Dual Antenna

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dosboot

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I was wondering is there anyway are a connector that will allow me to use to antennas' on on one scanner( Pro-97) I would like to use use my 800mhz and full range antenna is this possable something that will keep the impedance.
 

N1BHH

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Your question is hard to decipher, but I think you want to connect two antennas to your scanner, is that right? That's simple, just get a bnc tee connector and hook up two antennas, simple!
 

n5usr

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You can hook the two together with a tee, and it might work just fine - particularly if the "general coverage" antenna is deaf at 800 MHz and vice versa. However, usually all antennas will contribute some signal at all frequencies so you may have worse reception with both teed together.

The problem is if both antennas receive a given signal, the two will not be quite in phase with each other when the reach the tee (unless you do lots of careful calculations and measurements on the coax between them) so the out-of-phase signals will interfere with each other thus reducing the final strength and quality of the signal at the scanner.

The best ("ideal", "proper", whatever) way to do what you want is to use what's properly called a 'diplexer'. Most companies call them a 'duplexer', so that's probably the better term to search for. The diplexer will have two or more ports on one side, and a combined port on the other. You would hook your scanner to the combined port, and the antennas to the others. You would want to find a diplexer that has the proper frequency splits, which can sometimes be tricky. There have been one or two places mentioned here before that will make a custom split, but they will cost more too.

But, again, for a receive-only application it might just work okay to combine them with a tee. Certainly doesn't hurt to try, and might save you some money.
 

key2_altfire

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thewenk said:
Here are some of the numerous threads with discussions on diplexers and using 2 antennas.
You can also use a patch panel, which may well be the lowest-cost, highest-performance option, but not as convenient as a diplexer or antenna switch.
 

zz0468

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The problem with just hooking up two antennas with a tee is that the results are so unpredictable. It depends on the antennas spacing with each other, the line lengths from the tee to the antennas, and various other factors like that. What you end up with, in effect, is a single antenna with multiple frequency responses and directional characteristics. You might get lucky and have it do what you want, or maybe not. The professional approach to the problem is multiple receivers, each with the desired antenna. The low budget approach would use a diplexer that provides isolation between the antenna ports. I'm more or less providing the same answer N5USR did.
 

Airdorn

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Here's what I use for a couple of antennas on a single scanner:

(I guess this is considered a patch panel. Ignore the frayed connection in the back there. That was temporary and is correct now.)
 

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key2_altfire

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Airdorn said:
Here's what I use for a couple of antennas on a single scanner:
Say.. that's pretty clean and low cost! Thanks for posting the pic, it should stimulate the "how should I install this" juices of some folks around here (including me)!
 

k8mcn

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Airdorn said:
Here's what I use for a couple of antennas on a single scanner:

(I guess this is considered a patch panel. Ignore the frayed connection in the back there. That was temporary and is correct now.)
Very neat setup--nice and clean!!
The only thing i might add, is if you have not grounded the coax coming in to the house, i think i would ground your mount plate if feasible--
but again, great job!
 

thewenk

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Airdorn said:
Here's what I use for a couple of antennas on a single scanner:

(I guess this is considered a patch panel. Ignore the frayed connection in the back there. That was temporary and is correct now.)
Correct me if I'm wrong, but as I interpret your picture, you don't really combine the two antennas into one, you just change the cable depending on which antenna you want to use?

Dave
 
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