police laptop\radio frequency

**dementeddigital** · 01-06-2008, 06:57 PM

Since this thread is about radio and MDT detection, I figure I'd add my $0.02 regarding the MDTs.

I sold, installed, and maintained mobile computer systems for police departments in several states for a few years, and I have a reasonable understanding of them. I don't pretend to know a lot about P25, so I'll leave that to the others here who obviously know more about it.

ALL data to and from the police cruiser is encrypted. At most departments these days, the data (from NCIC, NLETS, RMV, AVL, etc) is carried over the cellular network (CDMA, EDGE, EVDO, etc). (Typically, the officers don't have unrestricted access to the internet, though.) Departments pay a monthly service fee for each car, just like you and I would. Since that is the case, it's impossible to tell what data signal is from a police car, and what signal is from the kid in the next car texting on his cell phone.

With that said, there are still some departments using private RF networks to communicate, but with NCIC2000 providing all sorts of data (including images), it's tough to push all of that through a 9600 baud pipe. Also, if a department uses the cellular network, they can access mobile data anywhere they get service. With a private RF network, they need to be within the footprint of the system.

Regarding the encryption - forget it. Even if you were able to break one key, the keys in most mobile software rotate often. The state and federal governments have very strict requirements regarding this data, who can access it, and by what means.

AVL is typically set up to send position data from the car at predefined intervals.

**oroboros_ARR** · 02-26-2008, 12:51 PM

I was never interested in actually recieving let alone decrypting police data. It is unlawful to defeat any encrypted transmission regaurdless of the sender, purpose, or medium IIRC. I initially looked into this stuff becuase I thought it might be possible to apply conventional direction finding techniques to various police (and other, such as WiFi hotspots, cell antennas, etc) RF emissions. The system would be completely passive.

The most obvious and useful purpose of this data would be to place this icon

on my gps screen; however for any such system to be useful it must be fairly reliable. Reliability requires continuous tracking which is impossible if police radio transmissions are intermittent rather than continuous.

**dementeddigital** · 02-26-2008, 01:29 PM

I like the icon!

Depending on the mobile software in use (i.e. how it communicates with its server), the system could operate continuously, or it could operate without too much overhead (think UDP). One system that I'm familiar with can be configured either way, to adjust for the quality and throughput of the carrier (or private RF) and/or what kind of data plan the PD had purchased.

If the departments in your area use a private RF system and you knew the frequency, you could set a scanner (or some receiver) on that frequency and get a signal strength from that. (The system may not be constantly transmitting, though, so you'd need to be really lucky with your timing.) That might give you *some* indication if there is a car nearby, but the signal strangth would heavily depend on terrain, antenna gain, orientation, and other facotors, so it wouldn't really be too accurate.

Given that (in most cases) this data is over the cell network, it would be next to impossible to determine if data from a captured RF packet was from a police car or a mobile sales guy sending an email joke through his VPN. The only way would be to capture all appropriate packets, decrypt them, and then understand the data contained inside.

I think that the technical hurdles would be extremely difficult for anyone except for some certain three letter agencies. Personally, I'd opt for the easy solution and either get a radar detector or drive slower (or do what I do - drive fast and cross your fingers).

**frollo** · 03-31-2008, 04:32 PM

http://www.spillman.com/Solutions/03...VL_Mapping.php

found some more info on the system the some police use didn't know if there had been any new developments since then.

another thing of note might be a gps based p2p tracking system where a user would indicate via gps where a police was sighted which is then transmitted to a central server and then broadcast back out based on location. This would have to be timestamped obviously as data wouldn't be real time accurate per say

just some things i think about while doing some low altitude bombing