NAB to Seek FCC Approval of Major IBOC Power Boost

[Mark]

NAB to Seek FCC Approval of Major IBOC Power Boost

Poet laureate Carl Sandburg once famously intoned that "the fog comes in on little cat feet." And so, apparently, do major proposals that could increase licensed digital operating power in hybrid IBOC Digital broadcast signals by as much as 10dB.

News regarding the proposal apparently first surfaced in published minutes of the NAB Radio Board's Jan. 29 meeting, where "acting upon a recommendation from the NAB Digital Radio Committee, the Board unanimously approved a resolution to seek FCC authorization for higher-power operation of FM HD Radio stations." Since that time, some rather low-key reports in trade publications have brought a couple of additional details to light, including the 10dB level of increase sought.

According to anonymous industry sources, proposals to up the digital component power of FM HD Radio hybrid signals were floated some time ago as an answer to signal penetration and coverage issues experienced by a number of stations then operating with HD Radio signals. STAs were filed for test stations belonging to several radio groups (most notably Clear Channel), allowing digital transmission power to be temporarily boosted to levels elevated as much as 10dB below analog carrier values. Consulting radio engineering firm and NRSC DRB Subcommittee member Hammett and Edison conducted data measurement and analysis.

Full article at: http://radiomagonline.com/digital_radio_update/digital-radio-update-020608/

Or do your own search to see what's brewing out there.....

[Mike-CT]

They can boost it up another 20db if they want and it won't matter here because the damage in the northeast has already been done. It's a shame. I've spent over 30 years as an FM Dxer but I honestly don't see any future to it here anymore, at least not while HD is on the air. Times change, for better or for worse...

[Mark]

What bugs me is the FCC doesn't require mask filters after the "HD" transmitter RIGS as they do on DTV transmitters, and there doesn't seem to be any enforcement or concern of the occupied bandwidth of HD stations, just the hustle to bail out iBiquity and try and make this boondoggle fly even using taxpayer money via the CPB through public radio stations. Clear Channel has sunk $$$$$$$ into this too.

Take a look at the iBiquity station contract, it’s scary. If I owned a station I wouldn’t jump into this: http://www.ibiquity.com/i/pdfs/2008%20Form%20SLA-A.pdf

This system http://www.dreinc.com/ looks much better without the contractual fees and loopholes. It uses as much spectrum as a station wants/needs to dedicate to it within the SCA region, a station can even go mono if they want to use the area where the stereo subchannel usually resides (23-53kHz). And it doesn’t require a transmitter system upgrade, just plug the encoder into an existing FM exciter/transmitter.

[PocketRadio]

Most major broadcasters will not be able to afford replacing all equipment for a proposed 10db power increase:

http://hdradiofarce.blogspot.com/2007/12/wsms-chief-engineer-on-hd-radio.html

[w9wi]

Most major broadcasters will not be able to afford replacing all equipment for a proposed 10db power increase:

http://hdradiofarce.blogspot.com/2007/12/wsms-chief-engineer-on-hd-radio.html

In many cases, it's likely to go well beyond simply replacing the digital transmitter and combiner.

The secret at the transmitter end of the HD Radio facility is the incredible inefficiency of the digital/analog combiner. http://www.ic.gc.ca/epic/site/smt-gst.nsf/en/sf08759e.html
details an IBOC test at the CBC's First Canadian Place transmitter site in Toronto. Note that ***90%*** of the power out of the digital transmitter is wasted as heat. (with obvious consequences for the air conditioning load. Maybe not an issue in Toronto in winter, but definitely a problem in Georgia in July!)

If you want 200 watts of digital power out of the combiner, you have to put 2,000 watts in.

In this test, roughly 2kw of heat was generated by the addition of HD to CBLA's normal analog broadcasts. Plus whatever was generated by the fact that the digital transmitter was not 100% efficient at converting 60Hz AC power to digital RF. (and one might expect the digital transmitter to be less efficient than an analog FM transmitter of equal power. The digital transmitter must be linear - not a requirement for analog FM - and linear amplifiers are less efficient.)

Now, let's increase the digital power to 2,000 watts, 10% of the 20,000-watt analog figure. The combiner is still only 10% efficient -- so you have to put 20,000 watts of digital RF into the combiner. Instead of having one 20,000-watt transmitter atop First Canadian Place, and an air conditioner large enough to keep the room down to a reasonable temperature, now you have two 20,000-watt transmitters. You need double the cooling capacity.

Except that it gets worse.

The 20,000-watt transmitter that's already there, most of its output gets radiated as RF and delivered to the CBC listeners of Toronto. The heat load is the result of the inefficiencies in the transmitter. The proportion of that 20,000 watts of analog power that goes to heat up the room is negligible.

You can't say that for the digital transmitter. The digital transmitter may be pumping out 20,000 watts, but only 2,000 of that is delivered to the HD listeners. **the other 18,000 watts is converted to heat**.

So you have to well more than double the cooling capability of the transmitter site to accomodate HD Radio at 10% of analog power.

Or, you go to a low-level combining system (which requires replacing the entire transmitter) or transmit the HD from a separate antenna. (if the tower permits enough windloading and you're willing to accept the risk that unexpected nulls and peaks in one of the antenna's patterns will create places where the digital signal will interfere with the analog.)

My point being that at many stations a 10dB increase in digital power is a VERY difficult project. I would suggest in many cases it's simply not possible.

[ALLANDUNN]

It is happening. Here is the link posted by Radio World.
http://www.rwonline.com/dailynews/index.cgi