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Thread ID: 66763	2006-03-06 21:29:00	UHF aerial in Kohimarama	chrisath (9927)	PC World Chat

Post ID	Timestamp	Content	User
436100	2006-03-06 21:29:00	I have just moved into the Kohi area of Auckland, and the previous owners had only a Sky TV digital feed into the house. I have installed a new VHF aerial which works fine for free to air channels and is sending strong signals to three TV's in the house. I have found an old UHF aerial (which looks in reasonable condition) under the house and installed it on its own post on the roof, with the feed going through a combining box (not sure what this is called) for VHF & UHF. i have pointed the UHF aerial in roughly the same direction as other UHF aerials around me. Unfortunately the UHF signal is not strong enough to pick up Triangle and Prime. When i connect just the UHF feed into the house i do get TV1 (not very well) and TV2 & TV3, so the aerial does seem to work, but perhaps not well enough? My wife has said i am not to spend money on it, and why do we need it! Any thoughts as to why this UHF feed does not work please?	chrisath (9927)
436101	2006-03-06 21:47:00	don't know the aera but generally speaking UHF is often weaker signal and you need it to be very strong to feed 3 tv's. if you connect it to one tv and you get an almost passable pic then simply change the combiner for an amp (boost UHF only) and feed it through. if no UHF pic then forget it, throw it out.	tweak'e (69)
436102	2006-03-06 23:11:00	First make sure that it looks similar to all the local UHF antennas around you, it may be inadequate for your locality, which might explain the previous owner's strategy . Also, if everybody else has the same type you can assume that they have adequate picture and you know to look at your installation for the answers . Alternatively, you could try raising the height of the UHF antenna, preferably by putting it above the VHF by up to a metre or more . A further problem could be the coax feeder, it may be an old VHF cable and they have significant losses at UHF, or it may have had water in it which increases the losses . It might be ok at VHF but useless at UHF . You could also use an amp as previously suggested, but use a masthead type, not one down at the TV end of the cable . If there is crap there now, all you will get is amplified crap . Make sure that you have actually wired the antenna correctly . I don't mean to insult your intelligence, but I have seen every possible variation from trying to take the signal feed off a mounting bolt, to bundling the coax inner and outer together under one terminal . Finally, there are two signals for Prime, if you can get it at all, tune for the second and see if it is better . My Prime is excellent, but once or twice a year signal propogation conditions wipe it out in the late evening, but changing channels gives me an alternative source (which is over your way I think) . Cheers Billy 8-{)	Billy T (70)
436103	2006-03-07 00:01:00	This bit interested me, as a layman.... i have pointed the UHF aerial in roughly the same direction as other UHF aerials around me. Where we live we have one antenna pointing east for channels 1 and 2 and a different, smaller, antenna on the same pole pointing west for 3 and 4 (Prime here).	Scouse (83)
436104	2006-03-07 00:12:00	it is not entirely uncommon to have multiple transmitter sites with the old VHF (TV1, 2, 3) at one, the UHF channels at another, and repeaters for difficult reception areas located at two or three other sites. More often than not though, all the main channels are co-located with only the repeaters (translators) for difficult reception areas breaking the mould. Cheers Billy 8-{)	Billy T (70)
436105	2006-03-07 22:19:00	many thanks to your responses. 1. The coax cable from UHF aerial to VHF/UHF joiner box is only 4mm gauge. i have some heavier gauge like that used for digital feed and will try that. 2. UHF Aerial is quite long, (looks similar to Long Tom made by LINCRAD aerial company). However on one side one of the aluminium ears is missing at the very end, this is one of about 20. (so i was thinking should not make much difference, but may be i'm wrong)! 3.i believe i have wired it correctly, and at the weekend will try a complete 360 degree sweep to see if i can pick up any Prime signals, rather that rely on what is see on roofs in vicinity. thanks for all yr comments.	chrisath (9927)
436106	2006-03-07 22:44:00	the aerial is long with a U shaped braket holding two halves? if so your in a weak signal aera and will most likly need a masthead amp.	tweak'e (69)
436107	2006-03-08 01:17:00	However on one side one of the aluminium ears is missing at the very end, this is one of about 20. (so i was thinking should not make much difference, but may be i'm wrong)! That's a Yagi antenna. The elements in front of the "driven element" (the one connected to the lead) are called "directors". Half of the one at the very end being broken off wil make the traditional five-eighths of very little difference. More than about six directors add only to the cost, not the signal. ;)	Graham L (2)
436108	2006-03-08 03:51:00	The coax cable from UHF aerial to VHF/UHF joiner box is only 4mm gauge. i have some heavier gauge like that used for digital feed and will try that. Well, IMHO 4mm sounds far too thin to be good quality UHF cable. 6-8mm sounds more like it. I believe i have wired it correctly, and at the weekend will try a complete 360 degree sweep to see if I can pick up any Prime signals, rather that rely on what is see on roofs in vicinity. You will have to retune for the Prime repeater. I'd phone and ask them where their repeaters are and what channel numbers they use. Give them your street address so that they can look at their coverage maps. At my location I find the repeater on approximately Ch45, about 10 channels below the main signal at around Ch55. These are only approximations. I don't agree with Graham that "more than about six directors add only to the cost, not the signal". Extra directors add directivity and gain, period. They may not be of any practical advantage in good signal areas but they sure as hell make a huge difference in fringe areas. Cheers Billy 8-{)	Billy T (70)
436109	2006-03-08 04:21:00	Billy, I've done the measurements. If the outer directors make no useful difference on a Yagi tuned for one frequency, they make 5/8 of not very much on a Yagi built for a band. What's the UHF TV band? 400Mhz-800 MHz or thereabouts? A 2:1 ratio. These are Yagis, not log periodics. Practical LPs don't use all that many elements either. There's a reason; beyond a certain point there's no point. ;) TV antennae are made to sell to non-technical people. "Longer must be better". There's a lot of antenna theory around. The practice is what happens when you get into the real world. Any elements beyond "about" six are just extra windage and cost. They do nothing.	Graham L (2)
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