Quote:
Originally Posted by wheels14
I'm new to antennas in general, but I'm having a hard time understanding why channels with weaker signals come in fine, but that channel in particular isn't being picked up.
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Think of a kid on a swing in the back yard. If you push (and pull) the swing at the same frequency the swing wants to oscillate at on it's own (natural frequency), the excursion will increase and the kid will be happy.
If you push (and pull) at a much higher frequency, the kid on the swing will sort of wiggle around a bit, but won't really get going in any meaningful way. You push a little, and the swing starts to move, but by then you're pulling and cancelling out a lot of what you just put into it, then you're pushing again, and so on. Same thing if you push/pull too slowly - it never really gets going.
Radio waves sort of work like that, in that the receiving antenna (and presumably the transmitting antenna) has its own natural frequency, and works best with a particular channel, but the element(s) is(are) close enough in size to get a range of imperfect frequencies (wavelengths) very well, but get too far away in frequency and the ability of the antenna to receive the signal is degraded to the point where the result isn't usable by the TV (pushing/pulling the kid on the swing too fast or too slow, so not enough excursion to drive the tv effectively).
Low-band VHF frequencies (channels 2-6) have wavelengths of something around 17 ft (channel 2) down to around 11.5 ft (channel 6), high-band VHF is around 5.5 ft (channel 7) down to around 4.5 ft (channel 13), and UHF band is around 2 ft (channel 14) down to 1.4 ft (channel 51).
Antenna elements are smaller than that, I think typically 1/2 wave or less, but you can see how big a difference there is just between channel 13 and channel 14 - your antenna wants to be pushed/pulled much quicker (473 million times per second on 14 up to 695 million times per second on 51) than the signal is pushing and pulling on channel 13 (213 million times per second).
Look at Antenna Direct H-VHF/UHF antennas, and you can see the short elements for UHF, and the much longer ones behind it for H-VHF. Then look at a full-range or L-VHF and you'll see the much much larger elements for channels 2-6.
Despite marketing claims by some manufacturers, you just can't change the laws of physics, and you need an antenna designed for the channels you want to receive.
Unless you have a super strong signal, in which case you can get tv with a paper clip. But that's like The Hulk pushing the kid on the swing - it'll go at whatever speed he wants it too, by brute force.
Just my take on it, but I'm a mechanical engineer, not an EE, and certainly not an expert (or even particularly knowledgeable) in RF.
