Tuesday, November 5, 2019

Thoughts On All Digital AM

The FCC's recent NPRM docket 19-311 has been brought forth proposing rule changes authorizing AM stations to commence all-digital broadcasting on the mediumwave band. The outcome should be interesting and may institute a sea-change in the direction of AM radio. Currently approved stations may transmit a hybrid digital-analog combination or "IBOC" signal (In Band On Channel, by iBiquity). As of this writing, some 237 stations are authorized by the FCC. Roughly only 114 are actively transmitting a hybrid signal at all, with only approximately 32 transmitting hybrid at night under skywave conditions.

Notice of Proposed Rulemaking, 19-311 (PDF)

Sit back and think for a minute what AM DXing might be like in an all digital environment. YouTube has a few videos showing tuning of digital AM DX. Search for "DXing AM HD Radio". In the United States, one must only look to when TV broadcast went to all (or virtually all) digital mode in 2009 to see the effect.

I don't know if you have ever done any TV DXing, but back in the day analog TV DXing was relatively easy when signals were in. You could see if a signal was there or not amongst the "snow" on your screen. Digital broadcasts are different. A signal is there or it isn't, and when it's there it's there in full HD. The penalty that digital imposes over the older analog method is this: any reception at all requires a signal level above a certain threshold. Software controls that threshold. If the threshold is exceeded, you have a picture. If not exceeded you have nothing, not even evidence of something lurking in the noise.

"AM" radio digital reception, or HD Radio as it is known,  brings with it similar characteristics as digital TV reception. The signal will either be there or not, as the YouTube videos prove. At night with skywave prevailing, with a few or many stations sharing the same channel, I would expect signals to be popping in and out in perfect clarity.... if they break the threshold. On weaker channels, there may be nothing where before there was something detectable. This will certainly make DXing interesting. Threshold levels of receivers, set by mass market engineers, will dictate what is receivable.

So what about extreme mediumwave DX? Cross-continent DX may become extremely rare if not non-existent. Extremely weak signals may never break the threshold to be received. This may mean no more logging KFI-640 on the east coast, or WGY-810 on the west coast. And intercontinental DX, like trans-Atlantic (TA) or trans-Pacific (TP) will become virtually non-existent when those countries go to an all digital format. While single hop DX out to maybe 1000 miles or so might be possible on occasion, the extreme may never be again.

Note, however, that the TV DXing hobby continues to survive in the United States, despite digital. What's left are a few low power analog TV translator stations (channel 36 out of Kingman, AZ is one here is the southwest). These are mandated to convert to digital soon. Mexico still runs much analog TV. And there are people and groups still pursuing continental digital TV DX via E-layer skip and also through troposhperic ducting, predominantly near coastal areas.

More on TV and FM DXing can be found here at the Worldwide TV-FM DX Association.

Mediumwave broadcast band DXing will not stop just because of an eventual all-digital changeover. And any changeover will be years in the making unless the FCC suddenly mandates exclusive rights to digital and bans analog altogether. HD Radio hardware is available today, and has been predominately produced for the automotive market but more and more is being seen in home entertainment equipment. We will use different techniques in DXing. What will vanish, to a large degree, is that experience of pulling a weak signal up out of the noise and identifying it. To a guy like me raised on 1950s radio, it will be a disappointment. But new experiences await I suppose.

The trend to eliminate weak signal "annoyances" in radio reception is already being set in the last few years with the advent of DSP receivers using the SiLabs DSP chips, the "radio on a chip". Soft muting in these DSP chips eliminates weak signals at the noise level on purpose. Almost all modern consumer grade radios are now using this chip. In rare cases, the soft-mute function can be defeated. Analog is disappearing in many forms. Try to find a new, true analog-tuned radio on Amazon and you'll be surprised that there are only a slender few to choose from.

Now that we are some 10 years into all digital TV, it is notable that TV tuners in modern TVs have been dumbed down, desensitized, and capture threshold levels increased to where weak signal TV reception is becoming a thing of the past. This is evident with the TV DXing crowd who prefer older, more sensitive TV tuners made at the start of the digital conversion era, and covet sensitive analog to digital converter boxes made at the transition time (example: 2009, the Zenith DTT901 Digital TV Tuner Converter Box).

Tecsun has announced the availability of the new PL-990 and H-501 for early next year, two new multi-band portables. However the long term trend in radio is not to expand this line but to curtail it. With the near total demise of high power international shortwave broadcasting, fewer and fewer consumer radios with shortwave will be produced. Shortwave awaits the final nail in its coffin and the younger generations shows little interest because other technologies have supplanted the need.

Log 'em while you can. Interesting times are ahead.

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