Cab company wants a repeater but....

Equinox · Post by **Equinox** » Fri Sep 12, 2003 1:28 pm

They are set up where the mobiles cannot talk to each other. What would be the easiest economical way to do this? One solution I thought of was to have two repeaters. #1 would receive from the base and transmit to the mobiles. #2 would receive from the mobiles and transmit to the base. In other words-

FOR EXAMPLE-

Base= 152.000 RX.......157.000TX

RPT1= 157.000RX........151.000TX

Mob= 151.000RX.........156.000TX

RPT2= 156.000RX........152.000TX

I THINK this would work, wouldn't it? They could still have the mobiles not hearing each other this way. Kind of elaborate but what the hey? My thing is, I have been told that most cab companies are set up where the mobiles can't talk to each other. WHY IS THAT?

larryepage · Post by **larryepage** » Fri Sep 12, 2003 1:44 pm

Half duplex operation is for some reason very common in transportation operations where a central dispatch needs to talk to drivers but there is no reason for the drivers to talk to each other. Another big user that sets their system up this way is SuperShuttle. I actually have some heartburn with these setups because they do not provide for listening before talking, meaning that there is frequently (or maybe occasionally) 'doubling' between units when they call dispatch.

I don't know if there is a reason to do this or if it is that it has just 'always been done this way.' And I am vaguely remembering that there may have been a thread on this board a year or so ago referencing this same topis. Do a search and see.

Now for some personal opinion and suggestion...

This is a case where there is probably very little benefit to be gained through the use of a repeater system versus use of a well-designed base station...a good transmitter and optimally mounted antenna will provide the same range as a repeater with less equipment to fail.

A better way to accomplish this would be to use one repeater with a multi-tone controller and use a split tone arrangement--taxis use one tone to access the repeater, which basically sends it through and unsquelches the dispatch station only. Dispatch responds on the same frequency but with a different tone, which does unsquelch the mobiles. Works just like half-duplex, but everyone can monitor the channel for activity by watching their 'Busy' lights. Hald as many frequencies, half as many repeaters, no combiner, (or half as many antennas).

Regards,

Post by **wavetar** » Fri Sep 12, 2003 1:59 pm

Everything Larry said is true. People associate 'repeater' with 'extended range'. While this is true compared to regular radio-to-radio simplex systems, there's no extended range when compared to a base station set-up. Assuming the TX power of the base station & repeater to be equal, as well as antenna location.
Most large cab company dispatchers spend 99% of the time 'on the air', dispatching thousands of calls a day. That's the main reason the drivers aren't set-up to talk to one another. Time is money, the company can't afford to lose it while the cabbies are discussing where to hold the weekly poker game over the radio. One of our local companies took it a step further recently & installed a complete data dispatching system. No talking going on at all, unless the dispatcher sends a signal to the driver to enable his radio to transmit! Why you ask? They average 5000 more calls per month compared to the voice system!
I'm not a fan of using PL to isolate groups using a common frequency. There's not much stopping the drivers from putting their radios in 'monitor' mode & talking to one another. Unless careful steps are taken, either in radio programming, or hardware modification, or both.

Todd

Znarx · Post by **Znarx** » Fri Sep 12, 2003 4:23 pm

assuming that dispatch is seeking better coverage...

the "repeater" is going to be set up at a remote location with better coverage characteristics i.e. top of building downtown or tower site

the best solution is to have a simplex UHF link connected to a half-duplex VHF drop (cross-band repeat)..this will allow dispatch to transmit to and receive all mobiles, but the mobiles will not be able to talk to one another.
Also this solution does not require duplexers (and being a cab company I'm sure they will jump at the idea to buy less infrastructure)

e.g. the "repeater" hears VHF A (from mobiles)and transmits UHF (to dispatch), the "repeater" hears UHF (dispatch) and transmits VHF B (to mobiles)...there is no repeat function from VHF A to VHF B therefore the mobiles cannot talk to one another

another solution is to remotely locate the base station and have a wireline control (again half-duplex can be implemented to prevent cabbies from interacting)

...Z

kf4sqb · Post by **kf4sqb** » Fri Sep 12, 2003 8:17 pm

I've also often wondered why some agencys set their radios up this way. Not allowing cabbies to talk to one another to save on dispatch time does make good sense, but I still need to figure out why Georgia State Patrol is set up this way! They use half-duplex car-base and base-car, although I think they do use one frequency of the pair for car-car. Also, they use the same half-duplex pair throughout the whole state!

k4wtf · Post by **k4wtf** » Fri Sep 12, 2003 8:43 pm

How about this:

Set the repeater up work with two different PL tones and also to retransmit the received PL tone.

Now, set the mobiles up to decode say 123Hz but TX 131.8Hz.

Set the base up to decode 131.8Hz (or CSQ) and ENCODE 123Hz.

Program the radios to NOT TX on a busy channel.

Now, the mobiles can talk to dispatch but not to each other. (They won't hear each other!) They also will be MUCH less likely to double with each other because they'll get the "bong" if the repeater is busy and the chance of two of them keying at the same precise time, effectively bypassing busy channel detection is very unlikely.

OH.. And DISABLE the MON button in the mobiles.

How's that?

--
John

k4wtf · Post by **k4wtf** » Fri Sep 12, 2003 8:47 pm

kf4sqb wrote:...but I still need to figure out why Georgia State Patrol is set up this way! They use half-duplex car-base and base-car, although I think they do use one frequency of the pair for car-car. Also, they use the same half-duplex pair throughout the whole state!

Could it be that they were all tieing up the repeater with the troopers all competing with each other for the best Beuford T. Justice impersonation and this was the only way they could get them to stop doing it?

--
John

ASTROMODAT · Post by **ASTROMODAT** » Fri Sep 12, 2003 9:07 pm

Many cab companies that have not yet switched to data dispatch still use a 4 wire leased line to a remote base. Generally, the dispatcher leaves their foot on the PTT, and since they use a 4-wire, full duplex circuit, they can still hear the cabbie.

Larry

CSHFD · Post by **CSHFD** » Fri Sep 12, 2003 10:27 pm

"...but I still need to figure out why Georgia State Patrol is set up this way! They use half-duplex car-base and base-car, although I think they do use one frequency of the pair for car-car. Also, they use the same half-duplex pair throughout the whole state!" The New York State Police has a ridiculous system. Dispatch and the "Emergency Channel" are transmitted CSQ. Troop K, which is in SE NYS, transmits on 155.505. So does Troop L (Long Island). The poor troopers on eastern Long Island have to hear Troop K's weak signal the whole shift. Why not just use PLs on the base station output?

nmfire10 · Post by **nmfire10** » Sat Sep 13, 2003 3:13 am

Making an entire angency or multi-agency system go from CSQ to PL is more of an operation than you may think. You have to re-program EVERY radio (hundreds) and you have to do it all at once, not little by little. Plus you have to deal with old radios that aren't programmable that are still in service. Plus you have to deal with other local agencies that have your frequency.

We had 3 small volunteer fire depts with I think 4 base stations on one low band frequency. It took almost a year of planning, coorordination, buying parts, etc etc. Then it was a mad rush to get it all done and make sure they all worked correctly. I started out thinking "This is so simple" but it isn't that easy.

kf4sqb · Post by **kf4sqb** » Sat Sep 13, 2003 5:27 am

Your right, Matt, it is more hassle than you would think, although this is where the "monitor" function on most radios comes in handy! Have all units that have had the PL installed run in monitor mode untill all units are programmed, then change to PL. The real question is, however, why they didn't go with PL in the first place!

K4WTF, as I stated, GSP is on half-dulplex, not a repeater, but you could still be right!

BTW, GSP is also running CSQ, although I can't figure out why.

powerlineman · Post by **powerlineman** » Sat Sep 13, 2003 6:05 am

CSHFD wrote:"...but I still need to figure out why Georgia State Patrol is set up this way! They use half-duplex car-base and base-car, although I think they do use one frequency of the pair for car-car. Also, they use the same half-duplex pair throughout the whole state!" The New York State Police has a ridiculous system. Dispatch and the "Emergency Channel" are transmitted CSQ. Troop K, which is in SE NYS, transmits on 155.505. So does Troop L (Long Island). The poor troopers on eastern Long Island have to hear Troop K's weak signal the whole shift. Why not just use PLs on the base station output?

Georgia State Patrol does this so the dispatcher doesn't have to listen to all of the other GSP bases. All they want to hear is the cars. Can you image using one freq on a 400ft. tower ...you would hear too much garbage. This is why the FCC has mobile only freqs...so the mobles don't compete with base signals elsewhere

CSHFD · Post by **CSHFD** » Sat Sep 13, 2003 6:24 am

I guess it is more of a project than I thought. I just think PLs are a great thing to have, especially on lowband. Suffolk County, NY fire has no PLs on any of the lowband channels, which makes it very difficult to communicate at times. It can be very frustrating!! We would hear transmitters 20 miles away better than our own dispatcher.

Equinox · Post by **Equinox** » Sat Sep 13, 2003 8:33 am

Znarx wrote:assuming that dispatch is seeking better coverage...

the "repeater" is going to be set up at a remote location with better coverage characteristics i.e. top of building downtown or tower site

the best solution is to have a simplex UHF link connected to a half-duplex VHF drop (cross-band repeat)..this will allow dispatch to transmit to and receive all mobiles, but the mobiles will not be able to talk to one another.
Also this solution does not require duplexers (and being a cab company I'm sure they will jump at the idea to buy less infrastructure)

e.g. the "repeater" hears VHF A (from mobiles)and transmits UHF (to dispatch), the "repeater" hears UHF (dispatch) and transmits VHF B (to mobiles)...there is no repeat function from VHF A to VHF B therefore the mobiles cannot talk to one another

another solution is to remotely locate the base station and have a wireline control (again half-duplex can be implemented to prevent cabbies from interacting)

...Z

That is the deal. Their office is located between two cities. They have a 50 ft tower with a DB 224 on it right now. They are covering one city just fine as is. The other (with more tall buildings) is having problems. They are considering putting the repeater setup on one of these buildings to solve their problems over there. Wireline is out of the question (with these people).

Equinox · Post by **Equinox** » Sat Sep 13, 2003 8:37 am

k4wtf wrote:How about this:

Set the repeater up work with two different PL tones and also to retransmit the received PL tone.

Now, set the mobiles up to decode say 123Hz but TX 131.8Hz.

Set the base up to decode 131.8Hz (or CSQ) and ENCODE 123Hz.

Program the radios to NOT TX on a busy channel.

Now, the mobiles can talk to dispatch but not to each other. (They won't hear each other!) They also will be MUCH less likely to double with each other because they'll get the "bong" if the repeater is busy and the chance of two of them keying at the same precise time, effectively bypassing busy channel detection is very unlikely.

OH.. And DISABLE the MON button in the mobiles.

How's that?

--
John

I thought of that but these guys do their own installs and I wouldn't trust them to have mic hangers with the mics in them all the time. I also thought of the old dtmf decoder thing where the radio's speaker is muted until the decoder goes off. But I think the time and cost of doing that would equal the cost of getting a moderately priced repeater. And the owner seems insistence on getting a repeater, so....

RKG · Post by **RKG** » Sun Sep 14, 2003 5:57 pm

Before getting too deeply into this, check the regulations. Repeating with the "input" freq as the repeater's output would violate the regulations, and I believe that repeating with the freqs in proper order would, as well.

Equinox · Post by **Equinox** » Mon Sep 15, 2003 12:47 pm

Znarx

after further review, the crossband repeater setup seems like the solution and quite frankly I don't know why it didn't cross my my mind earlier. I already have the pieces in stock to set up a demo unit and have bench tested it. Sounds like I have a project this week!

Thanks to the board for all replies.

Cowthief · Post by **Cowthief** » Tue Sep 16, 2003 3:38 pm

Hello.

The reason for half duplex in taxicab service is very simple.
The guys (and girls ), are just that, the child,in adult size.
Fights at taxicab stands are VERY common.
The few cab companies who have had the drivers in one pool have quickly changed this.

radioconsult · Post by **radioconsult** » Wed Sep 17, 2003 8:40 pm

Check the FCC rules for the Taxicab Radio Service. My recollection is that repeaters are not allowed, except with a specific rule waiver, which may bet hard to get. Look at their license and see what the base station class is, FBsomething. The actual mechanics of a repeater may be the easiest part.
RC

Cab company wants a repeater but....

Cab company wants a repeater but....

Cabbies and radios.