Aerial Installation to feed 3 tv's.

Bill Wright wrote:
Here's a general point which is more to do with human nature than aerials.

The original poster had decided to install three aerials and asked general
questions about this. The overwhelming response (unanimous I think, from
those in the aerial trade) was that one good aerial and a small amplifier is
a far better idea. But the original poster intends to ignore this advice.

Years ago a (non technical) chap at work bought himself a new telly on staff
sales. He'd discovered that it was one for the Irish rather than UK market.
'Is it any different' he asked me. 'Yes' I said, 'it'll have a VHF *and* UHF
tuner'. 'Oh ! is that a problem ?'; 'nope' I responded, 'we only use UHF here,
they use UHF and VHF in Eire, but their 'UHF' is exactly the same as ours'.

He bumped into me the next day, I asked how was the TV. 'Oh fine, it tuned
itself in to all four channels last night' 'great' I replied. He then frowned
and said, 'isn't the mains voltage different in Ireland ?'. I assured him not
to worry, the Irish versions had the same mains specs as the UK, and European
variants. A colleague who had overheard our conversations said to me; 'he just
wants you to say the TV is no good, so he can return it for a refund'. Sure
enough I discovered on the grapevine that he'd been asking others around the
building the same questions, and getting the same answers. After a week he
asked someone in accounts; they had said something like; 'that sounds dodgy,
I'd get a refund if I were you !' Which is what he finally did.


--
Mark
Please replace invalid and invalid with gmx and net to reply.

"Ian Jackson" wrote in message
...
I reckon that, provided the aerials are not too large, and the
installation is neat and tidy, separate aerials may be the better bet. The
installation of three aerials should not cost three times one aerial. You
won't need to buy an amplifier (and probably a power supply). As
everything is passive, there will not be much to go wrong.

Surely spacing out three aerials enough that they still perform well is
unlikely to be either cheap or neat and tidy.

--

Brian Gregory. (In the UK)

To email me remove the letter vee.

"Mark Carver" wrote in message
...
Bill Wright wrote:
Here's a general point which is more to do with human nature than
aerials.

The original poster had decided to install three aerials and asked
general questions about this. The overwhelming response (unanimous I
think, from those in the aerial trade) was that one good aerial and a
small amplifier is a far better idea. But the original poster intends to
ignore this advice.

Years ago a (non technical) chap at work bought himself a new telly on
staff sales. He'd discovered that it was one for the Irish rather than UK
market. 'Is it any different' he asked me. 'Yes' I said, 'it'll have a VHF
*and* UHF tuner'. 'Oh ! is that a problem ?'; 'nope' I responded, 'we only
use UHF here, they use UHF and VHF in Eire, but their 'UHF' is exactly the
same as ours'.

He bumped into me the next day, I asked how was the TV. 'Oh fine, it tuned
itself in to all four channels last night' 'great' I replied. He then
frowned and said, 'isn't the mains voltage different in Ireland ?'. I
assured him not to worry, the Irish versions had the same mains specs as
the UK, and European variants. A colleague who had overheard our
conversations said to me; 'he just wants you to say the TV is no good, so
he can return it for a refund'. Sure enough I discovered on the grapevine
that he'd been asking others around the building the same questions, and
getting the same answers. After a week he asked someone in accounts; they
had said something like; 'that sounds dodgy, I'd get a refund if I were
you !' Which is what he finally did.


--
Mark
Please replace invalid and invalid with gmx and net to reply.

I'll keep the rooftop aerial I already have for living room tv.

I'll use an indoor aerial for conservatory and baedroom.

Thanks for your help anyway.

I'm not having any kind of electrical amplification device or three aerials
if they look crap!

"Ian Jackson" wrote in message
...
In message , Bill Wright
writes
Maybe I shouldn't have suggested that an amplified system might not always
be that best way to do things. It's not that I'm against amplifiers. In my
field of work, I've been used to one aerial system feeding tens - and even
hundreds - of thousands of TV sets, sometimes using amplifiers in which I
have been involved with the design. However, I still reckon that there are
occasions where the use separate aerials should be considered, provided
they are relatively small, and the mast doesn't resemble a Christmas tree.

I sort of agree with you, a bit. Thing is though, suppose you want to feed
three downleads. It the signal is good you'll use one aerial and a three way
splitter. If the signal is not good enough to stand the splitter losses you
might say, "I'll use three aerials." But really, since the loss on a three
way splitter is only 6dB what you're saying is that you have only an extra
6dB above the point where you would consider that levels were inadequate. In
that case, you might then go on to think, "Well, I can fit a masthead amp
here for about the same cost as two aerial arrays. The advantages will be
all the obvious one (less wind loading, possibly cheaper fixings, etc) plus
the great benefit of the amplifier in what is by definition a
not-much-above-marginal-signal-levels situation.

Bill

Ian Jackson wrote:

And don't forget that you ought to keep the aerials reasonably
well-separated, so you'll probably need a somewhat longer mast than
is usual. I'm not sure what is considered good practice, but I would
think at maybe 18" between the booms (expert advice desirable!)
should be OK.

That's not really enough. If you want the aerials to function properly
the capture areas should not significantly overlap. Capture area is
G*lambda^2/(4*pi), G being the gain over isotropic, as a power ratio
(i.e. not in dB). If you assume this is circular the corresponding
diameter is sqrt(G)*lambda/pi. Taking G as 16 (~ 10 dBd) at 500 MHz
gives a capture diameter of about 0.75 m, and G = 25 (~12 dBd) at 800
MHz gives a diameter of 0.6m.

So at least 2 ft. is a more sensible guideline. For Yagis, where the
capture area is actually somewhat elliptical, this errs on the safe side
with horizontal polarisation (assuming vertical stacking). For vertical
polarisation the stacking distance should really be increased by 25% or so.

Invariably when I see these 'multi-aerial special rigs' I think the
spacing looks to be much too small.

--
Andy

Andy Wade wrote:

That's not really enough. If you want the aerials to function properly
the capture areas should not significantly overlap. Capture area is
G*lambda^2/(4*pi), G being the gain over isotropic, as a power ratio
(i.e. not in dB). If you assume this is circular the corresponding
diameter is sqrt(G)*lambda/pi. Taking G as 16 (~ 10 dBd) at 500 MHz
gives a capture diameter of about 0.75 m, and G = 25 (~12 dBd) at 800
MHz gives a diameter of 0.6m.

So at least 2 ft. is a more sensible guideline. For Yagis, where the
capture area is actually somewhat elliptical, this errs on the safe side
with horizontal polarisation (assuming vertical stacking). For vertical
polarisation the stacking distance should really be increased by 25% or so.

Invariably when I see these 'multi-aerial special rigs' I think the
spacing looks to be much too small.

Take a look at this mess visible from my back garden:-

http://www.markyboy.net/double.JPG



--
Mark
Please replace invalid and invalid with gmx and net to reply.

In article , Andy Wade
wrote:
Ian Jackson wrote:

And don't forget that you ought to keep the aerials reasonably
well-separated, so you'll probably need a somewhat longer mast than is
usual. I'm not sure what is considered good practice, but I would think
at maybe 18" between the booms (expert advice desirable!) should be OK.

That's not really enough. If you want the aerials to function properly
the capture areas should not significantly overlap. Capture area is
G*lambda^2/(4*pi), G being the gain over isotropic, as a power ratio
(i.e. not in dB). If you assume this is circular the corresponding
diameter is sqrt(G)*lambda/pi. Taking G as 16 (~ 10 dBd) at 500 MHz
gives a capture diameter of about 0.75 m, and G = 25 (~12 dBd) at 800
MHz gives a diameter of 0.6m.

So at least 2 ft. is a more sensible guideline. For Yagis, where the
capture area is actually somewhat elliptical, this errs on the safe side
with horizontal polarisation (assuming vertical stacking). For vertical
polarisation the stacking distance should really be increased by 25% or
so.

which is probably why, in EID, we used to recommend a metre spacing between
aerial.

--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11

I'll keep the rooftop aerial I already have for living room tv.

I'll use an indoor aerial for conservatory and baedroom.

Thanks for your help anyway.

I'm not having any kind of electrical amplification device or three
aerials if they look crap!

Pity, I was hoping I'd get to see what "two aerials installed for £55"
looked like.

In message , Bill Wright
writes

"Ian Jackson" wrote in message
...
In message , Bill Wright
writes
Maybe I shouldn't have suggested that an amplified system might not always
be that best way to do things. It's not that I'm against amplifiers. In my
field of work, I've been used to one aerial system feeding tens - and even
hundreds - of thousands of TV sets, sometimes using amplifiers in which I
have been involved with the design. However, I still reckon that there are
occasions where the use separate aerials should be considered, provided
they are relatively small, and the mast doesn't resemble a Christmas tree.

I sort of agree with you, a bit. Thing is though, suppose you want to feed
three downleads. It the signal is good you'll use one aerial and a three way
splitter. If the signal is not good enough to stand the splitter losses you
might say, "I'll use three aerials." But really, since the loss on a three
way splitter is only 6dB what you're saying is that you have only an extra
6dB above the point where you would consider that levels were inadequate. In
that case, you might then go on to think, "Well, I can fit a masthead amp
here for about the same cost as two aerial arrays. The advantages will be
all the obvious one (less wind loading, possibly cheaper fixings, etc) plus
the great benefit of the amplifier in what is by definition a
not-much-above-marginal-signal-levels situation.

Bill


What you say is, of course, quite correct. It's silly to struggle with
marginal signal levels. And once you have decided to fit an amplifier,
you can cater for the possibility of more outlets in the future.

To be honest though (and I know I shouldn't say this), I really prefer a
loft aerial, provided it works well enough. At least you know that
there's a good chance of working just as well in 50 years time. Of
course, there's more chance of having to use an amplifier with a loft
aerial.

Some 25 years ago, I fitted my neighbour up with an indoor aerial. We
live in a reasonable signal area, and the direction of the transmitter
was straight through the tiles. The attenuation seemed minimal. He
wanted four feeds, so I made him an amplifier and followed it by a
separate 4-way splitter.

Being a radio amateur, I also took the precaution of preceding the
amplifier with suitable filtering to reject all amateur frequencies up
to 440MHz (something often omitted in off-the-DIY-shelf amplifiers). [I
am suspicious of some of your actual 'masthead' amplifiers. Once they're
up, they're up. If they then have problems, they are difficult to deal
with. Loft mounting, although maybe a bit of a compromise, makes TLC a
lot easier.] 25 years later, my neighbour's system has been on
essentially 24/7/52, and is still working OK, and I've never had any
interference problems.
--
Ian

Being a radio amateur, I also took the precaution of preceding the
amplifier with suitable filtering to reject all amateur frequencies up
to 440MHz (something often omitted in off-the-DIY-shelf amplifiers). [I
am suspicious of some of your actual 'masthead' amplifiers. Once they're
up, they're up. If they then have problems, they are difficult to deal
with. Loft mounting, although maybe a bit of a compromise, makes TLC a
lot easier.] 25 years later, my neighbour's system has been on
essentially 24/7/52, and is still working OK, and I've never had any
interference problems.

Good for him. Some 15 years misspent in the TV trade some years ago said
otherwise with loft aerials!...
--
Tony Sayer