SINUS RDS PROJECT

[sinus trouble]

How can I make a high pass filter to stop it ?

Whilst Albert is correct! You could even use just a simple RC filter to roll off below 57Khz

There is a major conflict here! If you place any sort of high pass filter inline, The effect will be detrimental to your audio signal!

You would need to separate your audio from the RDS, Which is not a difficult task!

I would still argue that it is a pointless exercise! Complexity adds cost!

Good quality grounding and shielding wins all day long for me!

[Albert H]

You've missed the point, Sinus. The filter is only for the output of the RDS circuit, NOT the whole composite MPX signal. Unfortunately, the waveform coming from the chopper modulator in the RDS circuit isn't too clean. A bit of additional filtering really quietens the "burble" from the RDS board.

Incidentally, you should see the filtering that I've used in my commercial designs! One broadcast processor I designed used PWM level control (both for the slow-acting AGC and for the multi-band limiter), and used a total of 46 op-amps in the filters! The processor is designed as an audio to MPX processor - it does the lot in a 2U 19" rack case, and has plenty of blinking LEDs. It takes balanced, nominally line-level left and right audio, applies a slow-acting AGC to overcome the range of levels provided by programme makers, then does three-band stereo limiting, 15 kHz low pass filtering (-79dB at 18.4 kHz, and a further -40dB notch at 19 kHz), then 32-times oversampled stereo coding, RDS injection ( phase synchronised to the stereo pilot), and a final output filter to keep everything really clean. The MPX output is balanced at (nominally) 6.2 Volts p-p, so that it's robust enough for the electrically noisy environments at most broadcast Facilities Sites!

Designing gear like that is an interesting set of compromises, and it's fascinating to see how other manufacturers approach their airchain design. My product first came out (without RDS) in 1986, and has been through four subsequent revisions as components became obsolete! You wouldn't believe how difficult it is to get through-hole FETs in matched pairs these days. I gave up looking for them, and went for a different approach!

[sinus trouble]

I find the use of filters and how to incorporate them logically very interesting!

However, I get the feeling that you are wasting your time Albert!

XXL to say it as i see it? Is not interested in your solutions! Cheap, simple and minimum effort seems to be the agenda?

The whole point of the "Sinus RDS Project" was to revive the "MONRDS" as a usable tool for broadcasting! It was was never intended to revolutionise the Radio industry!

I have no problems with the system as it is? If others have doubts? They are welcome to make contributions!

[Albert H]

Sinus - all I've done is offer a simple minimal filter to improve the results from an otherwise impeccable RDS unit. You're right - you could use an additional LC filter instead, which - if the parts are carefully chosen - will give great results. However, accurate inductors are getting really expensive these days, and a cheap dual op-amp and slack handful of resistors and capacitors will be more cost-effective!

[sinus trouble]

Sinus - all I've done is offer a simple minimal filter to improve the results from an otherwise impeccable RDS unit. You're right - you could use an additional LC filter instead, which - if the parts are carefully chosen - will give great results. However, accurate inductors are getting really expensive these days, and a cheap dual op-amp and slack handful of resistors and capacitors will be more cost-effective!

I always learn something new from your contributions! And i want you to continue doing so

However, There are some on this forum who expect us to solve all their problems without putting in any effort!

All my projects are aimed at finding the simplest solutions for everyone who wish to take the risk and learn!

None are perfect? But may lead to that next innovative experiment!

[radium98]

Sinus - all I've done is offer a simple minimal filter to improve the results from an otherwise impeccable RDS unit. You're right - you could use an additional LC filter instead, which - if the parts are carefully chosen - will give great results. However, accurate inductors are getting really expensive these days, and a cheap dual op-amp and slack handful of resistors and capacitors will be more cost-effective!

I always learn something new from your contributions! And i want you to continue doing so

However, There are some on this forum who expect us to solve all their problems without putting in any effort!

All my projects are aimed at finding the simplest solutions for everyone who wish to take the risk and learn!

None are perfect? But may lead to that next innovative experiment!

[XXL]

I find the use of filters and how to incorporate them logically very interesting!

However, I get the feeling that you are wasting your time Albert!

XXL to say it as i see it? Is not interested in your solutions! Cheap, simple and minimum effort seems to be the agenda?

The whole point of the "Sinus RDS Project" was to revive the "MONRDS" as a usable tool for broadcasting! It was was never intended to revolutionise the Radio industry!

I have no problems with the system as it is? If others have doubts? They are welcome to make contributions!

Because I don’t have time to mess about building stuff that doesn’t work. Years ago maybe, but now I just need something that works. People are nice enough to post projects on here yes, but don’t say it’s “final” or works great when it just doesn’t. Iv seen many cheap and low budget encoders over the years that don’t make digital burble noises. There’s something wrong with it but I don’t have the knowledge or time to fix it unfortunately. The same as I don’t have time to build a band 4 link that Albert keeps talking about. It would take me years to build to achieve the same as buying a cheap micro link system.

[radium98]

The same as I don’t have time to build a band 4 link that Albert keeps talking about.<< this sentence make me laugh loud for two reasons , first as you said , and second you may need lots of experience in rf and materials to acheive that .
i suggest you to start with band 1 link . Honestly never build ,Sinus put a design anda working video of him , luck of some materials and some local problems,that do not make me do anything .
About the rds theproblem is nearly the high level that is a taboo and must be tweaked slowly , by ear if you dont have instrument , i saw someone out the forum does it better way , he was having burbuling .if u can put an audio voice to hear what is that kind of burbulng.

[sinus trouble]

I completely agree with XXLs point of view, Hence why i said experimental designs are of no interest!

Unfortunately, Unless highly experienced engineers like Analyser, Albert, RF-Head and Rev are willing to give you all their hard work for free? It aint gonna happen!!

I am giving my hard earned research and development away for FREE because it is experimental!

As Albert once said! "If you want to pay me 4000 quid for my services? I will deliver!"

Anyways back to the RDS! The "Burbling" noise is no where to be found if set up correctly!

I know this through my own testing and feedback from others who have installed them in their own Rigs!

As i am a nice guy, I will take some measurements of the audio spectrum surrounding the 57Khz! (For Free)

[Albert H]

Radium (and the rest of you):

Band IV is actually not difficult. The "quick 'n' simple" way (and the one that many folks have used) is to base the receiver on a TV tuner module. These are available from places that sell TV spares for just a few quid. Many of the more modern ones have built-in synthesisers (often the TSA5511 or 5512), and are simple to tune to the frequency you want. They're designed to be connected to a Yagi aerial with 75Ω coax, and you can get the aerials and coax from your local DIY shop or Screwfix for not a lot of money. The output of the tuners is (usually) a ~35MHz IF - it's easy to mix that with a crystal oscillator to give 10.7 MHz, and then go through a standard CA3189 IF strip to recover the modulation.....

The transmitter end is slightly more difficult, and it's best built on a ready-made PCB. I used to make them on a PCB with pre-etched Lecher Line "coils", and used the BFR91 (which is cheap enough and good to 1 GHz) for the oscillator, buffer and first RF amp. I used half-frequency generation, and a simple discrete PLL circuit using an SAB6456 prescaler IC (also good to >1 GHz) to keep it on frequency. The BFR91 stage would give ~250mW, which - when fed to a 20-element Yagi with ~12 dB forward gain - became a few Watts..... If I needed more power, I'd use 2N3866s - sometimes even pairs of them - because they're good to a few hundred megs.....

At some point, I'll do a couple of PCBs for transmitter and receiver, and get one of the well-known suppliers to sell kits for them.....

If you want some pointers to UHF linking, scout around the Interweb for the old Dutch "60cm" stuff......

[sinus trouble]

Albert is spot on!!

No doubt! complications will arise? But its not too difficult to solve problems if you put your mind to it!

For example! The same basic principles apply within my Band 1 receiver! The Local oscillator and input filter would need a redesign for higher frequency!

The JFet mixer and the rest of the circuit is more than capable of handling Demodulation!

[reverend]

For Band IV/V I designed a simple downconverter (with a fixed input/output frequency conversion) which took inputs in the UHF range and downconverted to Band-I. A Band-I receiver could then be tuned to the necessary frequency. Using a cheap 433 MHz resonator for the oscillator, you can convert 470 - 512 MHz to the frequency range 37 - 79 MHz. Different resonators provide different options for which part of the band is downconverted. Happy to share the circuit diagram if anyone is interested.

[radium98]

reverend if you can share just for teach..

[XXL]

When people posts designs on here I don’t usually use their gerba files. Instead I re-draw the entire thing and add my own bits on. But sometimes, I can sit there for hours to weeks on end trying to figure out how to stop a noise or amp up a signal. It’s just easier to speak to people who know what they’re doing first, get the circuit idea then use that.

[sinus trouble]

For Band IV/V I designed a simple downconverter (with a fixed input/output frequency conversion) which took inputs in the UHF range and downconverted to Band-I. A Band-I receiver could then be tuned to the necessary frequency. Using a cheap 433 MHz resonator for the oscillator, you can convert 470 - 512 MHz to the frequency range 37 - 79 MHz. Different resonators provide different options for which part of the band is downconverted. Happy to share the circuit diagram if anyone is interested.

Thats an interesting concept Rev!

I never really thought of that! But it makes logical sense!

[sinus trouble]

When people posts designs on here I don’t usually use their gerba files. Instead I re-draw the entire thing and add my own bits on. But sometimes, I can sit there for hours to weeks on end trying to figure out how to stop a noise or amp up a signal. It’s just easier to speak to people who know what they’re doing first, get the circuit idea then use that.

Thats Great XXL!

I like your thinking for customising projects to suit your needs!

You are certainly not alone with noise issues! They are an absolute pain to diagnose!!

I recently developed a noise problem which i can only describe as a "Rat scratching around in a nest"

This noise is totally random and lasts for only a few seconds??

It has to be either a loose bolt holding the PCBs! Or a dodgey cable??

Anyways, The best advice i can give is? Get rid of any pointless ground connections and use the chassis (Case) for all ground connections!

Wire up all the + Rails only! If you have to use ground supply leads? Twist them up with positives!

That should reduce differential potentials arising!

[Albert H]

TBH, earthing is one of the "Black Arts". I have spent many hours identifying the sources of noises. It can be a nightmare. "Starpoint" earthing generally helps, audio sockets isolated from the case (so they're earthed where they meet the board) and the use of low impedance balanced audio all combine to reduce noise.

However - I had one prototype exciter that hummed no matter what I did. After trying to move terminations, relocating various parts and extensively scoping the audio paths, I still couldn't find the source of the hum....

I moved it to the back of the bench and carried on with something else, thinking that I'd get back to it later.

Some hours later, we had all the additional lighting on in the workshop, since we had been doing some Surface-Mount work. I decided that I'd try to get rid of the hum: I fired the exciter (5 Watts in those days) into a dummy load, and monitored the audio. The hum was (mostly) gone!... I moved the exciter closer to me on the bench, so that I could examine it more closely, and the hum returned! After experimenting with its location around the bench, I located the issue: Fluorescent Lighting! We had tubes in the workshop for general lighting, and during the afternoon, that was all that was on. When it got a bit darker, and we were working with tiny components, we had additional halogen lamps (in those days) for the finer work....

The 50 Hz "flash" of the Fluorescent Lighting was affecting the glass-encased varicap diodes in the Voltage Controlled Oscillator! I proved it by putting a little piece of black insulating tape over the varicaps!

Ever after those wasted hours, we would dip the glass-encased Varicap Diodes we used into acrylic paint! Each particular type of diode had its own in-house colour. For example, if I wanted a BA121, it would be yellow! We dipped them as soon as they arrived from the suppliers, and marked the anode lead too.

[sinus trouble]

Haha! True Albert!

Now that you mention it! Theres a noise that i have comming through ALL my receivers!

I have been searching for the source for over 20 years! Still no closer to finding it!!

To describe? Its a short burst of white noise but NASTIER! Lasts for approx 5-10 seconds!

Still its one of those strange phenomena you come across with RF and electronics in general!

[sinus trouble]

Apologies for the delay!

I promised id take some measurements of the RDS spectrum! So lets get back to subject!

The first capture shows the 57Khz Pilot as the largest signal! We also have a harmonic @ 114Khz and another @ 171Khz!

These are expected during operation but should not affect the audio significantly!

Image below!

[sinus trouble]

RDS Spectrum.PNG