RNEI now broadcasting in Comb Stereo

Many thanks to SWLing Post contributor, Roseanna, who shares the following announcement from Radio Northern Europe International:

Hello everyone,

The show is finished, transmitter time booked and pre-processing done so it’s time to announce RNEI #3 & TIAEMS April 2020 to all of you!

Before we continue, we need to announce something pretty special and unique about this and future RNEI broadcasts:

RNEI is now broadcasting in Comb Stereo. It’s a standard we made and it’s a really nice addition to having a mono only broadcast. It’s easy to decode and it doesn’t degrade the mono signal!

For more information about the system and how it is decoded please see https://rnei.org/stereo/

RNEI #3 features 30 minutes of our favourite music from all over Northern Europe; Sweden, Finland, Norway, Denmark and Iceland this show. I’ve really enjoyed choosing the music and putting it all together, I really hope you enjoy listening to it.

We will also have the playlist sent in MFSK32 embedded into the final song, very similar to show #1 (we’ve worked extra hard to make it as hidden as possible which was a massive challenge this time, it’s in 2 parts during the final song with an RxID at the start of the final song).

Just like last month, TIAMS has been kind enough to join forces and make us a 30 minute express version of his show which I have loved listening to and I’m sure you will love it too![…]

Click here to continue reading the announcement and view the full RNEI schedule.

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8 thoughts on “RNEI now broadcasting in Comb Stereo

  1. Ron F

    > “It’s a standard we made …”
    > “… we invented this method!” … “The method we created …”

    It’s funny to watch comb-encoded stereo get re-“invented” every few decades. I first saw a simple passive-filter-based encoder-decoder in one of the pulp electronics magazines in the mid 70’s – so probably dating from the 60’s – presented as a way of recording and playing back the ‘new’ stereo FM broadcasts on a mono tape recorder. In the late 70’s or early 80’s, one of the local radio stations quietly did some late-night experiments (for fun more than serious purpose) of ‘stereo’ by the same method, using a BBD-filter-based “Stereo Synthesizer for VCRs and Tuners” published in Electronics Australia as the decoder. In the late 80’s / early 90’s one of the regular Pacific Island pirate/experimental SW broadcasters ran a regular weekly programme in “stereo”, with the EA decoder design pinched & repeatedly copied in multiple CB ‘zines

    As far as I’m aware, the basic method dates back to the mid-late 1950s or early 60’s.

    1. Daz Man

      Hi Ron,

      Which of your local radio stations ran the late night tests?

      Who was the Pacific Island pirate? They must have used some kind of callsign…

      How do you know there was really an encoder used on these broadcasts? Are there any recordings?

      Comb filters have been around a very long time, and are useful for many things. They are a very good way to produce simulated stereo from a mono source, but by itself this is not real stereo.

      Despite research, including with some people who have been in broadcasting and audio fields for decades, no references were found for any broadcasters ever having used the method for stereo encoding. But there are probably good reasons for that…

  2. RNEI


    We would love to have used ISB stereo however we don’t have access to a transmitter (this needs a modified transmitter). The other method, C-QUAM, along with needing a modified transmitter, is not really suited for shortwave due to the propagation of SW causing issues with it (it also needs a pilot tone so it ends up turning and on and off quite a bit which is unpleasant!).

    We rent transmitters so our only option is to do something to the mono audio we send to them which is why we invented this method!
    You also get the advantage of the protection against fading that having both sidebands gives 🙂

    The method we created generates adequate stereo seperation considering its traveling down a mono signal.
    On a technical level, it’s fake mono (in pure mono every frequency is L+R) that is returned to stereo at the receiving end, unlike using a stereoizer to generate fake stereo from a mono source. The most amazing thing is how little it affects the mono and, when testing, it can be hard to tell which is real and which is ‘fake’ mono!

    Receivers are the other big issue; I don’t know of a receiver that can decode AM Stereo on shortwave bands (outside of SDR) which is quite limiting.
    In comparison, this method is receivable on any Windows machine and can be done on recordings made from a radio at a later time, rather than requiring real-time decoding (and we will hopefully have a Linux plugin working soon too 🙂 )

    Hopefully you can give it a go and enjoy what we’ve achieved!
    All the best,
    Radio Northern Europe International

  3. April Ferguson

    Couldn’t AM Stereo have been used? I believe the XFM pirate does that. I’m not very well informed about the use of it on shortwave or if there are any receivers that could decode AMS on shortwave anyway.

    1. Redhat

      Yes, we are transmitting in C-QUAM stereo again as of last fall. We use a modified commercial exciter to do this, and a frequency agile unit is in development. Several SDR packages exist to decode C-QUAM, namely SDRDx and SoDiRa. Standalone receiver support is limited to a few high end models like the NRD-545, but a $30 demodulator can be added to any receiver with a 450-455KHz final IF.

      The comb stereo is a neat solution to those that rent airtime or do not want to, or can’t modify their transmitters for stereo operation. We wound up settling on C-QUAM based on equipment availability and receiver support. ISB would be a better choice, but the receiver support isn’t there.

      Airchecks of our station in stereo can be found on Youtube by searching for either c-quam or x-fm shortwave



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