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I have two antennas:

  • antenna 1 carries CATV signals channels 2-29 which I believe use carrier frequencies from around 55.25MHz up to 253.25MHz

  • antenna 2 carries OTA HDTV signals on UHF channels 21-49 which I believe use carrier frequencies from around 513.25MHz up to 579.25MHz

Other than using an antenna switch how can I combine these into 1 input?

I've tried using a basic antenna splitter/combiner but the tuner has a hard time picking up many of the channels. Why does that not work? I assume its because there is unwanted signal beyond each of those spectrums that creeps into the signals from the other antenna?

Is there equipment to cleanly filter out the unwanted bands and recombine the ones I want?

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  • \$\begingroup\$ What exactly does "basic antenna splitter/combiner" mean? Since we don't know what this is, the clue is not very useful. Typical splitters are divided between VHF (ch. 2~13 up to 220MHz) and UHF (ch. 14-69, 470MHz & up) \$\endgroup\$ – Richard Crowley Dec 22 '16 at 21:36
  • \$\begingroup\$ @ richard, really? \$\endgroup\$ – Octopus Dec 22 '16 at 21:38
  • \$\begingroup\$ VHF/UHF antenna splitters are quite common. They are often built right into the antenna in modern products. But since you mention CATV, we really don't know what you are trying to do here? \$\endgroup\$ – Richard Crowley Dec 22 '16 at 21:42
  • \$\begingroup\$ There are two different kinds of things called "splitters". One kind simply takes a broadband (multi-channel) signal and sends identical copies off to several different outputs. For example, to send an antenna signal to several TV receivers. The other kind of "splitter" is actually a frequency-dependent "crossover". It has a VHF (2-13) port, and a UHF (14-69) port. Freuently used to combine the VHF part of your antenna with the UHF part into a single down-lead. This is the kind of "frequency multiplexing" you seem to be asking about. \$\endgroup\$ – Richard Crowley Dec 22 '16 at 22:04
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    \$\begingroup\$ the devise you want is called a "diplexer", high frequencies get split off one way, lower frequencies go the other way. \$\endgroup\$ – Sam Dec 22 '16 at 22:33
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The device you want is a Diplexer. They are designed for doing exactly what you're trying to do. In fact, more than a few of the diplexers I've seen are actually for CATV in the first place, although I'm not sure if there's much choice of the frequency bands.

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  • \$\begingroup\$ Most of the ones available in North America seem to be for combining (or splitting) CATV and Satellite so the frequency split is at around ~900MHz or so. I have found some UHF/VHF diplexers with the split frequency around ~450MHz (the one I need) but they seem to be only available from Asia and Oceania. \$\endgroup\$ – Octopus Jan 11 '17 at 16:44
  • \$\begingroup\$ @Octopus In that case, you may need to build your own. You really just need a half decent high pass filter on one output and a low pass filter on the other. Thankfully there are plenty of RF filter calculators on the internet that will spit out component values when given cutoff frequencies and bandwidths and the like (the cutoff frequency is the point where the power through the filter is reduced by half) \$\endgroup\$ – Sam Jan 11 '17 at 21:52

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