To Jimbonzzz - possible to create a police radio detector?

[kpatz]

With the repeated discussions about Instant-On and its undetectability when the radar gun is on standby, that plus talk about RDDs and how they work, gave me a crazy idea.

I wonder how feasible it would be to invent a device that can detect the LO emission from the police car's radio. Of course, at first blush it might make more sense to have a device that alerts to activity on police radio frequencies, but that would only work when they are transmitting. If they aren't "keying-up", it's like keeping the radar gun on standby. But, when a police radio isn't transmitting, it's receiving. And police radios are superheterodyne, and have local oscillators. And since there's no market need to cloak the LO emissions of a police radio, would it be possible to detect with enough advance warning to alert a driver of activity up ahead?

I guess it would require knowledge of the radio's LO frequency (or primary leakage frequency) and hope that other common devices don't leak on the same frequency. And different makes/models of radios might have different LO frequencies.

I wonder if the feasibility of such a device has ever been researched.

Thoughts?

[AirMoore]

Well I will be honest, a CB radio does what you are asking extremely well on a highway/interstate/thruway (as far as the end result of picking out the LEO)...

For instant on (which make most detectors less then awe-insipiring in a state like NY on the thruway)... the CB (where truckers call out LEO's miles in advance) are most like what you are asking.


I know its not anything like what you are asking, but it essentially does the same thing (tells where LEO's are), just in a different way.


Anyways I would guess the big issue (as you mentioned) would be other devices to cause false alerts... not to mention you would have to create a market for the device, and it would soon be banned (a criminals dream).


All in all... its a VERY intriguing idea... until something like that is developed, I will stick with a CB+RD combo for instant-on, on the thruway.

[jimbonzzz]

It is technically possible to look for the LO's of police radios. But I would be very surprised if this was a practical method for advanced warning.

I can remember that there was a discussion about this before at some point... I'll try to look for it.

[JDS]

I think this would be easier than it sounds at first...as I've pointed out before, radar detectors don't transmit, and SPECTRE can pick them up directionally...isn't that device based on leakage from the LO? In theory, you'd just need to buy a SPECTRE and retune it.

[Lucky225]

Remember back in the day Uniden Bearcall or whatever that would detect CHPs within a 3 mile radius?.. Those days are over now I think.. Most LEO radios are trunked now-a-days over a data stream with shared frequencys for law enforcement, public safety and other services, detecting the frequency within a given radius wouldn't do much good as the false-to-positive alert would be much higher then it would be worth.

[Aggie]

I remember reading that it is possible because most cars are equipped with a repeater and you could detect the repeater keying up, which would occur with any broadcast on the frequency. However now with everything being trunked and shared across governmental departments, I think you would also be picking up the dog catcher, fireman, water dept etc.

[Stealth Stalker]

At one time it was a viable theory, and that is exactly what the Uniden Beartrackers were. However, the theory was much, much better than the reality. As you note, it's useless if they aren't transmitting. And radios aren't like cellphones, where they sit around gabbing while running radar. They don't say anything until they are already behind you with their lights on. Sometimes, not even then, if it is a true traffic detail. Also, even if they are talking, they're not saying anything that is going to mean anything to you. They don't alert the world with a broadcast of, "Hey, I'm running lidar on southbound 35 at the 287 mile marker for the next hour!" And, of course, police radio is just radio. No different than any other radio. If you pick them up, you pick up any other radio too, and they far outnumber the police radios. And nationwide, police radio systems are almost all changing rapidly to new bands, new channels, new frequencies, new modes of modulation, etc... The radio that knew where your local cops talk today will be obsolete in months. And again, it's all simply pointless because they don't say anything on their radios that give you any clue as to where they are or what they are doing.

People say they hate false alerts. Imagine how quickly you'd get sick of a "police radio detector" beeping everytime any cop within five miles of you checked out on the radio for coffee or a toilet break. You'd toss that thing real fast.

This is why I say over, and over, and over again in the radio section (where this should have been posted) that, unless you are a seriously dedicated scanner enthusiast, willing to spend a LOT of money on equipment, and a LOT of time learning all about communications, you don't have the slightest chance of really getting any countermeasure value out of a scanner these days, with very little exception.

[Veri]

At one time it was a viable theory, and that is exactly what the Uniden Beartrackers were. However, the theory was much, much better than the reality.

Beat me to it.

[Z1NONLY]

I am not up to date on police encryption, but as long as they generate a signal to communicate with other police radios that is stable, detecting it should be pretty easy.

If they are using frequency hopping or burst transmission methods, that would be another story.

Their encryption probably just makes it impossible to decipher what's in the transmission. But as long as they are using a stable carrier, picking it up should be no problem. (When they are transmitting)

[kpatz]

My original query wasn't about detecting them when they transmit. They rarely transmit while running a speed trap anyway.

I was asking about detecting the LO emissions from their radio when it's in RECEIVE mode, much like Spectre detecting an RD, which is "just" a receiver as well. This would be more consistent than the transmit signal.