Ensuring RDS Bit Errors Do Not Occur
Scope
Making sure bit errors do not occur when using MPX Nodes to pass RDS along with the main composite MPX signal.
Description
A customer who was testing an Omnia Volt FM with an external RDS generator and 2 MPX nodes ran into a problem:
- RDS doesn't work properly - their analyzer showed frequent bit errors.
The customer's stream, runs through an analyzer (RDS Spy) showed RDS errors (--) at regular intervals:
0A 0A 0A 0A -- 2A 0A 0A 0A 0A 2A 2A 0A 0A 0A -- 2A 2A 0A 0A 0A 0A 2A 2A 0A 0A -- 0A 2A 2A 0A 0A 0A 0A 2A 2A 0A -- 0A 0A 2A 2A 0A 0A 0A 0A 2A 2A -- 0A 0A 0A 2A 2A 0A 0A 0A 0A 2A -- 0A 0A 0A 0A 2A 2A 0A 0A 0A 0A -- 2A 0A 0A 0A 0A 2A 2A 0A 0A 0A -- 2A 2A 0A 0A 0A 0A 2A 2A 0A 0A 0A 0A 2A 2A 0A 0A 0A 0A 2A 2A 0A 0A 0A 0A 2A 2A 0A 0A 0A 0A 2A 2A 0A 0A 0A 0A 2A 2A 0A 0A 0A 0A 2A 2A 0A 0A 0A 0A 2A 2A 0A 0A 0A 0A 2A 2A 0A 0A 0A 0A 2A 2A 0A 0A 0A 0A 2A 2A 0A 0A 0A 0A 2A 2A 0A 0A 0A 0A 2A 2A 0A 0A --
Also, the RDS level is very low but the pilot level is correct. This is all consistent with a situation where the RDS carrier is not phase locked to the pilot per this excerpt from the RDS specification:
Solution
Indeed, the customer confirmed that there was no sync from the Volt to the RDS encoder. He changed that and now the errors are gone.
Most FM processors and stereo generators have a 19kHz output for use with external RDS encoders for sync. Many can also work with the full composite signal as well.
The solution is making sure the RDS encoder's Sync input is fed by either that 19kHz pilot output or by bridging off the full composite signal.
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