I was thinking more along the lines of a relay
box, if such a thing is possible, or maybe there is actually a gadget
that does something similar.

Along those lines, if connecting antennae of differing frequencies
together is not something that works, how does an antenna with multiple
different elements, like something like a scantenna
(http://i.imgur.com/D3Aeb58.jpg) get away with it?

Jon

On 3/22/2014 7:13 PM, Jeff Liebermann wrote:
On Sat, 22 Mar 2014 08:47:56 -0700, Jon Danniken
wrote:

I don't have any professional experience with aircraft antennas.
However, I have done some ADS-B 1090 MHz designs and tests. The basic
idea is that the antenna should have the most gain at the horizon and
somewhat above the horizon to get the most range. Commercial jets fly
at about 5 miles altitude maximum, so gain in the upwards direction is
less critical. That's quite opposite of what the discone and
biconical will do.

I thought the discone/biconicals were more of a horizon-looking antenna,
at least from what I have read on them?

After I ran the NEC2 models, that seems true for the low end of the
frequency range. They are suppose to look something like a broadband
version of a vertical dipole. However, as the frequency goes up,
additional lobes appear until at the top of the frequency range, most
of the RF is going straight up. A Biconical is somewhat better than a
discone at retaining a sane looking pattern and reasonable gain, but
not much better.

My point about listening to aircraft is that there's little difficulty
hearing aircraft that are overhead, and plenty of difficulty hearing
aircraft near the horizon. Therefore, the antenna should have most of
its gain towards the horizon, and less gain above the horizon to near
overhead. At low frequencies, the discone does that. At the high end
of the range, it's quite the opposite.


There is? I remember back in the 70's a United Airlines pilot who would
regularly work 146.52. I had no trouble chatting with him from almost
300 miles away, even though he was only using a 1.5W HT. And out here
on the east coast, it's impossible to use an HT on any 2M repeater
frequency without bringing up multiple repeaters, even when using 1W
at about 3,000 feet or above. From 10,000 feet, forget it almost
anywhere in the country.

And BTW - commercial planes generally fly at around 7mi (35,000-37,000
ft.) high - not 5Mi (26,000 ft.) as you claimed.

--
==================
Remove the "x" from my email address
Jerry, AI0K

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

On Sun, 23 Mar 2014 09:24:09 -0400, Jerry Stuckle
wrote:

On 3/22/2014 7:13 PM, Jeff Liebermann wrote:
My point about listening to aircraft is that there's little difficulty
hearing aircraft that are overhead, and plenty of difficulty hearing
aircraft near the horizon. Therefore, the antenna should have most of
its gain towards the horizon, and less gain above the horizon to near
overhead. At low frequencies, the discone does that. At the high end
of the range, it's quite the opposite.

There is? I remember back in the 70's a United Airlines pilot who would
regularly work 146.52. I had no trouble chatting with him from almost
300 miles away, even though he was only using a 1.5W HT. And out here
on the east coast, it's impossible to use an HT on any 2M repeater
frequency without bringing up multiple repeaters, even when using 1W
at about 3,000 feet or above. From 10,000 feet, forget it almost
anywhere in the country.

Yep. You can be heard for quite a distance from an airplane. The
problem is hearing anything as the chances of co-channel interference
is high.

I help maintain an ADS-B listening station (1090 MHz) with a good
view of the ocean. 200 Nm average range. I designed the antenna
specifically for the purpose and location:
http://802.11junk.com/jeffl/antennas/AMOS-5-1090MHz/index.html
The actual antenna system is somewhat more complex.

Also a VHF AIS receiver at a local hilltop. Great view from near the
coast from about 2,000 ft.
http://www.marinetraffic.com/ais/details/stations/112
(Note that it's NOT on Mt Umunhum. The receiver was moved to Bonny
Doon to eliminate weather xmitter interference). Average range is
about 200 Nm, and much more when ducting is available. If you're near
the coast, listen on 161.975 MHz and 162.025 MHz for the AIS traffic.

And BTW - commercial planes generally fly at around 7mi (35,000-37,000
ft.) high - not 5Mi (26,000 ft.) as you claimed.

True. The problem is that near the coast, most of the aircraft
traffic is on takeoff or approach and at much lower altitudes. Here's
a typical altitude profile for an KLAX to KSFO flight:
http://802.11junk.com/jeffl/crud/flight-profile.jpg
Data capture was from:
http://flightaware.com/live/flight/VRD935/history/20140323/1600Z/KLAX/KSFO/tracklog
which will change throughout the day. Notice that for a 500 Nm
flight, it doesn't stay above 30,000 ft for very long. By the time I
see the incoming data, it's usually between 10,000 to 15,000 ft. Of
course for cross country, they stay above 30,000 ft for much longer. I
just took a look at the raw data from the local ADS-B receiver. One
flight at 30,000 ft and everything else below about 15,000 ft over a
10 minute period.

Incidentally, until you mentioned radio range in an aircraft, I never
bothered to check how much TX power the aircraft was using for ADS-B
(1090 MHz). Looks like they deliver some serious power at altitude:
http://www.ads-b.com/PDF/UAT%20SARP.pdf
Table 12-1: Transmitter power levels
Transmitter Minimum power Maximum power Intended minimum
type at PMP at PMP air-to-air ranges
Aircraft (Low) 7 watts (+38.5 dBm) 18 watts (+42.5 dBm) 20 NM
Aircraft (Med) 16 watts (+42 dBm) 40 watts (+46 dBm) 40 NM
Aircraft (High) 100 watts (+50 dBm) 250 watts (+54 dBm) 120 NM
Note that the range is for air to air, not air to ground.

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