FM radio meets DOCSIS 3.1… and then what?

It is strange that in our fast paced digital world, there are still some analogue legacy platforms in our daily lives that are actually slowing down digitalisation. No, I am not talking about returning the tax forms, or scanning in the travel expense claims. It is the good old FM radio that I am thinking about. Actually, to be precise, FM radio signals in Cable Networks. In many countries, it is still mandatory to carry FM signals together with Cable TV signals.

Well, you may ask: What does it matter? Isn’t this a problem that you can solve by just throwing a bit of bandwidth at it? It is a problem, because in the new DOCSIS 3.1 standard, frequencies up to 200MHz are planned for the return path. If the operators are obliged to carry legacy FM signals, they cannot take advantage of the potential return path bandwidth increase.

Technically it is today possible to carry radio programs in a DVB multiplex and use a TV set or Set top box as the receiver. Or even use the DAB technology in the cable. This would still allow carrying the FM signals in the air. I personally think that today, there are very few cable customers who have their radio receivers connected to the “cable” outlet in their living room. Isn’t it pretty much streaming audio all over, also at home?

I think it would be time to address this matter through the industry associations toward our politicians.

But like always, content is the King, and let there be Rock, Jazz, or Classic, whatever way you want it, but digital 🙂 .



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Matti Nurmi

Matti Nurmi worked several years as a Regional Director (Nordics, Belgium, Switzerland) of Network Services at Teleste. In May 2017, he moved on to pursue new challenges in his career.

4 comments on “FM radio meets DOCSIS 3.1… and then what?

  1. Christian Schubert / Berlin on

    I found your posting via Google when I was searching for “DOCSIS” and “FM”. And I`m afraid you are a little bit wrong.

    I`m from Germany. In 2005 our public service broadcasting organizations bundled almost all of their radio services (approx. 60 throughout Germany including regional services!) into one DVB satellite channel with very high bitrate for each service. Most of the services run at 320 kbps MP2 and some cultural services have additional 448 kbps AC3 they can use for 2.0 and also for 5.0 audio. Yes, there are a few radio broadcasts in Dolby AC3 5.0 each week – mostly classical concerts and radio plays. There is no country with a higher radio transmission quality in Europe (however, Pop music services sound terrible due to their excessive sound processing in the studio).

    This channel is also transcoded to DVB-C and you can receive all services in most of the cable networks in this high quality (excluding Vodafone / Kabel Deutschland, they shrink the bitrate to only 192 kbps MP2, but this is still much better than most digital services on DAB and in other countries).

    And here is (at least one) German reality – a view into my parent`s living room:

    The stereo system can play CD, Vinyl and FM. FM brings 43 programmes via a small local cable operator. 13 local services are received via terrestrical FM in the headend and converted to other frequencies (via 2 RF mixers and IF filtering), 28 nationwide and 2 international services are received via DVB-S and transmodulated to FM (digital FPGA based FM modulators Blankom STR 821, 6 FM channels / device). There are 12 “serious” services of interest for my parents: Deutschlandfunk, D-Radio Kultur (the 2 national broadcasters), Bayern 2, BR Klassik, SWR 2, WDR 3, hr 2, MDR Figaro, MDR Klassik, MDR Info, NDR Info and OE2 from Austria. The other 31 services are mostly Rock/Pop music channels (a few private stations, a few from the public service broadcasters) and without relevant content. So they are not of interest and not stored in the stereo system.

    Reception quality is really good for a fully packed FM band in a cable network. Noise is not an issue at normal volume for listening in a living room. You can also use a good headphone without being annoyed about noise. Stereo separation is very good, sibilant sound is clear and without distortion also with this mid-class Onkyo stereo system.

    To be honest: I did the channel planning for this FM configuration in the headend to support the cable network operator and I payed attention to “intermodulation free” channel spacing, high reception quality and a great cultural variety of services.

    Of course the direct digital reception of those channels would bring a better quality compared to the FM conversion. But for this my parents would need an additional DVB-C receiver. This is not a problem (good receivers with alphanumeric display can be found at eBay, approx. 35 EUR), but the receiver needs to be placed on top of the stereo system. My parents would refuse this due to optical and aesthetical reasons (“no additional box allowed, there is already too much technical stuff in the living room!”). Just look at this photo – how would it look like with a black or silver plastic box smaller than the other components? And there would be the need for a display, at least to configure the DVB-C receiver. There is no TV set in my parent’s living room! So this would be the next “bricolage”, maybe like this (it is my work and I use it in my apartment, where FM is not used for more than 15 years, I have DVB-S instead for radio and do not own a TV set).

    Terrestrial DAB/DAB+ could also not give a good solution. 7 of the above mentioned stations cannot be received in this area via DAB. And the sound quality of all but one receiveable stations is terrible via DAB (HE-AAC @ 88 kbps or lower / MP2 @ 128 kbps). Most of the DAB stations are philistine crap in Germany. This is no alternative.

    DAB+ in a cable network is provided in Lausanne/Switzerland. They use channel 5 (around 178 MHz) with 4 blocks and pack 88 services into these 4 blocks:

    So the bitrate is approx 72 kbps HE-AAC – I never, never want to listen to such crappy audio with fake SBR treble! DAB in a cable network could be a good idea – but only because there are receivers you can use like a “radio”, without additional external displays and without on screen menu. To compete against the FM reception quality you need 144 kbps LC-AAC for each channel or better 192 to 256 kbps MP2 in “classic” DAB. This could give a good solution to replace FM, but we already have all we need and it is much more bandwidth efficient: DVB-C. The only problem: there is no DVB-C radio in the market except a 1400 EUR solution from HighEnd manufacturer Restek (if they can deliver it) and this one from Bemondis/LaSAT (OEM): – and this is not the solution for good HiFi systems.

    Internet radio is also not an option. Streaming quality is low (in germany mostly 128 kbps MP3) and my parents do not have broadband acces. They do not own any computer! This is quite common when people are 75+. Some neighbours are in the age around only 65, have internet and do not use it at all because it is to complicated for them! They would never install a WiFi radio.

    My best friend is 42, doctor in physics, married, has 2 children. Of course this family has broadband access, but “radio” means FM for him and is also received via a cable network (TeleColumbus). The FM receiver is the most simple device to receive radio. He could switch on his additional DVB-C receiver (his wife uses this to record TV programmes on USB harddisk) to listen to radio – this is to “laborious”. I`m afraid the DVB-C receiver is not connected to the stereo system at all.

    A nearly 90-year-old lady in Berlin, former room-acoustical engineer from the GDR public brodcaster (she engineered the worldwide well-known Nalepastrasse-Studios ) also uses FM via Cable (Tele Columbus Berlin) to listen to the cultural services of her interest. She also has no internet connection at home, but she is writing a lot with word on her laptop.

    When I did the channel planning in my hometown’s network I removed 4 Pop stations and added cultural stations instead. Some customers protested against this and demanded the Pop stations back. Firstly we answered them that they can use their DVB-C receiver (they have one, at least in the TV set) to catch these services again. They refused (“too laborious”) and wanted the stations back on FM! One customer wrote a letter and explained that his family bought a new stereo system with FM last year (!) to listen to one of these services and thus we have to supply this service again on FM. We did… so I inserted the 43rd FM service into this network.

    Other customers protested against a frequency change: I shifted a service from 103.75 MHz to 108.0 MHz and it turned out that people still use old FM radios from early 1980s with upper frequency limit @ 104 MHz. These were the 1st indications that FM in cable networks is still used.

    It seems that people mostly use FM because FM receivers are the most convenient way to listen to: no need for external displays, no menu based operation, station name display on the device, direct station access via favourite station buttons, a “living room compatible” feel of the surface… and because the FM receiver is a component of the stereo system, in most cases a component you cannot simply swap for a digital device without the need to buy a complete new system.

    So content is not the only king. User-friendliness and haptics are also king, at least in the living room. And sound quality should be also king – this speaks against the way we use DAB/DAB+ and livestream.

    I hope that DOCSIS 3.1 will stop at 85 MHz in the upstream for a long time to bring FM to the people via cable. If not, “normal” people would stop using radio at all. This is my experience.

    Kind regards from Berlin,
    Christian (DVB-S only listener)

    • Matti Nurmi on

      Dear Christian,

      Thank you for your very professional, in-depth and high quality comment to my blogpost! Very much appreciated. I can see your point: it’s not only about content, but user-friendliness and aesthetics do play a major role. I am afraid that there are not (at least to my knowledge) public statistics available about how widely FM-radio is used, but you are proving sound argumentation. In the public discussion, broadband speed is often the most commonly used as an argument, but the other points of view should not be left unnoticed.

      Real use of FM-channels in the cable networks could possibly be a very useful subject for someone to investigate a bit more.

      Regarding the DOCSISs 3.1 implementation the good thing is that return path spectrum could be left as it is now, for the time being, and the additional return path capacity could be achieved with further optical segmentation in the network. For the forward path, about 25% more capacity can be achieved just for the existing spectrum through improved modulation of DOCSIS 3.1, and respectively for the existing return path (5-65MHz) capacity increase of even up to 40% is possible.

      Kind Regards from Turku,


      • Christian Schubert / Berlin on

        Dear Matti,

        Thank you very much for your thoughts!

        First of all, I have an amandment. I mistyped “OE2” – the cultural service of Austrian Broadacsting Organization ORF is OE1 and of course this service is in our cable network. OE2 ist the regional network and only of interest in Austria, not in Germany. (Ok, OE1 is also not of interest in Germany but I wanted to offer this as an additional cultural service with high reputation in hope it will be found and listened to.)

        Concerning the statistics about FM usage I can add a little bit from Germany. The Media Authorities of all German federal states (“Medienanstalten”) publish a “Digitalisierungsbericht” (“Digitalization Report”) every year. The 2015 issue can be downloaded in German and English:

        In the English version FM is named “VHF”.

        The statistics of the number of households with DAB receivers may be wrong, if they only counted the number of devices sold in Germany and divided it by the number of households. To my experience, there exist true “DAB enthusiasts” who nearly “collect” these receivers, have one in the car (often not the 1st one, they started with the old Blaupunkt “Woodstock DAB 52” and upgraded to a DAB+ compatible device at the latest when they changed the car), and sometimes 3 or 4 other devices to “play” with, to check how good reception is… while other households think that DAB is a beer brand (Dortmunder Actienbrauerei, a Brewery from the city of Dortmund, see and never heard from DAB radio.

        But maybe the statistics is derived from a questionnaire and gives the right number of DAB households. I don’t know.

        Please look at page 33, English version. In 2015, “analogue radio” ist 92,8%, DAB is 10.6%, internet radio is 29.9%, radio via satellite is 15%, radio via cable is 15.9%. There was the option to answer positive to more than one reception way so the summation is >100%.

        But something is unclear and strange with these numbers:

        Does “VHF / analogue radio” mean only terrestrial reception? Or will it include FM reception via cable networks? Sometimes you cannot differentiate between both, when you have a wall outlet connected to a roof antenna. Is this “cable” or is this “terrestrial”? “Normal” people cannot differentiate this.

        DAB is of course only terrestrial, there is no DAB in cable networks with a very few exceptions in very small networks.

        Satellite is astonishing 15%. This would mean 15% of Germans use DVB-S radio, there is no other satellite radio system available. The analoge satellite radio services on FM subcarriers above the TV sound carriers starting at 7.38 & 7.56 MHz in the baseband and the digital hybrid system “Astra Digital Radio” on the same baseband frequencies stopped end of April 2012 when analogue satellite TV via Astra 19.2°E has been switched off. I cannot believe this high DVB-S usage because it has to be done via a TV receiver connected to a stereo system. I do only know some radio enthusiasts who use this due to the high quality and high number of nationwide cultural services. This is not a mainstream market.

        And then there is another 15.9% “cable”. Is this including FM or not? It is nearly the same number than “satellite”, so maybe this is only DVB-C in the same way “satellite” is only DVB-S? Nobody knows…

        Page 34 shows the most used ways of reception. According to this figure the usage of “cable radio” increases! But is this FM or DVB-C?

        A serious problem in German cable networks is a political problem: the Media Authorities force the network operators to pack lots of analogue PAL TV services into the networks – also in the year 2016! This seems to be done in close cooperation with the big players in the residential management / industry. The want to avoid that people use satellite dishes – in most cases it is forbidden to install a dish if you rent an apartment and often also if you bought your apartment, so you only have free decision if you own your house. So they want no change to the existing standard. They are afraid that a PAL switchoff would lead the people to install a dish.

        The result: 100% digitalization in satellite households and only 72.5% digitalization in cable households in 2015 (page 18 Digitalization Report).

        Here you can see how different the authorities in the federal states handle this:

        The small local network in my home town did something like a “lite analogue switchoff” in 2012. They stopped transmitting 40 PAL channels when the source (the analogue services via Astra satellite) ended 4/2012. It was the only wise decision not to invest in a few tens DVB-S->PAL modulators and not to waste customer’s money with a technology that came to its end.

        Now there are only 3 re-analogized channels in this network – one of the neighbours, a 70-year-old lady, used these only 3 channels on her small CRT TV-set for more than 1 year. After this she tried to move to another cable operator (which is not possible, this operator has no infrastructure in her street) because this operator still has >30 PAL channels. I went with her to the store to buy a DVB-C compatible 32″ LCD set. Now she has all the services in HD…

        Now it looks like 2018 will be the year of analogue switchoff in Germany’s cable networks. It is a close fight between network operators and residential industry. In Saxony FM radio was also planned to switch off then, but I expect this will not happen.

        In my 1st posting I wrote that DAB in cable networks would be a good idea due to the fact that a DAB receiver can be used without TV screen. There is another reason and this one comes from the industry. Just take a HiFi system’s DAB/FM tuner and look at it from the rear side. To save additional 2 or 5 EUR lots of DAB/FM tuners are equipped with only one antenna input that is shared for DAB and FM. This is not only a problem of “cheap” brands. You’ll find receivers made by Denon, Onkyo, Yamaha and other well known brands with this problem.

        So you can decide to use FM via cable and not to use DAB, or you decide to use DAB via an indoor antenna (if it is possible in your area) and then you`ll have no FM reception or only the strong regional services. Or you are “clever” and use a broadband 2-way-splitter to combine FM cable and a DAB indoor antenna. With a broadband wall outlet (not only 87.5-108 MHz at the “FM” outlet) this will not work if the terrestrial DAB channels are used in cable as TV channels, but it would send all cable content with the splitter’s 20-25 dB isolation ratio through the (passive) DAB antenna into the air, resulting in “Screening Class Z-” where Class A+ is requested. 😉

        Meanwhile you can buy special combiners, but nearly nobody knows this and these combiners are quite expensive:

        If radio industry would “invest” in a second antenna input with well-insulated relais switching like in the good old days of better FM tuners, a lot of situations could be possible:

        Antenne A: FM via cable / Antenna B: DAB via indoor antenna
        Antenne A: FM via cable / Antenna B: DAB and FM via outdoor antenna
        Antenne A and B: DAB and FM from different directions via 2 outoor antennas each band

        Industry needs to know this!

        And it is a scandal that we (not only Germany) ruined such high quality DAB receivers like the Sony ST-D777ES ( or tuners made by Denon, Pioneer, Harman Kardon and others by switching to AAC instead of MP2. The authorities and the broadcasters ruined customer’s (not only early adaptor’s!) investment instead of installing a 2nd DAB coverage that could give enough programmes with high MP2 bitrates. First of all the commercial stations request for cheap distribution platforms and often use DAB+ with only 72 kbps instead asking and (paying !) for 192 kbps MP2. As a result HiFi is not possible and DAB sounds worse than FM.

        Maybe interesting thing: we have 2 DAB blocks in the small network in my hometown and we plan 2 additional blocks, all of them terrestrial received, filtered (unfortunately with 7 MHz TV filters, not with narrow DAB block filters) and sent to the cable on their terrestrial frequencies. This is an experimental setup. I wish I would have a “DAB combiner” that could arrange 4 VHF DAB blocks from freely selectable frequencies to a full Block A-D VHF channel. This device existed in the 1990s as a demonstration object and was never manufactured in a higher quantity. The one or two engineering samples dissapeared… so we have to waste some VHF channels.

        The old engineering sample: -> Page 27-30. Turn your head clockwise. 😉

        The 2 planned DAB blocks will be blocks you cannot receive in the town (a valley), but we hope to catch these blocks in the headend 100 m above the hill.

        Kind regards,

  2. Christian Schubert on

    Here is an update… Sumatronic AG, a Swiss company, developed a quite simple system for “peaceful coexistence” of DOCSIS 3.1 and FM radio in cable networks. They named it “FMplus” (patent pending).

    There is a simple block converter that has to be installed in the headend. It is fed with the complete FM radio frequency spectrum and shifts it from 87.5 – 108.0 MHz to 263.0 – 283.5 MHz (other frequencies possible on request). So it can be transmitted through DOCSIS 3.1 capable networks without any problems. The end user installs a simple, plug&play frequency converter between the TV port (or a broadband port) of his wall outlet and his FM tuner and receives all FM services in the normal frequency range.

    The network provider can operate both FM versions parallel for a certain time. So customers can install their converter within a time window of e.g. 6 months and migration is without hassle. As the same FM headend feeds the “classic” FM block and the new frequency block there is nothing to do except installing the converter – all station memory settings at the FM tuners remain.

    A Swiss cable network organization did a field test that was successfully completed a few weeks ago. According to them the audio quality was not affected by this double frequency conversion, indicating stable PLL systems without added audible noise after demodulation in the tuners. It is quite possible that Swiss cable network operators will choose the FMplus system to retain FM radio in the future.

    I hope that other countries will follow as FM audio quality can be very good in cable networks, outperforming typical DAB+ bitrates, outperforming todays typical “classic DAB” bitrates, outperforming even DVB-C when low bitrates are used. And listerners can use their easy to handle, good-looking and proven HiFi systems at home. (User manual in German)

    Additional information (and photos of the headend converter) in this PDF:,file=11186,filename=FMplus_Prinzip_f_r_Fachpersonen_DE_AKTUELL.PDF


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