California Highway Patrol - FMN on low band?

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greenthumb

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Just loaded up some CHP frequencies and FM wideband seemed to sound pretty bad, and I switched to FMN and it cleaned up a lot of noise and brought the audio levels up substantially. Therefore, I believe that the CHP low band frequencies (at least in the Valley Division) are narrowband. Can others confirm that this is the case elsewhere in the state before I submit a DB update to change CHP low band frequencies to FMN?
 

mcjones2013

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Maybe I'm wrong, but I don't think narrowband is required nor is used anywhere in the low-band spectrum.

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greenthumb

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Yeah, it definitely was not required as narrow banding only applies to 150-174 MHz and 421-470 MHz (with a few exceptions in there). I'm just interested to see if others are having the same observation as I am.
 

mcjones2013

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I'm in the Valley Division area. I'll check myself when I go out tonight and tomorrow and see what is better for me and post back here. I can't remember what I have mine programmed as.

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mcjones2013

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So I tried both FM and NFM mode on my BCT15X I have in my car, and I definitely agree that CHP sounds louder on NFM mode. I still don't know if it's the proper way to program it, as I do think they're not actually transmitting in narrowband, just the scanner might be doing some extra work to punch up the volume. But maybe someone else has a better explanation for this.
 

pushnsteel

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700 Band

Curious if the NFM becoming better on low band is because they're simulcasting on 700 Band also. Don't know if they are or if this would cause the noise.
 
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RadioDaze

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Some of the dispatchers here in Orange County and Southern Division seem to have low mic volume compared to the mobile units, on average. Maybe just speaking distance from mic?
 

cmdrwill

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Some of the dispatchers here in Orange County and Southern Division seem to have low mic volume compared to the mobile units, on average. Maybe just speaking distance from mic?
IF the dispatcher's arm was longer, they would be farther from the microphone, a Major known problem.
 

mmckenna

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Curious if the NFM becoming better on low band is because they're simulcasting on 700 Band also. Don't know if they are or if this would cause the noise.
No, not related. While it may be the same audio, it's sent to two different transmitters. The low band and 700MHz systems don't influence each other when it comes to the bandwidth.
 

mmckenna

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What?

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What he means is that some dispatchers get lazy. The microphones are set up in a few different ways:
- some dispatchers use headsets.
- some dispatchers use a boom mic mounted to the console.

The headsets are a more expensive solution since each dispatcher usually has their own that they plug in during their shift. They are usually not shared due to hygiene reasons. They work well since the microphone is usually a uniform distance from the dispatchers mouth. As long as their speaking volume is close to other dispatchers, the audio is consistent from dispatcher to dispatcher.
Other issue with headsets is that they are generally fragile and are considered an expendable item. They require replacement depending on the amount of use/abuse they get. Getting a full year out of a headset would be nice, especially at a hundred bucks each or so.

The boom microphones are cheaper since there is just one for each console. Problem is that when the dispatchers get lazy or are doing something else that requires leaning away from the console, they'll still key the mic and sort of talk in the general direction of the boom mic. This doesn't work well, obviously. Teaching dispatchers to actually lean towards the mic and speak is difficult. Usually it takes a lot of officers complaining for them to realize they are the issue.

CMDRWill's comment was about dispatchers that seem to make a game of how far away they can get from the microphone and still be understood.
 

mcjones2013

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What he means is that some dispatchers get lazy. The microphones are set up in a few different ways:
- some dispatchers use headsets.
- some dispatchers use a boom mic mounted to the console.

The headsets are a more expensive solution since each dispatcher usually has their own that they plug in during their shift. They are usually not shared due to hygiene reasons. They work well since the microphone is usually a uniform distance from the dispatchers mouth. As long as their speaking volume is close to other dispatchers, the audio is consistent from dispatcher to dispatcher.
Other issue with headsets is that they are generally fragile and are considered an expendable item. They require replacement depending on the amount of use/abuse they get. Getting a full year out of a headset would be nice, especially at a hundred bucks each or so.

The boom microphones are cheaper since there is just one for each console. Problem is that when the dispatchers get lazy or are doing something else that requires leaning away from the console, they'll still key the mic and sort of talk in the general direction of the boom mic. This doesn't work well, obviously. Teaching dispatchers to actually lean towards the mic and speak is difficult. Usually it takes a lot of officers complaining for them to realize they are the issue.

CMDRWill's comment was about dispatchers that seem to make a game of how far away they can get from the microphone and still be understood.
Gotcha! Thanks for the explanation!

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gmclam

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VHF LOW

VHF low is 20MHz wide channels. The functionality of NFM will change from scanner to scanner. Some just implement a filter which I could see making some communication sound cleaner. On some models it would certainly increase the volume as you're telling the scanner it is narrower modulation.
 

cmdrwill

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VHF low is 20MHz wide channels. The functionality of NFM will change from scanner to scanner. Some just implement a filter which I could see making some communication sound cleaner. On some models it would certainly increase the volume as you're telling the scanner it is narrower modulation.
VHF LOW, 30-50 MHz IS 20KHz channel spacing and +/- 5 KHz deviation,aka modulation. Considered WFM.

And as above mentioned, scanners and even some commercial and Ham radios do not implement the receiver 'narrow band' properly.
 

gmclam

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VHF low is 20MHz wide channels. The functionality of NFM will change from scanner to scanner. Some just implement a filter which I could see making some communication sound cleaner. On some models it would certainly increase the volume as you're telling the scanner it is narrower modulation.
Obviously I meant 20KHz, not 20MHz.
 
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