JUL24

Adding RDS decoder to 1957' vintage radio

FM radio receivers usually don't have RDS decoder, but what about tube radio from year 1957?

This project is actually RDS decoder that is realised using TDA7330B RDS demodulator and ATtiny2313 microcontroller. Received and decoded RDS text is displayed on 2x16 HD44780 based LCD display with many options: displaying RDS time, displaying TA (traffic announcements) flag and scrolling 64 characters long RDS text. Here you can see integration of this RDS receiver into vintage tube radio receiver from year 1957.

Read on to see photos, how integration is accomplished and how to find discriminator output of your tube radio receiver.

When you want to connect RDS decoder (www.mictronics.de) to any FM radio, first you need to locate phase discriminator (actually FM signal detector). On it's output along with audio signal there is stereo carrier signal as well as MPX on 57 kHz that carries RDS information, so we just need to connect to that point through 470pF capacitor and that's it. Of course, GND should be connected also.

Now, if you don't know how to find discriminator output on any tube receiver, alternative would be to connect to volume's potentiometer's "hot" point by using the same capacitor - "hot point" is the one pin that is not middle (movable) and that is not connected to GND.
Even on my PHILIPS radio that signal is available on speaker and it works great, but this option is not recommended because of NF filters that might "damage" the RDS signal.
And in the end, the easiest option is with newer old tube radios that have output for tape recorder as SIMFONIJA AF model that is showed in the picture. 

Precautionary measures:
Above instructions are only for radios that have mains transformer. Cheaper old tube radios don't have that transformer so mains power can find it's way to our RDS decoder through GND. In that case, signal should be taken through two 4n7/630V capacitors, for GND and signal lines. These capacitors can also be used in radios that have mains transformer as it doesn't violate stability of system.

When programming ATtiny2313 care should be taken when choosing fuses: select external oscillator, and disable "Divide clock by 8" option.

© Edo Lelić

Now, imagine this RDS made with NIXIE tubes instead of LCD!

[ Source: Edo Lelic ]

Ugradnja RDS-a na radio prijemnik iz 1957. Link Comments (2)

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