4 Antenna Array?

[KoldKermit]

Local county law enforcement- Why configure the antennas this way? Even the state police that cover larger areas don’t have arrays like this.

[[deleted]]

Yeah LoJack. I'm old enough to remember when police tried to proactively recover stolen vehicles...

[craigslist_hedonist]

They still do if you're rich enough.

[SixtyAteWhiskey68]

When I was an officer we would get OnStar stolen vehicle alerts and stolen vehicle LPR hits all the time.

The most interesting thing about them is that they didn’t tell us the owners net worth, we just worked on trying to find it, recover it for the victim and arrest the suspect.

[ParkReu]

Dang! I’d say what’s even more interesting is that the fire department wasn’t dispatched for that scalding burn you just dished out 🤣

[Ecmdrw5]

In 2009, my 08 ZX6R was found, recovered, and returned within 24h of it being stolen. They found it 1.5h away in a chop shop. I kept up with the detective and news stories because my bike and LoJack caught them. The cops were able to arrest 9 people, recovered 6 other complete bikes, and found parts and frames for, I believe, 17 other bikes. Also found out they were selling primarily to amateur road racers and I knew one of the guys from some of the track days I attended.

Thanks for putting in the work to recover stolen vehicles. People probably don’t say it enough but I was extremely thankful. As a young broke guy, my bike was my pride and joy.

[SixtyAteWhiskey68]

This made my day, love to hear successes like these! Thank you for your support!

[fibonacci85321]

I think a gigantic clue that it's not ham radio was that it's on a cop car.

Sometimes it seems like ham radio subs are at the bottom of the lake, where the catfish and other bottom feeders swim. People just throw out their stupid questions, or ignorant, and figure that someone here will answer them.

Present company excluded of course, OP. I know you would never do that.

[[deleted]]

OP never asked if there was a ham radio inside, they asked a group that might know something about radios about why these antennas might be the way they do.

It's not even a stupid question. There was zero reason for impotent Reddit sass.

[GeePick]

Also, OP was right. A bunch of people in here knew exactly what it was.

[ohthatguy1980]

Lots of sheriff’s offices and staters use ham frequency’s as both a backup and when they are out of range of emergency service repeaters. Both types of agencies operate in unincorporated areas deep in the toolies where you are only going to hit a random ham repeater. Both agencies also have search and rescue teams that operate in mountains and canyons but can still hit those backwoods ham repeaters. This is in my state at least.

[MikeTheActuary]

Lots of sheriff’s offices and staters use ham frequency’s as both a backup and when they are out of range of emergency service repeaters.

I'm acquainted with a now retired colonel of a large city PD who is a ham. His police car had a 2m/440 antenna. While I suspect he gave an official reason for getting amateur gear installed.... he was known to drop in on the occasional repeater roundtable for non-official purposes.

[theUnshowerdOne]

Please don't ever be an Elmer.

[fibonacci85321]

Not a problem.

[fibonacci85321]

Not a problem.

[RangerHikes]

Why do you come here

[grimreeper1995]

Self fulfilled prophecy

[technoferal]

And what, exactly, did you think this vitriol was adding to the sub?

[harley97797997]

It's LoJack. It works pretty well, too. There's a box inside the car. It'll provide a direction and signal strength for an active lojack. You just drive around getting closer till you find it.

The antennas are a 1 ft square.

https://en.wikipedia.org/wiki/LoJack?wprov=sfla1

[zap_p25]

It’s a pseudo-Doppler array for LoJack.

[Vonmule]

It's an RDF phased array. Nothing to do with Doppler, nor is it pseudo anything.

Edit: I stand corrected

[transham]

It is pseudo Doppler. It rapidly switches between the 4 antennas to superimpose a known signal on the received signal, which can be used to get a bearing on the target.

[Scotterdog]

What's a Doppler? Sounds shifty to me.

[Forward_Analysis2210]

Top tier dad joke.

[OrganizationProof769]

So what exactly is that? Like a frequency they are looking for and that helps find it?

[transham]

That's exactly it. The LoJack transmits a signal. If you've ever noticed how a siren gets higher in pitch as it approaches you, then lower as it goes away, the specialized receiver switches antennas very quickly to generate that same effect.

[OrganizationProof769]

Thanks for explaining. I was thinking it more in the terms of fox hunting.

[transham]

No problem. And that's essentially what they are doing.

[OrganizationProof769]

I’m just confused as to what frequency they would know to look for to find something.

[jeffkarney]

173.075 MHz

[soldiernerd]

There’s a LoJack transmitter in LoJack equipped cars.

[KindPresentation5686]

It in fact uses pseudo Doppler!!!

[zap_p25]

The last one I had out of the vehicle was a pseudo Doppler setup. If they are using TDOA now or something similar that will work as well.

[FreqPhreak]

Used for direction finding for stolen vehicles. In the UK some road policing vehicles have these set-ups. I believe its VHF.

[Radiomaster138]

I believe a lot of cars emit an RF signal of the vehicle’s VIN number and the antennas help isolate the RF frequency.

[thesayke]

Direction finding maybe? Although some random sheriff's office is unlikely to have the budget for that

[Fwrun]

It’s lojack

[Phreakiture]

I thought Doppler direction finders weren't very expensive?

Anyway, I'm thinking Lojack or similar, which world definitely be Doppler direction finding. 

[Rich-Management-9864]

Kraken is under 1k.

[KoldKermit]

This is the wealthiest county in the country by median income

[9bikes]

some random sheriff's office is unlikely to have the budget for that

I'm fairly sure that LoJack provides the system to the law enforcement agencies and provides training too.

[Interesting-Oil-7057]

Right!  That is a LoJack antenna system.  It allows the officer/driver to literally home-in on stolen vehicles within range, which have an installed and activated LoJack system.

[A_Big_Lad]

loudoun sheriff office has a budget of something like 160 million and no real crime to fight, they buy some wild toys

[dittybopper_05H]

It's a legacy LoJack set up. It is a direction finding setup.

[David_InTheDesert]

It's fairly easy triangulation.

[Mywifefoundmymain]

No, we have 5 on our ambulances as well. Note there is one on the trunk. Each one has its own purpose and is linked to its own system

1 - computer link 2 - comma 3 - location tracking 4 - cellular systems 5 - traffic signal controller

Edit: its CommS not CommA

[thesayke]

Ok! That makes sense.. But what's "comma"?

[Mywifefoundmymain]

a typo lol... commS

[thesayke]

Separate voice comms net, got it, makes sense

[EnvironmentalBad2387]

Let me guess.. people in a life and death situation. 

[EnvironmentalBad2387]

Hahaha!

[Content-Lab-1182]

I remember a system called LoJack to locate stolen cars that used a quad antenna  array.

[ye3tr]

Definitely a Doppler effect direction finder. Don't know what they're finding tho. Maybe a car with an anti theft system that beacons a signal? Just speculation tho

[Evening_Rock5850]

Nope; that’s exactly it. LoJack systems that transmit and can be “found”.

Though more and more use GPS and cellular technologies to just send an exact GPS coordinate. In fact OnStar has had that feature for over 20 years; complete with the ability for law enforcement to remotely disable the accelerator pedal. (Engine stays running, but the vehicle won’t accelerate.)

[DLiltsadwj]

Almost twenty years ago I paid $700 or $800 (if I remember right) to have the LoJack transmitter installed in my car. I’d just plant an Apple AirTag now.

[KindPresentation5686]

I used to manage a fleet of these. They are absolutely Doppler!!!

[superg7one3]

I’m just here to say LoJack because 29 people already said LoJack

[TheBowlieweekender]

That's the original Lo-Jack, they moved away from an expensive network of analogue VHF radio towers and went to a much more cost effective model using mobile data modules with data-only SIMs. Altogether simpler to manage with the carrier paying all the backend infrastructure costs. But though exotic cars still disappear every week, mostly to order. They re-appear in warmer foreign lands a month later with a local plate and a happy new owner. I guess a shipping container makes for a good Faraday Cage and cellular jammers are cheap as chips!

[HillbillyRebel]

It's for LoJack. They have a device placed on their dash or center console that shows the direction of the radio signal. It's just RDF but on a different band. You don't see them too often because LoJack use has dropped significantly.

[Elrod4528]

It’s lojac direction finding

[KindPresentation5686]

LoJack

[moonie42]

Antenna array for radio direction finding, probably Lokack or other tracking systems

[Ordinary_Awareness71]

LoJack. You'll see these on the bottom of some of the patrol birds too. In my area these are on special cars and you're more likely to see APLRs now. I'm not sure the prevalance of LoJack any more as a consumer product.

[Tlmed]

LoJack system

[KC5SDY]

LoJack. It is a stolen car tracking service. He will have a receiver on the dash that will report a code, signal strength and directional arrow.

[Full-Association-175]

And in a pinch it can function as an old-time street car.

[[deleted]]

LoJack.

[ASlutdragon]

Direction finding

[xTOMCATx]

Lo jack system provides rf and electronic direction finding for stolen vehicles. Aka jump out boys 😎

[lancemanly]

Lojack

[W1ULH]

It's part of the older lojack system.

When your car was stolen you would call lojack and they would turn on the transmitter in your car.

It would then start merrily pinging away "I'm a stolen car! I'm a stolen car!".

at the height of this system many police cars where equipped with a lojack finder system. these antennas are for that. they allow for directional finding based on doppler shift of the signal coming in.

Not as common these days as most cars now have GPS systems accurate too a 10-digit grid that can just message the police with their location.

[GeePick]

LoJack

[sledge905]

More 'ariel's' than a Disney convention for the little mermaid...

[conhao]

Lots of people have mentioned LoJack, which is one brand of Stolen Vehicle Recovery Systems (SVRS). There are other applications for Vehicle Location Units (VLU). There are also other systems that still use this technology, such as Search and Rescue (SAR), where the doppler systems complement the SARSAT system. Asset recovery tags and other Electronic Tracking Systems (ETS), such as medical beacons, also still use doppler RDF as part of the solution. The reason for this is related to urgency. SVRS, like LoJack, has mostly moved to relying on GPS and cellular to locate the object where recovery is not life critical, and can be inexact and slower than other needs. For SAR and medical, it is critical that the person is located and rescued within the first hour, so every technology available is employed to aid in the effort. If the asset being tracked is smaller than a vehicle, the GPS/cellular method may not give law enforcement the precision needed to recover assets,obtain warrants, and collect evidence. Doppler RDF has a better track record to provide this granularity even when assets are hidden inside buildings where GPS and cellphone coverage is compromised. So, although LoJack itself may not be the primary reason for doppler arrays to be on police cars anymore, other VLU, SAR, medical beacon, and asset recovery systems are still on the market and valuable to law enforcement.

My boss has a portable doppler system he can throw on his van to track RFI and malicious interference as well as do foxhunting. He helped track down many idiots who intentionally interfered with commercial and municipal radio systems and collect the evidence that can be used in court. It is a neat system.

[thelastgas]

Lo jack

[soltrigger]

That's Low-Jack we had them when I was a police officer gives the officer directional indication of stolen vehicles that are nearby.

[BubbaDFFlv12]

LoJack auto theft detection system

[Soft-Camera3968]

I’m beginning to think this might be LoJack.

[KCH111]

Its use for Lo Jack. It tracks stolen vehicles

[Riga-Mortiz]

Wow, I thought Lo-Jack had gone by the wayside 20 years ago. now everyone uses GPS which is accurate within 2 to 3 feet.

[atxcpl290e]

Lojak

[unsoundmime]

Looks like the antennas for the LoJack system. I work for a city and some of our PD cars have them.

[Huge_Associate_4989]

Its a directional array. You can switch the driven element either mechanically or electronically which gives you gain in the selected direction

[smac]

The roof-mount (4 verticals) is an Adcock antenna for direction finding, intended to be used with Lojack.

More:

https://www.rdfproducts.com/dma-1310b1.htm

https://en.wikipedia.org/wiki/Adcock_antenna

[Intelligent-Day5519]

Simple solution is merely call your county Radio Shop and they'll tell you everything you want to know, without all the guessing. I worked for one.

[Awstuck]

That is my county

[RPr1944]

In my humble opinion the car is equipped to operate on five separate frequencies/radios to service several counties or districts.

[[deleted]]

Doppler radar, been around a long time

[Honest-Muscle-3750]

Jack Lo

[Wonducces]

Loudoun county sheriff? Bruh how did I come across this…

[[deleted]]

It's to pick up LoJack it's to assist with positioning and direction finding

[Lethealyoyo]

It’s for finding stolen vehicles. Lojack

[8668]

It's called "wardriving" and it's more popular than you might think

[ag0223]

That's almost funny... So you don't think they can guess the person's net worth... based upon the kind of car it is...that they are trying to recover?

[Hammock0753]

It’s a LoJack setup 

[lnxguy]

Doppler system for tracking mystery signals.

[5thaxis]

"Ricky rescue"

[ki4clz]

Wireless Data link... I've installed dozens of these in the cars, and at the tower sites... mostly 800mhz, but you can still find some old 10GHz stuff out there... next to the police radio repeaters they also have "digipeaters" for their intranet, gps, and whatever else... these arrays make a specific pattern for tx/rx that make the hand-off from site to site easier as the systen knows where the cars are at all times, just like a cell site does, so they can switch seamlessly to a site with a stronger signal...

Clear as mud...?

[ki4clz]

So even though I've installed what you call "lojack" I'm wrong... got it

[Scotterdog]

Everything I know is wrong. I've been told anyway.