Radio stations frequencies

Hello,

I am wondering why one radio station is on different frequencies in different cities in the same state? Can someone please explain it?

Thanks!

I think it depend on frequency location in every state, may be another radio station take that frequency before other stations or there is a control from state to organize the frequency in air

Its all to do with interference. Suppose a transmitters covering a certain city has to provide, say 2mV per metre for good reception. Any station on the same frequency must then provide LESS then -40dB (1/100) of 2mV in that city, else it would be interfering with the required signal. So this means that that frequency can only be reused over 100 miles away, so if the next city is only 50 miles away , a different frequency must be used.
Very specialised aerials can accomplish this, with 90 % of the transmitters power being spread around it but with very sharp nulls in certain directions (> 40 dBs) to overcome the interfering effect, so the frequency can be re-used at a much closer range. The MF Saffron Green Station (north of London) has three such nulls. one pointing towards Birmingham I can't remember which other two stations are involved.
Frank

What you call "one radio station" is really just "one program" or "one network", but not "one station". As others have already explained, different transmitters are assigned frequencies according to what they might interfere with. When you hear the same program content on one frequency in Chicago and on another frequency in Peoria, that's really two different radio stations, as will be clear when it comes time for station identification. The program content may be the same because the two stations are in a network.