On 1/09/2011 9:43 AM, Dr Who wrote:
>
> A while back I had a slightly OT discussion regarding the practicalities of fractal antennas for HDTV.
>
> I subsequently made an 8 element version and it works very well in areas of no line of sight/poor reception.
>
> I don't use a reflector on this and it's interesting that the antenna works well on both the horizontal and vertical plane indoors.
>
> See below using on the horizontal.
>
> http://users.tpg.com.au/agnet/unknown.jpg
>
> So any insight into which plane is optimum for this type of design ?
>
> I was quite surprised that it works in the alignment seen in the picture.
>
> Could it be used as a beam antenna with a suitable reflector at one end ?
>
> Maybe it's just picking up a reflected/multipath signal from the metal roof ?
>
>
>
>
>
Have you fiddled with it near an rf source watching signal ??
> On 1/09/2011 9:43 AM, Dr Who wrote:
> >
> > A while back I had a slightly OT discussion regarding the practicalities of fractal antennas for HDTV.
> >
> > I subsequently made an 8 element version and it works very well in areas of no line of sight/poor reception.
> >
> > I don't use a reflector on this and it's interesting that the antenna works well on both the horizontal and vertical plane indoors.
> >
> > See below using on the horizontal.
> >
> > http://users.tpg.com.au/agnet/unknown.jpg
> >
> > So any insight into which plane is optimum for this type of design ?
> >
> > I was quite surprised that it works in the alignment seen in the picture.
> >
> > Could it be used as a beam antenna with a suitable reflector at one end ?
> >
> > Maybe it's just picking up a reflected/multipath signal from the metal roof ?
> >
> >
> >
> >
> >
> Have you fiddled with it near an rf source watching signal ??
If I go outside it gets swamped with signal and there's no discernable difference between antenna orientation.
But using it indoors with no line of site and very bad reception conditions it's interesting that it works better on the horizontal plane than the vertical.
So getting back to my original question, could this type of array be used as a beam antenna ?
On Aug 31, 4:43*pm, "Dr Who" <dead_letter_off...@hotmail.com> wrote:
> A while back I had a slightly OT discussion regarding the practicalities of fractal antennas for HDTV.
>
> I subsequently made an 8 element version and it works very well in areas of no line of sight/poor reception.
>
> I don't use a reflector on this and it's interesting that the antenna works well on both the horizontal and vertical plane indoors.
>
> See below using on the horizontal.
>
> http://users.tpg.com.au/agnet/unknown.jpg
>
> So any insight into which plane is optimum for this type of design ?
>
> I was quite surprised that it works in the alignment seen in the picture.
>
> Could it be used as a beam antenna with a suitable reflector at one end ?
>
> Maybe it's just picking up a reflected/multipath signal from the metal roof ?
> On Aug 31, 4:43*pm, "Dr Who" <dead_letter_off...@hotmail.com> wrote:
> > A while back I had a slightly OT discussion regarding the practicalities of fractal antennas for HDTV.
> >
> > I subsequently made an 8 element version and it works very well in areas of no line of sight/poor reception.
> >
> > I don't use a reflector on this and it's interesting that the antenna works well on both the horizontal and vertical plane indoors.
> >
> > See below using on the horizontal.
> >
> > http://users.tpg.com.au/agnet/unknown.jpg
> >
> > So any insight into which plane is optimum for this type of design ?
> >
> > I was quite surprised that it works in the alignment seen in the picture.
> >
> > Could it be used as a beam antenna with a suitable reflector at one end ?
> >
> > Maybe it's just picking up a reflected/multipath signal from the metal roof ?
>
> You should model it in NEC2.
Common commercial HDTV antenna models:
<http://www.hdtvprimer.com/SimData/SimData.html>
<http://www.hdtvprimer.com/ANTENNAS/comparing.html>
<http://www.hdtvprimer.com/SIMS/>
Note: You're really asking this in the wrong newsgroup. Look for
something that discusses TV antenna. www.avsforums.com would
probably be a good place to start.
> On 4 Sep 2011 08:13:23 +1000, "Dr Who"
> <dead_letter_office@hotmail.com> wrote:
>
> > miso@sushi.com wrote:
>
> >> > http://users.tpg.com.au/agnet/unknown.jpg
>
> >> You should model it in NEC2.
>
> > Good thinking.
> > I will have a go tonight.
>
> Common commercial HDTV antenna models:
> <http://www.hdtvprimer.com/SimData/SimData.html>
> <http://www.hdtvprimer.com/ANTENNAS/comparing.html>
> <http://www.hdtvprimer.com/SIMS/>
>
> Note: You're really asking this in the wrong newsgroup. Look for
> something that discusses TV antenna. www.avsforums.com would
> probably be a good place to start.
Thanks for the links Jeff.
I posted it here just as a discussion on fractal antennas per se.
I will check out the avsforum. I wasn't aware of that one.
On 4 Sep 2011 17:10:05 +1000, "Dr Who"
<dead_letter_office@hotmail.com> wrote:
>> Note: You're really asking this in the wrong newsgroup. Look for
>> something that discusses TV antenna. www.avsforums.com would
>> probably be a good place to start.
>I will check out the avsforum. I wasn't aware of that one.
>Cheers
Oops. Wrong URL:
<http://www.avsforum.com>
<http://www.avsforum.com/avs-vb/>
Antenna discussions usually land in HDTV technical:
<http://www.avsforum.com/avs-vb/forumdisplay.php?f=25>
I didn't find anything specific on fractal antennas, but did find this
100+ thread on UHF TV construction:
<http://www.avsforum.com/avs-vb/showthread.php?t=798265&page=1>
I can't resist offering my never humble opinion on fractal antennas.
Methinks they only make sense when dealing with a specialized
radiation pattern (i.e. cell phone SAR) in a confined area (i.e.
inside a cell phone) such as a box. When there are few limits on the
size of the antenna, such as in an outdoor antenna, fractal antennas
are not the best solution.
Basically, it's compromise between size, gain, and bandwidth. You can
have any two, at the expense of the third. For example, the gain of a
simple dipole is about 2.1dBi. If you shrink the length of each
element, the gain remains about 2dBi until you get down to about
1/10th wavelenth. Of course, the tuning also changes, so you have to
add inductance (loading coils) to tune it, and a matching circuit to
reduce losses. Both of those drastically reduce the bandwidth of the
antenna. So, you keep your gain, reduce the size, but screw up the
bandwidth. That's not a good idea for a TV antenna, which needs
plenty of bandwidth.
I suggest you use 4NEC2 to model a simple dipole. Then change it to a
simple fractal dipole per your photo and compare the results. When
you model your completed antenna, compare it with the other similar
size HD antennas that I previously posted links. At some frequency,
your fractal antenna will probably have the same gain, be smaller, and
have a narrower bandwidth, so that it only works on some partial range
of TV channels.
> On 4 Sep 2011 17:10:05 +1000, "Dr Who"
> <dead_letter_office@hotmail.com> wrote:
>
> >> Note: You're really asking this in the wrong newsgroup. Look for
> >> something that discusses TV antenna. www.avsforums.com would
> >> probably be a good place to start.
>
> > I will check out the avsforum. I wasn't aware of that one.
> > Cheers
>
> Oops. Wrong url:
> <http://www.avsforum.com>
> <http://www.avsforum.com/avs-vb/>
> Antenna discussions usually land in HDTV technical:
> <http://www.avsforum.com/avs-vb/forumdisplay.php?f=25>
>
> I didn't find anything specific on fractal antennas, but did find this
> 100+ thread on UHF TV construction:
> <http://www.avsforum.com/avs-vb/showthread.php?t=798265&page=1>
>
> I can't resist offering my never humble opinion on fractal antennas.
> Methinks they only make sense when dealing with a specialized
> radiation pattern (i.e. cell phone SAR) in a confined area (i.e.
> inside a cell phone) such as a box. When there are few limits on the
> size of the antenna, such as in an outdoor antenna, fractal antennas
> are not the best solution.
>
> Basically, it's compromise between size, gain, and bandwidth. You can
> have any two, at the expense of the third. For example, the gain of a
> simple dipole is about 2.1dBi. If you shrink the length of each
> element, the gain remains about 2dBi until you get down to about
> 1/10th wavelenth. Of course, the tuning also changes, so you have to
> add inductance (loading coils) to tune it, and a matching circuit to
> reduce losses. Both of those drastically reduce the bandwidth of the
> antenna. So, you keep your gain, reduce the size, but screw up the
> bandwidth. That's not a good idea for a TV antenna, which needs
> plenty of bandwidth.
>
> I suggest you use 4NEC2 to model a simple dipole. Then change it to a
> simple fractal dipole per your photo and compare the results. When
> you model your completed antenna, compare it with the other similar
> size HD antennas that I previously posted links. At some frequency,
> your fractal antenna will probably have the same gain, be smaller, and
> have a narrower bandwidth, so that it only works on some partial range
> of TV channels.
Thanks again Jeff.
The thing that shocked me was that the fractal antenna worked so well laying on it's back pointing upwards towards the sky. I only discovered this by accident.
Up until then I had viewed it as a directinal panel antenna for Digital TV application and that it would be orientated on the vertical like a biquad.
Any reflector that is added seems to be also aligned in a similar fashion to a biquad. But as the fractal is used extensively as a patch antenna in mobile phones, I suppose element orientation isn't an issue.
That being the case it might be possible to use a reflector in a different alignment - eg. at the end of the array.
I will try and see if I can find a schematic of a fractal dispersion pattern.
On Sep 4, 9:48*am, Jeff Liebermann <je...@cruzio.com> wrote:
> On 4 Sep 2011 17:10:05 +1000, "Dr Who"
>
> <dead_letter_off...@hotmail.com> wrote:
> >> Note: *You're really asking this in the wrong newsgroup. *Look for
> >> something that discusses TV antenna. *www.avsforums.comwould
> >> probably be a good place to start.
> >I will check out the avsforum. *I wasn't aware of that one.
> >Cheers
>
> Oops. *Wrong URL:
> <http://www.avsforum.com>
> <http://www.avsforum.com/avs-vb/>
> Antenna discussions usually land in HDTV technical:
> <http://www.avsforum.com/avs-vb/forumdisplay.php?f=25>
>
> I didn't find anything specific on fractal antennas, but did find this
> 100+ thread on UHF TV construction:
> <http://www.avsforum.com/avs-vb/showthread.php?t=798265&page=1>
>
> I can't resist offering my never humble opinion on fractal antennas.
> Methinks they only make sense when dealing with a specialized
> radiation pattern (i.e. cell phone SAR) in a confined area (i.e.
> inside a cell phone) such as a box. *When there are few limits on the
> size of the antenna, such as in an outdoor antenna, fractal antennas
> are not the best solution. *
>
> Basically, it's compromise between size, gain, and bandwidth. *You can
> have any two, at the expense of the third. *For example, the gain of a
> simple dipole is about 2.1dBi. *If you shrink the length of each
> element, the gain remains about 2dBi until you get down to about
> 1/10th wavelenth. *Of course, the tuning also changes, so you have to
> add inductance (loading coils) to tune it, and a matching circuit to
> reduce losses. *Both of those drastically reduce the bandwidth of the
> antenna. *So, you keep your gain, reduce the size, but screw up the
> bandwidth. *That's not a good idea for a TV antenna, which needs
> plenty of bandwidth.
>
> I suggest you use 4NEC2 to model a simple dipole. *Then change it to a
> simple fractal dipole per your photo and compare the results. *When
> you model your completed antenna, compare it with the other similar
> size HD antennas that I previously posted links. *At some frequency,
> your fractal antenna will probably have the same gain, be smaller, and
> have a narrower bandwidth, so that it only works on some partial range
> of TV channels. *
>
> --
> Jeff Liebermann * * je...@cruzio.com
> 150 Felker St #D * *http://www.LearnByDestroying.com
> Santa Cruz CA 95060http://802.11junk.com
> Skype: JeffLiebermann * * AE6KS * *831-336-2558
As you shrink the antenna, the aperture also decreases. That is, your
antenna sits in a RF field, and the less area you occupy, the less RF
you get at the antenna terminal.
I will admit I have a hard time getting around the notion of antenna
aperture. However, if you look at the telescope analog, it makes more
sense. Think of gain is magnification, and aperture as the light
gathering ability. For any one setting of magnification, you can have
any amount of light coming out the ocular. Compare binocs with 50mm
objectives versus 20mm objectives. Same magnification, but one puts
out less light. At some point the light output is beneath what is
useful.
In ham land, lower frequency goes further tends to be the rule. But if
we stay away from ionospheric effects, as you go lower, for the same
gain, the antenna is getting larger, hence more aperture.
The wiki is kind of OK regarding aperture. http://en.wikipedia.org/wiki/Antenna_aperture
But I don't like how they tightly correlate gain to aperture. Compare
a pyramidal horn to a dish. If you could deal with the size, a horn
and dish could have the same aperture, but I think the dish would have
to be more directional. I'm not totally sure about them. But if you
look at those amateur SETI setups, many use big *** pyramidal horns
pointing straight up so as to not get too directional.
http://www.setileague.org/photos/wghorn/horn0302.jpg
Now I'd like to have this kind of person as my neighbor. Except I'd
encourage the guy to make a bigger antenna. As you know, the FCC rule
allow any CONUS homeowner to have any number of 1 meter dishes, but
I'm not so sure your right to a big *** horn is a done deal.
On Sun, 04 Sep 2011 13:13:04 -0700, AES <siegman@stanford.edu> wrote:
>Can fractal antennas solve the problem of the Penrose Unilluminable
>Room? [Smiley attached here]
>
><http://demonstrations.wolfram.com/ThePenroseUnilluminableRoom/>
>
>Drag the little omnidirectional light bulb around inside the room.
I had to install the CDF player (100 MBytes) before that would work. I
don't own Mathematica.
I then found that the resultant shadows were really rather large
granular regions, instead of ray tracing the shadows. Still, I can
see how it works and yes, there will always be a shadow region. I
could probably do the same with a labyrinth, but that doesn't count.
I don't see what a fractal could do for the problem. The light source
is defined as a point source and isotropic in the original problem. A
fractal version of the light would look like umm... a point source. No
change there. On the other foot, a fractal room would probably look
like something designed by M.C. Escher and have areas located in other
dimensions or hyperspace. Great science fiction stuff, but not very
useful.
> On Sep 4, 9:48*am, Jeff Liebermann <je...@cruzio.com> wrote:
> > On 4 Sep 2011 17:10:05 +1000, "Dr Who"
> >
> > <dead_letter_off...@hotmail.com> wrote:
> > >> Note: *You're really asking this in the wrong newsgroup. *Look for
> > >> something that discusses TV antenna. *www.avsforums.comwould
> > >> probably be a good place to start.
> > > I will check out the avsforum. *I wasn't aware of that one.
> > > Cheers
> >
> > Oops. *Wrong url:
> > <http://www.avsforum.com>
> > <http://www.avsforum.com/avs-vb/>
> > Antenna discussions usually land in HDTV technical:
> > <http://www.avsforum.com/avs-vb/forumdisplay.php?f=25>
> >
> > I didn't find anything specific on fractal antennas, but did find this
> > 100+ thread on UHF TV construction:
> > <http://www.avsforum.com/avs-vb/showthread.php?t=798265&page=1>
> >
> > I can't resist offering my never humble opinion on fractal antennas.
> > Methinks they only make sense when dealing with a specialized
> > radiation pattern (i.e. cell phone SAR) in a confined area (i.e.
> > inside a cell phone) such as a box. *When there are few limits on the
> > size of the antenna, such as in an outdoor antenna, fractal antennas
> > are not the best solution. *
> >
> > Basically, it's compromise between size, gain, and bandwidth. *You can
> > have any two, at the expense of the third. *For example, the gain of a
> > simple dipole is about 2.1dBi. *If you shrink the length of each
> > element, the gain remains about 2dBi until you get down to about
> > 1/10th wavelenth. *Of course, the tuning also changes, so you have to
> > add inductance (loading coils) to tune it, and a matching circuit to
> > reduce losses. *Both of those drastically reduce the bandwidth of the
> > antenna. *So, you keep your gain, reduce the size, but screw up the
> > bandwidth. *That's not a good idea for a TV antenna, which needs
> > plenty of bandwidth.
> >
> > I suggest you use 4NEC2 to model a simple dipole. *Then change it to a
> > simple fractal dipole per your photo and compare the results. *When
> > you model your completed antenna, compare it with the other similar
> > size HD antennas that I previously posted links. *At some frequency,
> > your fractal antenna will probably have the same gain, be smaller, and
> > have a narrower bandwidth, so that it only works on some partial range
> > of TV channels. *
> >
> > --
> > Jeff Liebermann * * je...@cruzio.com
> > 150 Felker St #D * *http://www.LearnByDestroying.com
> > Santa Cruz CA 95060http://802.11junk.com
> > Skype: JeffLiebermann * * AE6KS * *831-336-2558
>
> As you shrink the antenna, the aperture also decreases. That is, your
> antenna sits in a RF field, and the less area you occupy, the less RF
> you get at the antenna terminal.
>
> I will admit I have a hard time getting around the notion of antenna
> aperture. However, if you look at the telescope analog, it makes more
> sense. Think of gain is magnification, and aperture as the light
> gathering ability. For any one setting of magnification, you can have
> any amount of light coming out the ocular. Compare binocs with 50mm
> objectives versus 20mm objectives. Same magnification, but one puts
> out less light. At some point the light output is beneath what is
> useful.
>
> In ham land, lower frequency goes further tends to be the rule. But if
> we stay away from ionospheric effects, as you go lower, for the same
> gain, the antenna is getting larger, hence more aperture.
>
> The wiki is kind of OK regarding aperture.
> http://en.wikipedia.org/wiki/Antenna_aperture
> But I don't like how they tightly correlate gain to aperture. Compare
> a pyramidal horn to a dish. If you could deal with the size, a horn
> and dish could have the same aperture, but I think the dish would have
> to be more directional. I'm not totally sure about them. But if you
> look at those amateur SETI setups, many use big *** pyramidal horns
> pointing straight up so as to not get too directional.
>
> http://www.setileague.org/photos/wghorn/horn0302.jpg
> Now I'd like to have this kind of person as my neighbor. Except I'd
> encourage the guy to make a bigger antenna. As you know, the FCC rule
> allow any CONUS homeowner to have any number of 1 meter dishes, but
> I'm not so sure your right to a big *** horn is a done deal.
He looks pretty happy with his rig.
I detect a look in his eye that says, "and now for something bigger".
In article <cq7867hrquc91ga7qrgq315v2utccnvjek@4ax.com>,
Jeff Liebermann <jeffl@cruzio.com> wrote:
> I don't see what a fractal could do for the problem. The light source
> is defined as a point source and isotropic in the original problem. A
> fractal version of the light would look like umm... a point source. No
> change there. On the other foot, a fractal room would probably look
> like something designed by M.C. Escher and have areas located in other
> dimensions or hyperspace. Great science fiction stuff, but not very
> usefu
>He looks pretty happy with his rig.
>I detect a look in his eye that says, "and now for something bigger".
SETI horns:
<http://www.setileague.org/photos/wghorn.htm>
I like these old horn photo:
<http://www.nrao.edu/whatisra/hist_ewenpurcell.shtml>
Incidentally, RF horns are not the only types. There's also acoustic
horns, used before the introduction of radar.
<http://www.aqpl43.dsl.pipex.com/MUSEUM/COMMS/ear/ear.htm>
On Mon, 05 Sep 2011 09:53:17 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:
>Incidentally, RF horns are not the only types. There's also acoustic
>horns, used before the introduction of radar.
><http://www.aqpl43.dsl.pipex.com/MUSEUM/COMMS/ear/ear.htm>
Sorry. Old web site. This is the current version with more photos:
<http://www.douglas-self.com/MUSEUM/COMMS/ear/ear.htm>
\
--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
> On Mon, 05 Sep 2011 09:53:17 -0700, Jeff Liebermann <jeffl@cruzio.com>
> wrote:
>
> > Incidentally, RF horns are not the only types. There's also acoustic
> > horns, used before the introduction of radar.
> > <http://www.aqpl43.dsl.pipex.com/MUSEUM/COMMS/ear/ear.htm>
>
> Sorry. Old web site. This is the current version with more photos:
> <http://www.douglas-self.com/MUSEUM/COMMS/ear/ear.htm>
> \
Ha Ha those photos are classic.
Never seen those rigs before.
I hate to think what would happen to the poor operator if a cannon went off nearby or a flock of screeching birds flew through it's path.
On Sep 5, 1:12*pm, Jeff Liebermann <je...@cruzio.com> wrote:
> On Mon, 05 Sep 2011 09:53:17 -0700, Jeff Liebermann <je...@cruzio.com>
> wrote:
>
> >Incidentally, RF horns are not the only types. *There's also acoustic
> >horns, used before the introduction of radar.
> ><http://www.aqpl43.dsl.pipex.com/MUSEUM/COMMS/ear/ear.htm>
>
> Sorry. *Old web site. *This is the current version with more photos:
> <http://www.douglas-self.com/MUSEUM/COMMS/ear/ear.htm>
> \
> --
> Jeff Liebermann * * je...@cruzio.com
> 150 Felker St #D * *http://www.LearnByDestroying.com
> Santa Cruz CA 95060http://802.11junk.com
> Skype: JeffLiebermann * * AE6KS * *831-336-2558
Well I never knew they tried acoustic location. Of course Radar from
MASH was pretty good at hearing distance choppers. Then again, I
suspect he was tipped off by the radio dude in the comm shack.
I've read some of Douglass Self's papers. If anything, he tends to be
an audio foolery debunker. However, I haven't read any of his books.
There is a horn design program floating around the net. Freakin' dos.
I had to run it in dosbox. All that stuff is on a different PC that
I'm backing up at the moment. Horn antennas, being based on aperture,
probably work better in real life construction than say a yagi. It is
tough to cut and space yagi elements to exacting dimensions. But if
you play with the spreadsheet to simulate horn gain, you can screw up
a lot and not change the gain too much. Plus they are very broadband.
Gain analysis:
avsport.org/microcomm/software/horngain.xls
Here again you are gaining aperture and gain at the same time.
These are some superb links to the early history of radio astronomy,
horn antennas, the 21 cm hydrogen line, and early technology in
general; and also starting points for a lot of additional sources.
The third of these links eventually leads to a photo of Harold Ewen as
a grad student, and his hydrogen line apparatus on the fourth floor of
the Lyman Lab at Harvard:
and this in turn brings back a personal memory for me, which I might
as well set down for my own historical notes, if nothing else.
As a very young and naive major in "ESAP" (Engineering Science and
Applied Physics} I took a lab course in electromagnetism that was
taught in a student lab on an upper floor of Lyman sometime between
Autumn 1949 and June 1952, during which I noted this odd vertical horn
on the roof or parapet just outside one of the lab windows. I don't
recall it as being very large, and I think I initially tok it to be
some kind of rainfall collection device.
During these afternoon lab sessions, which must have been held in
either the room this photo was taken in or one very closely adjacent,
my lab partner and I measured things like how the resonant response of
two coupled audio resonant circuits formed from big clunky capacitors
and iron inductors changed and split as you detuned their resonance
frequencies or moved the inductors closer to each other.
During one of these sessions we also noticed this slightly older guy
climbing in and out the window onto the roof and messing with this
horn; and my lab partner asked him what he was doing with it. I quite
clearly recall him saying something very much like, "Oh, I'm watching
hydrogen molecules flip over out in space."
It was only several decades later that I realized that "this guy" must
have been "Doc" Ewen, and the horn must have been part of his hydrogen
line experiment (or at least some immediate predecessor to it).
>These are some superb links to the early history of radio astronomy,
>horn antennas, the 21 cm hydrogen line, and early technology in
>general; and also starting points for a lot of additional sources.
>
>The third of these links eventually leads to a photo of Harold Ewen as
>a grad student, and his hydrogen line apparatus on the fourth floor of
>the Lyman Lab at Harvard:
>
><http://www.nrao.edu/whatisra/images/ewenreceiver.jpg>
>
>and this in turn brings back a personal memory for me, which I might
>as well set down for my own historical notes, if nothing else.
You might also find this interview of interest:
<http://www.aip.org/history/ohilist/6659.html>
>As a very young and naive major in "ESAP" (Engineering Science and
>Applied Physics}
Well, at least it wasn't "natural philosophy". I didn't think you
were that old.
Incidentally, I majored in "Electrical and Electronic Engineering"
which was rather appropriate as neither the administration, faculty,
or students could distinguish between them. I learned the most about
electronics in the calibration lab, repairing the damage inflicted
upon the instruments by the students.
>I took a lab course in electromagnetism that was
>taught in a student lab on an upper floor of Lyman sometime between
>Autumn 1949 and June 1952, during which I noted this odd vertical horn
>on the roof or parapet just outside one of the lab windows. I don't
>recall it as being very large, and I think I initially tok it to be
>some kind of rainfall collection device.
I read somewhere that the unofficial description was a "coal hopper"
or something similar.
<http://www.setileague.org/photos/wghorn/ewenhorn.jpg>
I built a similar size device in jr high skool out of plywood and
aluminum foil. The intended purpose was to measure the RF level
produced by the sun at about 1.4GHz. It should have been a
no-brainer, but we kept blowing up 1N21 mixer diodes with ESD. Years
later, I calculated and later measured the front end noise figure of
the excessively wide-band radar IF receiver I was using for this test
at about 3000K. Oops. It was also lots of fun trying to track the
sun with this monstrosity. This was somewhat after Sputnik was
launched, and our efforts received a page two photo and story in the
papers as "young students advancing science". I'll see if I can find
some old photos.
It's still around in different forms. I once worked on an accoustic
direction finder for the blind. There's also the rooftop mounted
gunshot direction finder system (which works on different principles).
I used to play with a dish antenna and microphone, which was great for
listening to the neighbors argue across the road.
>I've read some of Douglass Self's papers. If anything, he tends to be
>an audio foolery debunker. However, I haven't read any of his books.
I like his collection of weird railroad locomotives.
>There is a horn design program floating around the net. Freakin' dos.
>I had to run it in dosbox.
These are much better, although not perfect.
<http://users.skynet.be/chricat/horn/horn-javascript.html>
<http://www.flann.com/imagenav/calculator.xls>
<http://www.qsl.net/n1bwt/chap2.pdf> <-- worth reading.
I have some others that are a bit more exotic if you want. Also some
nonograms out of various antenna design books.
>Horn antennas, being based on aperture,
>probably work better in real life construction than say a yagi.
That's an understatement. Methinks yagi antennas doth suck at
microwave frequencies. Except for the size, horns are probably the
best compromise of gain, bandwidth, and beamwidth.
>It is
>tough to cut and space yagi elements to exacting dimensions. But if
>you play with the spreadsheet to simulate horn gain, you can screw up
>a lot and not change the gain too much. Plus they are very broadband.
Yep. Think of the horn as a transformer between the waveguide input
impedance (same an the probe impedance or about 50 ohms), and the
impedance of free space (about 377 ohms).
The problem with the periscope antenna is that the beamwidth the feed
(dish) antenna has to be small enough to illuminate the reflector, or
most of the RF goes away behind the reflector. It has to be much
narrower than the -3dB beamwidth because that only guarantees that
half your power will hit the reflector. There are also reflection
losses (same as a dish) involved. It might work in the near field, or
with large billboard size reflectors, but not for small antennas.
Incidentally, by order of the FCC, that style of antenna is illegal
for commercial use on licensed microwave frequencies.
>
> >Gain analysis:
> >avsport.org/microcomm/software/horngain.xls
>
> Nice, but that spreadsheet only covers the water hole frequencies
> (1.4GHz) and is only useful for SETI.
>
> --
> Jeff Liebermann * * je...@cruzio.com
> 150 Felker St #D * *http://www.LearnByDestroying.com
> Santa Cruz CA 95060http://802.11junk.com
> Skype: JeffLiebermann * * AE6KS * *831-336-2558
There are just so many things engineered where the tolerances totally
wipe out the complexity.
The spreadsheet frequency range is a function of the waveguide
dimension, so as you scale the waveguide dimension downward, the
frequency range goes up. The dimensions are based on slant length,
while the horn design software is based on length of the horn along
the axis. Easily compensated with a bit of trig.
Most of the time you just see feed horns for dishes, but I've seen X
band horns used at FAA sites. I think for a link between sites. Also
police radar uses horns. Probably aircraft radar too, but I've never
seen the gear.
>Probably aircraft radar too, but I've never
>seen the gear.
Nope. Up to about 1975, it was a movable dish in the nose.
Afterwards, it's mostly electrically steerable phased arrays (some of
which can be tilted downward for terrain following).
<http://militaryforces.ru/firearms-1-11.html>
In article
<a2e99e81-4eae-4951-a644-8d5f920cf914@en1g2000vbb.googlegroups.com>,
"miso@sushi.com" <miso@sushi.com> wrote:
>
> Most of the time you just see feed horns for dishes, but I've seen X
> band horns used at FAA sites. I think for a link between sites. Also
> police radar uses horns. Probably aircraft radar too, but I've never
> seen the gear.
>
Is the "sugar scoop antenna" considered to be a horn? -- because there
certainly once were tons of those around.
On Wed, 07 Sep 2011 09:22:04 -0700, AES <siegman@stanford.edu> wrote:
>Is the "sugar scoop antenna" considered to be a horn? -- because there
>certainly once were tons of those around.
Yep. It's a horn with an added reflector at the top:
<http://long-lines.net/tech-equip/radio/BSP402421100/p03.html>
They would work from 4-12GHz (with different waveguides attached).
43dBi gain at 6GHz with about 1 degree beamwidth. Zero side lobes,
which was necessary to prevent co-channel interference. I worked on a
few of those in my checkered past. Aiming them was difficult. Dealing
with temperature drift was tricky. Dealing with the moisture
condensation problem was worse.
Many years ago, I had to deal with a 2.4GHz interference problem,
which turned out to be a plastic injection molding machine pre-heater.
It used a horn antenna feed by a microwave oven magnetron to evaporate
out any water in the feedstock before molding. They're still around,
but were moved to a different frequency a few years ago.
Also, there are moisture meters that use horns:
<http://www.kdctech.com/index.php?p=2_1>
An angled horn is used because it covers a wide area.
On Sep 7, 9:45*am, Jeff Liebermann <je...@cruzio.com> wrote:
> On Wed, 07 Sep 2011 09:22:04 -0700, AES <sieg...@stanford.edu> wrote:
> >Is the "sugar scoop antenna" considered to be a horn? -- because there
> >certainly once were tons of those around.
>
> Yep. *It's a horn with an added reflector at the top:
> <http://long-lines.net/tech-equip/radio/BSP402421100/p03.html>
I've seen lots of "sugar scoop" antennas in the boonies, but not
powered. I've been told the liability of keeping any antenna site
"legal" (as in strobe lights) far outweighs the cost of dismantlement
of the antenna, but it seems these sugar scoops don't follow that
rule. Now to be fair, many of these sites don't have strobes. The
telcos seem to favor serviceability of their sites over say being on
the highest peak. [Note how the telcos like to use microflects.] But
a few I've found strobes, but otherwise in use.
Come to think of it, I recall seeing those sugar scoops on a building.
Maybe in Stockton.
There is an antenna site in Hayward off of Santos Rd. that was an old
fly swatter site. Roughly N 37.65950 W 121.93320 Obviously re-purposed
into a comm site.
Unfortunately the info here is incorrect: here's is the fallacy--you are assuming the antenna works at one narrow passband.
When you shrink a dipole and load it you get a lossy small antenna that is still narrow band. It has a low radiation resistance when less than 1/12 of a wave--roughly--in size.
When you do this on optimum fractal designs, you get two current maxima, that constructively interfere to increase the gain stlightly and also increase the radiation resistance. Also, unlike the shrunken dipole, you get LOTS of very closely spaced resonances ABOVE the 'fundamental' that are NOT harmonics--there is no passbands making a picket fence. Hence the antenna can have TAILORED CLOSE SPACED passbands and still be electrically small. Obviously these higher frequency passbands get 'bigger' electrically as you go up in frequency, so issues of loss are moot. In addition, these multi-multi resonances can be MERGED to produce a much wider lowest passband.
My feeling is that no one has been trained in analog filter theory to have adjacent and merging passbands...so they skip this understanding.
Fractal antenna orientation 
Linear Mode
