Quick question

[radiopro52]

This may have a simple answer. If it does, tell me, cause I don't know it

I have the BCT15, which is able to receive FM broadcasts. I actually use it alot, as it gets better reception than my standard radio because of the outside antenna. Now, my question is: Why am I able to pick up some police stations 60 miles away (VHF) that output 90-100 watts, but yet I struggle to listen to an FM Radio station thats 50 miles away that outputs thousands of watts? I know the FM band and VHF band are different, but doesn't the output power count for something? Please explain this to me.

 

[gmclam]

Two main factors which affect radio transmission distance are the power being transmitted, and the height of the antenna. Do you know these factors for the signals you are comparing?

Lastly, FM broadcast is 200 kHz wide and a typical public service radio channel in VHF is only 15 kHz wide. This is the main reason a lot more scanners don't receive FM boradcast. Many public service channels in the UHF bands are 25 kHz wide, but that's still 1/8 of an FM broadcast signal.

 

[radiopro52]

Information about said radio station is located here. It outputs 6,000 watts, and I'm about 50 miles south of it. Impossible to listen to it in the car or on any other FM radio. I can usually hear it at night on the scanner.

Information about the police station is here. It's the Scottsboro, AL police dispatch. It's 64 miles from me with an output power of 90 watts. I can listen to it just fine. It's weak, but I can listen to it comfortably.

 

[SAR923]

You may very well have an almost direct line of sight to the Scottsboro PD whereas the FM station in Tennesee is undoubtedly blocked by the foothills. FM stations need line of sight to be received although certain propagation conditions may allow you to sometimes hear much further than usual. Since yur scanner antenna is higher than your car antenna, you can get the FM station better because the height adds to your line of sight toward the station. Once you get into the FM band, transmitter power has much less effect than on the commercial AM band. An FM station with twice the power will not send out a signal that goes twice as far. With FM, line of sight is everything.

 

[kb2vxa]

Reception is always better when you use a resonant antenna. Scanner antennas aren't resonant on the standard FM broadcast band nor on several bands the scanner receives so reception suffers. I'm sure many of you have recognized the problem particularly on 800MHz.

As for the car radio again resonance is everything. If the car has one of those dinky short antennas it won't receive nearly as well as a full 31" quarter wave.

"Once you get into the FM band, transmitter power has much less effect than on the commercial AM band."

Excuse me??? Somebody has a LOT to learn about antenna gain and signal propagation, far more than may be discussed on an internet forum so don't mind if I don't broach the subject.

 

[gmclam]

Location Location Height

Information about said radio station is located here. It outputs 6,000 watts, and I'm about 50 miles south of it. Impossible to listen to it in the car or on any other FM radio. I can usually hear it at night on the scanner.

Information about the police station is here. It's the Scottsboro, AL police dispatch. It's 64 miles from me with an output power of 90 watts. I can listen to it just fine. It's weak, but I can listen to it comfortably.

The antenna of the FM station is 365 m above sea level. The antenna of the police is 408 m above sea level. Can your receiving antenna "see" both of these antennas? That extra height of 43 m might just get the signal past something blocking your reception from the other, or perhaps the FM tower is basically "in a hole" from your location.

It would be interesting to use some mapping software and plot the 3 locations and the topography in between you and the two sites. I might add that 6K is not all that much power on the FM broadcast band. Most stations around me are 50K watts.

 

[zz0468]

The bandwidth issue mentioned by gmclam is the biggest single reason why you'd observe a difference. The other factors mentioned certainly play a part, but occupied bandwidth (and therefore rx bw) is the single biggest difference.

 

[radiopro52]

My antenna is about 21.5 feet in the air, pointed to the north east. I would say the antenna isn't high enough to have clear line of sight of anything, because there are trees everywhere here.

The radio station sometimes comes in full signal at night. Other times it may come in great if there's tropospheric ducting going on. Otherwise, it's pretty hard to listen to. And, yeah, 6000 watts for a radio station is pretty low. There's many stations around here that output close to 100k watts.