Mysterious 1/2 cab dispatch traffic on 152.2700

[natedawg1604]

So, I recently stumbled across the "dispatch-only" side of cab company dispatch traffic on 152.2700 (DCS 051) from Broomfield, but I'm only hearing one side of the conversations on that frequency. ULS indicates this frequency belongs CO Cab Company, so I programmed all their frequencies from all ULS licenses into my scanner. However, so far I've not been able to find the "cab side" of the conversations. I get 5 signal bars on 152.2700, and it definitely sounds like two-way conversations. So, I'm thinking they are using two repeaters/frequency pairs, one for dispatch and one for the cabs. Out of desperation I started running my scanner in search mode for the entire VFH High range, but haven't found anything yet.

Anyone have any ideas on where/how to find the "missing" repeater used by the cabs??

-Nate

 

[dw2872]

I would think that the cabs are using a repeater input frequency to transmit on that you would only be able to hear if you were near the cab that was transmitting. Good luck unless you call a cab or are near the cab lot/garage. You may get lucky if there is a random cab near you.

 

[mpg0515]

The mobiles are on 157.530, this is a half-duplex set-up by design. You are listening to Yellow Cab dispatch.

 

[dw2872]

MPG is right it is half duplex and the base station transmit is a lot stronger than the cab transmissions. Unless you are near a cab you won't hear their side even on their half of the transmit frequency.

 

[natedawg1604]

MPG is right it is half duplex and the base station transmit is a lot stronger than the cab transmissions. Unless you are near a cab you won't hear their side even on their half of the transmit frequency.

So, how are the cabs able to transmit without being near the base station?

 

[dw2872]

The base station has a large receive antenna. Same concept as cell phones.

 

[scanlist]

It's the Yellow Cab "Chew" channel. Most all the radio traffic is dispatchers yelling at cabbies over mistakes or unhappy customers. 99.999% of everything is done via MDC.

The split duplex VHF radio frequency pairs and systems for cab communications dates way back to at least the 1960's.

 

[N0GTG]

Taxis have long used a half-duplex radio system; that is, the dispatcher transmits on one frequency, and the cabs transmit on another. It's like a repeater system, except the cabs are not repeated, and do not hear each other. That prevents any intercommunication between cabs (and snide comments, etc.). Occasionally the dispatcher will keep his mike open and cabs can actually hear each other. Years ago, all fares were dispatched by radio; nowadays most of it is by MDT (mobile digital terminal). Smaller companies may still dispatch by voice.

 

[natedawg1604]

The base station has a large receive antenna. Same concept as cell phones.

I guess I don't get it; why is the Dispatch center able to hear a cab 30 miles away, but I can't hear that same cab tx frequency within the hypothetical 30 mile radius? If I had the same type of antenna, would I also be able to hear the cab tx side?

 

[N0GTG]

Yes, if you were listening to the cab transmit frequency of 157.53, you could hear the cabs. To hear the whole conversation, you would have to listen to both the base and cab freqs (and be in range of both the base and the cab).

In other words, this is the normal configuration:
Base - 152.27 transmit; 157.53 receive
Cab - 157.53 transmit; 152.27 receive
It's like a repeater except the repeat function is disabled; only the dispatcher hears the cabs. This setup allows a cab to interrupt the dispatcher, who is always listening to the cab transmit freq. The dispatcher doesn't have to keep pressing his foot pedal push-to-talk; he can keep transmitting while talking to a cab and listening.

CSP used to have a similar system in the old VHF days. Dispatch transmitted on one freq, cars on another. Cars normally did not hear each other. To talk car-to-car, a car had to switch freqs so he transmitted on the base freq. New Mexico State Police still have that system. CSP engineers helped set up that system.

 

[nd5y]

If your antenna was hundreds of feet up on a tower or thousands of feet up on a mountain you would easily be able to hear mobiles and hand helds 30 miles away

 

[ecps92]

Here is a good list of the OLD Taxi Pairs, both VHF and UHF

http://scan-ne.net/wiki/index.php?title=Taxicabs

So, I recently stumbled across the "dispatch-only" side of cab company dispatch traffic on 152.2700 (DCS 051) from Broomfield, but I'm only hearing one side of the conversations on that frequency. ULS indicates this frequency belongs CO Cab Company, so I programmed all their frequencies from all ULS licenses into my scanner. However, so far I've not been able to find the "cab side" of the conversations. I get 5 signal bars on 152.2700, and it definitely sounds like two-way conversations. So, I'm thinking they are using two repeaters/frequency pairs, one for dispatch and one for the cabs. Out of desperation I started running my scanner in search mode for the entire VFH High range, but haven't found anything yet.

Anyone have any ideas on where/how to find the "missing" repeater used by the cabs??

-Nate