Skip to main content

FM-RDS

RDS or Radio Data System is a very interesting thing. All of us have come across this in some point in life. RDS is a cool implementation. RDS shows radio stations name, frequency, song etc. A lot of car radios support this feature. So when you see “RAADIO 4” on your radio, it arrived there over RDS. It piggyback rides on the FM station at 57 KHz. So I wanted to learn more about it.

This is a typical FM stations baseband spectrum.

 

rdstext

 

 

Decoding RDS with some already made tools is somewhat simple. SDR Sharp has this feature built in. But rtl-sdr is not that sensitive receiving weak stations. So I started experimenting.

Firstly I hooked up my Panasonic car radio. It supports RDS. I listened to FM stations and it worked fairly well. Then for pure interest I connected the radio to my PC and fired up Spectrum Lab. And I was surprised it spit out the RDS data.

Then I thought what happens if I connect a Sony STR-232L to my PC. It’s a fairly old FM receiver. And yes, I was able to see RDS data. And I started using this as my main experimentation device because it is super sensitive. I was able to pick up quite far radio stations with it.

The most important thing is to sample at 192000Hz or you can not see the RDS stream.

I quickly found RDS Spy. You can even feed it directly with RDS data. The software works pretty well. It even decodes things that the car radio was not able to decode. It is even cooler to use the RDS Spy with my FM receiver. It’s an old analogue receiver but I am able to see RDS information on my computer screen.

RDS Spy and my FM receiver.

rdsparem

 

 

And I even was able to listen YLE YKSI from KO28XP. Here you can even see DARC.

To my knowledge nobody uses DARC in Estonia. More about DARC  HERE!

yledecoded

 

And YLEX.

ylex

 

Then I thought it would be super cool to actually send RDS data out myself. The simplest way to test this quickly was to record a radio station and then play it back to a transmitter. I tried with a car FM transmitter – that did not work. Then I tried the same with my FM transmitter bug that I had built couple of years back – That did not work.

So then I turned to my Raspberry Pi. The PiFM is a popular thing so maybe somebody has built RDS implementation into it? Yep.

And as you can see it works.

vlcsnap-2014-07-20-21h21m22s194

Now I need to buy this RDS+FM kit from Adafruit.

 

 

 

 

Comments

Popular posts from this blog

My take on a nixie clock

As a present I decided to build a nixie tube clock. It was essential to ditch my close-enough attitude and make it look as good as possible. For me the simplest way to complete this idea was to use a microcontroller. I am not cool enough to build a clock out of discrete logic, maybe in the future.

I had couple of nixie tubes lying around, I ordered some more to have a total of six. So the clock consist of an Arduino Nano, RTC DS3231, nixie tubes - IN-14 and a power supply. From the start I knew the biggest challenge is building the enclosure. I learned that the easiest way to drive these nixie tubes is with a driver called - К155ИД1.

It’s a binary to decimal decoder and it works quite elegantly. Depending on the binary input it enables the right output.

It does all the heavy lifting. And then I used three shift registers to drive all the drivers.

In addition I bought a nixie tube power supply that supplies the 170v I need. I could have used 220v wall power but I do not trust myself enou…

My take on the PA0RDT Mini Whip antenna.

I like shortwave radio because you can receive signals from all over the world, also there are all kinds of mysterious signals to explore.

In the grand scheme - the lower the frequency, the bigger antenna you would need. Well, there are all kinds of antenna designs but I like to think like that way. For example, I have a 27 MHz dipole on my roof that is around 5.3 meters long. If I wanted to listen to lower frequencies ~ around 3 MHz, for optimal performance I would need around 50 meter antenna, so using dipole for lower frequencies is not very space efficient, especially if you do not have any room.

So I decided to build the Mini Whip antenna. It is popular, simple to build and on paper receives frequencies from 10 kHz to 30 MHz, and also it is super tiny.

There are some variations between different designs, but the basic idea is the same.

The schematic I followed.







During my tests it performed well, I was able to receive DCF77 signal for the first time. All other bands seemed to work as w…

RFID experiments

Radio-frequency identification (RFID) is a way to use electromagnetic fields to send and receive data wirelessly. The system consists of two parts: reader and a tag.  Tags can be passive or active. I think the most popular are passive tags. Meaning, there are no batteries needed, the power comes from the reader. The reader constantly sends out an interrogation signal and when a tag absorbs the energy and powers up, it radiates back information from the embedded chip.

Then it divides further - different frequencies, generations, encryptions etc.

Also one popular part is NFC (Near Field Communication) which has better security and other improvements. Latest phones usually come with NFC read/write capabilities built in.  So you can pay with your phone or touch phones together to share information. A lot of possibilities.





RFID/NFC is quite popular in our commercial world.

Anti-theft – stores use it to stop people stealing stuff.
Tracking people - putting tags inside shoes to track people, some…