Simple TA plus FM sender

[Grubi]

First, I do not red all RDS specifications, so forgive me if my question sound quite stupid or impossible. Imagine simple, low power FM transmitter with microphone (even no need for Stereo) and RDS encoder which single functionality is a TA on/off switch - I guess such can be used as simple communication or safety system, range limited by FM transmitter power to 10 meters for example.
Is such application possible with using MRDS192(for example) and some (standard) low power FM transmitter? Or in any other simple way?

[Jan]

The MRDS192 based RDS encoder can send TA. However what's the purpose of such solution? TA does not instruct all receivers in the area of coverage to tune to your transmitter frequency. RDS does not work this way.

[Grubi]

Thanks for the answer, Jan!
OK, so you are saying "local broadcast" is not so simple. That's why I am asking...
Imagine situation you see truck with load that is falling apart (not obvious for the truck driver), and you want to warn him and all others in the area of maximim 1km (with TA enabled of course).

But if local radiostation can generate TA and instruct all RDS with TA enabled to this local radio frequency, why in theory a local encoder + transmitter can't? Other possibility is to transmit to entire FM band, but this will be jamming... I red RDS traffic info can be hacked, but hacking is not the purpose here - simple voice one communication is.
This application is just an idea, nothing definitive.

[Jan]

If you are listening a station at 93.0 MHz, how can the receiver know what is going on other frequencies? It is tuned to 93.0, not to your local transmitter with TA facility. Theoretically there may be two tuners in the receiver, one for listening and one for searching for another frequencies or stations with TA. However this is insignificant in occurrence.
Simple transmitting your emergency signal on all frequencies is also not real solution. Receiver that loses original RDS signal of the station tuned will probably start to search over the band for another frequency of the same station (PI SEEK). To avoid this, the emergency system must overlay all stations in the area and moreover RDS PI on each frequency must correspond to real situation so the receiver will not recognize that the station has changed. So there must be many unique RDS encoders and many unique FM transmitters in the emergency system, set especially for the area of operation.

[Grubi]

Hi Jan,
I can give you exact models of my two car radios/ at least 5 years old..., but they seems to perform exactly this way. Say I am tuned to 93MHz station, and TA coming from 100MHz station (P3 or something, I am in Sweden, and country is divided in several zones if I understood well).
So, when TA is enabled and there appears traffic message, it does not matter if I am on 93MHz, 100MHz or CD, radio is switching in station with TA and switch back when message is over (RDS station message changes, too). It can be some DTMF signalling or common RDS network between local radiostation - I don't know, please correct me if I am totally wrong. Also I guess every normal radio scanner (not RDS radio), can scan additionally to main frequency - for example weather and SOS channel, etc. waiting for some DTMF key.

Thanks for the useful discussion, hope not loosing your time 

 

[Jan]

The most important thing is that RDS standard (EN 50067 or EN 62106) does not define anything like continuous searching the band for TA or alarm PTY etc. Thus applying the situation proposed the receiver's behavior is undefined in general. Real emergency system cannot depend on this wobbly base.
Yes, maybe some receivers include the TA searching as a bonus feature (and there are still other preconditions - for example the feature must be activated by user or the stations of interest must be stored in preset memory, otherwise it will not be included in the searching). The question is: how many receivers? Imagine 100 cars. How many receivers present? How many turned on? How many equipped with RDS? How many equipped with secondary RDS tuner? How many enabled by user for TA searching? In my opinion the result is a few % in the best case. Of course it may be enough for some applications. This must be taken into consideration first - you can never speak to all. If this is not a real problem, then you can make some research to find the % value and compare it with your needs.
As I told before - the RDS system does not guarantee this facility as it has no support in the standard.