All posts by Chris S
Below are all of Chris S's postings, with the most recent are at the bottom of the page.
Nick. Its unfortunate that the reduction in available channels forced on the tv industry means that an area like yours is bound to suffer since it is over 50 miles away from a main transmitter. Since you already have a high gain aerial for the high frequency end of the band I think this is the best you can use for getting com7 and 8 from Tacolneston short of using two of them! If you added a small vertically polarised aerial for Alderborough at least you should get good reception of multiplexes 1, 2 and 3.
My situation is similar on the coast so I have gone for the satellite solution .free to air satellite receivers can be had much cheaper than a freesat receiver . (but I don't recommend the really cheapest ones) These pick up freesat channels (plus other satellites if wanted) but just don't have the programme guide. by using a quad LNB head four receivers in four rooms can be used from one dish.
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re optimising gain and avoiding interference. adjustable gain amplifiers are not that expensive . Mounting the aerial in the clear to avoid picking up reflections helps as does multi element and stacked aerials .Where interfering transmitters are behind the aerial choose one with low reverse pick up.
"foreign" interference comes via refraction in the atmosphere (trophospere) rather like the effect of a mirage where a distant town can be seen further away than it should. UHF does not bounce from the ionosphere. Its best to have gain in the aerial as amplifier gain comes with noise and the possibility of strong interference knocking out several channels rather than one.
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There are variable gain masthead amplifiers readily available. The ones I have seen cannot be adjusted remotely. Though it sounds like a great idea. Stacked aerials are two or more above each other. They might reduce pick up of distant transmitters. Whereas side by side aerials will narrow the reception beam to reduce pick up of unwanted transmitters near to the same direction as the wanted transmitter.
You could have the amplifier in the loft preferably connected by low loss coax (satellite type) but next to the aerial is the best position. At 30miles from Tac I have set my amp to about 18db ,but may reduce it when I get a higher gain aerial.
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Nick . This is a typical variable gain amp . you set gain with a screwdriver anywhere between 7 and 22 db.
Proception 7-22 dB 1 Way Variable Gain Aerial Masthead Amplifier with F-Type Connection Power Supply: Amazon.co.uk: Electronics
The aerial principles such as combining and stacking from analogue days . are still valid . Of course baluns are now always used and correct methods of filtering and impedance matching too. Even connecting two parallel aerials to a standard splitter will give correct matching .Though only around 2db gain over a single aerial the combination has a narrower beam . Useful to reject off beam interference. Like you say some of the modern aerials are as good as a pair of yagis .Combining bigger aerials gets expensive.
heres a website with loads of info and aerial tests that might help. Aerials, TV Aerial and Digital Aerial
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Nick . Yes . The setting would be different between 8ft and roof top. Actually as youre over 50 miles away from the main transmitters the maximum gain may well be the best setting!
Incidentally in that website of aerial info I mentioned he doesn't think much of the tri beam aerials . Theyre no better than good x beam aerials and catch the wind . Its quite common to see the reflectors blown off!
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nick. yes I remember the j-beam square reflector . The x shaped elements give wider bandwidth . The triax or Wolsey modern aerials use rounded elements . The gain seems no different than x beams. I believe the large reflectors are to reduce pick up in the 180 degree direction . (quite useful for you as probably some of you interference is from Dutch and German transmitters ) They must also act as "corner reflectors" presumably to boost performance over part of the frequency range . Its true that too much amplification can be as bad as too little but can't tell if that's your problem. I thought you were aiming for Tacolneston because Sudbury does not have com7 and 8 . Agreed that the coverage checker indicates you get a slightly weaker signal from Tacolneston.
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The x is a way of simulating a thick element . Its cheaper and lighter than a true thick element . Thick elements have a wide bandwidth and are shorter than thin elements for a given frequency . You can see true thick element aerials at airports . The j aerial was described as a skeleton slot . I think its more like a stacked quad. Your version of the j is interesting . I think if you like building aerials a "grid" (bill board antenna) is less critical to get right . That's four dipoles in front of a flat screen. It is a medium gain slightly better than a log . I would like to build one with directors tuned for com7/8. In recent times a new version of this a "Hoveman Grey " is popular . seemingly having the same performance but easier to build. Look online.
I will probably stop discussing design here as this site is mainly for answering peoples reception problems. If you would like further discussion I am at dottir@hotmail.com
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Robert the coverage checker indicates that at your location you should get a good signal with a medium size wideband aerial. I assume that you already have a wideband aerial if you used to get all the cannels listed on this page . The channels you lost are in mid band so I suspect a fault in your wiring. or if in the loft the aerial is in a poor position.
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yes a Kooman . but nowadays they use large x shapes rather than true fullwave dipoles to get the full UHF bandwidth . I am 30 miles from Tacolneston so am thinking of building one as it covers the full band with a peak near UHF channel 55 56 handy for com 7 and 8.
A large group K is probably the best you can purchase.
Home building in your area I would build or buy a small group A vertical polarised for ALderbrough com 1 2 3 and combine it with a narrower band amplified version of a group B (horizontal) . com 4 5 6
Adding reflectors wont increase the gain . Would it cut down unwanted reverse direction reception any better than a single large grid reflector?
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Monday 13 August 2018 2:27PM
Jo . Some of the Sudbury channels have moved to a lower frequency since the 1st of august . You probably now need a wideband or group K aerial. The retune is because under pressure from mobile phone companies the tv in Britain Europe and America have had to loose some frequencies. Freeview cannot give you a free aerial because your house can watch tv on sky . You will need to buy your own aerial. They can be bought for diy under 50 . Its the cost of an installer that might be 500 though it should be possible to find some one considerably cheaper than that.