When: February 20, 2001 7:00 PM
Our guest speaker was Jeff Detweiler of iBiquity Digital.
Nominations and volunteers for new SBE board members were taken. Here is the list of potential candidates:
- Jeff Loughridge
- Fee Lee
- Bob Clinton
- Dan Ryson
- Mike Friedman
- Ed Bukont
- Eric Hoehn
- John Bisset
Because the March meeting will be the all-day Zenith seminar, it seemed appropriate to put off the vote for the board until the April meeting.
March 23 is the date of the Zenith Seminar. A small team of representatives from Zenith will be in town with equipment to demonstrate the latest DTV technology. Some of the pros and cons of the top two systems will be discussed. The primary purpose of the seminar is to acquaint television engineers with the system which has been approved by the FCC for HDTV transmission. The benefits of attending this seminar include being able to hear first-hand from one of the inventors of the system.
Jeff Detweiler of iBiquity Digital spoke on the current state of Digital Radio broadcasting. iBiquity is the merged entity that came into being between Lucent Digital Radio and USADR. The primary benefit of this merger is the expected acceleration of FCC standards setting.
iBiquity is working with the FCC and the NRSC, as well as manufacturers, to get an optimum In Band On Channel (IBOC) system approved and transitioned in the US and abroad. The International Telecommunication Union (ITU) recently recommended the approval of iBiquity's AM IBOC system as meeting their standards of digital broadcasting for frequencies below 30 MHz.
Perceptual Audio Coder (PAC) is the data reduction scheme developed by Lucent Digital Radio. The merger with USADR made PAC the defacto standard for DAB.
At first, there will be a hybrid of digital and analog broadcasting. This will allow time for the new receivers to be introduced and gain acceptance in the marketplace. The FM hybrid will allow for the normal analog signal, and a 150 kHz data stream, of which 96 kHz will be used for audio, and 54 kHz will be used for auxiliary data. Plans are already in the works for traffic information services to provide full-time traffic data, which can be based on receiver GPS location. In the future, if the marketplace allows, stations may opt to drop the analog portion of the broadcast, and double the data stream to 300 kHz. This data stream will be used for additional auxiliary data, plus a new lower rate audio bit stream, which will be used for fast acquisition and the fallback audio channel when good reception is challenged.
The hope is that the FCC will finalize the DAB standard in the second half of this year, immediately followed by commercial transmission equipment orders. Radio station conversion would then begin in the first half of 2002. Receiver rollouts will begin the second half of 2002. Broad base receiver rollout and OEM receivers will follow in the first half of 2003.
iBiquity has introduced a program called Early Adopt Station Enhancement (EASE). By signing up, stations will be provided with early access to manufacturers, as well as "most favored" pricing from the manufacturers. An IBOC Broadcaster Rollout Advisory Board will be assembled from representatives in the EASE program.
For station engineers looking to prepare their facilities for DAB, following is a list of some of the things to keep in mind:
· 44.1 kHz sample rate should be the plant standard
· Air control rooms need to be able to monitor "pre-delay" audio
· UPS / power protection for CPU equipment in the air chain
· Moving the air chain audio processing to the transmitter
· Upgrade STL to pass AES signal
· Separate processing for digital and analog audio
· Current TX needs about 10% more output to compensate for combiner loss
· Power requirements at TX for additional 30% more power consumption
· Floor space requirements for second TX
· Cooling and air handling load increased significantly
· Most AM's will have to upgrade STL to stereo or AES
· AM's will have to upgrade TX to solid state
· AM's will have to be flat to ± 5 kHz bandwidth
Digital broadcasting will introduce some unexpected changes for some. The biggest will be the nearly ten second delay between program origination and audio coming out of the receiver. This will mean changes in the air control rooms where many stations still monitor directly off air. This will also mean having a second audio processing chain just for the headphone feed for the DJs.
Besides pre-delay monitoring, the prime studio consideration will be in the sample rate standard. With DAT tapes at 48 kHz, and CDs at 44.1 kHz, and many standards in the digital audio processing, the best thing you can do is reduce the number of sample rate changes the audio has to go through before transmission. The same goes for data reduction schemes. Everyone will probably tire of the familiar "cascading algorithms" issue.
There is much more to consider at the transmitter site. With the introduction of the DAB transmitter, and its associated reject load, calculations say that you will have nearly three times the heat load you currently have. There will have to be a way to deal with all the extra heat. Don't even think about just adding an exhaust fan.
Some transmitter sites have UPSs because of the newer STL and digital exciters and processors. They may need to be upgraded now to handle more equipment. At the transmitter, the STL will feed an AES signal into a 10 second delay (currently part of the DAB equipment - needed to time align the digital audio with the analog audio), and come out as AES 44.1 kHz into your analog audio processing. (Some early digital audio processors will have to be upgraded to handle 44.1 kHz.) This must be done pre-processing, because the DAB signal will have to be processed separately to optimize it for the data-reduced signal.
Your current transmitter will have to increase its output (some upgrades needed) by 10% to accommodate the loss in the combiner. The combiner is only a little larger than a line section, about three feet long, with two extra ports - one for the digital transmitter, and the other for the reject load. Unless your TPO exceeds 30KW, a 5KW air cooled load works fine. It will generate a lot of heat. Having monitor points for RF power are a must for troubleshooting. An RF patch bay or switch might be considered for bypassing the combiner. The combiner does come with a "bypass" switch, which shunts all of the digital TX output to the load.
Thankfully, the typical FM antenna handles the digital signal as well as the analog signal, so the antenna is not going to be a concern.
Typical conversion costs ranged in the $94,000 to $215,000 for digital equipment purchases and other upgrades. The heat handling and additional power issues alone could cost an additional $5,000. Naturally, these are ballpark numbers, and each site will have to be surveyed for current capacity and needs. The AM transmitter sites ranged from $27,000 to $187,000 depending largely on how much work has already been done to the site for such things as AM stereo, broadbanding, and pattern optimization.
Some of this was mentioned at the meeting, and some was taken out of the experience of hosting one of the DAB test transmitters. This meeting was very exciting because it marks a turning point in the planning stages for most of us who must begin preparing our plants for the DAB era.