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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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New TV aerial for 'strong' or 'weak' signal?
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 |
#2
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New TV aerial for 'strong' or 'weak' signal?
Lobster wrote: 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. |
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New TV aerial for 'strong' or 'weak' signal?
On Fri, 04 Nov 2005 09:55:24 GMT, Lobster
wrote: 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? 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 |
#4
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New TV aerial for 'strong' or 'weak' signal?
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? 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. |
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New TV aerial for 'strong' or 'weak' signal?
On Fri, 4 Nov 2005 10:17:45 -0000, "Christian McArdle"
wrote: 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? 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. 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. -- Frank Erskine |
#6
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New TV aerial for 'strong' or 'weak' signal?
Frank Erskine wrote:
On Fri, 4 Nov 2005 10:17:45 -0000, "Christian McArdle" wrote: 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? Compared with a lower-gain TV aerial, a higher-gain aerial will in general: * be physically larger * produce stronger signals from the direction in which it's pointed * have a narrower beamwidth for signals coming from that direction * have less gain in other directions. So... The weak signal aerial may be larger and more intrusive visually. It definitely should be! It may overload your set unless you insert an attenuator (easily obtained and cheap). 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). 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. Agreed. 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. 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. 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). 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. Some experimentation is often required. 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. -- Ian White |
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New TV aerial for 'strong' or 'weak' signal?
Matt Beard wrote:
Lobster wrote: 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? 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. 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 |
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New TV aerial for 'strong' or 'weak' signal?
On Fri, 04 Nov 2005 13:45:00 GMT, Lobster
wrote: Matt Beard wrote: Lobster wrote: 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? 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. 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? http://www.wolfbane.com/ |
#9
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New TV aerial for 'strong' or 'weak' signal?
sPoNiX wrote:
Lobster wrote: 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? http://www.wolfbane.com/ You could always borrow a freeview box, and plug it in - there's a "configuration" section on the menu on mine that shows s/strength. |
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New TV aerial for 'strong' or 'weak' signal?
Chris Bacon wrote:
sPoNiX wrote: Lobster wrote: 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? http://www.wolfbane.com/ Thanks sPoNiX - should have just guessed the URL, eh? It says I'm 'log periodic' whatever that means; so I spose a standard aerial will do. You could always borrow a freeview box, and plug it in - there's a "configuration" section on the menu on mine that shows s/strength. 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 |
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New TV aerial for 'strong' or 'weak' signal?
In article , davidlobsterpot601
@hotmail.com says... Chris Bacon wrote: sPoNiX wrote: Lobster wrote: 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? http://www.wolfbane.com/ Thanks sPoNiX - should have just guessed the URL, eh? It says I'm 'log periodic' whatever that means; so I spose a standard aerial will do. That's a special type of aerial. |
#12
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New TV aerial for 'strong' or 'weak' signal?
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#13
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New TV aerial for 'strong' or 'weak' signal?
In article ,
Lobster wrote: 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? 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. -- *If tennis elbow is painful, imagine suffering with tennis balls * Dave Plowman London SW To e-mail, change noise into sound. |
#14
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New TV aerial for 'strong' or 'weak' signal?
Lobster wrote:
It says I'm 'log periodic' whatever that means; Are we back onto the subject of Bristol Stool Charts again? ;-) -- |
#15
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New TV aerial for 'strong' or 'weak' signal?
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. ;-) 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. |
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New TV aerial for 'strong' or 'weak' signal?
Christian McArdle wrote: snip Don't even think of using crappy "TV coaxial" cable, you might as well use garden twine. 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? -- Steve F |
#17
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New TV aerial for 'strong' or 'weak' signal?
In article , Dave Plowman (News)
writes In article , Lobster wrote: 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? 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. ;-) Good advice there 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. 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?.. -- Tony Sayer |
#18
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New TV aerial for 'strong' or 'weak' signal?
In article , Matt
writes Lobster wrote: It says I'm 'log periodic' whatever that means; 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... http://www.wrightsaerials.tv/LP45tiltedminidish.htm -- Tony Sayer |
#19
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New TV aerial for 'strong' or 'weak' signal?
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? 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% 30m = you might struggle to get a 100% decent connection (although it might work a bit) 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. |
#20
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New TV aerial for 'strong' or 'weak' signal?
In article ,
tony sayer wrote: 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... http://www.wrightsaerials.tv/LP45tiltedminidish.htm Classic type I remember was a 'V' with sort of half width reflectors spaced along either leg. -- *If Barbie is so popular, why do you have to buy her friends? * Dave Plowman London SW To e-mail, change noise into sound. |
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New TV aerial for 'strong' or 'weak' signal?
In article ,
Christian McArdle wrote: 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. It's not just losses but picking up rubbish on a poorly screened downlead. Made worse by many cheap aerials not actually being matched to 75 ohms. -- *No sentence fragments * Dave Plowman London SW To e-mail, change noise into sound. |
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New TV aerial for 'strong' or 'weak' signal?
On Fri, 4 Nov 2005 14:58:01 -0000, Rob Morley
wrote: http://www.wolfbane.com/ Thanks sPoNiX - should have just guessed the URL, eh? It says I'm 'log periodic' whatever that means; so I spose a standard aerial will do. That's a special type of aerial. A good one, with low/medium gain but a very clean polar diagram and wide bandwidth. If that's what wolfbane is suggesting there must be reason for it, not that WB can't be wrong, but if it's just a matter of sourcing a log periodic against a random alternative, if I were you that's what I'd use. You could do worse than make a posting on uk.tech.broadcast reporting your Wolfbane results. There very helpful professional aerial contractors on there. Bill Wright is one of them. http://www.wrightsaerials.tv/ DG |
#23
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New TV aerial for 'strong' or 'weak' signal?
tony sayer wrote:
In article , Matt writes Lobster wrote: It says I'm 'log periodic' whatever that means; 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... http://www.wrightsaerials.tv/LP45tiltedminidish.htm Thanks, but I knew that anyway. -- |
#24
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New TV aerial for 'strong' or 'weak' signal?
tony sayer wrote:
In article , Dave Plowman (News) writes In article , Lobster wrote: 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? 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. ;-) Good advice there 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. 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?.. OK, I'm learning fast today (from a standing start as regards TV aerials etc!). Here's my Wolfbane table: http://tinyurl.com/7kuhv or http://www.wolfbane.com/cgi-bin/tva.exe?DX=L&HT=10&OS=SJ907730 I assumed the top transmitter was the one to go for being nearest (1 mile away); that's the one which said "log periodic" aerial. But I gather that's not the transmitter to go for then?! In fact, my PC TV card has come back to life (sort of) and shows it was tuned into Winter Hill, 30 miles away. All the aerials in the street point that way (and it's consistent with the quoted bearing of 329 deg. And for that, "amplified extra hi-gain" aerial is specified. "Weak" signal then? I'm a bit ****ed off the aerial's come down, as I had a guy up there about a year ago rewiring it when I set up an internal distribution system (yes, all CT100 cable!) and funnily enough he didn't mention it was obviously on its last legs (the square section has corroded right through and snapped). Anyway, the bugger's not getting a return trip out of it as I'm planning to diy. So do I gather the Screwfix aerials (16203 looks very like the old one, and I think the neighbours) are a bit crap then? Thanks David |
#25
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New TV aerial for 'strong' or 'weak' signal?
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?.. OK, I'm learning fast today (from a standing start as regards TV aerials etc!). Here's my Wolfbane table: http://tinyurl.com/7kuhv or http://www.wolfbane.com/cgi-bin/tva.exe?DX=L&HT=10&OS=SJ907730 Yes, well a mile away from a small repeater no problem at all unless you have a stonking great big hill in the way. That TX is on Group A for analogue transmissions but the log would have been recommended for future digital services unless their already in existence. A wideband type will do fine I can't see any engineering reason why a log should be used. And with those sort of powers involved no worries about overload. The neighbours aerials were probably put up a long time ago before the existence of the relay station, and perhaps some of them are now tuned to that perhaps, but not pointing at it!. In any case they'd be from group C and well of resonance for the local.. -- Tony Sayer |
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New TV aerial for 'strong' or 'weak' signal?
On 4 Nov 2005 08:51:25 -0800, Fitz wrote:
Christian McArdle wrote: snip Don't even think of using crappy "TV coaxial" cable, you might as well use garden twine. 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? No. Poor coax will attenuate - some frequencies more than others, but if the antenna kicks out enough, it will not be an issue. Poor coax unless its totally BROKEN and in high signal areas, will not introduce ghosts or pickup MUCH in the way of noise and interference. Good coax is better, but bad coax and a decent antenna beats good coax and a piece of coat hanger any day |
#28
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New TV aerial for 'strong' or 'weak' signal?
In article ,
The Natural Philosopher wrote: No. Poor coax will attenuate - some frequencies more than others, but if the antenna kicks out enough, it will not be an issue. Your knowledge of this subject is lacking. Poor coax unless its totally BROKEN and in high signal areas, will not introduce ghosts or pickup MUCH in the way of noise and interference. Rubbish. A kink or badly made off connector WILL intoduce reflections and losses. Poor quality cable will also have poor impedance consistency, again adding to the problem. Couple that with the increase in attenuation with higher frequency and you have a recipe for disaster. I do understand YOUR motivation to do every thing "cheap", but don't advise others to waste their money in the same way please. Good coax is better, but bad coax and a decent antenna beats good coax and a piece of coat hanger any day Not necessarily. -- AJL Electronics (G6FGO) Ltd : Satellite and TV aerial systems http://www.classicmicrocars.co.uk : http://www.ajlelectronics.co.uk |
#29
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New TV aerial for 'strong' or 'weak' signal?
In article , Mark
wrote: Lobster typed: Both Macclesfield and Langley are only local repeaters which may have only recently been erected and at 36 and 6 watts ERP respectively are very low power and intended to fill dead spots locally, fine if you are in one of these, but note that they are Vertically polarised. Have you checked what is being broadcast? Most repeaters carry only 4 analogue channels. A broadband Ariel may work fine with the two local transmitters but may struggle receiving digital from Winter Hill. I fear that any sort of washing powder will not receive digital TV services. :-) -- AJL Electronics (G6FGO) Ltd : Satellite and TV aerial systems http://www.classicmicrocars.co.uk : http://www.ajlelectronics.co.uk |
#30
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New TV aerial for 'strong' or 'weak' signal?
In message , Chris Bacon
writes sPoNiX wrote: Lobster wrote: 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? http://www.wolfbane.com/ You could always borrow a freeview box, and plug it in - there's a "configuration" section on the menu on mine that shows s/strength. Well, when you can buy them for less than forty quid, just buy one -- geoff |
#31
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New TV aerial for 'strong' or 'weak' signal?
I assumed the top transmitter was the one to go for being nearest (1
mile away); that's the one which said "log periodic" aerial. But I gather that's not the transmitter to go for then?! Log periodics are used for transmitters that are located very close to the receiving station. The advantages of them for this situation a 1. Very even frequency response means that a lower frequency high power transmission (think analogue) won't overpower the weak low power transmission which might happen to be at a higher frequency (think digital). Log periodics are inherently wideband and suitable for digital transmissions that may be far from the original analogue band of the site. They tend to be more expensive and have lower gain than a conventional Yagi, though. 2. Very tight side and rear lobes help prevent the reflections and ghosting that are characteristic of being in a high power area close to the transmitter. However, most of the aerials might use a high gain pointed at the far away transmitter either because 1. the relay wasn't known about. 2. the relay is of exceptionally low power or is not line of sight 3. the relay doesn't support digital. 4. there is a large reflective object, such as a gasometer causing an exceptionally hard ghost image from that relay which is easier solved by pointing at Winter Hill than by fiddling about with stacked arrays. Christian. |
#32
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New TV aerial for 'strong' or 'weak' signal?
In article , Christian
McArdle writes I assumed the top transmitter was the one to go for being nearest (1 mile away); that's the one which said "log periodic" aerial. But I gather that's not the transmitter to go for then?! Log periodics are used for transmitters that are located very close to the receiving station. The advantages of them for this situation a 1. Very even frequency response means that a lower frequency high power transmission (think analogue) won't overpower the weak low power transmission which might happen to be at a higher frequency (think digital). Log periodics are inherently wideband and suitable for digital transmissions that may be far from the original analogue band of the site. They tend to be more expensive and have lower gain than a conventional Yagi, though. 2. Very tight side and rear lobes help prevent the reflections and ghosting that are characteristic of being in a high power area close to the transmitter. Umm, that doesn't sound like very precise science Christian. Can you give your reasoning in a bit more detail?... However, most of the aerials might use a high gain pointed at the far away transmitter either because 1. the relay wasn't known about. Correct.. 2. the relay is of exceptionally low power or is not line of sight Well if the main TX is sufficient then yes why bother to move/change the aerial.. 3. the relay doesn't support digital. Yes.. 4. there is a large reflective object, such as a gasometer causing an exceptionally hard ghost image from that relay which is easier solved by pointing at Winter Hill than by fiddling about with stacked arrays. Is there such a large object?. And if so, wonder hoe Wolfbane would have known about it?... -- Tony Sayer |
#33
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New TV aerial for 'strong' or 'weak' signal?
2. Very tight side and rear lobes help prevent the reflections and
ghosting that are characteristic of being in a high power area close to the transmitter. Umm, that doesn't sound like very precise science Christian. Can you give your reasoning in a bit more detail?... The gain response of a log periodic is very smooth, without and rear or side lobes that can make setting up in a reflective environment so difficult. A quick browse of the internet should find you some charts of log periodics and yagi arrays for comparison. Christian. |
#34
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New TV aerial for 'strong' or 'weak' signal?
Christian McArdle wrote:
Log periodics are inherently wideband and suitable for digital transmissions that may be far from the original analogue band of the site. They tend to be more expensive and have lower gain than a conventional Yagi, though. Actually the gains of typical TV log-periodics are not so low as commonly supposed. They compare well with the so-called 'wideband Yagi' types, particularly at the LF end of the band. The trouble is that the manufacturers only tend to quote the gain of Yagis at the HF end of the band, where they are actually working as Yagi arrays. At the LF end they are really corner reflectors - all the gain comes from the arrangement of the dipole and the angled reflector and the directors are doing very little. The gain at channel 21 is typically 3 dB (or more) less than at channel 68. In the past the manufacturers haven't told you that, and some may have quoted exaggerated gain figures anyway. Take a look at the DTG/CAI document "Guidelines for the use of Benchmarked Aerials" http://www.dtg.org.uk/publications/b...rk_aerials.pdf. Most of the wideband Yagi products which have been approved under this scheme fall in Standard 2 or 3, the former requiring forward gain of 7 to 10 dBd and the latter 5 to 8 dBd. In comparison the spec. for log-periodics (Standard 4) requires a flat 7 dBd. So in Group A, a small Yagi (Standard 3) actually has 2 dB less gain than the log and the quite large Standard 2 product only equals the log's performance. For an up-to-date list of benchmarked aerials see http://www.cai.org.uk/downloads/CAI%...g%20Scheme.pdf The list on the DTG site seems to be out of date. -- Andy |
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New TV aerial for 'strong' or 'weak' signal?
So in Group A, a small Yagi (Standard 3) actually has 2 dB less gain
than the log and the quite large Standard 2 product only equals the log's performance. I hadn't realised that the wideband yagis were quite so bad. I thought that the wideband criteria would favour log periodic, but I hadn't realised that they would actually surpass yagis in gain for large parts of the spectrum. Christian. |
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New TV aerial for 'strong' or 'weak' signal?
Lobster wrote:
Here's my Wolfbane table: http://tinyurl.com/7kuhv or http://www.wolfbane.com/cgi-bin/tva.exe?DX=L&HT=10&OS=SJ907730 I assumed the top transmitter was the one to go for being nearest (1 mile away); that's the one which said "log periodic" aerial. But I gather that's not the transmitter to go for then?! In fact, my PC TV card has come back to life (sort of) and shows it was tuned into Winter Hill, 30 miles away. All the aerials in the street point that way (and it's consistent with the quoted bearing of 329 deg. And for that, "amplified extra hi-gain" aerial is specified. "Weak" signal then? I'm a bit ****ed off the aerial's come down, as I had a guy up there about a year ago rewiring it when I set up an internal distribution system (yes, all CT100 cable!) and funnily enough he didn't mention it was obviously on its last legs (the square section has corroded right through and snapped). Anyway, the bugger's not getting a return trip out of it as I'm planning to diy. So do I gather the Screwfix aerials (16203 looks very like the old one, and I think the neighbours) are a bit crap then? OK, update from the OP... I went up to the chimney for a shufti yesterday and really wasn't happy up there, so decided I'd best get a pro in. Today I was quoted 47+vat for a straightforward replacment of the existing bog-standard 8-element aerial; or about 90+vat if I wanted a digital-compatible one (and that's definitely just for the aerial, as all the cable is already new CT100). Wow! The guy said it would be one like 'next door's - which from my uneducated viewpoint looks something like this one: http://www.wrightsaerials.tv/029%202%20hi%20gain%20&%20DAB.html. I reckon about 1 in 20 aerials in our street are like that; the rest are like mine. Is this beast really so much more expensive than a common or garden aerial, and is it necessary? Assuming labour is the same for both aerials, this fancy thing alone is about 50 quid *more* than the standard item. And Screwfix sell a digital aerial (Maxview) for 7 quid. So is this rigger guy taking the proverbial? Seriously thinking about diy'ing again, if I'm going to have to pay 100 quid :-( I'd definitely rather be future-proof and have a definitely digital-compatible aerial. Incidentally, I already use a feed off the (now broken) aerial for the digital TV card in my PC, and that seemed to work perfectly OK. Does that mean a standard aerial should be OK? As in, is digital TV reception "all or nothing"?? Thanks David |
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New TV aerial for 'strong' or 'weak' signal?
Incidentally, I already use a feed off the (now broken) aerial for the
digital TV card in my PC, and that seemed to work perfectly OK. Does that mean a standard aerial should be OK? As in, is digital TV reception "all or nothing"?? Nah. It's not all or nothing. The bit rate gets worse and you start getting drop out, particularly in bad weather. If you're going to pay for someone to be up there, you might as well fit something decent rather than a crappy contract aerial. Christian. |
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New TV aerial for 'strong' or 'weak' signal?
On Mon, 7 Nov 2005 17:43:20 UTC, Lobster
wrote: Assuming labour is the same for both aerials, this fancy thing alone is about 50 quid *more* than the standard item. And Screwfix sell a digital aerial (Maxview) for 7 quid. But I guess you get what you pay for. I got a nice 45 element wideband antenna for about 30 quid (plus VAT). The 75 element one was about 10 quid more, AFAIR. That's a Televes DAT 45 (or 75) which is on the DSG 'recommended' list. Oh, that's from CPC. -- The information contained in this post is copyright the poster, and specifically may not be published in, or used by Avenue Supplies, http://avenuesupplies.co.uk |
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New TV aerial for 'strong' or 'weak' signal?
In article , Christian
McArdle writes I assumed the top transmitter was the one to go for being nearest (1 mile away); that's the one which said "log periodic" aerial. But I gather that's not the transmitter to go for then?! Log periodics are used for transmitters that are located very close to the receiving station. How do you work that one out?. Are we at the TX or RX end?. Actually logs are used extensively at small relay stations but mainly for logistic reasons.. The advantages of them for this situation a 1. Very even frequency response means that a lower frequency high power transmission (think analogue) won't overpower the weak low power transmission which might happen to be at a higher frequency (think digital). That can be either way round and why should a log aerial be sooo much better?. Sorry but that reasoning is rather weak... Log periodics are inherently wideband and suitable for digital transmissions that may be far from the original analogue band of the site. They tend to be more expensive and have lower gain than a conventional Yagi, though. Not so simple as that. Wideband yes, but if your digital transmissions are in a group setting like Crystal palace in London, no particular sense in a wideband aerial there.. 2. Very tight side and rear lobes help prevent the reflections and ghosting that are characteristic of being in a high power area close to the transmitter. Not really that simple as the AGC will adjust the TV RX gain accordingly. Anyway digital, does it matter?. -- Tony Sayer |
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New TV aerial for 'strong' or 'weak' signal?
Christian McArdle wrote:
I hadn't realised that the wideband yagis were quite so bad. Bad in Group A - my point exactly. And I was talking about 'quality' benchmarked product. If you look at the cheapo contract wideband 10-eles you can find gain at 470 MHz of less then 0 dBd! (Also beware vendors who quote gains in dBi and hope you haven't noticed.) I thought that the wideband criteria would favour log periodic, but I hadn't realised that they would actually surpass yagis in gain for large parts of the spectrum. NALOPKT. Log-periodics make a lot of sense, especially if you want to fit Group W for future-proofing. -- Andy |
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