Narrow band/wide band

[SouthernRailFan]

I have a motorola CM300 mobile unit setup for receive only for the AAR railroad channels. Will i have to change my frequencies to narrowband or can i keep them wide band and will i still pick them up just as good in wide band once they change over to narrowband. Thanks.

 

[mmckenna]

You will not need to reprogram the frequencies now. You will want to reprogram the channels to narrow band at some point.

A "wide" receiver will receive a "narrow" radio just fine, it will just be quieter. It will work, but you would want to correct it at some point.
I'm doing it now with one of my two way radios. Our fire department went narrow band earlier this year, and I have a new VHF mobile on the way, so I haven't wasted my time reprogramming the channel. I also use an older scanner that only does wide band to listen in on the VHF police and Fire systems at work. PD is wide band still and fire is narrow, it works just fine.

 

[GBLOCK]

You will not need to reprogram the frequencies now. You will want to reprogram the channels to narrow band at some point.

A "wide" receiver will receive a "narrow" radio just fine, it will just be quieter. It will work, but you would want to correct it at some point.
I'm doing it now with one of my two way radios. Our fire department went narrow band earlier this year, and I have a new VHF mobile on the way, so I haven't wasted my time reprogramming the channel. I also use an older scanner that only does wide band to listen in on the VHF police and Fire systems at work. PD is wide band still and fire is narrow, it works just fine.

What about transmitting a wide band radio on a newly narrow band adjusted frequency? You mentioned a wide receiver will receive the narrow radios fine, just quieter. Will the transmit be the same ?

 

[KG4INW]

Listening to a wide signal on a narrow channel will be choppy, or distorted somewhat.

 

[jackj]

FM transmitters use something called pre-emphasis. This is where the modulation circuit emphasizes the amplitude of high frequency sounds. The receiver has a circuit which emphasizes the low frequencies restoring a flat frequency response. This is done to improve the signal-to-noise ratio of the system. There is a formula to compute the pre-emphasis curve needed and one of the variables used is the modulation bandwidth. The FCC specs the curve that must be used in the transmitter. If your receiver doesn't use the same deemphasis curve then your audio will have either too much treble or bass.