Advice needed

Andy Burns wrote:

A Balun is used to match the aerial to the cable, a good thing.

Maybe, but its main purpose is to effect a proper transition between the
balanced connection at the centre-fed dipole of the aerial and the
unbalanced coaxial feeder, an even better thing.

A balun helps to prevent signals and interference which are inevitably
picked-up on the outer of the coax from entering the signal path to the
receiver. Using a centre-fed dipole aerial with no balun is like taking
an imaginary perfect aerial with balanced feeder and then connecting a
random length of dangling wire directly to one side of the dipole.
Clearly this wire will pick up signals and interference[*] and generally
screw-up the directional pattern and cross-polar discrimination of the
aerial.
[*] Particularly the dreaded impulsive electrical interference from
sparking switches and so on, which has such a destructive effect on
DVB-T signals. (The coax feeder will typically pass close to mains
wiring and sources of such interference.)


Some general background reading on 'digital aerials' he
http://www.dtg.org.uk/publications/b...rk_aerials.pdf

--
Andy

On 09/07/2007 19:44, Andy Wade wrote:

Andy Burns wrote:

A Balun is used to match the aerial to the cable, a good thing.

Maybe, but its main purpose is to effect a proper transition between the
balanced connection at the centre-fed dipole of the aerial and the
unbalanced coaxial feeder, an even better thing.

I was only giving the layman's version :-)

A balun helps to prevent signals and interference which are inevitably
picked-up on the outer of the coax from entering the signal path to the
receiver. Using a centre-fed dipole aerial with no balun is like taking
an imaginary perfect aerial with balanced feeder and then connecting a
random length of dangling wire directly to one side of the dipole.
Clearly this wire will pick up signals and interference[*] and generally
screw-up the directional pattern and cross-polar discrimination of the
aerial.

[*] Particularly the dreaded impulsive electrical interference from
sparking switches and so on, which has such a destructive effect on
DVB-T signals. (The coax feeder will typically pass close to mains
wiring and sources of such interference.)

Some general background reading on 'digital aerials' he
http://www.dtg.org.uk/publications/b...rk_aerials.pdf

thanks for the chapter and verse though ...





--
Statistics are like a bikini, what they reveal is suggestive,
but what they conceal is vital - Aaron Levenstein.

"André Coutanche" wrote in message
...
. I've done similar things before with
FTA-satellite dishes and they seem to work fine. Or does aerial
installation require special test equipment?

Go for it! Who needs aerial riggers, eh, Bill?

Hopefully, no-one. Then I can get a refund on my £5m public liability and
personal accident policies, throw away my PPE, and put my analysers and
meters on eBay. I'll keep the ladders though, because I might turn to window
cleaning.

That sounded a bit grumpy but it wasn't meant to.

Bill

Am Mon, 9 Jul 2007 19:26:54 +0100 schrieb André Coutanche:

Andreas Schulze-Bäing wrote:
What you say makes me wonder if it is possible to do a DIY-install
of an aerial? I helped a friend choosing a TV the other day. Then we
found out that the aerial on the roof has a loose "reflector" at the
back, moving in the wind, bumbing on the rest of the antenna and
causing funny effects for analogue and digital reception. My initial
idea was to walk into a shop, get a standard aerial for £20 or £30,
borrow a large ladder and put it on the existing mast to replace the
existing one. According to their website they seem to have some of
those on offer in Maplin. I've done similar things before with
FTA-satellite dishes and they seem to work fine. Or does aerial
installation require special test equipment?

Go for it! Who needs aerial riggers, eh, Bill? Seriously, it is in
principle a straight forward DIY job, the problems only arising if you
are in a particularly difficult or complex area for reception (and I
don't know your neck of the woods, so I can't comment) or if the
access for siting the aerial or running the (CT100) cable is
difficult.

The house is located in Birkenhead/Wirral. I found this great website
http://www.ukfree.tv/ indicating that the transmitter Winter Hill is 46 km
northeast. That's where most of the aerials in the area seem to 'look' at.
In the neighbourhood there seem to be some new aerials installed which are
a bit bigger than the standard 10 element aerials, presumably due to change
to digital. Maybe that's an indication that it would be advisable to get a
slightly bigger model? Can the signal also become too "strong" when using a
big aerial?
Has anyone got experience with this online shop?
http://www.brymar.co.uk/acatalog/TV_Aerials_12.html
They seem to have quite competitive prices. Also they offer the option to
choose the aerial for the right group, instead of a wideband. It seems that
I need group C/D. Maplin seem to sell just wideband aerials.

I'm not sure if I should replace the cable as well. It's probably as old as
the house - 20 years or more, not sure which quality. I've still got some
unused satellite coax cable here. Would that be suitable for aerial
connection as well?

Test equipment? Essential in difficult cases; a compass and a steady
hand should do it otherwise.

I've got a simple analogue signal meter for installation of satellite
dishes. But I guess it won't work on normal aerials as it requires power
supply from the digital box.

Andreas

On 10/07/2007 09:56, Owain wrote:

You're not allowed to use ladders for window cleaning any more ... all
the local window cleaners now use pressure washers with very long lances
for anything above ground floor.

The ones round here seem to take less notice of the H&SE then.

....snip...
The house is located in Birkenhead/Wirral. I found this great website
http://www.ukfree.tv/ indicating that the transmitter Winter Hill is 46 km
northeast. That's where most of the aerials in the area seem to 'look' at.
In the neighbourhood there seem to be some new aerials installed which are
a bit bigger than the standard 10 element aerials, presumably due to
change
to digital. Maybe that's an indication that it would be advisable to get a
slightly bigger model? Can the signal also become too "strong" when using
a
big aerial?

Yes, the signal can be too strong. Quality not quantity (but of course
sufficient) is what you need. Also, many dodgy riggers are putting up
wideband aerials and making up for the poor response (wideband =
jack-of-all-trades, master of none) by fitting larger aerials.

Has anyone got experience with this online shop?
http://www.brymar.co.uk/acatalog/TV_Aerials_12.html
They seem to have quite competitive prices. Also they offer the option to
choose the aerial for the right group, instead of a wideband. It seems
that
I need group C/D. Maplin seem to sell just wideband aerials.

I'm not sure if I should replace the cable as well. It's probably as old
as
the house - 20 years or more, not sure which quality. I've still got some
unused satellite coax cable here. Would that be suitable for aerial
connection as well?

Yes, old cable is probably knackered by now and was probably poor to begin
with. Satellite coax is probably fine - is it CT100? There are various
grades of "satellite" cable. Google for CT100 and see - you want good coper
sheet screening, not the aluminium stuff which is sometimes sold as
satellite grade.


Test equipment? Essential in difficult cases; a compass and a steady
hand should do it otherwise.

I've got a simple analogue signal meter for installation of satellite
dishes. But I guess it won't work on normal aerials as it requires power
supply from the digital box.


Totally wrong frequencies so the satellite finder is useless.

Andreas

In message , Andreas
Schulze-Bäing writes



Has anyone got experience with this online shop?
http://www.brymar.co.uk/acatalog/TV_Aerials_12.html
Is the first one (the DAB aerial) assembled correctly? It does look a
bit odd.
Ian.
--

André Coutanche wrote:
Test equipment? Essential in difficult cases; a compass and a steady
hand should do it otherwise.

My little daewoo setpal has a status display which includes
signal strength. Ever so handy for pointing an aerial :-)

BugBear

"Owain" wrote in message
...
Bill Wright wrote:
Hopefully, no-one. Then I can get a refund on my £5m public liability and
personal accident policies, throw away my PPE, and put my analysers and
meters on eBay. I'll keep the ladders though, because I might turn to
window cleaning.

You're not allowed to use ladders for window cleaning any more ... all the
local window cleaners now use pressure washers with very long lances for
anything above ground floor.

Anyway, without the hard hat what would you wear to "Village People Night"
down at the Ferret & Firkin? Can't see you in a Red Indian costume.

That sounded a bit grumpy but it wasn't meant to.

You couldn't possibly sound grumpy no matter how hard you tried, Bill!

That's not when they said in B & Q yesterday.

Bill

On Mon, 9 Jul 2007 18:41:18 +0100, Andy Burns wrote
(in article ):

I don't know what the intended area for the relay is, but thought it
worth mentioning JIC.

Thanks for your replies, I've had a thought though:

The house also has a Sky dish on it which suppose I could use instead, what
would I need to get the equivalent of Freeview, I don't like the sound of
Freesat much as I'd like to avoid giving Murdoch money?