Related: FM SCA analysis with GNU Radio
FMeXtra can use 20% or 30% of the FM modulation, making up to 110% or 82.5 kHz deviation.
|Main channel||SCA modulation|
From Radio World reporting, the one-time cost of FMeXtra was ~ $10K, with no periodic licensing fees. The FMeXtra receivers were to be of comparable cost to HD Radio receivers; in fact the proposed FMeXtra receivers could also decode HD Radio, DRM, DAB, etc.
That seems like a great deal, and the Radio World testing showed that for 20% modulation depth, FMeXtra coverage was roughly comparable to -20 dBc HD Radio. So why did FMeXtra/VuCast fail to be adopted?
In effect we’re discussing energy/bit, which translates into energy/revenue for broadcasters.
The most typical mode FMeXtra would be used in, in my opinion would be the mode preserving FM analog stereo and RDS, while precluding analog SCA.
Thus, 62.5-98.5 kHz baseband in the
lu;rds mode yielding 48 kbps, which could be split into 4 audio streams of low mono fidelity or 2 streams of medium fidelity or 1 stream of good fidelity (not quite high fidelity).
In comparison, HD Radio offers 96-120 kbps in hybrid and extended hybrid modes respectively. I have listened to WCSP in Washington, D.C. with 4 digital subchannels and been pleased with the quality. I have listened to numerous music stations that have 2 digital subchannels and also been well-pleased with the music audio quality, particularly as compared to the high artifacts of the old codecs used by Sirius XM SDARS satellite radio.
To make a digital transition worthwhile for the broadcaster and the listeners, there must be additional digital audio streams of at least FM stereo quality. That is, the sales staff must be able to sell advertisers on additional audio streams. Generally listeners are OK with analog FM on modern receivers that employ DSP stereo blending and diversity receive antennas, but prefer the clarity of 48-64 kbps AAC audio. HD Radio is an improvement in audio quality over analog FM, particularly in multipath prone urban environments, but what drives listeners to buy a new digital FM radio is extra subchannels.
RF bandwidth: FMeXtra vs. HD Radio
FMeXtra adds one additional music channel at 48 kbps. For talk subchannels, at least 16-24 kbps is preferred. HD Radio gives a high quality digital copy of the analog channel and adds a second high quality digital channel, or gives two additional digital-only music channels. HD Radio transmitter basic install is ~ $50K. So for about 4 times the capital cost for HD Radio over FMeXtra, the broadcaster gets 2.5 times the digital bitrate.
The appeal of RDS is the ability to build station affinity by showing callsign, current song playing, station phone #, etc. at least than $400 broadcaster hardware cost, while nearly every modern automotive receiver will display RDS as well as cell phones, the main means of FM listening. To invest $10K in FMeXtra, with no current receiver availability, is a non-starter, perpetuating the chicken and egg program of FMeXtra.
Back to the energy/bit argument, with HD Radio’s extended hybrid 120 kbps available for audio, the sales staff has 4 medium fidelity subchannels + 1 analog subchannel. Or, 1 analog + 2 high fidelity subchannels. What happens in urban areas is that a station will sell 1 or 2 medium fidelity subchannels to foreign language programming or talk radio that would normally be on an AM station + one medium-high fidelity copy of their analog channel. Or, one high fidelity copy of analog channel + one high fidelity second music channel.
FMeXtra in the same scenario adds two foreign language or talk radio or one music without helping the existing analog. In effect, with FMeXtra I have “lost” one music subchannel to sell vs. HD Radio–and that lost relative revenue keeps accumulating. Stations also get the benefit of more reliable modern equipment when upgrading, more amenable to remote operations and maintenance. The affluent customers reached first by HD Radio could demand higher CPM (advertising rates).
ROI: HD Radio vs. FMeXtra
Successful ROI has been achieved by FM HD Radio stations able to:
- lease HD subchannels to serve particular markets (instead of/in addition to AM broadcast)
- HD-on-translator, where a large subset of main coverage is narrowcasted to college, minority, etc.
- onboard advertisers of modest means on subchannel, revenue not reachable at main channel cost structure
These techniques implicitly on having lots of receivers in the field. With over a third of new automobiles having HD Radio–primarily affluent and high tech models, audiences appealing to advertisers, FMeXtra is nudged out by having no available receivers. 1⁄2 the digital subchannels for 1⁄4 one-time capital is offset in the ROI game.
When it comes to full digital HD Radio, FMeXtra is left in the dust as it’s currently a hybrid-only system. As with HDTV, broadcasters will be able to cut their transmitter power (and electricity bills) significantly, while offering better coverage, quality and more channels.
If FMeXtra were free to the broadcaster, they still may choose HD Radio for the ability to have twice as many subchannels and the entrenched market of receivers. DAB has tried and failed in North America (Canada) due to the dispersed population. Sirius XM’s half-billion dollar Series A investment in Pandora in 2017 may allow an instant tripling of subscribers by combination.