Why so many vehicle antennas?

WK4U · #1 (**permalink**) 03-19-2013, 9:38 AM

I saw a Cobb county PD vehicle this morning with six antennas. Five of them were quarter wave whips for 800 MHz. The sixth antenna was a black plastic antenna about two or three inches in diameter, and about and inch or two high.

Three of the quarter wave antennas were along the trunk. The other three were along the back of the roof.

So why would a PD vehicle require so many antennas? Perhaps diversity reception!? Maybe that's how Motorola gets better reception in a multi-site TRS over my 396 and 800?

Tim, WK4U

lep · #2 (**permalink**) 03-19-2013, 10:11 AM

Likely for the lojack system.

ab5r · #3 (**permalink**) 03-19-2013, 10:14 AM

Consider RDF of bank robberies. That will utilize 4 antennas. An additional antenna for communications plus possible GPS antenna for vehicle location system. Just guessing, but possible depending upon local systems utilized.
73,
Jerry AB5R

kayn1n32008 · #4 (**permalink**) 03-19-2013, 10:31 AM

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LoJack is VHF, not 800mhz

WK4U · #5 (**permalink**) 03-19-2013, 11:54 AM

Yep, not lojack.

Each of the three antennas were in a row, not a square. Three 800 MHz antennas in a row along the inside lip of the trunk lid (left, middle, right), and three additional antennas also in a row along the back side of the roof top (left, middle, right).

Tim

ab5r · #6 (**permalink**) 03-19-2013, 12:51 PM

Tim, is this common to ALL the police or fire department vehicles, or just one that you saw? Possible that it was a supervisor of some sort with inter-agency comms.?
73,
Jerry

bgav · #7 (**permalink**) 03-19-2013, 12:57 PM

Consider it's common for most public safety/police vehicles to have scanners, primary radios, county/regional/mutual aid radios, mobile data terminals, GPS, portable repeaters for areas of poor coverage while the officer is out of the vehicle, and the # of antennas add up quickly.

1 - VHF-Low
2 - Comtelco (not Larsen) Scanner Antenna (Uniden BCT15/BCD996XLT)
3 - 700MHz Portable Repeater
4 - 800MHz
5 - Mobile Data Terminal/Laptop

lep · #8 (**permalink**) 03-19-2013, 2:41 PM

Quote:

Originally Posted by kayn1n32008

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LoJack is VHF, not 800mhz

Correct. However it is difficult to determine the frequency of a short whip from a drive-by looksee. I have seen other cities using a configuration somewhat similar to that described which was definetly lowjack.

CapStar362 · #9 (**permalink**) 03-19-2013, 5:41 PM

isnt LoJack 4 antenna's in a square config?

rapidcharger · #10 (**permalink**) 03-19-2013, 6:18 PM

I'm guessing it's so they can look awesome.

I would have also guessed you're seeing lojack plus the VHF antennas for their backup/interop/fun-talk radios plus their 800mhz ant but I guess not.

ab5r · #11 (**permalink**) 03-19-2013, 8:03 PM

WAIT Guys, The photo is NOT what the original message was about, only a example from elsewhere. Tim saw 800 Mhz antennas.

kayn1n32008 · #12 (**permalink**) 03-19-2013, 8:39 PM

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3 inch: 800mhz
6 inch: 450mhz
18inch: 150mhz

Pretty easy for me to tell. Even different antenna types too.

ki4wbn · #13 (**permalink**) 03-19-2013, 8:49 PM

With it being Cobb county, I imagine they go to several different radio systems.
All of this is pure speculation, but just some ideas to consider...

One is also likely devoted to data only-for mobile computer terminal.

With that, that leaves 4 left...which could go to other radios. Each radio requires an antenna, and with all of the separate radio systems in the Atlanta area, there could very well be 4 radios in the vehicle.
One is likely for the Cobb County P25.
The others could be Atlanta TRS and also Fulton County TRS. While it might seem impractial to have more than one radio to access the same type of trunking system, most of the time vehicles that have access to radio systems get a radio from that agency for tracking/inventory purposes (in addition to make sure there is no conflicts with getting to their radio system).

The puck type antenna is likely GPS.

MTS2000des · #14 (**permalink**) 03-19-2013, 9:01 PM

the only voice radios in CCDPS units are 800MHz XTL5000's, and only one per vehicle. Most are programmed with templates for Cobb- some have Atlanta DTRS and Fulton county. All of them also have UASI wide area TG's.The other two 800 antennas are for mobile data/AVL. The VHF quarterwave (lone) are for picking up body mike audio. Four VHF quarterwaves on the roof are for LoJack.

Some CCSO cars do have an additional VHF analog mobile, usually have a spring loaded 1/4 on the left side, body mike on the right.

Some CCPD STEP cars also have a CB, usually a K-40 trunk lid mount.

shanny19 · #15 (**permalink**) 03-19-2013, 9:31 PM

Sounds like MTS2000des has the inside info for Cobb Co., but one thing that I rarely see mentioned in "antenna count" threads is cell boosters. Nearly every emergency vehicle in my neck of the woods has a Willson cradle installed.

jim202 · #16 (**permalink**) 03-19-2013, 9:55 PM

Quote:

Originally Posted by shanny19

Sounds like MTS2000des has the inside info for Cobb Co., but one thing that I rarely see mentioned in "antenna count" threads is cell boosters. Nearly every emergency vehicle in my neck of the woods has a Willson cradle installed.

There are not that many locations that I have traveled to around the country that don't have reasonable cell coverage. If all the vehicles have a "cell booster" installed, I would have to wonder if they got sold a bill of goods. Then on the other hand, if they are on the wrong service provider, then that answers most of it.

I will give a good example. When on the road, I usually travel with another person from the office. He uses AT&T. My phone is with another carrier. I have seen many times when he has no service and my phone is working fine.

Not a big fan of using additional amps just to hit a cell service provider. If you can't do it normally, then your in a no coverage zone. Use of the amp might just squeeze another 1/2 mile further out, but when you get into good coverage, you really screw up the cell site operation with the amp. You might even cause a service problem by getting connected to multiple sites at the same time. That is not a good thing and generally causes you to have your call dropped.

MTS2000des · #17 (**permalink**) 03-20-2013, 11:37 PM

CCPD/SO use a mix of at&t and Verizon data cards, most of them are being phased out in favor of Verizon LTE mobile hot spots.

Cellular coverage on all the major carriers is not a problem in this county, we have a population of close to 800,000- Cobb county is not "the hills" anymore, and the cellular providers have been forced to take notice. Hardly a place you can't go with at least usable street level coverage on most major providers, Metro PCS and T-Mobile are exceptions.

procopper7005 · #18 (**permalink**) 04-03-2013, 1:22 PM

If its STEP or DUI task force they have an additional UHF antenna which receives the audio from the officers lapel mic to extend its range so they don't lose the audio when the officer is doing the field sobriety.

Also the K-9 units have a UHF antenna for the hot box alarm which alerts the officer if the car is too hot and on some models allows the officers to remotely open the door to release the dog.