FMN and FM

[tkenny53]

So here is my question, why are some freq;s in the same range in FM mode and others are NFM. So LACo FD had their Blue channels in FM, but the sheriff's is mixed between NFM and FM. The same applies to LACoFd.
Any reason why there all are not NFM?

 

[mmckenna]

Where are you seeing this?

Depends on the frequency. Only sections of the VHF high and UHF bands were impacted by narrow banding.

If it's 800MHz, VHF low, and a handful of other specific frequencies, they were not impacted by narrow banding.

If it's data you are seeing on the Radio Reference database, it's because someone forgot to update them.

 

[tvengr]

FCC mandated that most VHF high and UHF frequencies be narrowbanded (FMN or NFM). Some of the frequencies, such as NOAA weather and VHF marine band, are exempt and remain FM. The database has not kept up with the changes. I would program any VHF high or UHF frequencies as NFM. The VHF low band (30-50 MHz) was not part of the mandate and should remain FM. There are some frequencies used by TV and radio broadcast stations licensed as remote pickup that use wideband transmissions. 800 Mhz frequencies also were not part of the mandate.

 

[jonsmth]

As mmckenna & tvengr mentioned in their replies, VHF/UHF narrow-banding required, effective January 1, 2013, for the 150-174mhz & 421-470mhz bands to change from FM(25khz) to NFM(12.5khz) for Municipal Govt, State & Local Public Safety Systems and Industrial/Business.

 

[tkenny53]

So 470-510mhz and 480-484mhz should be NFM, I know the db is not that way, so its a manual edit on my end, thats easy

 

[tkenny53]

here is the example

 

[LAflyer]

Db is correct. LACoFD Blue frequencies are wideband. They have not been narrowbanded.

Same goes with LASD, who only in the last year as part of LARICS build out narrowbanded much of their stuff, but still have wideband frequencies.

There are other agencies in LA basin also continue to have wideband frequencies.

 

[tvengr]

Db is correct. LACoFD Blue frequencies are wideband. They have not been narrowbanded.
Same goes with LASD, who only in the last year as part of LARICS build out narrowbanded much of their stuff, but still have wideband frequencies.
There are other agencies in LA basin also continue to have wideband frequencies.

Now that UHF T-Band giveback has been repealed, are new licenses still being accepted and are they required to be narrowbanded? Are old licenses grandfathered to remain FM?

 

[jonsmth]

This is an overview of VHF UHF Narrow-banding from the FCC's website:

Narrowbanding Overview

Narrowbanding refers to public safety and industrial/business land mobile radio systems migrating from 25 kHz efficiency technology to at least 12.5 kHz efficiency technology. Narrowbanding is also referred to as VHF/UHF narrowbanding because the frequency bands impacted by narrowbanding are in...

www.fcc.gov

 

[Ravenfalls]

Changing them to NFM help the scanner pull in the signal better than FM.

LA County has so much information, it's overwhelming. I just did a So Cal pull, it's a fast way to import info & sort it. Then use agency information to fix all database errors. The RR database is more up to date than I realized.

All LA County Fire is FMN. VHF & UHF.

700/800/900 should be FMN for commercial & public safety.

Ham & FRS are usually FM.

Correct me if any of my Info is incorrect.

 

[mmckenna]

700/800/900 should be FMN for commercial & public safety.

For analog 800 systems, you'll find they are usually Wide FM (FM in scanners, 25KHz channel width/5KHz deviation)

Changing them to NFM help the scanner pull in the signal better than FM.

Might make it sound louder since the deviation of the transmitted signal will be wider than what the scanner is looking for in NFM mode.

 

[GTR8000]

Now that UHF T-Band giveback has been repealed, are new licenses still being accepted and are they required to be narrowbanded? Are old licenses grandfathered to remain FM?

The freeze on T-Band applications was lifted earlier this year. New or major applications must be narrowband; incumbents that are wideband are still covered by the waiver (not yet revoked), however applications that are wideband are still frozen.

 

[tvengr]

The freeze on T-Band applications was lifted earlier this year. New or major applications must be narrowband; incumbents that are wideband are still covered by the waiver (not yet revoked), however applications that are wideband are still frozen.

Thank you!

 

[LAflyer]

As I stated prior the LACoFD UHF Blue frequencies have remained wide. See below County document dated April 2021.

LACo Sheriff similarly only got around to narrowbanding bunch of their frequencies in the last year as part of station equipment upgrades in preparation for LARICS.

There are a bunch of other entities in LA basin that have remained wide for their legacy UHF systems. For LA City, the LAFD 800Mhz is also wide.

 

[gmclam]

Changing them to NFM help the scanner pull in the signal better than FM.

Might make it sound louder since the deviation of the transmitted signal will be wider than what the scanner is looking for in NFM mode.

In a perfect receiver, this is true. Unfortunately, the selection between FM and NFM in most scanners merely changes a filter. To be proper, the discriminator BW must be changed and that would affect the volume.

 

[Mike_G_D]

In a perfect receiver, this is true. Unfortunately, the selection between FM and NFM in most scanners merely changes a filter. To be proper, the discriminator BW must be changed and that would affect the volume.

Actually only true for GRE-based designs. In the olders series Unidens (pre-436/536) it's the exact opposite - only changes the audio processing (whether by actual discriminator changes or just some kind of audio boost, I don't know) but only one wide IF filter is used. This is why there was a long thread in the Uniden section for a while discussing swapping out the IF filter in those scanners to a narrower version. I found this out the hard way when I bought a BCT15 and ran into issues trying to seperate out the narrowbanded CDF channels! Starting with the 436, however, they started using seperate filters for FM and FMN.

 

[tkenny53]

One thing I did notice on the sds100, If I take the Blue freq's to WFM, its really bad reception, If I put them in NFM, its louder. FM is about as normal as it gets.