coax tee vs multiplexer.

[theshepherd3]

I am looking to purchase a second scanner and would like to use a single antenna for both.
I am going to use the set back antenna until I get set up later with an outdoor antenna.
My question is if all I am doing is receiving a signal and not broadcasting, would a coax tee work with out the expense of a multiplexer?
I realize when broadcasting there is a need to isolate the radios, but is this necessary with receive only?
Thanks-Frank

 

[WouffHong]

Not a good idea

I am looking to purchase a second scanner and would like to use a single antenna for both.
I am going to use the set back antenna until I get set up later with an outdoor antenna.
My question is if all I am doing is receiving a signal and not broadcasting, would a coax tee work with out the expense of a multiplexer?
I realize when broadcasting there is a need to isolate the radios, but is this necessary with receive only?
Thanks-Frank

Frank - It would be nice, but each local oscillator can be interjected into the other receiver and lock up the scanning on both. :roll:

Da Wouff

 

[N5TWB]

Frank - It would be nice, but each local oscillator can be interjected into the other receiver and lock up the scanning on both. :roll:

Da Wouff

Interesting - I understand the electronics behind the statement but I haven't experienced it in a single antenna setup that feeds two scanners (RSPro95 & BCD996T) through a tee connector in my SUV. I have purchased a four-port Stridsberg unit but have not installed it yet. My primary reason for it is the little bit of signal boost it gives to the received signal to overcome the loss of splitting that should also help on fringe area reception on the local TRS. Of course, YMMV...

 

[jackj]

The main problem with using a 'T' connector is impedance. In order to get the most efficient power transfer all of the impedancies need to be pretty close to the same. Your antenna's impedance will be close to 50 ohms as will your coax's and the antenna input of your scanner. Using a 'T' not only splits the signal between two radios but the two radios will look like one 25 ohm load to the antenna. Some of the signal coming down the coax will be reflected back to the antenna and re-radiated. Signal that doesn't make it to your receiver doesn't do you any good. If you really need to run two radios off one antenna then you should at least use a splitter. A splitter will give you a consistent 50 ohm load at all ports, if you buy a 50 ohm splitter. You will end up loosing a little over half of the signal at each radio but you should get somewhere around 6 to 9 db of isolation between ports. The more isolation the better.

 

[LtDoc]

Will it work? Yes, it will. There will be some impedance mismatch though. There will also be some loss of signal strength, no way of telling how much or if it would really be bad or not. Would there be as much signal loss as with using a 'splitter'? No idea, and there will be losses with either, right? But considering the cost of a 'T' and a 'splitter', why not try that 'T' first?
- 'Doc

 

[radioman2001]

Since we are not talking commercial grade radios here, but consumer grade, a single tee will work just fine. If you were to actually measure it you would lose 3db of signal, but for most monitoring configurations especially if you are using it mobile you won't notice the difference. Believe it or not in one of our buildings we used an amplified 12db 4 way TV splitter, again we are not talking commercial grade communications here.
Now for isolation, you might and I mean might have a problem with some scanners interfering with close spaced radios. I know I had RS scanners that had different antennas and still would receive each others channels when within 1-2 ft of each other probably coming in the IF.

 

[gmclam]

A splitter is best

Regardless of the fact it is used for receive only, you are better off using a splitter. You do NOT need anything fancy. I just use some decent quality cable TV splitters.

You will have a mismatch with just a T and will likely have interaction from each receiver. An amplified "splitter" or multicoupler has its own set of issues.