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Showing posts from July, 2014

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.









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 …

RTL_SDR Direct Sampling Mod

Listening to various radio signals is fun with vanilla rtl-sdr. The range is 22 MHz to 2200 MHz So that means there are pretty different things to listen to for a while. Couple of day’s back I wanted to listen medium and high frequency bands. Because radio waves in that spectrum travel a lot further than VHF and UHF signals. I know there are up converters that don’t cost very much and are easy to use. There are many other benefits using an up converter. But I wanted to do a direct sampling mod to one of my rtl-sdr. This so called “mod” is not very difficult. So I decided to try it out.

Source: 1 , 2 and 3

I should use a right ferrite for the job but I found this random one.



To the SDR I connected a 20M dipole.  So the rtl_sdr is not very good but the antenna makes somewhat up for it.



I’m using an old laptop as a server for the SDR. To add Direct Sampling mode in SDRSharp in TCP mode: LINK   And what do you know it works!