I'm about to mount a loft aerial for TV...

[The Natural Philosopher]

The map has a sorta built in compass.

[pehowland]

I'm afraid most of the replies above are missing the point. The correct direction for your antenna may, in fact, not be the same as for your neighbour - which is why all the antennas in your street are not all pointing in the same direction. In reality, the TV signal from the transmitter may not only come directly from the transmitter, but also after reflection for local hills, buildings, etc. This is called multipath. The net effect of all these reflections is that the direction of the strongest signal at your house may not be exactly in the direction of the transmitter. The only correct way to align your antenna is to measure the signal strength. In the absence of a meter, the best way to figure out this is to connect a TV. Someone else mentioned this above. Don't muck around with a compass - even if your trigonometric skills are spot on, the signal won't be...

[Bob Eager]

Of course. But the original point I made was that you have to start somewhere - inside a loft it is difficult to know a good starting point. So, use of the bearing, as I did, gives one an initial direction to point the thing. After that, it takes only one brain cell to realise that you adjust it for maximum signal strength and minimum gosting, etc.

[Huge]

On a related topic, anyone know why the Freeview channel numbers in the RT don't correspond with those displayed by the Freeview TV, PVR and digibox I own?

[Mungo "Two Sheds" Toadfoot]

Yeth.

Si

[Andy Hall]

It's free. Did you expect precision? ;-)

[Andy Burns]

I don't buy the RT, but ...

The channels occasionally get a re-shuffle, have you re-scanned?

If you live somewhere that receives signals from more than one digital transmitter the duplicates can get shunted into the 800 range.

If you have older Sony kit that only uses 2 digit channel numbers it can shunt the 3 digit channels around to fit in the gaps.

[Huge]

Could be, although Sandy Heath is only about 20 miles away, and both the "nearest transmitter" websites posted earlier point to it; the signal is so strong you don't need an aerial on the side of the house facing that way.

I suspect this is the most likely case. Accroding to gtg.org.uk, 5US should be on Ch35 on Sandy Heath, but it's Ch801 here.

Naah, the Sony telly is only a few weeks old & the PVR almost a year. They both do 3 digit channel numbers.

[Andy Burns]

Do you have anything else on ch35, or is it just empty?

[Huge]

OK, a brief investigation determines that the TV is actually correct, it's the PVR that's wrong. The channels are all over the place. It's retuning now as I type.

[MM]

One final question: Can I mount the aerial on a wooden pole? I couldn't buy a metal one this morning, so I bought a thicker type of broom handle from the local hardware store for £2. Does the aerial (normally fixed to a chimney or external metal wall bracket) need to be earthed in some way? The pole will be mounted on a flat piece of timber that runs across the joists in the centre of the loft space.

MM

[tony sayer]

No.. you can tie it up with string if you want!..

[Andy Burns]

yes (given that it's in the loft)

no

[Jethro]

I found a cracking site which had the grid references of all UK transmitters (google for it - I CBA) ... couple of minutes work with a pen & paper, and I had the angle off the north. Took a compass into the loft, and away I went.

I ahd to do that, as it seems no one round my way has an external ariel. Not sure why ....

[Lurch]

On Mon, 09 Jul 2007 06:29:02 -0700, Jethro mused:

Because you're not allowed an external aerial?

[Jethro]

Possible, I guess ... one day I'll stop being so anti social and ask :-) Looking at our deeds and covenants, there's nothing disallowing an external arial ... when we moved in, there was already an internal loft arial, which I was rather chuffed at (not a great head for heights me). As with a lot of things in this house, it was badly fitted, which I corrected, but apart from that I have no complaints. We have cable, so I don't know if it's good enough for freeview (yet).

[Bob Eager]

No problem. One of mine is mounted on a thing called a 'loft lance', which is a pole with a woodscrew-y thing on one end. No good if it's a big aerial, though!

[MM]

Well, it's now done and it is a total success! My picture quality has never been better and I can now even get a watchable Channel Five, too. So much cheaper than forking out £170 for the aerial man to install one on the chimney. Cost to me: Wilkinson 18-element aerial for weak signal areas: £8.99, pole: £2, Wilko coaxial plugs and sockets: £2, Wilko 4m of cut-your-own coaxial cable £1, plus a few sundry screws and clips. DIY at its finest!

Thanks to everyone for all the advice.

MM

[Hugo Nebula]

On Sun, 08 Jul 2007 22:19:30 +0100, a particular chimpanzee, Harry Bloomfield randomly hit the keyboard and produced:

Or wait until a sunny day, measure the angle of the shadow cast by the sun at its highest (up to a few minutes before or after 12:00GMT depending on how far east or west you are of the Greenwich Meridian) relative to the orientation of your house. You then need to adjust for the difference between true north and OS grid north (as shown on your OS map).

[Andy Hall]

Yes but this only works on the 21st June.