Batboard

I've been improving the VHF radio system for a taxi fleet in a remote rural area of scotland. I've installed an old repeater which has dramatically improved range & reliability. However, a big complaint is increased radio traffic (and too much "chat").

Pre-repeater, the taxi firm used to operate on a duplex system: the car radios would Tx on freq. "A" and Rx on freq "B". The base radio was the other way around, it would Tx on B and Rx on A.
in this way, the drivers could not hear each other (and therefore could not chat to one another) they could only hear the office. The base could hear everything,
When we installed the repeater (on input freq A, output freq B), we had to reprogram the base radio to the car "personality" so that it could access the repeater.
The most obvious result to the drivers being that they could now hear each other.

so now, although range & performance is increased, the drivers are essentially abusing the privilege (we originally thought that inter driver chat would be an advantage, re logistics but the disadvantages outweight the advantages on a busy night)

The "holy grail" that we are now after is to use the repeater but to make it impossible for the drivers to hear each other - only the base op must be able to get thru to the cars.

We use CTCSS, 186.2 Hz on everything at present (instead of the alternative, a carrier squelch)

I feel that it must be possible to use CTCSS at the repeater to do this. My initial theory is to have a "conditional toning" system at the repeater:

if the repeater receives tone X on input then it transmits with tone Y encoded onto the output
AND
if the repeater receives tone Y on input then it transmits with tone X encoded onto the output.

Then the car radios can all remain programmed as they are; Tx on f=A with CTCSS=X AND Rx on f=B with CTCSS=X
But, we could reprogram the base radio with same Tx & Rx freqs but with Tx CTCSS=Y & Rx CRCSS=Y


My questions are, 1. would this actually work and 2. are there any "kits" that do this already?
the repeater we are currently using is an old "Motorola Compact", I believe called a R100 in the US.
We have also just bought a GM300 repeater set (apparently constructed of 2 GM300 units)
73 de MM0TJR

Is the repeater located at dispatch or on a remote location?

If located at dispatch, then you are back to the same issue, the dispatcher will hear everyone, but the cars wouldn't hear each other.

You CAN program the repeater to send different tones, and perhaps multiple tones (but certainly NOT the R100- too old), but the simplest thing for the driver to do is just lift the mike from the hook, which would automatically put the radio in carrier squelch, negating your 'special' PL plan.

Sounds to me like the solution is MDC ID on the radios to identify the offenders, and then some disciplinary action if the nonsense doesn't stop.

This is why the FCC originally, "back in the day" mandated transportation systems to be half-duplex. The idea was that the radio would be abused, so they put carriers on the half duplex plan to negate this type of operation.

You didn't mention if you have wireline to the repeater or not. I assume that you are using RF at the dispatch center to talk into the repeater. If you had a wireline circuit to the repeater, you could do things like setup/knockdown the repeater, etc.

Most taxi cab radios use a remote base. If you use a repeater the drivers tie the channel up with chit chat. The base would look on the input and talk on the output.

Most drivers lease their cabs and they are very competitive. If they can, they will steal a dispatch. Taxi's are a real zoo!

What you are talking about doing is possible but it's going to take some work and money to complete.
And ANY of this can be negated by lifting the mike from the holder, but that is a programmable function on most radios and can be turned off as well. Once off the radio will receive ONLY in PL and not the other traffic. Since they are communicating on a repeater the output will need multiple PL's and the receiver will need to be able to decode multiple PL's and switch the transmit PL.

Here's how it's done
get two PL decoders and two encoders.
Set the taxi radio's for a specific transmit PL and different receive PL choose a low or high PL for both but they should not match
Set the dispatch radio with a DIFFERENT transmit PL than the taxi's.
Set the Receive PL on the dispatch radio different than the taxi's

Set the first decoder to the PL of the taxi's
set the second decoder to the PL of the dispatchers radio.

Here's were you need to watch and follow along.
set the first encoder to the PL of the dispatch receiver.
set the second encoder to the PL of the taxi's

When the dispatcher keys up the PL generated will open the receivers of the taxi's
When the taxi's key up the pl generated will open the receive for the dispatch radio, not the other taxi's.

This is as close to duplex as you can get without it being duplex.

forgot to mention
you will need to reprogram everything for this.
all radios and the repeater,,, it will be set for CSQ and the PL decoders will need to key it

everything still gets transmitted across the airwaves, and everything said will be heard by all taxis if the dispatcher is talking.

If your fleet is small and you want to REALLY get in depth and talk to each taxi seperately, then you could get a multichannel tone remote and replace the repeater with one that supports toner remote control. Each unit gets a seperate PL for receive. You program the repeater with the number of transmit channels that you have units and have the tone remote change channel depending on the taxi you want to talk to. The channel frequency stays the same and only the PL changes. a scanner will still pick everything up but it eliminates everyone from hearing everything in the taxi's.

Turn the rptr into a full duplex base, and wireline control it from dispatch. If you don't have wireline, use an rf link.

Do the radios in the cabs do 5 tone signalling? Selectively calling the cars this way is popular in .au

THanks VERY much for all the comments
to clarify:
the repeater is on a local hilltop. the dispatch radio is in the middle of the small town.
the cab radios are a very disparate mixture of old PMR stuff. there's a few GM300s but there are Tait500s, icom V200s, maxons etc etc. As time goes by I'd like to standardise the fleet to all GM300s for simplicity and cheapness. Cheapness is a big factor here, as the budgets are obviously not large.
The cabs are all owned by the company. the territory is pretty small also (the county is 1 island about 900 square miles)
select five would be nice but cost prevents it. wed have to put sthg like GM360's in all the cars. And the dispatch may not get their head around it.
We definitely dont have any of the radio functions associated wth "mic on hook". these are all programmed out of any radio that could do it.
it really dont matter what goes on the air, as long as we can use PL/CTCSS to mask the drivers from hearing each other.


Desperado: can you clarify your plan a bit further? it sounds complex. where do the encoders/decoders go?

Also, could someone please tell me if or why my plan is wrong?!

a "refinement" to my plan would be to just get the repeater to transparently "pass" a tone through it.
ie:
Cars all have PL decode ON, lets say tone X. (so they all have tone squelch using tone X)
cars all transmit with NO TONE.
dispatch has no PL decode (so it has carrier sq ONLY)
dispatch always encodes PL X

the repeater simply retransmits the PL that it decodes.
so if the repeater decodes PL X on input, it encodes PL X onto its output. and all the cars can hear dispatch
if the repeater decodes NO PL on input, it encodes NO PL onto its output. and none of the cars will open squelch. but the dispatch will have its CSQ opened and can hear everything.

???!!
seems easy enough? why might this not work anyone!?

also could anyone advise whether a GM300 type repeater provides this level of functionality?
I absolutely realise out R100 ancient repeater will not of itself do this.

Most repeaters will not pass a tone, as there is a high-pass filter in the repeater receiver that strips the tone off before passing the audio on to the controller.

Wireline would be great for this, or microwave. If none of this is available, obtain a UHF freq. pair (I have no idea what the process is or availability of obtaining freqs in Scotland) and run simultaneous crossband links.

You will need a VHF repeater with repeat disabled or full duplex radio, a UHF transmitter, a UHF receiver (these need to operate separately), and a UHF transciever with power supply. You probably already have a VHF duplexer, but you will need a UHF duplexer and two small yagis.

The VHF receiver would be connected to the UHF transmitter and the VHF transmitter would be connected to the UHF receiver. In the office you would need the UHF transciever. When the dispatcher keys their radio it is sent to the UHF receiver that keys the VHF transmitter to the mobile units. The mobile units transmissions are received by the VHF receiver and transmitted over UHF back to the office. The VHF is never repeated back over VHF so the issue of people talking to each other is eliminated. The dispatcher always has access to the VHF transmitter and always has supervisory control of the dispatch channel. This elminates any custom tone scheme that will always be an issue when radios have to go in for repair, it can't be defeated by clever employees obtaining scanners to listen to the output of the repeater - low power point-to-point links using directional antennas have limited range for monitoring unless the monitorers are in the link path. You won't need to go out and reprogram anyone's radio, this is all done on the infrustructure side.

I do like the idea of the PTT ID's and enforcing a no-chat policy but that's probably not going to happen.

Had a similar problem with a package delivery service, quick fix was to program the mobiles with one set of PL tones and the dispatcher with another set. Program the radios for Busy Lockout, the radio is in permanent PL only mode and basically they can't talk when another user is transmitting, and you don't have to monitor before transmitting. The dispatcher transmits on PL "A" the mobile is programmed for receiving PL '"A", the mobile transmits PL "B" and the dispatcher receives PL"B". There won't be any way for the mobile to receive another mobile since he cannot decode the mobile PL"B" code.
If your repeater isn't capable of multiple PL codes repeater panels are real cheap on E-bay and the like.Usually around $100.00 US.

MM0TJR wrote:THanks VERY much for all the comments
to clarify:
the repeater is on a local hilltop. the dispatch radio is in the middle of the small town.
the cab radios are a very disparate mixture of old PMR stuff. there's a few GM300s but there are Tait500s, icom V200s, maxons etc etc. As time goes by I'd like to standardise the fleet to all GM300s for simplicity and cheapness. Cheapness is a big factor here, as the budgets are obviously not large.
The cabs are all owned by the company. the territory is pretty small also (the county is 1 island about 900 square miles)
select five would be nice but cost prevents it. wed have to put sthg like GM360's in all the cars. And the dispatch may not get their head around it.
We definitely dont have any of the radio functions associated wth "mic on hook". these are all programmed out of any radio that could do it.
it really dont matter what goes on the air, as long as we can use PL/CTCSS to mask the drivers from hearing each other.

Your plan would work, but will require that you use a separate tone panel rather than the PL functions in the repeater radios, and continue in your practice (which is not OK in the US) of forcing the mobiles to use PL decode at all times. You could make the tone panel with standalone PL decoder/encoders, or use an all-in-one "community repeater panel" such as those made by Zetron, CSI, Midian or similar companies.

Desperado: can you clarify your plan a bit further? it sounds complex. where do the encoders/decoders go?

Also, could someone please tell me if or why my plan is wrong?!

a "refinement" to my plan would be to just get the repeater to transparently "pass" a tone through it.
ie:
Cars all have PL decode ON, lets say tone X. (so they all have tone squelch using tone X)
cars all transmit with NO TONE.
dispatch has no PL decode (so it has carrier sq ONLY)
dispatch always encodes PL X

the repeater simply retransmits the PL that it decodes.
so if the repeater decodes PL X on input, it encodes PL X onto its output. and all the cars can hear dispatch
if the repeater decodes NO PL on input, it encodes NO PL onto its output. and none of the cars will open squelch. but the dispatch will have its CSQ opened and can hear everything.

???!!
seems easy enough? why might this not work anyone!?

That would work too, but would require bypassing the audio filtering at the repeater radios which is intended to send the low frequencies to the PL decoder and the highs to the transmitter. This is a trivial modification to make but would compromise FCC approval in the US as it would involve a modification of the transmitter; I imagine it would be the same with OFCOM regs in the UK. You'd want to have some PL encode/decode for the dispatch to prevent the repeater being keyed up by random interference landing on the channel.

also could anyone advise whether a GM300 type repeater provides this level of functionality?
I absolutely realise out R100 ancient repeater will not of itself do this.

It doesn't inherently. You need to get flat audio out of the repeater (you could do it just as easily with the R100) and back in again, doing your own PL filtering, decoding and generation. This is done all the time in the amateur radio community but radio techs tend to shy away from it in commercial licensed systems. In the US, this sort of thing is done in public safety/government work by techs who realize that if they do the modifications properly and measure the results to be within specification, while technically illegal, no interference is caused and no complaints would be generated.

The FCC allows for PL lock(Busy Channel Lockout) if the radio is prohibited from transmitting if another co-channel user is transmitting. I don't think Motorola would allow a setting in their radio that goes against FCC rules. I did mention you would need an external PL panel for this to work, it is probably the easiest and least expensive to implement, and hooking into a GM300 isn't that hard. Plus all the work is done at the repeater, no need to mess with the mobiles, except for reprogramming

fcc don't apply in Scotland. Sounds like they need to make examples of a couple drivers. Use the mdc to identify who's doing it and fire them. Real simple