We’ve been having trouble with our TV aerial, which I bought about 10 years ago–and not just that we’re a few miles downwind from the ocean or that birds have occasionally pooped on it. :rolleyes: UHF stations like 24, 38 (“world channel”),48, 50, and 67 have come in poorly since:
I replaced a fitting that connects wires to screw-down terminals on top of the aerial; a short connector (double-female receptacle), and a splitter to run one line into two. All three fittings were badly worn.
I impulsively lowered one of the short, angled arms that pivots and faces toward the end of the aerial with the short “ribs,” which ideally points toward the region where the transmitters stand; it had been almost parallel to the ground.
One (detachable) section of the 20-foot-tall antenna mast actually bent, and I had to replace it with a new one.
One of the two longest “ribs” broke, and I slipped a wooden dowel into the broken ends, crimped it with a vise-grip, and stuck the broken rib to the aerial frame with duct tape.
However, I am beginning to think, since the reception isn’t what it had been, that the aerial has given up the ghost.
Any Dopers know something about this?
I have only a little personal experience of TV and radio aerials in the UK, but perhaps I can help.
On a TV aerial, the antenna itself is usually quite small. It ‘collects’ the signal and passes it down via a co-axial cable to the TV or whatever. The signal is very weak, so it is important to do everything possible to conserve it. The number of connectors should be minimised and the cable should be as short as possible without introducing any tight bends. The connectors and cable should be of a high quality. Kinked or crushed cable may need to be replaced.
The other parts of the aerial (other than the antenna itself) are the reflector dipoles. The reflector is either a perforated sheet of metal or a some rods organised into a plane. The dipoles are a sequence of rods spaced out at different distances from the antenna. Note that the intervals between the dipoles are all slightly different. Now, I’m not sure about this, but I imagine that the the reflector and dipoles work together to separate out the various channels. If you imagine the radio signal as a wave, then waves will reflect back and forth from the reflector and dipoles. Where the waves are of a length that is a multiple to the distance between the reflector and a dipole, the reflections will be re-inforced and other wavelengths will be cancelled out.
So, it is important that the aerial is made acurately and that its proportions match the channels broadcast by the transmitter. And, of course, this is why the aerial has to point at the transmitter! If the aerial is damaged in any of these ways, you must expect a loss of signal.
Invest in a new antenna and lead-in cable.
Yep, your TV antenna is whats called a Yagi-Uda array. All those elements (reflective, directive, and driven) are supposed to be of a certain length and certain distance from each other, or your performance will really start to go downhill.
It’s probably time for a new one, and replacing the leads wouldn’t hurt either. Especially if they have splices in them.
Probably not. Yagi-Uda arrays have a single driven element, and tend to work best for small bandwidths. dougie_monty’s antenna sounds closer to a log periodic antenna, for VHF, and not really named for UHF.
dougie_monty, the longest horizontal elements are for the lower VHF channels, 2-6, and possibly also for 7 - 13, so your broken rib shouldn’t be affecting UHF. You might have some intermediate length elements, about a two and a half feet long measured tip to tip (or half that long measured from the central bar to the tips, if they don’t go across the central bar) which also contribute for 7 - 13. For UHF, it’s the smaller elements with a total length of under about a foot, as measured from tip to tip, which matter. It sounds like you also have UHF reflectors like mine, which are bars which point up and forward, and down and forward, at about 45 degree angles, and which each have a bunch of horizontal bars on them. These act crudely like a dish. Since you moved one, and got worse recpetion, try moving it back and see if that helps.
Oops, you are 100% correct. I got them switched in my head. Sorry.
I read you all… 
The aerial was in fact the oldest part of the system. I had replaced the cable only a few years ago.
We live in a mobile home in Gardena, about 35 miles, roughly, southwest from transmitters like Mt. Wilson in the San Bernardino Mountains north of the Los Angeles Basin. Our space is about 300 feet south from east-and-west running high-tension power lines, which have rarely, if ever, affected our reception (in 15 years). The mobile home runs roughly east-west, with the antenna atop the 20-foot mast clamped to the outside wall of the shed, less than 3 feet from the MH wall at the southeast corner. The TVs are near the middle of the dwelling (living room), the southwest corner (dining room), and northeast corner (my room). I used two splitters to connect the one aerial to three TVs.
I forgot to mention that one of the plastic fittings fastened between the screw-on terminal (one of the two) and the metal frame cracked and broke when I first disconnected the worn-out cable adapter; the fitting, of course, had been at the top of the antenna all those years in the hot sun.