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One scanner, multiple antennas?

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buffalogoat

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I know several people have tried using one antenna with multiple scanners but I was wondering if anyone has tried multiple, specific band antennas hooked up to one scanner. For example, hooking up a 800MHz antenna along with a VHF-Lo antenna with a BNC tee adapter.
 

JohnWayne

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This is done all the time. I even do something similar in my vehicle where I have separate VHF and UHF antennas connected to my dual band ham radio.

The key is you need a diplexer (or triplexer) - not a simple BNC T connector. A diplexer is basically a set of filters that allow a specific frequency range to pass through them. For example, the one I use for my ham radio is something like 140-170MHz on the VHF side and 400-500MHz on the UHF side. Connect the antennas to their respective ports, and then connect the radio to the common port. A triplexer is the same thing except it has three ports. These devices also work equally well to connect multiple differing-band radios to a multi-band antenna.

There are a couple reasons you don't want to use a T connector. The important one for receive-only purposes is that the lowband antenna and 800MHz are both receiving the exact same signals, but maybe at slightly different times and strengths. Because there is no filtering to separate the signals, you will get some "mixing" because the signals from the two antennas are slightly out of phase, and this can result in attenuation, noise, and other undesirables on the signal.

For your application, something like the Comet CF-416W would work well. It is 1.3-250MHz on one port and 400-1400MHz on the other port.

Jeff
 

buffalogoat

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Thanks for the info Jeff. This is for a mobile install. But If I have to spend $70.00 on the duplexer, I might as well just get a good multi-band NIlJON mobile and stay with one antenna.
:)
 

JohnWayne

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The single antenna is definitely the simplest way to go. However, the dual antenna setup will give you the best performance. It's hard to make one antenna that does well on both 800MHz and lowband, but it's easy to make two different antennas that work well on two bands. It's always a trade-off between money/performance/size/etc.

Jeff
 

prcguy

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So Cal - Richardson, TX - Tewksbury, MA
Who says the Niljon is a good antenna at 800MHz or worse yet, VHF lo?
prcguy
buffalogoat said:
Thanks for the info Jeff. This is for a mobile install. But If I have to spend $70.00 on the duplexer, I might as well just get a good multi-band NIlJON mobile and stay with one antenna.
:)
 

kb2vxa

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Hi all,

John Wayne has the right stuff BUT the 'plexer must match the antennas frequency range wise and that's not always possible with an off the shelf item. You'll have to do some research finding one that does and if you have some oddball situation like mine you'll have to have one custom made. Search and read "Diplexer Trek" for details.

BTW, that oddball is more common than you think, no antenna made works equally well on all bands, especially VHF Lo and 800MHz and mobiles are the worst in this respect so separates for those bands are highly recomended. If you're in a strong signal area where these bands are concerned the average scanner antenna or a 2M/70cM ham "dual bander" will give satisfactory results with optimum performance on VHF Hi and UHF.

Only you know for sure which way is the best for your particular circumstance so use your noodle. In any case NEVER connect antennas willy-nilly with T connectors or combiners (signal splitters hooked up backward, or those ones I've seen with two labels AKA snake oil) because like the man said you're only buying trouble. The all important thing is to educate yourself with a little radio and antenna theory, you all saw what happened to Victor Frankenstein and all because he forgot one all important thing, the brain.
 

buffalogoat

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According to everything I have seen & read about the NIL-JON Super M mobile antenna, it's the best thing since the invention of the scanner!
:)
 
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