SINUS RDS PROJECT

[3metrejim]

Out of interest, is there still a market for any of the FM radio stuff and RDS encoders? I know ready made RDS modules are relatively cheap these days (the one from PIRA) - even the business that sounds like a stifled sneeze (the one that Albert detests) uses one as a bolt-on to the 'hole-y', non properly filtered stereo coder.

People interested in the design of RDS encoders should read the technical description in the manual of the Inovonics 710 RDS coder, it's so well written that you can piece together any needed 'sub circuits' to beef-up (clean up), the SINUS coder, although will take time to do (of course), and a fair bit of external hardware to the PIC. You will be hard pressed to get a simple PIC to generate the 57kHz modulated signal with a 4.332MHz crystal as there is barely enough speed (unless that is all you are doing), but there is plenty of speed to generate an oversampled data stream and then externally modulate onto the 57kHz carrier.

[Albert H]

Did some hard old hard drive archaeology and dug up the scans of the original broadcast warehouse rds coder. Not so much use without firmware and it is around 24 years old, but shows how it was done (the sync). Sorry about the quality of the scans, they were kindly provided by Stephen Moss back in 2001 and I certainly wasn't going to moan - I was super lucky to get them in the first place.

Enjoy...

I remember that circuit. The use of the 1310 came from an article in Elektor a few years before, where they were extracting the 19 kHz pilot off-air, and using it to synchronise some clock oscillator. As far as I recall code in the PIC came from a paper from a guy called Hameed Haddadi . As I recall, Scott got a guy in the Netherlands to write the PIC code, and they were charged a fortune for it. I have an Italian RVR RDS coder here from about the same time that uses the same mathematics, but works by reading the RDS data from a big EPROM, and feeding it to a Manchester Encoder. The RVR thing only has about 12 ICs in it, and does everything in hardware.

[Albert H]

Out of interest, is there still a market for any of the FM radio stuff and RDS encoders?

Yes. Broadcasting in the UK and much of Northern Europe (except the Netherlands) is in a bit of a slump. The move to digital (DAB and the Interweb) is gathering pace - there's no longer much need to risk arrest and loss of gear by trying to broadcast to a large potential audience. It got to the point in London that most of the stations were broadcasting to themselves and a few of their friends.

However, the situation in the rest of the World is pretty buoyant. My company are shipping plenty of VHF FM stereo gear (often with RDS) and plenty of AM stuff as well. Power outputs tend to have reduced (except for the AM gear), and customers who'd order a 5kW box five years ago are ordering 1 or 2 kW transmitters nowadays. The move to digital has benefited small scale broadcasters - Band II is emptier in ;ots of places, and the general noise floor has returned to 1970s levels. In markets where you'd need 5 - 10 kW to get noise quietening a few years ago, you can get away with 1 - 2kW today.

The market for gear to make your station sound good is still big - outside Northern Europe. We've shipped plenty of 110V 19" rack-mount processors to the Americas lately.

[3metrejim]

Thanks for the reply Albert. It's been a fair while since I've heard of anyone tuning around the dial to see whats about, that's what got me wondering. The only time I've noticed anyone listening to FM is in a vehicle, or occasionally a factory - but I hear you need a licence for that these days. I imagine most teens are fixated on an internet connected device rather than checking a radio, and from what I've noticed, a lot of adults too.

I had an attempt at an RDS coder around 1998, everything hardware except the message source ( an 8 bit Atari 800 ). I could get a screen display, but at the time, couldn't get the modulator and filtering right, so it was terribly noisy. I used to do a lot of PIC programming and it's always interesting to get a block diagram or a piece of hardware and figure how much could be usefully crammed into a PIC. I am a bit of a fan of 'hardware acceleration' still though (bigger physical size but less fiddly/time critical firmware).

[sinus trouble]

Excellent points 3metrejim!

Just to address some of your comments, Commercial radio was a massive market as you know!

There is no "Tuning round the dial" because most of the youth are on "Smartphones" scrolling through mindless Tik Tok etc......

Getting back to markets, I see a huge rise in alternative media also! Such as vinyl, AM restorations and vintage audio gear!

As with all markets, These can change within a heartbeat! If the internet collapsed one day? Communication would be F*cked!!

But not us on Radionecks!!

Regards to the Sinus RDS? I guess it is not essential for broadcasting, whilst far from perfect? It is likely the most simple solution available!

If i could improve it? I would add a basic LCD with manual controls to deem it independent from any PC interface!
(Similar to the original BW system)

As with all my designs, The goal is to keep things simple so that they work in harshest environments with little maintenance!

[radium98]

My question is , why i have seen no one did this ?
http://www.g.laroche.free.fr/francais/h ... ega32.html

[3metrejim]

My question is , why i have seen no one did this ?
http://www.g.laroche.free.fr/francais/h ... ega32.html

Why? I sort-of did, but life got in the way, also:

* Declining pirate radio scene in the UK at the time
* No time for Radio experimenting because of work.
* No one wanted a big ugly board (even if it worked well) when they could get a Broadcast warehouse coder that was small and did the job
* No proper filtering on the data stream (only the subcarrier)
* Didn't want to rely on the TDA7330
* Could only program PIC and not the Atmel (which Microchip eventually bought out)
* Was adverse to using USB direct to the processor as had no idea how to implement it

Of course nowadays you can easily use an Arduino to provide the data stream. Personally I'm only interested in getting a decent modulator made, which is what I failed on the first time (got a display but was horrendously noisy) - It's more of a curiosity rather than something to produce and try to sell. Now there are simulation tools available (something I couldn't get back then), I'm going to attempt the modulator again - If it works it can be cut down slightly (remove the bi-phase data pulse creator - three ICs, one resistor and one capacitor), and powered from by SINUS chip.

[sinus trouble]

I totally agree!

Whilst Radiums project looks great? I do not see RDS as an essential piece of hardware!

More of a fancy toy to reinforce the idea of "Professional Broadcasting" I hold a similar contempt for Stereo too!

What i love about Pirate radio is the amateur and impulsive nature that you would never hear on commercial radio!

I doubt listeners give a sh*t about your superior, ultra processed signal!!

[radium98]

Thank you for the nice words , sinus ....Hugs from Lebanon to our freinds of the forum .
out of curiosity question , what tool can i make to check if too signal are locked in phase or not any circuit etc any hand on that , can be done with cd4046 ,my idea is to make the stereo and the rds in phase lock , but i need this by hardware .Thanks

[3metrejim]

Do you want to phase lock the 57kHz RDS carrier to 19kHz from a composite signal (output of a stereo coder) or from a logic level 19kHz direct from a stereo coder? The second option would be easier.

My idea is to lock 57kHz from the RDS coder PIC (assuming you are using the sinus version) to the pilot tone reference, by adjusting the processor clock (just like on the old bw diagram). A quartz crystal can be pulled off frequency slightly, not by much, but enough for the idea to work.

First get the 57kHz and divide by 3, feed the result into comp_in of a 4046, feed the 19kHz into the sig_in of the 4046. From the 4046, feed the PC2_out to a simple loop filter, and the feed the voltage from the loop filter to a varicap (or a 16v zener) diode which has a small capacitor (10pf?) connected to it's cathode, and the combination connected across C7 on the sinus coder schematic. You will need to decrease the value of C7 slightly to make the crystal run a touch higher in frequency than it should, the maximum frequency variation above and below 4.332MHz should not exceed more than a few hundred Hz to ensure the RDS carrier is still in spec even when there is no 19kHz to lock to (it should go to the lowest frequency without a reference input).

My choice of using PC2 instead of PC1, is that you can add a lock detect and that the 57kHz divided by three will not be a square wave of 50:50 duty cycle.

You would need a frequency counter and an oscilloscope to make sure the idea works. Probably also some way to adjust the 19kHz phase to get the 57kHz into phase with the pilot from the stereo encoder output (a simple variable resistor and capacitor arrangement before the 4046 sig_in pin). The PLL will keep the phases aligned where they are compared, but they will most likely be altered further along in the circuitry (a phase adjust control in the stereo coder, filtering in either the rds coder or stereo coder)

Sounds relatively simple, but a pain to set up.

If there is an easier way, I'm sure someone will provide it.

[Albert H]

I did it the other way 'round - I used the 4332kHz RDS rock as the reference for the stereo coder too! It's easy enough to do, and you don't have to try to "pull" a crystal's frequency (never a good thing to do in my experience). I'll dig out the circuit - I had to build some drive-in cinema rigs a while ago, and they wanted stereo and RDS, so that was the last time I had to do this.

I have synchronised the RDS board to a stereo coder too, but did it by using the 76kHz from the 4864 kHz crystal divider chain (in a 4060) as the reference for a PLL locked to 4332 kHz to clock the RDS IC. Dividing by 57 is easy enough with a 4040, so the 4046 oscillator locked in an accurate phase relationship with the stereo coder reference entirely reliably.

However, the first approach us better (it uses fewer ICs!).

[radium98]

i have already did that since years , but i need to make a tool with only 4046 that can have two inputs , like bnc .
and a visual lock led from pin1 .
so one or both rds or stereo can be slightly tune so the detect lock led go stable .

[XXL]

Here’s the nasty noise that comes from the monrds/sinus design. This rds encoder needs more work.

https://emalm.com/?v=KLxVC

[radium98]

Need filter for 57khz carrier

[Albert H]

Turn down the RDS level! You only need a really tiny amount of RDS signal for the receiver to detect it.

The easiest way to set the level is to:

• Turn off your transmitter,
• Turn the RDS level preset all the way DOWN,
• Set your transmitter to a new frequency (you'll see why in a moment),
• Turn on the transmitter into a dummy load,
• Tune your receiver to the new transmitter frequency,
• Very slowly turn up the RDS level until the data appears on the receiver display,
• You're done! You should now find that the RDS data signal is inaudible.
• Tune your transmitter to the frequency you actually want to use.

The reason for selecting a new frequency is that your receiver may "remember" that the old frequency contained particular RDS data, and "helpfully" display it even if no data is received! My Sony portable sometimes does that.

If you find that there's still noise evident, you have a problem with the coder producing subharmonics of the 57kHz subcarrier. If this is the case, add a 56kHz highpass filter to the output of the RDS coder (NOT to the whole modulation path). This will strip off any lower subharmonic images from the RDS signal, whilst still letting through the crucial 57kHz subcarrier. Here is a simple circuit for an op-amp filter:

56kHz HPF.jpg

Is your transmitter stereo? If it is, you need to synchronise the 57kHz RDS subcarrier with the 19kHz stereo pilot tone, to eliminate any spurious "beat" products. I put a suggested circuit on here (earlier in the thread) to synchronise the RDS subcarrier.....

If you still have problems, let us know!

[3metrejim]

High pass is a good idea to remove the baseband from a switching modulator, but doesn't help clean up harmonics of the 57kHz.

I've been messing with spice again and found that two low Q bandpass filters spaced around 57kHz might do a better job. Not built and tested yet, but I did remember to reduce the GBW of the 'ideal' op-amps to try to better model real life. Intended to clean above and below 57kHz.

57Khz bandpass.png

Tried to make sure the components were available values (have slightly upset the filter, but not a great deal). 44k resistors are 2x22k in series, the 300pf capacitors 2x150pf in parallel.

I left my notes on the diagram too, good for calculating these filters, but not meant to go above a Q of around 5 with 'normal' op-amps. Can ground the ends of the 820R resistors and feed half supply to the non-inverting inputs of the op-amps, as in Alberts diagram to make it work on single supply.

[XXL]

Turn down the RDS level! You only need a really tiny amount of RDS signal for the receiver to detect it.

The easiest way to set the level is to:

• Turn off your transmitter,
• Turn the RDS level preset all the way DOWN,
• Set your transmitter to a new frequency (you'll see why in a moment),
• Turn on the transmitter into a dummy load,
• Tune your receiver to the new transmitter frequency,
• Very slowly turn up the RDS level until the data appears on the receiver display,
• You're done! You should now find that the RDS data signal is inaudible.
• Tune your transmitter to the frequency you actually want to use.

The reason for selecting a new frequency is that your receiver may "remember" that the old frequency contained particular RDS data, and "helpfully" display it even if no data is received! My Sony portable sometimes does that.

If you find that there's still noise evident, you have a problem with the coder producing subharmonics of the 57kHz subcarrier. If this is the case, add a 56kHz highpass filter to the output of the RDS coder (NOT to the whole modulation path). This will strip off any lower subharmonic images from the RDS signal, whilst still letting through the crucial 57kHz subcarrier. Here is a simple circuit for an op-amp filter:
56kHz HPF.jpg

Is your transmitter stereo? If it is, you need to synchronise the 57kHz RDS subcarrier with the 19kHz stereo pilot tone, to eliminate any spurious "beat" products. I put a suggested circuit on here (earlier in the thread) to synchronise the RDS subcarrier.....

If you still have problems, let us know!

This just isn’t true though because when using scrolling PS and rds level is low, it can’t pickup the rds if the fm signal degrades even slightly and you get all broken text coming through or just stops. If it’s higher it can but then you get that noise. Some stations iv noticed the rds will come through even when I can barley pickup the fm signal, others I can even tune to one side and still pickup rds. I just dont get it.

[XXL]

@albert also does this mean the sinus rds doesnt have a filter, thats why its giving off a nasty noise ? The original MonRDS had alot more components on it and then eventtually got slimmed down by people online and finally by sinus. I also get the noise using the "Vincent" rds encoder which isnt as good as you cant add RT but is even less conponents than the sinus.

[Albert H]

There is a very basic resonant filter, but the add-on I've suggested quietens anything lower than the 57 kHz RDS subcarrier (which is why it's connected to the wiper of the RDS level preset.

Other designs made use of the TDA7330 RDS filter IC. This is a great solution, but that IC is virtually impossible to find these days, and tends to be expensive if you can find one.

Remember - if you're running stereo, the 57 kHz subcarrier must be phase coincident with the 19 kHz pilot. If this condition isn't satisfied, you can get all sorts of weird whistles and burbles in the audio.

[3metrejim]

Came up with this, could be useful if the digital part goes inside a PIC. The D input to the flip-flop is meant to go elsewhere, the connection was for simulating. Also probably needs more filtering.

adpm.png