RDS appearing only when the signal has partially faded

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John Faulkner, Skegness
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RDS appearing only when the signal has partially faded

Post by John Faulkner, Skegness » 20 May 2015 15:34

I hadn't thought of mentioning this before but I think it will be of interest. It concerns RDS data when the signal is only just strong enough to produce RDS.

It's a phenomenon I first observed on my XDR-F1HD, once I had done the Konrad i2C modification. It wasn't immediately obvious to me for a while, and would probably be even less likely to be observed on a conventional hi-fi tuner. It concerns the most likely time when the RDS will appear. The FDM-S2 also highlights this nicely: When a signal reaches its peak (was the apostrophe in the correct place, Stuart?), you would expect this to be the most likely moment for the RDS to form on your display. On borderline-RDS signal levels, this doesn't usually happen, unless the signal is stable, in which case, given time, the RDS should pop up eventually. But in the case of tropo and sporadic E propagation, when such a borderline RDS signal fades, I have noticed that the RDS will usually appear only when the signal has started to fade away.

I have observed this consistently over the last year or so. Why would RDS be more likely to form when an Es or tropo related borderline RDS signal has partially faded and not before?

The answer will probably be too technical for my old analogue brain cell to comprehend, but there must be a solid scientific reason.

Jim (Bournemouth)
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Re: RDS appearing only when the signal has partially faded

Post by Jim (Bournemouth) » 20 May 2015 17:58

I am thinking that it might be a delay between the signal peaking, and the RDS being processed, decoded and sent to the display. A lag effect, if you like...
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satnipper
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Re: RDS appearing only when the signal has partially faded

Post by satnipper » 20 May 2015 18:16

John Faulkner wrote:When a signal reaches its peak (was the apostrophe in the correct place, Stuart?)
I have never known you get it wrong to date, JF, and you may rest assured you have not now started to insert extraneous apostrophes.

And I concur with Jim regarding a computational delay.

Stuart

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John Faulkner, Skegness
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Re: RDS appearing only when the signal has partially faded

Post by John Faulkner, Skegness » 20 May 2015 18:41

Thanks for that Jim and Stuart.

It's definitely not a delay relating to the processing of the RDS by the computer or the software (as far I can guess). I am sure it relates to the effects of propagation. I thought it might make an interesting topic.

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