Posted: 4/21/2011 7:21:54 PM EDT
| I am fairly certain that you can use one antenna for multiple receivers. Can you use a single antenna for multiple transceivers? |
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I am fairly certain that you can use one antenna for multiple receivers. Can you use a single antenna for multiple transceivers? yes, but you need to isolate the tx and rx freq's from each other we're talking duplexers, combiners and couplers. you don't want the Tx output to get into the receivers. power levels and frequency separation will be the biggest issues. if you have specific frequencies in mind, post 'em and we can go from there |
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Are you talking about transceiver on different bands going to a multiband antenna, or multiple radios on the same band? And what bands?
Different bands to a multiband antenna is trivial, at least at VHF/UHF frequencies. Devices called "diplexers" are commonly available in the roughly $50 range, and used to separate 2m (and everything lower) in frequency from UHF (70cm band) for example. Other combinations of bands and even 3 or 4 bands are possible. I have one that splits 6m from 2m that I use to combine separate radios on those frequency bands into a common mobile antenna. In other cases I've used a diplexer to separate the 2m and 440 coming from a dual band radio, to send them to separate antennas. At frequencies lower than VHF, these kinds of devices would become very large and unwieldy due to the size of the components necessary to build a sharp enough filter, although they have been done for some large commercial and military users. As far as multiple radios on a single VHF or UHF band, it's possible, with some massive limitations. That's how repeaters (usually) work for example. A duplexer is two sets of very selective tunable frequency filters... connected together at one end (antenna), separate on the other (radios). These radios are limited to a single frequency effectively, and the duplexer would have to be tuned to the desired frequencies on each side, and they must have enough separation between the two frequencies for the duplexer in question. Additional sets of filters can be added to create a "triplexer" or even more, although these start to get tremendously ungainly and difficult to deal with when you go over two. As an example a good quality bandpass/reject notch type duplexer for VHF (2m) would typically have a minimum separation of 600kHz, would consist of four cylinders ("cans") roughly 8" in diameter and 24" tall, and cost in the range of $600-$1000 new or $200-$400 used. And you'd need a $5,000 to $10,000 piece of test equipment to tune or retune it... so if you order one, be real sure what frequencies you want it tuned for at the factory. If you happen to have a duplexer sitting around and the ability to tune it, you can do fun things like running a packet/APRS transceiver on 144.390 and a 2m simplex transceiver on 146.520 into a single high gain antenna at field day  Or you could do the same at your house if you have the space for the duplexer. For most amateurs though this kind of thing is unworkable for anything other than repeater stations.
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| I understand duplexers and have one to use both outputs on an IC-706miig on the same antenna. Could I run 3 different radios all using 2 meters monitoring 3 different frequencies and still be able to transmit on those different frequencies with a single antenna? |
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I understand duplexers and have one to use both outputs on an IC-706miig on the same antenna. Could I run 3 different radios all using 2 meters monitoring 3 different frequencies and still be able to transmit on those different frequencies with a single antenna? you obviously don't. what you're looking to do, on the big scale, is expensive. If you want to do it for a mobile set up, it'll hog some space and/or cost even more. You'll also have to start dealing with signal losses from all that hardware. just take one radio, program the channels you want to monitor, put the radio into scan mode and let it run |
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I understand duplexers and have one to use both outputs on an IC-706miig on the same antenna. I don't think you do.... reread my post above, so that you understand the distinction between a diplexer (which separates or combines different frequency bands into a common port) and duplexers (which separate or combine discreet frequencies on the same band into a common port). What may seem like a small distinction is in fact a massive difference in the difficulty and cost. Could I run 3 different radios all using 2 meters monitoring 3 different frequencies and still be able to transmit on those different frequencies with a single antenna? Yes, but the practical answer is really no. If you have 3 individual frequencies (NOT repeaters) that you want to operate on, which don't change, you can get a duplexer with an extra set of filters in a triplexer setup. It will cost roughly $800-$1500 and be roughly the size of a small desk. Each frequency will have to be at least 600kHz apart, probably a little more for the "extra" third frequency. And the whole assembly is rather sensitive to vibration and temperature changes so forget mobile operation. What I would suggest would be a dual band radio that does dual in-band, that way you can monitor two 2-meter frequencies simultaneously. For more than that, get something that scans I guess. |
| I guess that I was not very clear when I said that I understood duplexers. I have one and use it. I was not suggesting that I use a duplexer for my original question. I was just curious if this could be done. My understanding is that I could used a splitter with an antenna and hook up multiple receives or scanners to it. I did not know if that would or would not work for transmitting and could not find anything on the Internet about it. I am guessing that it cannot be done and will use separate antennas for the radios. |
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I guess that I was not very clear when I said that I understood duplexers. I have one and use it. I was not suggesting that I use a duplexer for my original question. I was just curious if this could be done. My understanding is that I could used a splitter with an antenna and hook up multiple receives or scanners to it. I did not know if that would or would not work for transmitting and could not find anything on the Internet about it. I am guessing that it cannot be done and will use separate antennas for the radios. keeping things basic: you can connect multiple RECEIVERS up to one antenna, just don't try and connect a transmitter to this circuit (you'll kill your receivers). you will be sharing the signal received between the X number of receivers so expect a decreased performance vs direct connection to one. you could use a pre-amp to overcome this loss (all depends on frequency and lineloss). you could use filters here for better isolation (bp/br) or notch. this may be a good idea depending on how close the transmit antenna is to the Rx. if you want to share this same antenna with a transmitter, it's a whole other ball game. |
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I understand duplexers and have one to use both outputs on an IC-706miig on the same antenna. the device you are referring to above is a diplexer, not a duplexer. see photos above. ar-jedi I see what you guys are saying, but it is confusing when what I bought is called a duplexer. Comet CF-706a Duplexer |