Mobile Extenders

[Tumbleweed]

Can someone please explain Mobile Extenders to me? Is it like a repeater in the trunk? If I am listening to Mobile Extender frequencies will I hear everything or do I need to monitor their 'regular' frequencies as well?

Tumbleweed
Lassen County, Kalifornia

 

[SCPD]

It's essentially a "link" between the officers portable radio and the radio inside the police car. A mobile extender will allow the police officer to use his/her vehicle radio as a "repeater". For example, here in Georgia the Georgia State Police use a portable radio on a UHF frequency. When they're out of their vehicle they use the portable to "talk" to the vehicle radio, the vehicular radio receives the UHF frequency and then re-transmits the signal out on the VHF frequency to the dispatcher. To me there are pros and cons to this setup. 99% of the counties around here use VHF. Their mobile and portbale radios are all on VHF, if they're not in a good location their signal gets really crappy on their portable because of the low power. But, they can use their portable anywhere in the county. When GSP uses their portable they have a good signal because the mobile radio puts out a lot of power so their signal to the dispatcher is much better. On the other hand, their portable is useless if they get too far away from their vehicle.

I've been able to hear mobile extenders as far as three miles before. The good thing about that is GSP uses their mobile radios to scan the radio traffic of the areas they patrol. That means that their moble extender transmits alot. If I can hear them they're very near.

Hope that may help explain a little better??

 

[Tumbleweed]

Thanks for the info. So, if I'm monitoring the extender output frequency then I'll hear the the portable & the mobile transmissions?

I just won a scanner on eBay that should be here soon. It has an 'Alert' that works off the extender frequency. I think it's a Uniden BCT-7. Looking forward to playing with it.

So if you are within 3 miles of GSP and you hear the extender are you hearing the extender transmitting to the mobile?

So I guess the best thing to do is monitor the mobile frequencies?

Thanks again!

 

[jparks29]

It's a crossband repeater....

as an example...

portable talks on 155.0 Mhz .. it's then relayed to the MOBILE, which REtransmits it on 455.0 Mhz ... Essentially putting a high power radio in your pocket...

on the REVERSE end of it...

when the mobile RECEIVES 455.0 Mhz, it's relayed to the extender/vrs/'crossband repeater' , and REtransmits it on LOW POWER on 155 Mhz, so the portable can hear what the mobile is hearing, essentially putting a 7+ foot antenna on a portable (Height AGL, length of antenna).



SO...

TX FROM ..........................................TX ON
Portable 155 -> <VRS/extender> -> Mobile 455

RX FROM .......................................... TX TO
Mobile 455 -> <VRS/extender> -> Portable 155

 

[mjthomas59]

Not sure how uptodate that bct-7 will be with the preprogrammed frequencies, however you will certainly want to monitor not just the extender frequencies but also the mobile frequencies as well. In Missouri they don't necessarily have to use the mobile extender in their vehicle to talk on their mobile, so if you only had the mobile extender frequencies programmed in you would be missing a lot of the action.

Your best bet is to ask the same question in the area you live in and see how often(if at all) the mobile extenders are used. They are becoming a thing of the past in many states, in fact i've probably only picked up extender frequencies maybe 2 or 3 times ever.(i live in highway patrol troop C in missouri) I own a BCT-8, BCT-12, and a 2051 all with the "beartracker" feature.... all i can say is that it was the hot setup when those (namely the bct-12) were new... but that was over 10 years ago and frequencies and radio systems have made major changes in most states since then.

 

[radio10-8]

In California you will want to monitor 154.905 for the CHP mobile extender. You will hear both sides of conversation IF you are relatively "close" to the CHP unit. Thats why some people call them "police or bandit stalkers." Let's say your on 395 to Honey Lake and your hearing CHP on the 154.905, I'd say you are within 1,2,or 3 miles from the CHP unit. Also when you pass CHP stations you will hear the traffic due to cars being on in the parking lot.
I always monitor this freq. Hope this helps.

 

[Tumbleweed]

Thank you. This is good to know. They have construction going on on 395 all summer and sometimes the CHP sits right in front of my place. I hear the Susanville dispatcher on 42.08 and I guess the mobiles are on 42.76 (?) but I don't hear them. I'll check out 154.905 this morning!

 

[kb2vxa]

Hi Tumble and all,

The CHP Lo Band frequencies are particularly difficult to monitor because of the way the system is set up. Rather than go over old ground (it's been discussed to death) I suggest doing a quick search to find the threads. Lindsay provided some of the most useful information by starting discussion of the specifics.

Now that you've brought it up, if the extenders work any way like the old systems here no longer in use the above discussion is valid but only to a point. They are cross band mobile repeaters but one way only, Hi Band input and Lo Band output. The portables are cross band simplex transmitting on Hi Band to the mobile repeater and receiving the base station on Lo Band, the repeater is not involved. The repeater operates in similar fashion to a semi duplex base repeater, the mic operates the radio in simplex mode while the Hi Band receiver and controller operates it in semi duplex repeat mode. In this system the Lo Band base signal is strong enough to be heard by the portable and needs no repeating, the weak portable transmitter does.

Don't take this as gospel, some systems are different and I'm not entirely familiar with the CHP being I'm considerably out of range and have no interest. (;->)

Just for fun, surely you noticed our favorite CHiPies Ponch and Jon never had radio problems even with those inefficient setups and never used portables. Good advertising for Motorola and Kawasaki though. A couple of decades before Broderick Crawford (Highway Patrol) was a rolling ad for Dodge in his black "heavy cruiser" but I never figured out what he meant by "six two and even, over and out". (;->)

 

[Tumbleweed]

This make sense. Why run the base transmission through a repeater? If they can reach the extender then they'd reach the handheld.

Ole Broderick wasn't to good in a foot pursuit! "21-50 By, Over & Out".

 

[radio10-8]

If this helps? The officers handheld transmits on 154.905, This is to the mobile extender in the car, NOT to the dispacther, The car transmits the 154.905 transmission on 42.?? to the dispatcher. The mobile extender transmits what it hears from the dispatcher on 42.?? on 154.905, this is how you can hear both sides of teh conversation, the mobile extender does not rebroadcast teh officers transmission. Is thiS MAKE MORE SENSE OR DID i REALLY CONFUSE MYSELF??

 

[Tumbleweed]

Thanks! I can understand this. What I'm curious about is this: Does the extender TRANSMIT to the MOBILE or is it hooked up by coax cable? I'm assuming the EXTENDER and MOBILE are seperate units. Thanks!

 

[w0fg]

If they're using something like the Motorola PAC-RT system I have hooked up to my Syntor then they're cabled together. The PAC-RT receives the portable signal and its audio output is then fed to the Syntor's microphone input circuitry. A VHF signal received on the Syntor is fed to the PAC-RT and retransmitted on UHF. I assume that California is doing something similar, though the frequencies are different.

 

[ofd8001]

Mobile extenders are fairly low power - units less than one watt of power (if my memory serves correctly). Thus one would have to be pretty close to hear it.

 

[radio10-8]

they are cabled together...I read (10 plus years ago) they were 5watts, Please dont quote me on that, I would say less, maybe 2-3Watts...

 

[Tumbleweed]

Help!

I just screwed up big time. :-( Where can I get my 'new' BCT-7 repaired? Any good techs on this board or should I send it to Uniden?

 

[JESSERABBIT]

FWIW-Before a local jurisdiction went digital, the units used rat-packs (as the users described them). When two or more Deputies were on the scene at the same time things got interesting. If the two or more Deputies pulled their portables when exiting their cruisers, and one tried to transmit to HQ, the received signal at HQ was completely garbled. When this happend, HQ advised all units except the lead one to turn off their portables. When that happened, the lead unit had no problem.

 

[garys]

Now that you've brought it up, if the extenders work any way like the old systems here no longer in use the above discussion is valid but only to a point. They are cross band mobile repeaters but one way only, Hi Band input and Lo Band output. The portables are cross band simplex transmitting on Hi Band to the mobile repeater and receiving the base station on Lo Band, the repeater is not involved. The repeater operates in similar fashion to a semi duplex base repeater, the mic operates the radio in simplex mode while the Hi Band receiver and controller operates it in semi duplex repeat mode. In this system the Lo Band base signal is strong enough to be heard by the portable and needs no repeating, the weak portable transmitter does.

This is incorrect. The low band signal from the base is retransmitted by the vehicle radio on VHF back to the portable. In effect, it's a crossband repeater in the vehicle. The portables have no Low Band receive capability.

This site http://www.mbay.net/~wb6nvh/CHP2001.htm has some fairly recent information on the CHP set up, including the HT1000 channel plan.

Gary

 

[JESSERABBIT]

I just screwed up big time. :-( Where can I get my 'new' BCT-7 repaired? Any good techs on this board or should I send it to Uniden?

Exactly what did you do? Maybe someone here can help.

 

[jparks29]

FWIW-Before a local jurisdiction went digital, the units used rat-packs (as the users described them). When two or more Deputies were on the scene at the same time things got interesting. If the two or more Deputies pulled their portables when exiting their cruisers, and one tried to transmit to HQ, the received signal at HQ was completely garbled. When this happend, HQ advised all units except the lead one to turn off their portables. When that happened, the lead unit had no problem.

they weren't configured properly...

 

[Tumbleweed]

Exactly what did you do? Maybe someone here can help.

I was plugging in the power cord and accidentally tried to plug it in the external speaker jack. It actually came on momentarily. It still seems to work but there is no sound-internal or external speraker. I guess a diode?