What is a "mobile relay station?"

Discussion in 'Mobile Radio Systems' started by KA5LQJ, Dec 19, 2010.

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  1. KA5LQJ

    KA5LQJ Ham Member QRZ Page

    This can probably be answered by a two-way radio tech.....

    Many years ago, the Shreveport, LA Police Department operated a "mobile relay station" on 155.310MHz. The base power was 300 watts and the mobiles were 110 watt. There was no secondary frequency (3 MHz up) for the mobiles to transmit on, they transmitted on 155.310 MHz as well.

    Now, mobiles could hear every other mobile and the base as well, with the exception of when two units were transmitting, then you got a hetrodyne, LOL!

    Today, a secondary frequency is transmitted by the mobiles. At the Base,
    there is usually a very tall tower structure with an antenna that matches the mobiles transmitting frequency. As it goes down the coax, it opens the squelch on the receiver, which then activates the base transmitter on another close by frequency and that enters a series of brass cavities to "delay" the transmitted signal just enough to not re-activate the receiver relay. After coming out of the brass cavities the signal goes up the coax to the transmitting antenna and out into the air.

    Ok, so how does a mobile relay work?

    Respectfully, submitted,
    73,

    Don/KA5LQJ
     
  2. K7JEM

    K7JEM Ham Member QRZ Page

    A mobile relay is a repeater. The brass cavities are tuned circuits with a very high Q. They don't delay the RF, they just filter it. A duplexer is composed of several of those cavities that allow simultaneous transmission and reception on one antenna by two separate frequencies.

    Joe
     
  3. KI6ZIF

    KI6ZIF Ham Member QRZ Page

    In the radio setup's that I am familiar with is...

    The person has a low wattage portable radio (HT). Which transmits on one frequency, to a receiver in the vehicle. The vehicle has a second transmitter, that acts as a repeater for the HT.

    Make sense?
     
  4. KB0TT

    KB0TT Premium Subscriber QRZ Page

    Parrot

    ZIF:

    You just said the same thing that ' JEM ' said . :)



    JB


    NNNN
     
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