can you use an antenna splitter for running two mobiles off one antenna? like this splitter pictured?
antenna splitter question.
- Thread starter drbeede
- Start date
- Status
doctordialtone
Member
If you plan to transmit - No.
You're going to overload the receiver and possibly cause damage.
ok would it still cause damage if one radio was turned off and I wanted to transmit? if I decided to transmit just reach up and switch one off is what I mean.
doctordialtone
Member
You'd probably be OK but it really depends upon the radio(s).
If you simply connect two antennas in parallel, the math is just like connecting two resistors in parallel: the impedance is halved. This is in principle a problem, because there will be losses due to the mismatch reflecting some received power.
The “correct” thing to do is use a power combiner (a.k.a. power divider (when used in the other direction) or “splitter” in TV-cable-land). This device has three ports with equal impedances, one of which goes to your receiver and the others go to the two antennas
Last edited:
ok thanks for the help, I appropriate it very much.
In short if you transmit 1/2 the power goes to the antenna and 1/2 the power goes to what ever is hooked up to the other port.
Turning a radio off does NOTHING to prevent damage from excessive RF overload. The transistors and protection diodes will fry just as fast.
Yep, it's about the same as tuning the receive radio way far away in frequency of the transmit radio! The same components will still fry just as fast.
nd5y
Member
The OP's picture is not a splitter it's a T connector. There is a difference.
Ubbe
Member
Most scanner are designed the same way. There will be protection diodes that perhaps can handle up to a 1/2 watt of power, then they will blow and go open circuit and usually are blown off the circuit board if the power are high enough and stops protecting. There are bandpass filters for each frequency band that are enganged by forward biasing switch diodes. If the filter pass the frequency that enters the antenna port it will go straight to the first transistor and damaged it. Perhaps only partly so it will not have full sensitivity and will have lots more interferencies.
When a scanner are powered off all filters will be disengaged and will not pass any signal at all. But if the power coming from the antenna port are high enough the switch diodes will start to conduct from the peaks of the frequency wave. There are switch diodes both at the start and at the end of the bandpass filter that will need to conduct to pass any power. The bandpass filters have an impedance so the diodes at the end will have a series impedance that requires a higher powered signal from the antenna port to start to conduct. There are also diodes that will start to conduct that will direct the signal to ground.
When a scanner are powered off it will be much less damage from high power signals compared to when it is powered on. Always turn scanners off when not in use to reduce damage from voltage spikes from nearby lightning strikes and transmit sources. Hopefully only the two protection diodes at the antenna port will blow but you will be oblivious to it as the scanner probably works as normal but there will be no frontend protection at the next high power encounter .
/Ubbe
When a scanner are powered off all filters will be disengaged and will not pass any signal at all. But if the power coming from the antenna port are high enough the switch diodes will start to conduct from the peaks of the frequency wave. There are switch diodes both at the start and at the end of the bandpass filter that will need to conduct to pass any power. The bandpass filters have an impedance so the diodes at the end will have a series impedance that requires a higher powered signal from the antenna port to start to conduct. There are also diodes that will start to conduct that will direct the signal to ground.
When a scanner are powered off it will be much less damage from high power signals compared to when it is powered on. Always turn scanners off when not in use to reduce damage from voltage spikes from nearby lightning strikes and transmit sources. Hopefully only the two protection diodes at the antenna port will blow but you will be oblivious to it as the scanner probably works as normal but there will be no frontend protection at the next high power encounter .
/Ubbe
For two radios to one antenna I'd use a coax switch like this -> Daiwa CS-201A Coax Switches CS-201A These switches ground the unused input so there can be no chance of damage to the front end of the radio not being used.
doctordialtone
Member
That looks good but he may want PL-259 connectors.
What is pictured is a T connector. How would you expect the receiver to determine which is the antenna and which is the "other radio"? It can't. That's just one way to state why you don't want to use a T where a splitter is needed. Yes you will get 3 to 3.5dB of loss with a splitter, but that's the best it can do. If you can't accept the loss, you'll need a multi-coupler, which is a device with amplification to overcome the loss. It is not without its issues.
thanks for all the input everyone.
- Status
