Menomonie Police APCO P25 System

[CFScanMan]

I've been updating my frequency database over the past couple of weeks and noticed that over in Menomonie the police department (KZQ729) has switched to a new P25 mobile repeater system on 155.31750 MHz. On a conventional analog scanner set for that frequency, their transmissions sound like a combination of buzzsaw and white noise (static) when there is a transmission and is completely quiet when there is not. The duration of the buzzsaw noise varies, which would seem to suggest that what I am hearing is actual coded conversation and not a control channel. I also cannot find any 800 MHz frequencies assigned to this agency in the FCC database, which would also suggest this is a non-trunked system operating on this sole frequency.
Without getting into too much detail, I spoke to a reliable source in the MPD and he indicated that their agency has moved to a P25 system on a narrow-band digital frequency. They have the ability to encrypt their transmissions, but at this time are not doing so because of technical issues. Once they work out these issues, he indicated that encryption on this P25 system will be used on a part-time basis when needed for secure communications and in unencrypted digital during routine transmissions or in analog on their original 155.5500 MHz frequency when communicating with other agencies.
I've been a regular scanner user for the past 25 years, but this APCO P25 system is new to me and I have no idea how to decode these digital transmissions. I contacted the Menomonie Radio Shack and the employee there, who has been quite helpful, punched in the aforementioned frequency into a PRO-96 handheld scanner he had in stock. Much to my surprise, when the next transmission on that frequency came over, it still sounded like a buzzsaw, like on my old PRO-2004 I have at home, and according to him there was nothing on the display indicating that this was a digital signal. It's as if the unit wasn't even aware that this was something present other than an analog FM signal. I read the on-line manual and suggested that he change the mode from FM to MO, but that setting switch didn't change the outcome either.
Anyway, I have been looking over this web site for the past week or so and haven't come across any specific entry regarding this issue. Any input I could get about what this system is and what brand or type of scanner receiver might be able to properly decode it would be appreciated. I know in the past the MPD has used a Motorola dealer and equipment, so that might be something to go on.
Thanks in advance.

 

[N9NRA]

I`ll take a stab here, what ya are hearing is the actual P25 transmissions as they would sound on a regular (non-digital capable) scanner, what ya need is a scanner like the BCD396T, which can decode this type of transmission. As to monitoring these, with my `396T i didn`t have to do anything except program the freqs into the unit. Be aware that ya do need to set the channels as conventional (for the system type), and the modulation as NFM (narrowband FM, what i did on mine). Also, the unit still will not be able to recieve encrypted stuff even though it`s a digital transmission. In some cases with some scanners there`s some kinda cool additional features as well, but i`ll leave that for another time. Good luck with your scanner. 73. N9NRA

 

[Karl_KS9E]

P25 Scanning

Be aware that when scanning P25 digital that the CTCSS/DTCSS (PL/DPL) must be OFF (not in search either). P25 systems use a NAC (Network Access Code) instead. Some digital scanners support the NAC, others do not.

There are times when it takes a while for a digital scanner to detect and decode the signals (often referred to as a motor boating sound). Encryption sounds like unintelligible digitized voice fragments until the radio mutes when it recognizes the encryption.

In further review of the City Of Menominee (Dunn County, WI) they are licensed for narrowband DIGITAL on 155.3175 MHz and on 156.0375 MHz.

 

[CFScanMan]

Thank you!!!

Gentlemen,
Thank you so much for your assistance. I took a road trip over to the Radio Shack store in Menomonie today and met with the employee I had been working with over the phone all week. He was rather elated because his PRO-96 he had in stock suddenly seemed to "get all its ducks in a row" and started decoding the MPD's P25 signal properly. I played around with the receiver myself and sure enough it was properly receiving the department. This employee was happy that he had the correct frequency the MPD uses and that he could finally inform his local customers that their police department could still be monitored.
Based on what I've learned this week and the advice you have provided, I feel that I'm a little more knowledgable now about these systems when I start looking to upgrade to a digital receiver.
Thanks again.

 

[N9NRA]

Hey thre, you`re very welcome! Nice to be of help! N9NRA