Connect Multiple Radios To One Antenna?

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OneBadUukha

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I have three radios that I use to scan essentially the same bands: VHF/UHF. Is it technically possible and/or prudent to connect all three to one larger antenna? What are the implications? Thanks.
 

JamesO

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No problem, but there are many options.

Something like this may be a good option - 4 Port MCA204M VHF/UHF Receiver Multicoupler - 25 MHz to 1 GHz | Scanner Master

You could possibly use a CATV splitter but there will be RF path loss associated with the splitter so some sort of amplifier may be needed as well. But you have to be careful with amplifiers.

Search these sections of the forum for more info:

Antennas and Associated Hardware - The RadioReference.com Forums

Splitters, Filters and Multicouplers - The RadioReference.com Forums
 

n5ims

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Just remember that there's a HUGE difference in answers (and complexity) between a receive-only situation, such as with scanners, and a situation where one or more of the radios will transmit. With scanners, the solution is cheap and simple, one of those splitters or "multi-couplers". Once you add transmit into the mix, you're no longer cheap nor simple.
 

jonwienke

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Splitting the antenna output to feed multiple receivers is fairly simple. If the signal is reasonably strong, you can use a cable TV splitter to divide the antenna feed to each receiver. Keep in mind the following:

1. Splitting the input reduces the output proportionately, minus an insertion loss. A 2-way splitter outputs slightly less than half of the input signal power to each output. A 4-way splitter outputs slightly less than one quarter of the signal power to each output.

2. Use all of the splitter outputs. If the splitter has more outputs than you have receivers, get a splitter with fewer outputs. Splitter loss isn't a big deal for strong signals, but for marginal ones it can make the difference between hearing the call and not.

3. There are amplified splitters that can boost the signal power at each output vs the input, but they tend to have bandwidth limitations that must be considered. An amplified splitter designed for UHF and VHF broadcast TV reception will work well for signals in those frequency ranges, but may completely block 800MHz signals. Passive splitters typically have an upper frequency limit, and will pass anything below that limit.

4. As has been mentioned, all of the above applies to receiving only. Connecting multiple transmitters to a single antenna without frying anything is much more difficult, complicated and expensive.
 
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For receive, the concept behind a multicoupler is quite simple. Input goes to the coupler which consists of multiple matches outputs (look up info on co-phasing for the info on impedance). Then a LNA makes up for the losses though the coupler and then adds a little system gain in. Usually, the band limits are defended by the LNA and not the coupler. Spare outputs do require loads to keep the impedance correct though.


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What about digital decoding? If you use a multi-coupler, will it mess up the data so that software programs like DSD+ and PDW won't wprk?
 

nd5y

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What about digital decoding? If you use a multi-coupler, will it mess up the data so that software programs like DSD+ and PDW won't wprk?
No. Not by itself. The only way it could affect digital decoding is if the signal was too weak and a non-amplified multicoupler/splitter reduced it further, or you introduced noise or intermod from a preamp.
 

n5ims

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What about digital decoding? If you use a multi-coupler, will it mess up the data so that software programs like DSD+ and PDW won't wprk?
At the antenna and feed line point, it's just RF and RF is RF is RF. There's no real difference on what may be modulated on that RF, digital, analog, pulse, television, whatever, it's just RF. What may matter is if you reduce the level to a point where the receiver doesn't have enough signal to demodulate the signal or if you introduce some distortion in the signal (intermodulation, noise, change the phase or timing of the signal, etc.) so it can't be correctly demodulated.

It's possible to have a single antenna going through a splitter that feeds your analog scanner, digital scanner, HDTV, and a tapped scanner feeding DSD+ with all working just fine.
 
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