MicroRDS + Veronica 50mW Stereo

[Leo]

Hi -

I'm trying to work out how to hook up my MicroRDS to a Veronica 50mW stereo transmitter.
Unfortunately I lost the schematic for the transmitter so I've had to following the PCB trace and try and figure out how it works.

I think the pilot tone comes from a 4060 which divides a 4.68MHz crystal by 256 to give a 19kHz square wave out from pin 14 on the 4060.
It looks like this then goes through a 4 stage RC filter.
I think I want to take the square wave directly from the 4060 before the filter and feed this into the MicroRDS pilot input. That's ac-coupled, so I don't need to worry about the fact that this will be a 12v square wave.... do I?

So then the 19kHz sine wave coming out the RC filter is mixed resistively with the L/R multiplex, then fed into a TL074 and thence to the VCO I think.
I'm guessing I want to mix in the RDS signal from the MicroRDS at that same point just before the op-amp.

Does that sound right?

Many thanks.

[Jan]

Never take the pilot directly from output of the logic gate. Always use serial resistor (about 10k) placed near the output pin, otherwise the connection would emit strong harmonics of the 19 kHz up to several tens of MHz. This serial resistor also fits the signal level to the MicroRDS as 12V square connected directly may damage it.

In unknown circuits I prefer connecting the RDS directly to varicap through a resistor, as showed on the picture here http://pira.cz/rds/enccon5.gif but of course, this can be made on opamp input as well.
The resistor value should be 5 to 10 times higher than the resistor that is already present on the board that feeds the MPX signal. (The more the better but RDS level must be sufficient for proper reading on the receiver.)

[Leo]

Thanks Jan - I took your advice, and it seems to be working very nicely.