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September 5th 07, 05:14 PM
posted to rec.radio.amateur.equipment
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Antenna coupler for 50-900MHz
Thanks, all of you!
"Dave Platt" wrote in message ... In article , GGap wrote: Thanks Dave, by antenna coupler I meant a power combiner, but, precisely, since channels which are emitted from tv transmitters (obviously in 2 directions from my home) are not overlapping, nor are adjacent, I think of pointing logperiodical antennas to transmitters and couple them into one tv cable towards receiver. That may work acceptably, if your log periodic antennas have a high enough front-to-back ratio, so that each is rejecting the signals coming from the transmitters "behind" it. Without sufficient F/B rejection, you'll end up with some amount of cancellation/interference between the two. And, even with high F/B rejection in the antennas, you can still end up with ghosting and interference if the antenna pointing "away" from a transmitter picks up a signal reflected from buildings, trees, or mountains. You'll have to accept some amount of signal loss, no matter what you do... the combiner will have some loss, and (to the extent that it doesn't isolate one antenna from the other) each antenna will act as a load on the other and will actually re-transmit some of the other antenna's signal. Building an effective broadband signal combiner isn't rocket science, but neither it is trivial. Frankly, in your situation, I'd recommend that you just buy a commercial combiner. For example, http://www.starkelectronic.com/cmjoiner.htm The first item #0538 is a two-way combiner/joiner made by ChannelMaster, which appears to be designed to do just what you want... $9.95 plus shipping. It takes 75-ohm coaxes from the antennas (you'd need 75-to-300-ohm balun on each antenna) and feeds a 75-ohm downlink with the combined signals. Click on the "Winegard Combiners" link on that page, and you'll see the Winegard CC-7870 (same idea, higher cost) as well as the SD-3700 (which has 300-ohm inputs and a 75-ohm output - no need for separate baluns on the antennas - just run some 300-ohm twinlead from each antenna to the joiner). The other alternate solutions to this problem that wouldn't have the potential ghosting problem would be: use filtering combiners (feasible for one or two "joined" channels, probably too expensive for more than that), or use one antenna with a rotator, or use two antennas and two feedlines and a "which antenna?" switch at the TV set. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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