Whether a radio plant runs with analog audio, digital audio or streaming media, test and measurement gear is key to a successful operation. It facilitates maintenance of a top-quality signal, enables troubleshooting and in the case of terrestrial stations helps to ensure compliance with FCC regulations.
When you talk to industry manufacturing experts, several trends in test and measurement technology become apparent.
The transition to HD Radio is one of the driving forces in new measurement gear. Further, David Day, president of DaySequerra, notes that “anywhere-anytime” access to signal information also has become an expectation, which crosses into the area of monitoring.
“Most of the monitoring gear is at the transmitter, but that information needs to be accessible not only at the studio, but also via cell phones and e-mail. These demands create a level of complexity in the development of monitoring gear.”
There is also an interest in extreme portable gear to measure digital radio signals, perhaps with a laptop. Designing such a device with DSP technology is not difficult, according to Day. “The question is, with design and manufacturing overhead, can it be delivered at a price point where consumers will buy it in significant numbers?”
On the spectrum
As digital transmission becomes more widespread, the spectrum analyzer, once considered a luxury, is now becoming a necessity.
David Maxson, managing partner at Broadcast Signal Lab, said, “A spectrum analyzer has been required to measure the FCC-required mask for analog FM signals as well as the NRSC-2 mask for AM, but these measurements were usually done by consultants. As the costs of spectrum analyzers have come down, more stations or groups are able to acquire them. At the same time, however, measuring digital signals has become more complicated.”
Maxson said confusion over measurement techniques for IBOC signals led the National Radio Systems Committee to create more specific guidelines; you can download the NRSC-G201 documents at www.nrscstandards.org.
The appendix to this document provides a list of test equipment that has been self-certified by manufacturers, along with the list of requirements, so that engineers can check equipment that may not be on the list.
When stations or networks send audio signals through a third party, such as the phone company, a unique set of test and measurement requirements arises.
Dan Knighten, director of products for Audio Precision, said, “Contracts for program distribution usually come with a Quality of Service (QoS) agreement. To keep providers honest, contracts should specify how testing is to be done, and broadcasters should schedule regular tests. HST (High Speed Testing), also known as multitone testing, can send a burst as short as 250 ms which is barely noticeable by most listeners.”
Knighten adds that source tones can be stored on CDs or as digital files. Analyzers at the receiving points will recognize the burst, analyze it and e-mail test results to a central location. According to Knighten, there has been a 50 percent reduction in the cost for multitone technology, while the quality has been greatly improved.
A standout signal also requires careful maintenance of the analog and digital paths back at the studio plant.
Art Constantine, vice president of sales and marketing for Audio Technologies Inc., said, “Although analog audio remains an acceptable method of handling audio in a facility, more and more stations are going all digital.” A portable digital audio monitor enables an engineer to check parameters such as audio level, sample rate, digital errors and headroom below 0 dBFS.
According to Constantine, some analog testing techniques are becoming lost art. The use of white and pink noise generators is one example.
“A savvy engineer knows how to investigate the psychoacoustic effects of audio, and do room EQ with a noise generator.” He adds that audio begins in the analog realm, and any imperfections will only be worsened with the conversion to digital formats, making the maintenance of analog quality all the more critical.
The explosive use of the wireless spectrum by radio broadcasters for wireless microphones, IFB and remote control has created the need for a new type of test equipment.
Mark Kaltman, president of Kaltman Creations, said, “Dropoffs of signal can be the result of weak batteries, blocked line of sight or interference from someone else’s wireless devices. A handheld spectrum analyzer can quickly isolate interference problems and allow users to change frequency on the spot.”
He adds that before the advent of handheld devices, users had to bring large, laboratory-grade spectrum analyzers into the field, something that is not often practical.
“Setting up wireless remote broadcasts without having a way to visualize the wireless spectrum you’re using is like flying blind,” said Kaltman. “The situation will only get worse as these devices become more popular with broadcasters.”
New digital technologies and DSP power have enabled improved equipment performance, mainly in term of precision, according to Christophe Poulain, president of WorldCast Systems Inc., which incorporates Audemat, Ecreso and APT.
He said test and measurement gear, though still a significant investment, need not be super-expensive, in part because more features now are being built into single products.
“That’s what we are doing with our FM Modulation Analyzer; it replaces about six or seven legacy units.” Also helping keep costs down is that in some cases, factory calibration is no longer needed because analog components largely have disappeared from hardware designs.
Remote access via TCP/IP is exciting, he continued. “You can also create some automatic sequences and cycles of measurement. This means you can leave the test and measurement unit to run and operate by itself at a site for hours or even days, then come back and analyze all the data. It will even generate automatic reports.”
Poulain thinks engineers might make better use of the intelligence and automatic operation that are built into today’s products.
“Some of our field measurement equipment can be set up so that all an operator has to do is connect the antennas and power and start driving. In one case, a user hired a limousine company to drive around a city nonstop for three straight days. The customer didn’t even have to be there, and the limousine company kept up with its normal business, they just made all of their appointments with the measurement equipment in the trunk of the car.
“At the end, the user had hundreds of thousands of data points to analyze the signal coverage of every station in the market, with very little investment of his personal time.”
What trends in test and measurement do you see in your workplace? Tell us at[email protected].
Tom Vernon is a regular contributor to Radio World.