Need a new TV aerial; I note Screwfix sell different models for 'strong' and 'weak' signal areas. AFAIK we're in a fairly OK area, but my question is, is there any disadvantage in fitting the 'weak signal' type if it might not be necessary? Otherwise it's clearly not worth even considering paying two quid less for the 'strong' variety?
David
Aerials for weak areas have greater gain, this means that you get more signal, but you also get more noise. If you have a strong enough signal to use a "strong area" aerial you are probably better off using that, otherwise using a "weak area" one may pick up noise that is in the UHF band, but is not the desired signal.
As always it's a case of horses for courses.
Yes. The signal may be too strong for your telly and cause reception problems..
However, if it causes problems it's easily solved by adding an attenuator to the download. A couple of quid each from Maplin)
sponix
Disadvantages I can think of:
The weak signal aerial may be larger and more intrusive visually. It may overload your set unless you insert an attenuator (easily obtained and cheap). It may have a tighter frequency band which makes it less suitable for digital reception on certain transmitters. It may not, but you need to check. Get a wideband version if possible.
However, it doesn't increase the noise as well as the signal. That's the whole point of it. It takes the signal from a smaller segment of the sky, so you get more of the available signal (which can be regarded as a point source) without swamping it from the noise you get from a less directional aerial that takes in the noise from a larger area.
Christian.
The higher the gain, ie the more directional, the more likely it is to have "side lobes", which means that it picks up signals from the _side_ as well as ahead. If you do have a high gain aerial and large metallic structures at certain angles to your line of fire, you risk ghosting (with analogue reception anyway). Some experimentation is often required.
Compared with a lower-gain TV aerial, a higher-gain aerial will in general:
So...
It definitely should be!
The extra gain is not likely to overload your receiver unless you're already in a very strong signal area (and it can never physically damage the TV).
Agreed.
The received signal power increases with a higher-gain TV aerial, but the total received noise power (from all directions) generally stays about the same. This means that the signal-to-noise ratio increases by the amount of the extra gain.
A good high-gain design should not have larger sidelobes (they represent wasted forward gain), so the narrowing of the forward beamwidth will in general *reduce* the risks of ghosting.
If ghosting is a problem, then yes. This is especially true if the aerial is mounted in an attic full of reflecting walls, water tanks and wiring, or outside in a forest of other aerials. Also, TV aerials will not perform correctly if they're mounted too close to other metal objects.
The narrower beamwidth of a higher-gain aerial also means that it needs to be pointed more accurately when it's installed. (Do NOT rely on pointing the same way as all the other aerials in the street - guess why not?) Tune to your weakest *analogue* channel from that transmitter, and get someone to shout (or phone) reports of the picture quality as you turn the aerial.
Thanks to all for the replies.
Without resorting to special equipment, is there a way of finding out the signal strength in my area, eg by entering my postcode onto a website or something?
Thanks David
"configuration" section on the menu on mine that shows s/strength.
periodic' whatever that means; so I spose a standard aerial will do.
Sounded like a good idea - in fact I was just about to double-click on the TV card icon on my PC desktop and read it off there, when I remembered, duh - the aerial's fallen down!!
David
That's a special type of aerial.
And is easily fixed by sticking an attenuator on the cable where it goes into the TV, rather than fitting a lower-gain aerial.
Have a look at what others have in your street.
And I'd then go for a good quality make like Triax and use a double screened downlead - satellite cable. The cost of the materials is low against the labour involved - even when DIYing. ;-)
If you end up with too much signal this is easily cured by an attenuator. The idea is to get a high quality signal and feed it to the receiver with nothing spurious being picked up on the way.
It says I'm 'log periodic' whatever that means;
Are we back onto the subject of Bristol Stool Charts again?
;-)
Yeah. Never use anything worse than CT100, although you need to look hard to get it much under 99p/m for short lengths. The best I could manage was 82p/m inc VAT and delivery for 30m, although did also include 2 F plugs and a coupler. You can get much cheaper copies, though, if you know what you're looking for, but I don't like going up ladders to replace possibly 2nd rate materials, and sometimes the specs aren't as forthcoming.
Don't even think of using crappy "TV coaxial" cable, you might as well use garden twine.
Christian.
Oh dear.
I fear I may have cocked up.
We have just finished (for normal DIY values of finished) our three year house renovation and I left in place the existing cable coming down from the roof, through the wall and under the suspended floor in the living room into the brand new built in cabinets.
We've never had brilliant digital reception, usually ok in good weather but suffers in bad weather and some channels never come through. I put this down to a tiny aerial and the yards of extension cable and about 4 connections needed to make the tv work in it's previous temporary home.
I thought I could simply replace the exisiting tiny aerial with one designed for digital and that the cable would not be the limiting factor.
If I want to stick a new aerial on is it likely that it will be crippled by the undoubtedly poor quality tv aerial co-ax?
In article , Dave Plowman (News) writes
Good advice there:)
Unless your in spitting distance of a main high power transmitter I'd very much doubt that you'll have a problem. Where are you BTW?..
Its a very wideband aerial that looks like a TV aerial but the rods are very short one end and much longer 't other. Useful for ghosting elimination sometimes.
A piccy of one curtsey of Bill Wright...
It depends on many factors.
If you have one run of crappy co-ax with no connections or splices, then the length of the cable is likely to be the main factor. These cable types have very high losses (although for reasons of historical accident are called "low loss" cables). You may find that with a decent high gain wideband aerial and a modest cable run it will work OK.
You could help out a high attenuation run by installing a masthead (or in loft) amplifier, preferably with a frequency response intended to counteract cable loss rather than just a wideband constant type. This will counteract the excessive attenuation of the cable and boost the signal levels so that the noise induced by the inadequete screening is reduced in comparison to the signal.
However, all this depends on cable length. I would say:
< 15m = you might well be lucky anyway 15-30m = an aerial side booster will help you achieve near enough 100%You could also replace the cable from the aerial through the loft and down the wall and just convert to the crappy cable for the concealed section that is too difficult or expensive to replace. If you do this, you must take great care to make a waterproof splice as the cable will be massively affected by water ingress.
Christian.
spaced along either leg.
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