Hal Kneller is a 40 plus year veteran of the broadcast industry working both as an engineer for WGCU, WGSM, WCTO, WPAT as well as owner/operator of five of his own stations.
Hal is a past International Sales Manager for Europe for Nautel. He also worked for iBiquity Digital Corporation as Director of International Broadcast Development where he played a pivotal role in the promotion of Digital Radio.
Read more Digital Radio Showcase
by Hal Kneller
Welcome to Digital Radio Showcase, a regular column featuring the latest technical news and information regarding in-band digital radio solutions including HD RadioTM technology and Digital Radio Mondiale (DRM).
While these two systems digitize existing broadcast bands (see band chart below) and offer OFDM technology, considerable differences are apparent as they seek to evolve analog broadcasting to digital. In future issues I will explore these systems from a technical standpoint but today I will discuss HD Radio and then DRM and DRM+.
Recent discussion with engineers centers around the recent FCC-approved HD Radio power increase which permits virtually all stations a 4-times boost to -14 dBc (or 4% of the analog power) with many able to go all the way to 10%. Raising the HD power levels has a remarkable impact on the transmitter power rating, thus Nautel has developed a convenient calculator tool to give station engineers information as to what size transmitter would be required to increase their HD Radio power, or conversely, if the station already has a Nautel NV Series transmitter, what the capabilities using existing equipment would be.
Nautel would be pleased to supply you with this information.
Engineers should be aware that several factors enter into consideration as HD Radio power levels increase, such as: the actual level of injection; frequency; transmission line VSWR; and choice of iBiquity operating mode (MP3 causes a further de-rate). Charts can be provided to you either with or without HD PowerBoost, but if asymmetrical sidebands are required, then HD PowerBoost would also be required.
Asymmetrical sidebands are not currently approved by the FCC, but most engineers believe they ultimately will be. A station desiring to operate in this mode would apply to the Commission for Experimental Authority (as opposed to Special Temporary Authority or STA). Part of the provisions of such authority would require the station to submit a report on the operation authorized which would ultimately be used by Commission staff to determine the feasibility of permanent authorization of the technology to all broadcasters for which it might be applicable. This is the same path that separate IBOC antennas followed in 2003-2005 as the Commission considered that matter which ultimately became part of the rules.
Why would a station need to use this differential sideband power? Based upon an individual allocation, the consultant studies a proponent station and then reports back on clearances (signal overlaps) on each side of the station’s assigned frequency.
We might find one side has an interference issue that will limit a given station to 4% power in that sideband, but the other sideband may have no adjacent channel issue, hence the full 10% could be available there. In this case, the station’s total digital power would be 7% rather than 4%, maximizing digital coverage. Some engineers who possess the software could run this allocation themselves, but many will use the services of an outside consultant. This formula was developed by NPR Labs during the course of their interference studies, and incorporated in to the FCC report and order, to become part the permanent rules.
The same standard is applied to the first adjacent channel on each side of the proponent station, thus maximum power is the lesser value obtained (if symmetrical power is used).
The FCC has recently issued notification guidelines for stations desiring to increase their HD Radio signal power, whether to 4% (-14 dBc) or all the way to 10% (-10 dBc).
Next issue we will cover some of the new features that will be part of the HD Radio system such as multicast HD-4 and graphics images of artists, station logos or client logos, and more.
I would be remiss if I did not mention Digital Radio Mondiale (DRM) and regulatory progress there. Last September, the DRM+ standard was formalized and approved for frequencies from 30-174 MHz. by ETSI (European Technical Standards Institute), with ITU recommendation pending at this time. DRM is an open global standard in use in many countries outside of the U.S.
DRM+ is a 96 kHz wide all-digital system which can be placed on an open frequency (even as close as 150 kHz to an existing FM station). It offers up to four music and data channels. Unlike HD Radio technology which has the digital frequencies at a uniform offset, DRM+ can occupy any available spectrum from 30-174 MHz. DRM is an interesting technology to many because it permits a uniform standard covering multiple bands as shown in the chart which indicates where the various digital radio technologies fall into the RF spectrum.
DRM30, as it has become known, is used in bands other than Band II (which is where DRM+ fits) and has far greater flexibility than HD Radio technology. By that I mean that the user can select the occupied bandwidth and various levels of digital throughput versus robustness. DRM can nicely fit a 9 kHz channel on Medium Wave with +/- 4.5 kHz or it can use more spectrum if available. DRM originally was developed as a digital replacement to analog for short wave broadcast and provides very good fidelity (with stereo) for a far more satisfying listening experience than analog.
Over time, DRM evolved to Medium Wave and Long Wave as well. The standard was considered complete with DRM+ up to 174 MHz, but now we hear reports that a university in Germany is experimenting with DRM+ on Band III (see DMB on chart above). Although this is not currently the official position of the DRM Consortium, we will have to wait to see if this will signal a change for additional spectrum for DRM+.
While numerous manufacturers (including Nautel) build transmitters for DRM30 (in fact all transmitters we currently manufacture are 100% compatible with both DRM and HD Radio technologies), Nautel is the only supplier of DRM+ transmission equipment at this time. This is still considered experimental as we continue to work with broadcasters and DRM Consortium partners to create a formal product.