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Old 18-Oct-2016, 6:14 AM   #1
ZippyTheChicken
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why can't i use a single Channel 2 Dipole and pick up all uhf vhf signals

I know that antenna dipoles are specific lengths to pick up channels and that you can normally pick up most of the UHF range with just a dipole about 12.5 inches

but if I want all the stations from 2 up why can't I just put up one 108" dipole and be done with the whole thing? shouldn't the higher stations also be passed through the longer dipole?
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Old 18-Oct-2016, 3:31 PM   #2
ADTech
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You probably can, you'd just have a lousy antenna on many frequencies. It might be good enough given the digital cliff effect with digital TV, or you might not.

Effectiveness (VSWR) and predictability (reception pattern) both will degrade substantially the further you are from the dipole's resonant frequency.
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Old 19-Oct-2016, 3:13 PM   #3
ZippyTheChicken
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It sure would make life a lot easier...

So what about these homemade antennas then.. most of them for UHF.

How exact do the dimensions of the dipoles have to be for them to work really well? I see the UHF ones like the bay type have one length of dipole. If you are off by a couple inches making them would that throw off the quality of reception a large or little amount?

like what would you guess the amount you could be off in length? 5% 10% or 25%?

some people can just put up anything and get reception but if they were on the lower end of the scale on available nmdb
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Old 19-Oct-2016, 3:56 PM   #4
ADTech
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The engineer's maxim of "TANSTAAFL" applies.

Effective antenna design relies on mathematical relationships.

Well-designed antennas keep both of these principles in mind.

Quote:
How exact do the dimensions of the dipoles have to be for them to work really well? I see the UHF ones like the bay type have one length of dipole. If you are off by a couple inches making them would that throw off the quality of reception a large or little amount?

like what would you guess the amount you could be off in length? 5% 10% or 25%?
Impossible to quantify in general terms. A poorly executed antenna will work adequately, assuming it works at all, until the conditions (signal power, frequency, angle, etc) change enough to throw reception off the digital cliff into the digital abyss. The well-designed and executed antenna will continue to perform well as the conditions change or degrade as long as the user understands its characteristics and properly exploits them.
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Last edited by ADTech; 19-Oct-2016 at 4:04 PM.
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Old 19-Oct-2016, 6:40 PM   #5
ZippyTheChicken
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so then what? manufacturers build to theoretical designs?

I guess there is no real wind tunnel to test all the frequencies at a distance to evaluate design.. you can get a number of station frequencies I would guess or you could put up a very very low power broadcast tower and see how it responds across the whole spectrum.

but like bunny ears you can modify on the fly .. maybe you could do that with a larger design to fine tune it.

anyway .. just a thought that had been going through my head for the past week or so...

the UHF antennas do well without the fine tuning of lengths but VHF requires almost single station dipoles for each frequency .. not really but .. and then UHF is added on ...

I was just wondering that a Channel 2 dipole would have all those Higher Band signals passing through it multipal times which i thought would improve the possibility of catching those signals...

Like a 2 dipole would would catch one 54mhz signal and then that 2 dipole would catch many instances of a 470mhz and above so it would be that much better for UHF.. but seems not

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