Maury Markowitz
Antenna-Theory.com Newbie
Joined: 07 Oct 2015
Posts: 3
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 Posted: Wed Oct 07, 2015 8:33 pm Post subject: Old VHF/UHF combo antennas |
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I was walking around the neighbourhood admiring all the old TV antennas still up there with broken dipoles, rusted rotors and cut-off wiring.
But then I got to wondering. Reading the classic on merging antennas:
http://www.hdtvprimer.com/antennas/merging.html
The basic rule seems to be that you're going to lose 1/2 of your signal if you combine.
But it seems these antennas did just that, I can convince myself I see two feed lines, one from the VHF and one from the UHF portions. I suspect they didn't lose 1/2 of the signal?
What is the obvious thing that I'm missing here? |
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admin
Site Admin
Joined: 03 Jan 2007
Posts: 247
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| Posted: Thu Oct 08, 2015 5:50 pm Post subject: merging antennas |
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The problem is you don't know the phase of the signals coming down the transmission line. They could be in phase, 180 degrees out of phase, 90 degrees out of phase, whatever.
If signals add in phase, the power adds directly. If 180 degrees out of phase, powers subtract. Everything else is vector summation.
If you add antenna signals, it will likely add for some frequencies and subtract for others, which is why it can be a bit more complicated than you would expect. |
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