Published: TV Technology

Issue:  11/6/97



Digital Microwave Crucial to DTV Distribution

By Joe Fedele





MIAMI--As everyone is now well aware, the FCC-approved digital television standard provides 

stations with the opportunity to broadcast multiple channels. Each 6 Mhz channel is capable of 

transmitting approximately 20 megabits per second (Mbps) of digital data, and advances in 

MPEG compression algorithms allow for the multiplexing of up to six individual program 

channels.

        

The Studio-to-Transmitter Links (STLs) used by many stations to feed programming to their 

transmitter sites generally consist of one main analog microwave path and one backup.  With the 

advent of multichannel broadcasting, the majority of stations simply do not have the 

infrastructure in place to provide for the mass distribution needed for DTV.

        

Then there is the issue of shrinking microwave bands.  In the September 11, 1997 issue of TV 

Technology we discussed how the Broadcast Auxiliary Band (BAS) was scheduled to be 

reduced.  Although the final disposition of the band remains uncertain, most fear a reduction in 

channel bandwidth from its current 17 Mhz to as little as 10 Mhz.

        

In most cases broadcasters will have to add capacity and convert to digital transmissions in order 

to accommodate the extra loads imposed by both multichannel applications and reduced 

bandwidth.  Currently, only a few companies offer lines of microwave equipment capable of 

meeting this digital challenge.

        

One such company is Nucomm, Inc., a Hackettstown, N. J.-based microwave equipment 

manufacturer that offers a digital video microwave system covering from 1.3 to 15.35 Ghz. The 

FT/FR6 Gigalog Radio series is a heterodyne radio system designed to deliver "broadcast 

quality" programming for STLs, Transmitter-to-Studio-Links (TSL), Intercity Relays (ICR) and 

Multihop microwave applications.



        

Gigalog radios will accept a compressed digital signal with data rates of up to 45 Mbps, making 

them ideal for multichannel configurations when used with an MPEG encoder. Originally 

developed as a digital transmission system, it can even be modified to operate in analog mode. 



        

The Nucomm digital system will also accept a 70 MHz IF signal from any external modem, 

multiplexer or codec.  This allows for the distribution of a modulated baseband signal without the 

need to downconvert and remodulate a signal. 

        

In its present form the Nucomm system consists of three or four separate pieces of equipment, 

but future versions will include a consolidated systems that integrates all the codecs, 

multiplexers and modulators into one box. 

        

Available in Simplex, Duplex or Hot Standby configurations these radios can also be equipped 

with up to six analog audio program channels.  Optional accessories for the line includes an 

internal test generator, video presence detector and 70 Mhz insert oscillator.  



        

Nucomm also markets its Surface Mount Technology, a low-cost maintenance method that 

reduces parts count and requires less power.  This, the company claims, reduces heat damaging 

effects for long term reliability.  "Turn it on and forget it" is the Nucomm slogan.



        

When asked what makes Nucomm different from other microwave equipment manufacturers  

David Thomas, Director of Sales and Marketing for Nucomm replied, "the real difference is not in 

the equipment but the knowledge of implementing the systems," he said. "Nucomm was the first 

company to install a digital video microwave system and that system has been up and running 

for over two years."



        

Thomas also remarked that he sees "a lot of confusion among the broadcasters" with regard to 

the transition to DTV.  "We are helping as many broadcast groups and networks as we can," he 

continued.  "It is our understanding that broadcasters need to figure out what their studio 

infrastructure system and their acquisition method will be."

        

California Microwave, (parent of Microwave Radio Communications, MRC) provides a full line of  

broadcast microwave equipment, antennas and accessories.  MRC fixed microwave systems 

consist of several subcategories in both a "long haul" and "short haul" series.  

        

The company's FLH-DAR series is a heterodyne microwave system that can operate using either 

analog composite or digital modulation, capable of covering different frequency bands from 1.9 

to 13.2 Ghz.  The FLH-DAR can be purchased for use in analog systems and later upgraded to 

digital (QPSK or 16QAM) operation by internal switch changes and the addition of a 45 Mbps 

digital modem. 

        

The equipment can be purchased with up to four audio channels and in simplex, duplex or hot-

standby configurations.  Both space or frequency diversity are also available to enhance 

reliability. 

        

MRC also offers 34 and 45 Mbps digital links for the transmission of E3 and DS3 data streams.  

Their DAR34 and DAR45 units use high order QPSK and 16QAM modulation techniques to 

provide what MRC calls "a highly reliable and cost-effective" STL/TSL, multi-hop, and 

multichannel digital video transport system.

        

The DAR45 is optimized for DTV STL operations and includes a dual-channel-per-carrier 

system.  This allows both an NTSC and DTV signal to be multiplexed and transmitted 

simultaneously over a single microwave channel.  The DAR45 can easily be converted to analog 

operation by a simple internal switch reconfiguration and with the addition of analog modem 

cards. 

        

"Some of the 'digital-ready' analog systems on the market include third-party modems developed 

for cable or satellite applications," said David E. Glidden, director of Fixed Radio Systems for 

MRC. "[Our] modems were designed specifically with forward error-correction schemes 

optimized for terrestrial microwave applications."

        

He reports that MRC also plans to introduce a space diversity receive system before the end of 

the year.  This is an important feature when 16QAM modulation techniques are used because 

they inherently reduce transmitter output power and receiver threshold levels. Space diversity 

systems compensate for this by increasing overall system gain.

        

The company's DAR45 system is currently in place at WCBS-HD, NY and the model HDTV 

station in Washington, D.C. 

        

Finally, Harris Broadcast (Quciny, Ill.) is testing a new digital microwave system reported to be 

capable of DS3 transmissions.  Although still in the developmental stages, its final version will 

permit simulcast transmissions of either an NTSC and DTV program or two DTV channels.  At 

this point in time it remains unclear as to exactly when Harris will begin to ship the new line, but 

sources say it will likely be available by NAB 98.