bowtie panel antenna...

S

server

Guest
On Fri, 7 Jan 2022 18:05:49 -0800 (PST), Phil Allison
<pallison49@gmail.com> wrote:

Jasen Bullshits wrote:

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

I think signals from multiple dipoles can be combined without altering
the far-field pattern. I can think of several ways to do that.

You\'re mistaken. if you build a phased-array antenna you get increased
directionality (so a tighter far field pattern) and a stronger signal.

Gain and directionality are inextricably linked for passive antannnae.


** ROTFL - insects have \"antennae\" !!!

Worse than that idiocy, is that everyone but me has arrogantly ignored the OP\'s context.
Colossal pedant Ralph Mowery kicked it off and all the sheep here followed.

For fixed location antennas, only the *horizontal * pattern ever matters and is the only one speced.
So \"directionality\" = horizontal pattern.

FFS when are you going to learn that queries posted here are NOT fucking exam questions.


( except when some wanker sneakily posts one they need to answer)



..... Phil

If some idea violates a basic conservation principle, it can be
instantly rejected... but actually shouldn\'t be too soon.

Most people are hostile to new ideas. They live at the bottom of the
pay scale.



--

I yam what I yam - Popeye
 
J

John Walliker

Guest
On Saturday, 8 January 2022 at 16:24:50 UTC, jla...@highlandsniptechnology.com wrote:

It\'s easy in the plane of a bunch of dipoles: for horizontal dipoles,
stack them verticaly on a pole and connect in parallel with equal
length feeders. The horizontal far-field pattern doesn\'t change. I
think Chain Home did that.

There may be a way to fix the vertical axis, but in a terrestrial
situation one doesn\'t usually care about that.

One widely used application where one does care about it a lot is
for mobile phone base stations.

John
 
S

server

Guest
On Sat, 8 Jan 2022 09:07:31 -0800 (PST), John Walliker
<jrwalliker@gmail.com> wrote:

On Saturday, 8 January 2022 at 16:24:50 UTC, jla...@highlandsniptechnology.com wrote:

It\'s easy in the plane of a bunch of dipoles: for horizontal dipoles,
stack them verticaly on a pole and connect in parallel with equal
length feeders. The horizontal far-field pattern doesn\'t change. I
think Chain Home did that.

There may be a way to fix the vertical axis, but in a terrestrial
situation one doesn\'t usually care about that.

One widely used application where one does care about it a lot is
for mobile phone base stations.

John

Once you have a lot of antennas and a lot of DSP, most any antenna
pattern is possible.

If one digitizes the signals from an array of dipoles, it should be
possible to synthesize any pattern.



--

I yam what I yam - Popeye
 
P

Phil Hobbs

Guest
John Walliker wrote:
On Saturday, 8 January 2022 at 02:05:53 UTC, palli...@gmail.com wrote:


For fixed location antennas, only the *horizontal * pattern ever matters and is the only one speced.
So \"directionality\" = horizontal pattern.

Almost every antenna data sheet I have looked at gives horizontal and vertical radiation
patterns. For TV antennas - which are relevant to the OP\'s question - both are needed
because the manufacturer will not know whether the transmissions to be received
are horizontally or vertically polarised and therefore will not know which orientation
of the antenna is horizontal when installed. Around here, for example, there are two
TV transmitters within range and one is horizontally polarised while the other is
vertically polarised.
Mobile phone base station antennas definitely have vertical as well as horizontal
radiation patterns specified. Both are important.

John

And for HF DX, you care a lot about low-angle radiation because that\'s
what bounces off the ionosphere most readily.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
K

ke...@kjwdesigns.com

Guest
On Saturday, 8 January 2022 at 09:24:38 UTC-8, jla...@highlandsniptechnology.com wrote:
....
Once you have a lot of antennas and a lot of DSP, most any antenna
pattern is possible.

If one digitizes the signals from an array of dipoles, it should be
possible to synthesize any pattern.
....

And that is what is commonly done in cellular base stations, radar and astronomy.

There are still limits set by the various propagation rules regarding beam width and gain - there is no free lunch.

The system I an involved with currently has 192 virtual antenna elements and requires about 4 million FFT\'s a second for the processing, all with a power budget of a few Watts. The one I worked many years ago took about 100W to do about 150 FFTs/sec.

kw
 
J

John Walliker

Guest
On Saturday, 8 January 2022 at 19:11:37 UTC, ke...@kjwdesigns.com wrote:
On Saturday, 8 January 2022 at 09:24:38 UTC-8, jla...@highlandsniptechnology.com wrote:
...
Once you have a lot of antennas and a lot of DSP, most any antenna
pattern is possible.

If one digitizes the signals from an array of dipoles, it should be
possible to synthesize any pattern.
...

And that is what is commonly done in cellular base stations, radar and astronomy.

There are still limits set by the various propagation rules regarding beam width and gain - there is no free lunch.

The system I an involved with currently has 192 virtual antenna elements and requires about 4 million FFT\'s a second for the processing, all with a power budget of a few Watts. The one I worked many years ago took about 100W to do about 150 FFTs/sec.

kw

Another parameter which nobody has mentioned so far is bandwidth.
Trying to get an array of radiators to form a desired beam shape at
one frequency involves some unavoidable trade-offs, but doing so over a wide
bandwidth gets even harder.

John
 
P

Phil Allison

Guest
John Walliker wrote:
=================
Wot a wanking IDIOT
--------------------------------
For fixed location antennas, only the *horizontal * pattern ever matters and is the only one speced.
So \"directionality\" = horizontal pattern.

Almost every antenna data sheet I have looked at gives horizontal and vertical radiation
patterns.

** Fuck knows what shit data YOU look at.

Here are some examples of the data sheets I look at for a few different antenna types:
amphenolprocom.com/media/pdfdocs/s-m4-490.en-GB.pdf
amphenolprocom.com/media/pdfdocs/lpu-r.en-GB.pdf
amphenolprocom.com/media/pdfdocs/7042440.en-GB.pdf
amphenolprocom.com/media/pdfdocs/7050108.en-GB.pdf

** Irrelevant crap.

When intended for broadcast TV reception, it is just as I stated.

The second link above is for a TV antenna.

** No it isn\'t.

As it happens, they are almost identical, but that does not apply to
some of the other types.

** Yawnnnnn....

For TV antennas - which are relevant to the OP\'s question - both are needed
because the manufacturer will not know whether the transmissions to be received
are horizontally or vertically polarised .....

** Total crap.

In the places cases where TV signals are vertically polarised, the exact same antennas are mounted at 90 degrees.
That is exactly what I said.

** Bullshit you did.

Polarisation is a total red herring here.


Many TV and FM transmitters use circular polarisation that work fine, both ways.
FM yes, TV seldom.

** Polarisation is a total red herring here.

Crawl back under your rock.
I\'ll be happy to.

** Fuck off - pedant.
 
C

Clifford Heath

Guest
On 9/1/22 6:11 am, ke...@kjwdesigns.com wrote:
On Saturday, 8 January 2022 at 09:24:38 UTC-8, jla...@highlandsniptechnology.com wrote:
...
Once you have a lot of antennas and a lot of DSP, most any antenna
pattern is possible.

If one digitizes the signals from an array of dipoles, it should be
possible to synthesize any pattern.
...

And that is what is commonly done in cellular base stations, radar and astronomy.

There are still limits set by the various propagation rules regarding beam width and gain - there is no free lunch.

The system I an involved with currently has 192 virtual antenna elements and requires about 4 million FFT\'s a second for the processing, all with a power budget of a few Watts. The one I worked many years ago took about 100W to do about 150 FFTs/sec.

How big are the FFTs? What devices are they implemented in?

I\'m curious for SDR use. The Hermes project has what they call Direct
Fourier Conversion DFC where they interface 120MSPS 16-bit ADCs via an
FPGA to a PCI-e port and inject data almost straight into a GPU, that
does 1-million point FFTs on it. They can then extract up to 80 channels
from the frequency data and iFFT them back to time domain to demodulate
the audio. Useful to have that many channels in a WebSDR.

But I\'m interested to know how much FPGA resource (or other, DSP chips
maybe?) it would take to do the same without a honking computer_ &
GPU... How would you tackle this problem in hardware?

Clifford Heath
 
J

Joe Gwinn

Guest
On Sat, 8 Jan 2022 12:28:46 -0800 (PST), John Walliker
<jrwalliker@gmail.com> wrote:

On Saturday, 8 January 2022 at 19:11:37 UTC, ke...@kjwdesigns.com wrote:
On Saturday, 8 January 2022 at 09:24:38 UTC-8, jla...@highlandsniptechnology.com wrote:
...
Once you have a lot of antennas and a lot of DSP, most any antenna
pattern is possible.

If one digitizes the signals from an array of dipoles, it should be
possible to synthesize any pattern.
...

And that is what is commonly done in cellular base stations, radar and astronomy.

There are still limits set by the various propagation rules regarding beam width and gain - there is no free lunch.

The system I an involved with currently has 192 virtual antenna elements and requires about 4 million FFT\'s a second for the processing, all with a power budget of a few Watts. The one I worked many years ago took about 100W to do about 150 FFTs/sec.

kw

Another parameter which nobody has mentioned so far is bandwidth.
Trying to get an array of radiators to form a desired beam shape at
one frequency involves some unavoidable trade-offs, but doing so over a wide
bandwidth gets even harder.

It\'s a solved problem. Here is the classic on the subject.

..<https://www.amazon.com/High-Resolution-Radar-Artech-Library-Hardcover/dp/0890067279>

Wehner, High-Resolution Radar, 2nd edition, Artech House 1994.

Joe Gwinn
 
J

John S

Guest
On 1/6/2022 1:52 PM, Dave Platt wrote:
In article <d2255b5c-a796-4ed2-bafb-800ed2bebe04n@googlegroups.com>,
Sid 03 <sidwelle@gmail.com> wrote:

I see a lot of articles where combiners are mentioned, but I find it hard to find good information on the subject.
From what I have read if the two antennas are not combined correctly the signal received from one antenna is simply
radiated out by the 2nd antenna.

Some power is _always_ radiated out by the antenna. In fact, even
with a single antenna, at least 50% of the power which reaches the
antenna from the transmitter, is re-radiated by the antenna. If the
antenna system is mismatched to the feedline and load, even more of
the power will reflect from the mismatch point and re-radiated.

I said the same thing but Phil H. said that is not necessarily so.



What\'s important, in the case of a \"stacked\" antenna pair, is that the
signals from the two antennas reach the combining point in the proper
phase. This helps minimize the mismatch and thus the amount of \"lost\"
power.

The worst case is if the two signals reach the combiner 180 degrees
out of phase, and cancel at the combining point. You\'ll get no power
into your TV or tuner, and everything will be re-radiated (or lost as
heat into the cables\' resistance).

Some splitters are advertised as combiners and other websites caution against using splitters/combiners are combiners.
Can I get some clarification on the subject ? maybe some links to info on the subject, where to buy one, how to build one ?

https://www.americanradiohistory.com/Archive-All-Audio/Audio-Magazine.htm
has an excellent archive of PDFs of the late, lamented Audio Magazine.
I subscribed to this quite steadily from my college years in the
1970s until they folded/merged (into High Fidelity Magainze, I think).

What I found, looking back, is a very nice five-part series of
articles on FM antennas, feedlines, preamplifiers, and distribution
systems, by M.J. Salvati, in the January - April issues in 1978 and
the January issue in 1979.

This was followed up by the article I had remembered reading when it
first appeared - \"Kill FM interference with two antennas\", by Richard
Modafferi, in the January 1980 issue.

Although the specific equipment models described in these six articles
are surely all obsolete by now, the information and knowledge is not -
I gave them a quick skim and they\'re a great read.
 
K

ke...@kjwdesigns.com

Guest
On Saturday, 8 January 2022 at 15:46:10 UTC-8, Clifford Heath wrote:
....
The system I an involved with currently has 192 virtual antenna elements and requires about 4 million FFT\'s a second for the processing, all with a power budget of a few Watts. The one I worked many years ago took about 100W to do about 150 FFTs/sec.
How big are the FFTs? What devices are they implemented in?

A mixture of 128, 256 and 512 point complex FFTs. Each axis has different number of samples.

NXP, TI and Infineon have DSPs with FFT accelerators and other special purpose accelerators for radar processing.
....
But I\'m interested to know how much FPGA resource (or other, DSP chips
maybe?) it would take to do the same without a honking computer_ &
GPU... How would you tackle this problem in hardware?

The FPGA solution we did first required a $30,000 FPGA from Xilinx, then we used a $3,000 Altera/Intel Stratix 10.
The special purpose DSPs with accelerators take much less power (and are orders of magnitude cheaper). Even a \"honking computer and GPU\" would be hard pushed to provide the performance needed.

kw
 
S

server

Guest
John Larkin <jlarkin@highland_atwork_technology.com> wrote in
news:e1metglue8alf2jalkt3nm3f7at3lmb3kp@4ax.com:

On Thu, 6 Jan 2022 14:13:52 -0500, Ralph Mowery
rmowery42@charter.net> wrote:

In article <om9etg5bfjcn9ngm3piu4o1q1324tlanj8@4ax.com>,
jlarkin@highlandsniptechnology.com says...

If a dipole gathers a milliwatt, another dipole some modest
distance away will gather another milliwatt. Seems to me that
the powers can be added without altering the far-field patterns.





That is true about gain if the spacing and impedance matching are
correct, but the pattern still changes. If the dipoles are too
close or too far apart the phasing is not correct and the signals
cancel. Instead of gain, the pattern breaks up and you may get no
signal at all or a very small signal. They still modify the
pattern in some way.

If and only if the spacing is correct two dipoles will double the
signal, not counting on a small loss of interconnecting cables .
To double that you need 4 dipoles for 8, to double that you need
16 dipoles all phased correctly. With each set of dipoles the
beam will narrow so you have to aim the antenna closer to the
station.

I think signals from multiple dipoles can be combined without
altering the far-field pattern. I can think of several ways to do
that.

Ever herd of diversity. Far better to array 8 antennas and then
let some hardware pick the best signal. Not the strongest signal,
the best signal. That was analog NTSC broadcast days.

If the guy is in the US he is talking about digital signals on the
old UHF TV band, now referred to in the US as Broadcast HDTV.

In getting the signal most HDTV recievers usually either get ALL of
the signal, or simply mute that channel when not able to gather the
perfect packet data. There is no snow and there is no ghosting.

Anyway... diversity receivers never added channels because
strength was not the issue. It was about quality. So around a race
track they would have diversity recievers and antenna arrays to get
the best audio signals from the drivers as they circled the track.
The hardware did not add channels it switched to the best channel.
It is similar to what cell service does as you leave one cell and
enter another.

There are plenty of applications.
 
P

Phil Hobbs

Guest
John S wrote:
On 1/6/2022 1:52 PM, Dave Platt wrote:
In article <d2255b5c-a796-4ed2-bafb-800ed2bebe04n@googlegroups.com>,
Sid 03  <sidwelle@gmail.com> wrote:

I see a lot of articles where combiners are mentioned, but I find it
hard to find good information on the subject.
From what I have read if the two antennas are not combined correctly
the signal received from one antenna is simply
radiated out by the 2nd antenna.

Some power is _always_ radiated out by the antenna.  In fact, even
with a single antenna, at least 50% of the power which reaches the
antenna from the transmitter, is re-radiated by the antenna.  If the
antenna system is mismatched to the feedline and load, even more of
the power will reflect from the mismatch point and re-radiated.

I said the same thing but Phil H. said that is not necessarily so.

That\'s a common misconception based AFAIK on a statement by Kraus
concerning wire antennas specifically. There\'s a lot of life after wire
antennas. ;)

If half the power is reflected, the antenna has a VSWR (on the business
end) of no better than

1 + 0.707
VSWR = ---------- = 5.8 : 1.
1 - 0.707

Your average HP waveguide-to-coax transition is a 1/4 wave antenna stuck
through the H face, 1/4 wavelength from a waveguide short. Its
efficiency is way over 90%.

In free space, there\'s more than one mode to worry about, of course, so
things generally aren\'t that good, but you can make adiabatic waveguide
horns that have VSWRs near 1:1. Here\'s a small one that\'s specified at
1:1.15:

https://www.fairviewmicrowave.com/images/productPDF/FMWAN1032.pdf

By reciprocity, the coupling is the same in both directions, considering
only the antenna mode. Of course it\'ll reflect a lot more if you come
in with an orthogonal mode--ideally 100%.

As I pointed out way upthread, a single pair of wires can interrogate
only one optical mode, corresponding to an etendue of lambda**2/2.

That\'s a super useful fact when considering how various detection and
transmission schemes scale with wavelength. If you want the RF to come
out of one pair of wires, the projected solid angle Omega\' subtended by
the antenna pattern has to obey

Omega\' <= lambda**2 / (2 * collection area).

By building sufficiently bad antennas, you might think you can
interrogate a wider Omega\', but that\'s illusory--it just means that the
matched mode is more complicated, so that it doesn\'t quite match the
incoming field anymore. (You can derive the etendue limit from
thermodynamics, so arguing otherwise eventually amounts to asserting
that one can make a perpetual motion machine.)

Incoherent combination techniques, e.g. a photodiode or (at RF) N
antenna/receiver sets with their outputs summed, can interrogate many
modes at once, at the price of squaring the required dynamic range.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
R

Rich S

Guest
Nice, Jan.
Finding a hotspot can be necessary.
As someone who lives a few km away from
the actual objects shown in your
wallpaper (source of many
ATSC signals), even my TV has trouble
now & then, with a simple antenna
at the window (...is not on a high floor)
cheers, RS
 
J

Jan Panteltje

Guest
On a sunny day (Sat, 15 Jan 2022 15:41:51 -0800 (PST)) it happened Rich S
<richsulinengineer@gmail.com> wrote in
<a95fe49c-ef57-4cec-84aa-cf2311f1faa0n@googlegroups.com>:

Nice, Jan.
Finding a hotspot can be necessary.
As someone who lives a few km away from
the actual objects shown in your
wallpaper (source of many
ATSC signals), even my TV has trouble
now & then, with a simple antenna
at the window (...is not on a high floor)
cheers, RS

Yes, terrestrial,
but I am so glad I have a satellite dish...
Reception here from all over the world, Germany, UK, Russia, China, even Cuba is 100% !
Only problem I ever had was when a big thunder cloud passed between satellite and dish.
And now we have interference from the new local radar station..
but most channels are transmitted both in normal and HD resolution
and somehow HD works anyways.
There is also the issue of that national TV networks only show you what they want you to know / think,
while the world via satellite shows all sides of the political / economic spectrum.
I have a choice of more than 900 free to view satellite channels with my movable dish.

As to ATSC it was developed after DVB-T in Europe to deal with multi path reflections IIRC:
https://en.wikipedia.org/wiki/ATSC_standards

We went completely digital a bit earlier in 2006 with DVB-T:
https://en.wikipedia.org/wiki/DVB-T
These days we have DVB-T2 here.

Satellite uses DVB-S and DVB-S2
S2 is close to the Shannon limit:
https://en.wikipedia.org/wiki/DVB-S2
 

Welcome to EDABoard.com

Sponsor

Top