The RF Spectrum On-Line

The Latest in Broadcast Technology - SPRING, 1997

Copyright ©1997, RF Specialties Group.

Moseley Puts the SQUEEZE on Competition with
Uncompressed Digital STL

Occupied Spectrum
Spectral Occupancy, Moseley Starlink 9003 QAM

Technology took a giant leap as Moseley introduced at NAB ‘97 a 16-bit, linear uncompressed audio 950MHz digital QAM STL. That’s Quadrature Amplitude Modulation. The new Starlink 9003 QAM STL is like all other systems in Moseley’s Starlink series in that it includes audio encoding and decoding, an intelligent multiplexor and optional daughter cards for audio bit rate reduction and telephone communications. It uses the same personality modules found in Moseley’s T1 and spread spectrum products, but it also has a QAM RF transmitter/receiver module. QAM is a digital modulation method that is used in satellite delivery services. It is the most spectrally efficient modulation scheme developed, making it ideal for the limited bandwidth of 950MHz STLs. Basically, it allows for 4 bits of modulation in 1 Hz bandwidth, according to Dave Chancey of Moseley. The unit can run two compressed and two linear channels, in other words four 15kHz audio channels, over a single 950MHz channel.

Modulation is done in a quadrants of 16, 32 and 64kHz sample rates for spectral efficiencies by a factor of four, five or six respectively. "If you’re doing linear audio at say 32kHz sample at 1,024 kilobaud, the spectral efficiency would mean you can do that at slightly more than 250kHz of occupied bandwidth," explained Chancey. At 64 QAM, the Starlink 9003 STL can run full T1 data rates of 1.544 mbps within 300kHz of occupied spectrum.

QAM is very robust, being very tolerant of low signal levels and interfering signals. "It’s not an eggshell modulation scheme, where interfering signals or an adjacent channel is going to make it topple like a house of cards," said Chancey. Moseley is the first RF Specialties supplier to use QAM for STL use. The unit is expected to start shipping in September.

Moseley also announced they are now shipping their Starlink spread spectrum wireless audio links, with over a dozen in the field. This military-developed method of frequency hopping or sequence coding can be a very robust and secure means of getting information in general, and audio in particular, to and fro. Among other benefits, spread spectrum generally requires no FCC licensing or phone lines and is of near-CD quality.

Moseley's Starlink 9001 digital RPL is a natural for point-to-point remote broadcasts of 30 miles or less, line-of-sight. Source coding is selectable on the unit (ISO/MPEG Layer II or apt-X), as is the sample rate, for 32, 44.1 or 48kHz. It’s pretty easy to set up for a remote, as the unit uses an antenna mounted amplifier/LNA.

For more details on either of Moseley's new Starlink products, call your nearest RF Specialist.