Author Topic: Locking to the 19kHz pilot  (Read 3480 times)

TeknoTone

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Locking to the 19kHz pilot
« on: May 10, 2012, 11:26:13 am »
Hi Jan,

I've been unable to replicate the locked waveforms you show in your YouTube video Jan. The level of RDS injection shown here is the minimum required to bring up the RDS flag on a receiver. The scope sync is taken from the 19kHz pilot tone shown as the upper trace. The board is a MicroRDS bought very recently and it's integrated with a Taylor modulator.

My RDS does decode on all receivers I've tested although it does seem to need more RDS deviation than I would have expected.

My video response is here
http://www.youtube.com/watch?v=TphpQELGn6E&list=UUYlMJ3dCr-Vo8_lQF8RnKNg&index=2&feature=plcp

Regards

Tony

Jan

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Re: Locking to the 19kHz pilot
« Reply #1 on: May 10, 2012, 02:01:31 pm »
These conditions must be met to get the RDS subcarrier locked to pilot tone:

1) Pilot tone level on the PLT pin must be 250 mV pp or more
2) Pin /SNC must be tied to ground to enable PLL
3) Clock source must be set to Auto in the Windows control software (already set in factory)
4) Pilot frequency must be accurate (19 kHz +/- 2 Hz). The RDS unit does not lock to a pilot frequency that is outside this range, required by broadcast standards, because this would cause the RDS subcarrier frequency to be outside the required range too. In that case trim the stereo encoder oscillator or disable the PLL (set to internal clock source).

All units are tested for pilot locking before dispatch.

TeknoTone

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Re: Locking to the 19kHz pilot
« Reply #2 on: May 10, 2012, 03:07:26 pm »
Many thanks for your swift reply Jan. All conditions were good with the exception of the pilot frequency which I had not checked. On the exciter I have on the bench right now, the pilot is showing +6.7 Hz so I guess you've nailed it for me. There's no trimmer unfortunately so I'll have to bend it with a fixed cap.

Best regards

Tony

Jan

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Re: Locking to the 19kHz pilot
« Reply #3 on: May 10, 2012, 05:23:06 pm »
The MicroRDS internal clock is tuned to 57 kHz +/- 2 Hz (this is checked on each piece), thus you may use it as a frequency reference for adjusting the stereo encoder's oscillator. Here's how to do it:

1) Connect pilot to channel #1 of the oscilloscope. Set the channel #1 as the trigger source.
2) Connect RDS to channel #2 of the oscilloscope.
3) On the MicroRDS disconnect the /SNC pin so PLL will be disabled.
4) Now you see stable pilot on the oscilloscope and "running" RDS.
5) Adjust the stereo encoder's oscillator until RDS stops "running" and becomes very slow on the screen (no more than a few "nodes" per second). Now the pilot is 19 kHz +/- 1 Hz or better.