Published: TV Technology

Issue: 10/9/97



Acrodyne is Getting Their ACT Together

by Joe Fedele





BLUE BELL, Pa.--In an effort to defray the high cost of implementing DTV, Acrodyne 

Communications is working on a new broadband transmitter technique called Adjacent Channel 

Technology (ACT) that will allow broadcasters with adjacently assigned NTSC and DTV channels 

to transmit both simultaneously, using the same transmission system.  

        

The new technology is expected to work on N+1 (DTV channel assigned above the station's 

existing NTSC) or N-1 (DTV channel assigned below the existing NTSC) arrangements and 

could be good news for over 300 full-power television stations. To date, Acrodyne stands as the 

only manufacturer offering a solution that addresses both N-1 and N+1 situations.

        

Due to the linearity and bandpass capability of the Diacrode, advanced tetrode and associated 

cavities, the new Acrodyne transmitter is able to pass two adjacent channel signals that are then 

combined and fed into the final amplifier.  Combining is accomplished within the transmitter to 

avoid expensive external high-power combination networks.

        

An ACT transmitter is configured using separate NTSC and DTV exciters with proprietary low-

level combining and standard Diacrode or advanced tetrode HPA.  The single transmitter feeds a 

single transmission line and dual channel antenna.

        

That may be of particular interest to adjacent channel broadcasters facing zoning and signal 

interference issues because ACT users will not have to install an additional antenna for DTV 

during the simulcast period.  

        

All these factors have a direct effect on your capital budget.  Tom Newman, National Sales 

Manager for Acrodyne, states that with ACT "broadcasters will be able to take care of their 

analog/digital needs without the expense of an additional transmitter," he said. "And the cost 

advantage of ACT is not only in the transmitter, but in the antenna and transmission line as well."  

        

With testing now under way, Acrodyne expects to have a finished product ready for sale by the 

end of the year.  Working with Thomson Tubes Electroniques, the France-based supplier of 

Diacrodes, advanced tetrodes and associated cavities, Acrodyne appears to be well on their way 

to launching this new innovation in transmitter technology.

        

Although this ACT technology was only announced in August, Newman points out that industry 

reaction already has been tremendous. "The feedback from clients has been very positive," he 

states. "Our existing customers invariably allude to the lower initial cost and the lower operating 

cost of advanced tetrode and Diacrode transmitters. Considering the additional costs 

broadcasters are already facing during this transition period, we expect this technology to be an 

attractive investment."

        

With an ever increasing volume of inquiries from broadcasters facing adjacent channel 

allotments Acrodyne is actively working with groups to select beta test sites.  "We are anxious to 

team with broadcasters who are willing to partner with Acrodyne in the early stages of adjacent 

channel technology."

        

Spirits are running high these days at Acrodyne, notes Robert Mancuso, Acrodyne's chief 

executive officer. "We are excited to be playing such an important role in the advent of digital 

television and plan to offer ACT to broadcasters nationally. With the coming of DTV upon us, it 

brings great market opportunity for Acrodyne, as we are filling a niche for those broadcasters 

with adjacent channel transmission challenges. ACT joins the Diacrode in providing cost-

effective alternatives for transmission system purchases."

        

ACT is targeted at the approximately 320 full-service broadcasters that have been assigned 

adjacent channels.  Many of these broadcasters have low- and medium-power level 

requirements, in addition to high power, and can benefit from single-sourcing their transmitter. 

        

"We are the only transmitter manufacturer to offer Diacrode, advanced tetrode and solid-state 

technology in analog from 10 watts to 240kW peak and in digital from 250 watts to 100kW 

average," reports Newman. "This places us in a very unique position for service and after-sale 

support."

        

Timothy P. Hulick, vice president of Engineering for Acrodyne, is the man charged with making 

ACT work.  He points out that developing a system such as ACT is not an easy task. 

        

"A tube has a peak envelope power limitation equal to its single channel equivalent NTSC limit," 

he explained. "Like any tube, Diacrodes can only be pushed so far when it comes to output 

power. But the trick in making ACT work is not to exceed the peak envelope power limit of the 

tube by any combination of signals at specified individual power levels."

        

The ACT process is further complicated, Hulick adds, when channel combining is addressed.  "It 

is a major challenge to the companies that make channel combining equipment because there is 

little or no guard-band to work with for the N-1 situation where the DTV channel is below the 

NTSC channel. Filter skirts must be extremely steep and yet produce manageable group delay 

perturbations."

        

While other transmitter manufacturers using IOTs have attempted to refute Diacrode and 

advanced tetrode technologies as a means of accomplishing this wideband technique, Newman 

notes "Acrodyne high power transmitters are proving themselves daily and we expect our 

adjacent channel solution to be no different."



        

More information on ACT technology can be found on the Acrodyne Internet web site at:  

http://www.acrodyne.com