I am looking at adding a weathervane to the roof of my house. The first location considered is not suitable, as the chimney stacks are tooWill it be within the main lobe of your aerial, and at the same height ?
large and tall for the weathervane.
There is another chimney stack, but it has the TV antenna attached to
one corner. If the weathervane were to be attached to the same chimney
stack, as far away as possible, would there be any likely effects on
the TV signal, either from the stationary 'vane, or when it rotates?
Thanks for any help. I don't want to install the weathervane, and find
that I then get pixellated TV pictures.
I am looking at adding a weathervane to the roof of my house. The first location considered is not suitable, as the chimney stacks are too
large and tall for the weathervane.
There is another chimney stack, but it has the TV antenna attached to
one corner. If the weathervane were to be attached to the same chimney
stack, as far away as possible, would there be any likely effects on
the TV signal, either from the stationary 'vane, or when it rotates?
Thanks for any help. I don't want to install the weathervane, and find
that I then get pixellated TV pictures.
"Davey" <davey@example.invalid> wrote in message news:tlionb$443a$1@dont-email.me...
I am looking at adding a weathervane to the roof of my house. The first
location considered is not suitable, as the chimney stacks are too
large and tall for the weathervane.
There is another chimney stack, but it has the TV antenna attached to
one corner. If the weathervane were to be attached to the same chimney
stack, as far away as possible, would there be any likely effects on
the TV signal, either from the stationary 'vane, or when it rotates?
Thanks for any help. I don't want to install the weathervane, and find
that I then get pixellated TV pictures.
What's the weather vane made of? I have a plastic anemometer (wind
speed) and weather vane (wind direction) mounted on the metal pole to
which the TV aerial is attached. The sensor unit is probably about 2m
below the aerial and stands about 20 cm off the pole. The actual
sensors will have some metal in, but the cups/vane are plastic - maybe deliberately to avoid satellite/terrestrial signal reflections.
On 22/11/2022 15:09, Davey wrote:
I am looking at adding a weathervane to the roof of my house. The
first location considered is not suitable, as the chimney stacks
are too large and tall for the weathervane.
There is another chimney stack, but it has the TV antenna attached
to one corner. If the weathervane were to be attached to the same
chimney stack, as far away as possible, would there be any likely
effects on the TV signal, either from the stationary 'vane, or when
it rotates?
Thanks for any help. I don't want to install the weathervane, andWill it be within the main lobe of your aerial, and at the same
find that I then get pixellated TV pictures.
height ?
If not, don't worry
On Tue, 22 Nov 2022 15:18:21 +0000I really wouldn't worry about it then, it's only going to be a problem
Mark Carver <mark.carver@invalid.invalid> wrote:
On 22/11/2022 15:09, Davey wrote:Not being familiar with antenna design, I had to look this up. The
I am looking at adding a weathervane to the roof of my house. TheWill it be within the main lobe of your aerial, and at the same
first location considered is not suitable, as the chimney stacks
are too large and tall for the weathervane.
There is another chimney stack, but it has the TV antenna attached
to one corner. If the weathervane were to be attached to the same
chimney stack, as far away as possible, would there be any likely
effects on the TV signal, either from the stationary 'vane, or when
it rotates?
Thanks for any help. I don't want to install the weathervane, and
find that I then get pixellated TV pictures.
height ?
If not, don't worry
answer is that the weathervane will be at worst directly behind the
main lobe, quite possibly in the area of the 'back lobe'. It might be possible to change this so as to get it out of the lobe area. As for
height, it will probably be very close to the height of the antenna.
Material is mild steel.
I am looking at adding a weathervane to the roof of my house. The first
location considered is not suitable, as the chimney stacks are too
large and tall for the weathervane.
There is another chimney stack, but it has the TV antenna attached to
one corner. If the weathervane were to be attached to the same chimney
stack, as far away as possible, would there be any likely effects on
the TV signal, either from the stationary 'vane, or when it rotates?
Thanks for any help. I don't want to install the weathervane, and find
that I then get pixellated TV pictures.
--
Davey.
On 22/11/2022 15:23, NY wrote:
"Davey" <davey@example.invalid> wrote in message
news:tlionb$443a$1@dont-email.me...
I am looking at adding a weathervane to the roof of my house. The first
location considered is not suitable, as the chimney stacks are too
large and tall for the weathervane.
There is another chimney stack, but it has the TV antenna attached to
one corner. If the weathervane were to be attached to the same chimney
stack, as far away as possible, would there be any likely effects on
the TV signal, either from the stationary 'vane, or when it rotates?
Thanks for any help. I don't want to install the weathervane, and find
that I then get pixellated TV pictures.
What's the weather vane made of? I have a plastic anemometer (wind speed)
and weather vane (wind direction) mounted on the metal pole to which the
TV aerial is attached. The sensor unit is probably about 2m below the
aerial and stands about 20 cm off the pole. The actual sensors will have
some metal in, but the cups/vane are plastic - maybe deliberately to
avoid satellite/terrestrial signal reflections.
DTT signals have a guard interval that can cope with displaced signals arriving with a path difference of around 20 km, unless the device is
going to reflect a distant signal from a hill or building literally miles away, and that reflection is in the same order of strength as the 'wanted one' (Clue: Almost impossible that would be the case) it really is totally insignificant.
As for satellite interference, unless it's actually right in the downlink beam, how could it possibly have any measurable effect ?
Get a plastic Weather vane.
Brian
On Wed, 23 Nov 2022 09:14:39 -0000I'd be more worried about rust stains all over your roof tiles
"Brian Gaff" <brian1gaff@gmail.com> wrote:
Get a plastic Weather vane.The one I am thinking of getting is a bespoke one, which only comes in
Brian
mild steel.
I really wouldn't worry about it then, it's only going to be a problem
it it obstructs your signal, which with it behind the aerial, isn't
going to be happening .
On 23/11/2022 08:15, Mark Carver wrote:
I really wouldn't worry about it then, it's only going to be a
problem it it obstructs your signal, which with it behind the aerial,
isn't going to be happening .
A lot of these answers are treating the antenna as a point source,
with only far field behaviour.
If the vane is close enough to be in the near field, the effects could
be difficult to predict.
A metal object behind the aerial, could reflect signals, and at some distances, the reflection could cancel the wanted signal.
On 23/11/2022 12:07, Mark Carver wrote:Well, and I see Bill has jumped in with his eons of practical
Explain how with a COFDM signal using 8000 separate carriers, and a
guard interval that is 'kms' (NOT mm) wide for path length  ?
Gain aerials wouldn't work at all if that were a let out!
When you get multipath with COFDM, the guard interval is protecting
you against interference between signalling units, which are
transmitted quite slowly (the baud rate, in the true meaning of that,
is low).
It doesn't protect you against phasing effects within a single
signalling unit, which are sensitive to distances of the order of the
carrier wavelength. COFDM survives these because only some
frequencies are cancelled sufficiently to make them unusable, assuming
a reasonable starting SNR. If the path difference is of the order of wavelength equivalent of the channel spacing (~37m), or greater, only
some sub-carriers will be unusable.
Individual bits will be spread across sub-carriers in such a way that
the error correction can make up for a small number of missing
sub-carriers.
However, once you are in, or close to the near field, the cancellation
will spread over many multiplexes, so all the sub-carriers in a
particular multiplex can become unusable.
I'm not disputing there wouldn't be reflected signals produced, the
point is no aerial (tx or rx) lives in splendid isolation
I install CODFM based wireless mics and cameras in TV studios.
Well, and I see Bill has jumped in with his eons of practical
experience, I'm not disputing there wouldn't be reflected signals
produced, the point is no aerial (tx or rx) lives in splendid isolation, they are all subject to no end of static and dynamic reflective clutter
that is nearby, but the decoding (because of the parameters selected)
sorts it out.
Behind a high gain antenna there may be a near-null away from the antenna
on its extended beam axis.
On 24/11/2022 10:37, Mark Carver wrote:
I'm not disputing there wouldn't be reflected signals produced, the
point is no aerial (tx or rx) lives in splendid isolation
Traditional Yagi TV aerials can be considered to be a dipole aerial not
in isolation, but rather surrounded by a dozen or so pieces of metal.
The polar diagram, and therefore gain, of an isolated dipole is very different from that of the complete Yagi with all of its directors and reflectors.
I install CODFM based wireless mics and cameras in TV studios. The Rx antennas are often up in the lighting grid, in a jungle of metal work.
I've never heard or seen disturbance, and the devices often carry on
with useful output a surprising distance away from the studio....
On 24/11/2022 17:46, Jim Lesurf wrote:I had something like that published in a mag a good few years ago. I have a field behind the house that is big enough to carry out meaningful antenna tests, and at different times I did all sorts of things.
Behind a high gain antenna there may be a near-null away from the antenna on its extended beam axis.I remember many years ago seeing an article in a magazine that showed
the polar diagrams for various TV receiving antenna when used on the
wrong groups.
You tend to think that they will just have a bit less gain etc but many
had lobes going in all sorts of directions and even often no gain in
what might have been thought to be the front where the gain is wanted.
Charles and Bill will remember that when new UHF TV relays came on,Many such aerials were installed using the Sheffield (Crosspool) relay. When Channel Four started (late) on ch21 the shit hit the fan. See
there would be often be the proverbial "men in white vans" going around offering to fit new antenna cheaper than local dealers. Apart from
shoddy workmanship and cheap cable, they often had cheap antenna. In a
number of areas where there were low channels in use, it was often found these antenna did not work down to Ch.21
- The wind unit is a bit low, probably only about 10 cm higher than the
ridge tiles of the roof, which may lead to "boundary effects" with the
wind and the ridge, and hence lower window speeds and maybe some bias on
the direction. Unless I get a longer ladder, I've got it as high as I can.
On 22/11/2022 15:23, NY wrote:
- The wind unit is a bit low, probably only about 10 cm higher than the
ridge tiles of the roof, which may lead to "boundary effects" with the
wind and the ridge, and hence lower window speeds and maybe some bias on
the direction. Unless I get a longer ladder, I've got it as high as I
can.
And as a sailor, but not an aerial engineer, that's the bit that matters.
If you want an accurate reading off your wind vane it needs to be significantly higher that the roof and all the other chimneys. Not to
mention the trees you mentioned.
Didn't you mention also in the early days of UHF, a firm based inCharles and Bill will remember that when new UHF TV relays came on,Many such aerials were installed using the Sheffield (Crosspool) relay. When Channel Four started (late) on ch21 the shit hit the fan. See
there would be often be the proverbial "men in white vans" going around
offering to fit new antenna cheaper than local dealers. Apart from
shoddy workmanship and cheap cable, they often had cheap antenna. In a
number of areas where there were low channels in use, it was often found
these antenna did not work down to Ch.21
http://www.wrightsaerials.tv/articles/whatsat-short-reflector-syndrome.pdf
Many such aerials were installed using the Sheffield (Crosspool) relay. When Channel Four started (late) on ch21 the shit hit the fan. SeeDidn't you mention also in the early days of UHF, a firm based in
http://www.wrightsaerials.tv/articles/whatsat-short-reflector-syndrome.pdf
Newbury were producing Group B yagis, except their idea of Group B, was
what we had locally here from Hannington [1].
39, 42, 45.
All fine, until you try it on Emley, 44, 47, 51 ?!
... Why they didn't opt for rechargeable batteries, which have a much
longer life as long as they are charged during the day, is a mystery.
But Davis (the maker) said that a rechargeable battery, even if they
make one in that size/voltage), is not an option because the solar panel
has no way of feeding power to the battery.
On Wed, 23 Nov 2022 09:14:39 -0000By the way, you could lash up a dummy Weathervane made up of tinfoil and cardboard, and try that in the vicinity of your aerial.
"Brian Gaff" <brian1gaff@gmail.com> wrote:
Get a plastic Weather vane.The one I am thinking of getting is a bespoke one, which only comes in
Brian
mild steel.
On 23/11/2022 09:28, Davey wrote:
On Wed, 23 Nov 2022 09:14:39 -0000
"Brian Gaff" <brian1gaff@gmail.com> wrote:
By the way, you could lash up a dummy Weathervane made up of tinfoilGet a plastic Weather vane.The one I am thinking of getting is a bespoke one, which only comes
Brian
in mild steel.
and cardboard, and try that in the vicinity of your aerial.
That would be a valid experiment.
Davis (the maker) said that a rechargeable battery, even if they make one in that size/voltage), is not an option because the solar panel has no way of feeding power to the battery.
NY wrote:
Davis (the maker) said that a rechargeable battery, even if they make
one in that size/voltage), is not an option because the solar panel
has no way of feeding power to the battery.
Slip rings? Inductive charging à la toothbrush?
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