bowtie panel antenna

[Sid 03]

I want to setup a bowtie panel antenna to receive UHF Terrestrial TV transmissions in my area. I live between two stations approximately 180 degrees from each other.
Is it practical to build and setup a Bow-tie Panel Antenna and leave off the reflector to cause the antenna to receive signals front and back ?
How much does the reflector add to the gain ? -or- is the reflector primarily there to prevent the antenna from receiving signal reflected off large buildings/mountains from being received by the back of the antenna ?

Any help is appreciated.
Thanks

[Ralph Mowery]

In article <6e98dc29-c716-4ac4...@googlegroups.com>,
sidw...@gmail.com says...

The reflector does several things. It gives gain to the antenna, it
sets the impedance of the antenna, and in a minor sense it prevents the
signals off the back from being received very well.

Antenna gain can only be had by modifying the antenna pattern. Just
like a light bulb with a reflector. The more gain , the narror the
beam. Think of a light bulb , it sends light out in almost all
directions. PUt a reflector and it sends the light out in mostly one
direction and is much brighter. It also works similar in reverse when
receiving light or radio/TV waves.

YOu can try with out a reflector and see if you get the signal you need
for the stations.

[jla...@highlandsniptechnology.com]

On Thu, 6 Jan 2022 11:07:59 -0500, Ralph Mowery
<rmow...@charter.net> wrote:

>In article <6e98dc29-c716-4ac4...@googlegroups.com>,
>sidw...@gmail.com says...
>>
>> I want to setup a bowtie panel antenna to receive UHF Terrestrial TV transmissions in my area. I live between two stations approximately 180 degrees from each other.
>> Is it practical to build and setup a Bow-tie Panel Antenna and leave off the reflector to cause the antenna to receive signals front and back ?
>> How much does the reflector add to the gain ? -or- is the reflector primarily there to prevent the antenna from receiving signal reflected off large buildings/mountains from being received by the back of the antenna ?
>>
>> Any help is appreciated.
>> Thanks
>>
>>
>
>The reflector does several things. It gives gain to the antenna, it
>sets the impedance of the antenna, and in a minor sense it prevents the
>signals off the back from being received very well.
>
>Antenna gain can only be had by modifying the antenna pattern.

Or by making the antenna bigger, to intercept more power.



--

I yam what I yam - Popeye

[Jan Panteltje]

On a sunny day (Thu, 6 Jan 2022 07:47:44 -0800 (PST)) it happened Sid 03
<sidw...@gmail.com> wrote in
<6e98dc29-c716-4ac4...@googlegroups.com>:

Antennas and RF fields are a bit of a mystical thing for the not initiated.
I have a big nice bowtie (was once for TV) and got no usable signal at all
in this location for DVB-T.

Using a cheap Chinese DVB-T2 reeiver from ebay.
So now the magic
Took a piece of 75 Ohm coax made the magic move and removed something like 12 cm from the shield, then moved it around along the wall
INSIDE and hit a point where reception was error free, bended it a bit and taped it to the wall with double sided tape.
http://panteltje.com/pub/DVB-T2_antenna_IXIMG_0757.JPG
It is probably the iron of the bridge,
And no, the transmitter is miles away.
The magical hotspot is well guarded as you can see,

[Ralph Mowery]

In article <v56etgd4fv65afprq...@4ax.com>,
jla...@highlandsniptechnology.com says...

>
> >Antenna gain can only be had by modifying the antenna pattern.
>
> Or by making the antenna bigger, to intercept more power.
>
>
>

Bigger antennas only work better because they modify the pattern.

Big does not get you anyting unless the antenna is designed to use the
larger size.

[Don]

Ralph Mowery wrote:

<snip>

> Bigger antennas only work better because they modify the pattern.
>
> Big does not get you anyting unless the antenna is designed to use the
> larger size.

Notwithstanding big business' belief in too-big-too-fail, bigger isn't
better for a microwave bowtie antenna etched on FR-4.

In regards to the OP's question, instead of reflector removal, perhaps,
if your budget permits, you can put two reflective bowties back-to-back?

https://www.ebay.com/itm/123382428258?epid=17026547448

Danke,

--
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.

[jla...@highlandsniptechnology.com]

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.

[Wond]

UHF bowties are easily made; its harder to make the mounts.
Suggest two bowties, one on each side, with two feedlines or
a two-signal combiner.

[Arie de Muijnck]

On 2022-01-06 17:46, Jan Panteltje wrote:

> Antennas and RF fields are a bit of a mystical thing for the not initiated.
> I have a big nice bowtie (was once for TV) and got no usable signal at all
> in this location for DVB-T.
>
> Using a cheap Chinese DVB-T2 reeiver from ebay.
> So now the magic
> Took a piece of 75 Ohm coax made the magic move and removed something like 12 cm from the shield, then moved it around along the wall
> INSIDE and hit a point where reception was error free, bended it a bit and taped it to the wall with double sided tape.
> http://panteltje.com/pub/DVB-T2_antenna_IXIMG_0757.JPG
> It is probably the iron of the bridge,
> And no, the transmitter is miles away.
> The magical hotspot is well guarded as you can see,
>
>

Your action reminds me of Mr Bean's TV aerial:
<https://www.youtube.com/watch?v=Sm3_qEMTdc4&ab_channel=MrBean>


Arie

[Ralph Mowery]

In article <om9etg5bfjcn9ngm3...@4ax.com>,
jla...@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.

[Sid 03]

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 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 ?
Thanks

[Dave Platt]

In article <d2255b5c-a796-4ed2...@googlegroups.com>,

Sid 03 <sidw...@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.

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.

[John Larkin]

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

--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon

[Ralph Mowery]

In article <e1metglue8alf2jal...@4ax.com>,
jlarkin@highland_atwork_technology.com says...

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

Then you have exceeded the laws of antennas.


Care to tell a way to do that in any prctical antenna ?

[Phil Allison]

jla...@highlandsniptechnology.com wrote:
===================================

>
> >
> >Antenna gain can only be had by modifying the antenna pattern.
>
> Or by making the antenna bigger, to intercept more power.
>

** Both remarks are ambiguous as written.

The first can be reworded as
" for a given ( VHF / UHF ) antenna, increased forward gain = more directivity".

The second can be restated as :
" an antenna array has more forward gain than a single unit "

Simples.

...... Phil

[Joe Gwinn]

It's widely done in radar systems. It's called spoiling the beam.
This is typically done to the transmit beam, so multiple overlapping
receive beams can be used per TX pulse.

All it takes is some random detuning of the drive phases at the
various elements.

Joe Gwinn

[Ralph Mowery]

In article <d2setgldhnfr1v7h3...@4ax.com>,
joeg...@comcast.net says...

> > I think signals from multiple dipoles can be combined without altering
> >> the far-field pattern. I can think of several ways to do that.
> >>
> >>
> >>
> >
> >Then you have exceeded the laws of antennas.
> >
> >
> >Care to tell a way to do that in any prctical antenna ?
>
> It's widely done in radar systems. It's called spoiling the beam.
> This is typically done to the transmit beam, so multiple overlapping
> receive beams can be used per TX pulse.
>
> All it takes is some random detuning of the drive phases at the
> various elements.
>
> Joe Gwinn
>
>

The antenna uses around 1000 to 2000 dipoles. The beam width is about 1
or 2 degrees. The antennas are phased electrically so you sweep that
small segment over a larger area. It replaces the mechanical need to
rotate the whole antenna.

So with the beam width being so small instead of 180 degrees of a dipole
you have modified the pattern of a single dipole.

[Phil Allison]

John Larkin 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.
>

** Yep - one type is called a "collinear " antenna.

https://en.wikipedia.org/wiki/Collinear_antenna_array

The one caveat is the "pattern" is only being considered in the horizontal plane.
Standard practice for any broadcast antenna set up.


..... Phil

[Ralph Mowery]

In article <63ea7b65-0507-4902...@googlegroups.com>,
palli...@gmail.com says...

>
> > I think signals from multiple dipoles can be combined without altering
> > the far-field pattern. I can think of several ways to do that.
> >
>
> ** Yep - one type is called a "collinear " antenna.
>
> https://en.wikipedia.org/wiki/Collinear_antenna_array
>
> The one caveat is the "pattern" is only being considered in the horizontal plane.
> Standard practice for any broadcast antenna set up.
>
>
>

The collinear modifies the horizontal patern by taking some signal from
the vertical. Think of a baloon. You press it from the top and bottom
and the horizontal gets larger. If the antenna is high enough stations
close in will often loose most of the signal as the pattern shoots over
the top of lower stations. Been there and done that .

Pattern still modified for gain.

[John Larkin]

On Thu, 6 Jan 2022 16:42:26 -0500, Ralph Mowery
<rmow...@charter.net> wrote:

>In article <e1metglue8alf2jal...@4ax.com>,
>jlarkin@highland_atwork_technology.com says...
>>
>> I think signals from multiple dipoles can be combined without altering
>> the far-field pattern. I can think of several ways to do that.
>>
>>
>>
>
>Then you have exceeded the laws of antennas.

Laws of antennas? Or folklore?

>
>
>Care to tell a way to do that in any prctical antenna ?

One obvious way: run a feeder from N antennas to a central point.
There, run each signal into a receiver. Combine the receiver outputs.
The RF phase information is lost.

There's probably a passive way to combine an array of dipoles but keep
the same far-field pattern.

[whit3rd]

On Thursday, January 6, 2022 at 7:47:48 AM UTC-8, sidw...@gmail.com wrote:
> I want to setup a bowtie panel antenna to receive UHF Terrestrial TV transmissions in my area. I live between two stations approximately 180 degrees from each other.
> Is it practical to build and setup a Bow-tie Panel Antenna and leave off the reflector to cause the antenna to receive signals front and back ?

Sure; a dipole antenna has a figure-eight reception pattern, you'd be aiming a lobe at each of the
sources.

> How much does the reflector add to the gain ?

Usually, a reflector removes one lobe, replacing it with a stronger 'other' lobe (but
this is all frequency-dependent, the reflector spacing can be important). That'd be 3 dB gain.
There's usually a broad range of acceptable sensitivity for an antenna, the 'extra gain'' isn't crucial.

[Ralph Mowery]

In article <63ea7b65-0507-4902...@googlegroups.com>,
palli...@gmail.com says...
>

> > I think signals from multiple dipoles can be combined without altering
> > the far-field pattern. I can think of several ways to do that.
> >
>
> ** Yep - one type is called a "collinear " antenna.
>
> https://en.wikipedia.org/wiki/Collinear_antenna_array
>
> The one caveat is the "pattern" is only being considered in the horizontal plane.
> Standard practice for any broadcast antenna set up.
>
>
>
>

https://www.everythingrf.com/community/what-is-a-collinear-antenna

The horizontal pattern stays the same, but the vertical pattern changes.

If the antenna is somethat higher or lower than another antenna even
the horizontal pattern will seem to change as one antenna over shoots
the other.

[Phil Allison]

Ralph Mowery 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.
> > >
> >
> > ** Yep - one type is called a "collinear " antenna.
> >
> > https://en.wikipedia.org/wiki/Collinear_antenna_array
> >
> > The one caveat is the "pattern" is only being considered in the horizontal plane.
> > Standard practice for any broadcast antenna set up.
> >
> >
> The collinear modifies the horizontal patern by taking some signal from
> the vertical.

** Did you read my caveat comment at all ?

> Pattern still modified for gain.

** But not relevant to the original question re BROADCAST reception.

Context, context, context, context !!!!!!.


...... Phil

[whit3rd]

I think he's talking about a wollenweber array of dipoles, with preamplification
then phase-shifting and combination afterward. That worked with lots of operators
trying combinations, for directing fighter craft against bombers, around (for instance)
Berlin, 1943. The linkage used by wool thread spinners to gather their product
is a 'wool-weaver' which is what the dipole array must have suggested.

Alert operators can do the tuning dynamically (those fighter craft MOVED).

[Phil Allison]

John Larkin 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.
> >>
>> >
> >Then you have exceeded the laws of antennas.
> Laws of antennas? Or folklore?

** Smartarse.

> >Care to tell a way to do that in any prctical antenna ?
>
> One obvious way: run a feeder from N antennas to a central point.
> There, run each signal into a receiver. Combine the receiver outputs.
> The RF phase information is lost.
>

** Loud ring goes off !!
That idea is *outside* the parameters of the question re:

" signals from multiple dipoles can be combined "

> There's probably a passive way to combine an array of dipoles but keep
> the same far-field pattern.

** But JL has no idea nor cares a hoot what it is.



.... Phil

[Jan Panteltje]

On a sunny day (Thu, 06 Jan 2022 15:32:16 -0800) it happened John Larkin
<jlarkin@highland_atwork_technology.com> wrote in
<4fuetgtesrbtt5on9...@4ax.com>:

>On Thu, 6 Jan 2022 16:42:26 -0500, Ralph Mowery
><rmow...@charter.net> wrote:
>
>>In article <e1metglue8alf2jal...@4ax.com>,
>>jlarkin@highland_atwork_technology.com says...
>>>
>>> I think signals from multiple dipoles can be combined without altering
>>> the far-field pattern. I can think of several ways to do that.
>>>
>>>
>>>
>>
>>Then you have exceeded the laws of antennas.
>
>Laws of antennas? Or folklore?
>
>>
>>
>>Care to tell a way to do that in any prctical antenna ?
>
>One obvious way: run a feeder from N antennas to a central point.
>There, run each signal into a receiver. Combine the receiver outputs.
>The RF phase information is lost.
>
>There's probably a passive way to combine an array of dipoles but keep
>the same far-field pattern.

One important thing to take into account is all the cable losses.
The reason mine works so well is
1) length cable only 2 meters
2) antenna is about 1/4 wavelength
3) no connector losses
4) indoors fields and phases combine and all sort of wave patterns exist, use a local one that is strong.
5) no pre-amps no power needed.

[John Walliker]

Passive combining of multiple antennas will always change the directional
response in some way.
Combining the outputs of multiple receivers to improve performance without
modifying the directional response is standard practice and was first done
about 100 years ago.

John

[amdx]

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

[amdx]

No one has mentioned that this constructive addition, needs to work over
470MHz to 698 MHz, and if you happen to have a VHF station,

 it might need to work down to 54MHz.

                                      Mikek

[jla...@highlandsniptechnology.com]

Given a defense-sized budget, one could digitize each antenna signal
and combine them digitally. Add phase shifts as needed. That's a
project but it's not totally crazy, with modern multichannel ADCs and
an FPGA.

At one frequency, move the dipoles around to tweak the pattern.

Or switch in some delays with relays or something. That could be cool.
Try every combination for max signal strength.

[Phil Hobbs]

You only win SNR like the square root when you combine the demodulated
outputs, whereas you win linearly with coherent combining.

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

[Jan Panteltje]

On a sunny day (Fri, 07 Jan 2022 08:06:01 -0800) it happened
jla...@highlandsniptechnology.com wrote in
<8rogtg9p9akf3ltub...@4ax.com>:

>Given a defense-sized budget, one could digitize each antenna signal
>and combine them digitally. Add phase shifts as needed. That's a
>project but it's not totally crazy, with modern multichannel ADCs and
>an FPGA.

Not sure there is much point in digitizing 2 signals that are mostly in the noise.
You want an as large as possible signal before processing?

It is all phased arrays in the new Russian radars,
and in Elon's sat receivers.
https://hackaday.com/2020/11/25/literally-tearing-apart-a-spacex-starlink-antenna/
Look at that board!
It can direct the tx beam and rx direction in any angle.
Same for modern flat satellite dishes

[ke...@kjwdesigns.com]

On Friday, 7 January 2022 at 08:06:10 UTC-8, jla...@highlandsniptechnology.com wrote:
...

> Given a defense-sized budget, one could digitize each antenna signal
> and combine them digitally. Add phase shifts as needed. That's a
> project but it's not totally crazy, with modern multichannel ADCs and
> an FPGA.
>
> At one frequency, move the dipoles around to tweak the pattern.
>
> Or switch in some delays with relays or something. That could be cool.
> Try every combination for max signal strength.

...

That's how most automotive (and many military) radars work. You can do four receivers for $25 and cascade up to four of the devices together to give 16 receivers (and 12 transmitters)

https://www.ti.com/product/AWR1843

By doing appropriate processing (mainly multiple axes of FFTs) the equivalent of a wide field of view antenna is created but with the gain of a narrow beam width.

kw

[John Walliker]

On Friday, 7 January 2022 at 16:23:28 UTC, Phil Hobbs wrote:

> > Passive combining of multiple antennas will always change the directional
> > response in some way.
> > Combining the outputs of multiple receivers to improve performance without
> > modifying the directional response is standard practice and was first done
> > about 100 years ago.
> You only win SNR like the square root when you combine the demodulated
> outputs, whereas you win linearly with coherent combining.
>

Yes, but the reason for combining receiver outputs is often to overcome fading
rather than just to improve snr. In that case, the final output will usually be the
"best" of the multiple receiver outputs or a weighted combination rather than
just a linear sum.

John

[Jasen Betts]

On 2022-01-06, John Larkin <jlarkin@highland_atwork_technology.com> wrote:
> On Thu, 6 Jan 2022 14:13:52 -0500, Ralph Mowery
><rmow...@charter.net> wrote:
>
>>In article <om9etg5bfjcn9ngm3...@4ax.com>,
>>jla...@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.

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.

If you have some way to connect multiple antennae without creating a
phased array I'd like to hear about it.

--
Jasen.

[Phil Allison]

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

[John Walliker]

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

[Phil Allison]

John Walliker wrote:
=================
Wot a wanking IDIOT
--------------------------------

> 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.

** Fuck knows what shit data YOU look at.

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

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

Crawl back under your rock.



...... Phil

[John Walliker]

On Saturday, 8 January 2022 at 11:43:14 UTC, palli...@gmail.com wrote:
> John Walliker wrote:
> =================
> Wot a wanking IDIOT
> --------------------------------
> > 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.
> ** 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

They all have E-plane and H-plane polar response plots.

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

The second link above is for a TV antenna. It has E and H-plane plots.
As it happens, they are almost identical, but that does not apply to
some of the other types.

> > 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.

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

FM yes, TV seldom.

> Crawl back under your rock.

I'll be happy to.

John

[jla...@highlandsniptechnology.com]

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.

[jla...@highlandsniptechnology.com]

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.

[John Walliker]

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

[jla...@highlandsniptechnology.com]

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.

[Phil Hobbs]

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

[ke...@kjwdesigns.com]

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

[John Walliker]

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

[Phil Allison]

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.

[Clifford Heath]

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

[Joe Gwinn]

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

[John S]

On 1/6/2022 1:52 PM, Dave Platt wrote:
> In article <d2255b5c-a796-4ed2...@googlegroups.com>,
> Sid 03 <sidw...@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.

[ke...@kjwdesigns.com]

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

[DecadentLinux...@decadence.org]

John Larkin <jlarkin@highland_atwork_technology.com> wrote in
news:e1metglue8alf2jal...@4ax.com:

> On Thu, 6 Jan 2022 14:13:52 -0500, Ralph Mowery
> <rmow...@charter.net> wrote:
>
>>In article <om9etg5bfjcn9ngm3...@4ax.com>,
>>jla...@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.

[Phil Hobbs]

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

[Rich S]

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

[Jan Panteltje]

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

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