THE BIRO TECHNICAL BULLETINS 
SEPTEMBER 2007


DIGITAL CONVERSION?
TROUBLED SEAS AHEAD FOR THE FCC

The approaching digital conversion date of February 2008, makes everybody nervous.Congressional leaders, led by Rep. JOHN DINGELL and EDWARD MARKEY, are convinced that the analog shut-off is a public disaster to happen.If you ask someone in Washington when and how the Analog to High Definition TV conversion will be solved, the usual answer is: We donít know.

Digital conversionís greatest impact will be on the 20 million households without cable, proud owners of old analog TV sets.To watch TV after February 2009 they must purchase and install special Digital/Analog converters.Now, American households have more than one TV set, so we are talking about 50 to 60 million converters.Neither a small number, nor a negligible expense.

While those 20 million old TV sets represent a serious HDTV challenge, the Cable TV industryís conversion to the HDTV age is not freeof potential technical problems.

A case in point is CLEARVIEW CABLE, serving Harford, Md and South York, Pa counties.The system carries the popular HARRISBURG, Pa. UHF TV stations Channels 21 and 27.After the analog cut-off they have no other choice, they must switch to the stations HDTV affiliates.

The HDTV affiliate of Channel 21 is Channel 4, WHP-DT and for Channel 27, it is Channel 10, WHTM-DT.

The reception of these VHF stations represent a serious technical challenge, as demonstrated with the aid of the following Co-Channel Signal Direction Sheets.

Desired Station:
CHANNEL4 WHP-DT HARRISBURG CBS 2.3 kW 47.66 MILES
 
Undesiredco-channel interference:
CHANNEL†† 4 WRC WASHINGTON, D.C NBC 100 kW 63.94 MILES

Note the extremely low 2.3 kW output of Harrisburg, versus thepowerful 100 kW Washington station.The Washington transmitter is only 24% further awaythan Harrisburg.

The implications are obvious. The FCC approved digital affiliate channel selection is less than desirable.

Desired Station:
CHANNEL10 WHTM-DT HARRISBURG ABC 16.2 kW 48.05 MILES
 
Undesiredco-channel interference:
CHANNEL†† 10 WCAU PHILADELPHIA NBC 137 kW 68.21 MILES

The high output power Philadelphia transmitter, only 29% further away than the desired station, will affect the reception of Channel 10, Harrisburg.An elaborate phased antenna-array is needed for interference protection.The FCC approved digital affiliate channel selection is quite unfortunate.

Our research indicates that the improper DTV affiliate channel selection is not limited to Pennsylvania.Similar problems may cause head-aches for CATV operators in every state east of the Mississippi.

In North Carolina, the Brevard CATV system carries Channel 13, WLOS, ASHEVILLE, an ABC network station.†† After the analog cut-off date it must be replaced by the HDTV affiliate, Channel 56, WLOS-DT, Asheville.Channel 56 reception troubles are demonstrated on the Signal Direction Sheet below.

Desired Station:
CHANNEL56 WLOS-DT ASHEVILLE ABC 1000 kW 12.88 MILES
 
Undesiredco-channel interference:
CHANNEL†† 57 WHNS-DT GREENVILLE FOX 1000 kW 4.98 MILES

The undesired adjacent channel digital TV stationis located 2.6 times closer than the desired!

The Channel 57 adjacent channel DTV interference can be considered a daunting but hardly insurmountable obstacle.Remember that the usual solution of installing of a bandpass filter or a trap does not work on UHF frequencies.The application of a properly designed and installed phased-array is mandatory, but under the given unfavorable distance conditions picture quality cannot be guaranteed.

Another case in point is the selection of Channel 12 as the DTV affiliate of CH 20, WTXX, Waterbury, Ct.†† Observe the distances and output powers involvedin GILMAN, Ct.

Desired Station:
CHANNEL12 WTXX-DT WATERBURY UPN 2 kW 35.02 MILES
 
Undesiredco-channel interference:
CHANNEL†† 12 WPRI PROVIDENCE CBS 316 kW 49.41 MILES

How do you ascertain interference elimination when the undesired stationís output is 316 kW versus the desiredís 2 kW, and the distances are almost equal?

Not even Biro Engineeringís custom designed phased-array can guarantee the necessary co-channel protection 100% of the time.

CONCLUSION

Hardly rocket science, you might say, but the development of these Signal Direction Sheets have given the HDTV affiliate channel selection process a radically new perspective.

Biro Engineeringís Signal Direction Sheet services are available to everybody in the CATV industry, including the staff of the FCC.It is still the best way to identify potential HDTV reception interference situations, or to search for interference free solutions.

The best time for corrective action is now.


For emergency engineering services:
Call: (609) 883-9866
E-mail: steven@biroengineering.com
Web site: www.biroengineering.com

Biro Engineering
P.O.BOX 2175
PRINCETON, N.J. 08543