Has San Mateo County, California, gone to Narrow band FM?

[PCTEK]

I just received my new SDS200. I noticed that the audio on the analog UHF frequencies sounded garbled (overmodulated) after trying everything I knew to do, I thought that perhaps the county had implemented narrow FM, so I changed Burlingame PD & San Mateo PD to Narrow FM. The audio is not as loud, but now it doesn't have the overmodulated "garbled" sound. I know that there was plan to change to NFM. I checked the RR Database and the only NFM I see if for the various cities fire departments.

Does anyone know if San Mateo County Analog UHF Police departments have switched to NFM and the RR hasn't been updated. If they are still standard FM, any idea's why the audio on the SDS200 is so garbled?

I know my question straddles two forum topics. Sorry

 

[GTR8000]

Just to clarify for the sake of those reading...the Part 90 narrowband mandate deadline was over a decade ago, however at the time the T-Band giveback was looming and users in that band fought for and were successful in getting T-Band exempted from narrowbanding. In early 2021 the T-Band giveback was mercifully killed off, and the band now remains in limbo as far as whether the FCC will force legacy/grandfathered frequencies to be narrowbanded, or if they will leave well enough alone.

So to address Mateo County, any UHF frequencies within the "standard" range of 450-470 should have been narrowbanded long ago. The T-Band frequencies (470-512) may or may not have been narrowbanded, as they would've been exempt from the mandate. It all depends on whether new infrastructure was installed, which may use 2.5 kHz transmit deviation.

By the way, it's usually the reverse of what you're describing. Trying to listen to a "wide" analog signal on a receiver set for narrow will usually result in audio distortion. Listening to a narrow signal with a wide receiver normally only results in lower audio than expected and possibly interference from adjacent frequencies.

One way you can probably figure it out for yourself is with a cheap RTL dongle and software like FMP24/DSD+. You can look at the width of the carriers on the frequencies you're wondering about to determine if they are wide (~25 kHz) or narrow (~12.5 kHz).

 

[AK9R]

Question continues here: New SDS200 with an odd Issue