THE BIRO TECHNICAL BULLETINS
This Technical Bulletin deals with undesired post digital
transition reception situations, qualified as “
MISSION IMPOSSIBLE #1:
The reception of Channel 13, WJZ-DT,
Before June 12, 2009, WWPX, Martinsburg, W.V., was operating on
Channel 60, with 2040 kW effective radiated power. After the Digital Transition WWPX-DT was
assigned to Channel 12, exhibiting the following reception parameters in
Observe the Channel 13, Baltimore and Channel 12, Martinsburg distances. The undesired adjacent channel station is six times closer than the desired. The net result: tremendous adjacent channel interference problems on the desired Channel 13, Baltimore.
Nor was the reduction of Channel 13,
Another reception difficulty is demonstrated on the Signal Direction Sheet below. The undesired Channel 12 Martinsburg is almost in-line with the desired Channel 13, Baltimore.
Consequently, the original high-gain Channel 13 antenna, receiving comfortably the analog Channel 13 before, could not differentiate between the desired and undesired stations. The main lobe of the antenna’s radiation pattern was much wider than the angular separation between the two stations.
There are two alternatives to reduce the adjacent channel interference, producing interference free digital Channel 13 pictures.
This is a practical, economical alternative; actually the only chance to receive Channel 13, Baltimore with acceptable picture quality.
However, even the best design effort may be easily confounded by Mother Nature. Under inclement weather conditions, when Channel 13 reception is exposed to fading, picture quality may deteriorate.
MISSION IMPOSSIBLE #2
The reception of Channel 33, WCBS-DT, New York in Southbury, Ct.
Channel 2 WCBS,
Conditions changed drastically after June 12, when Channel
2, WCBS-DT started operation on its assigned new digital channel, Channel 33,
with 284 kW effective radiated power. Suddenly, the
Observe the reception parameters of Channel 33, WFSB-DT,
undesired Channel 33,
The co-channel signal direction sheet below delivers no new technical information, but it is an excellent visual presentation of actual co-channel conditions.
The interfering co-channel is not arriving exactly 180° off-the-desired direction With other words it is not a perfect Front/Bank ratio problem. The 169.5 degree angular separation requires the application of a phased-array of two, horizontally stacked Channel 33 Yagis, to force a deep radiation pattern null into the direction of the co-channel offender.
course, these Channel 33 interference conditions did not need to develop. Somebody at the FCC assigned the same UHF
channel for a
The FCC, responding to this uproar, sent engineers to the affected areas and granted output power increases.
Channel 6, WPVI-DT,
|NEW YORK METRO AREA|
|CHANNEL 7||WABC-DT||12 kW output power before|
|Approved for 27 kW.|
|CHANNEL 33||WCBS-CT||170 kW output power before|
|Approved for 400 kW.|
|CHANNEL 44||WNYW-DT||74 kW output power before|
|Approved for 500 kW.|
|PHILADELPHA METRO AREA|
|CHANNEL 6||WPVI-DT||6 kW output power before|
|Approved for 30 kW|
|CHANNEL 12||WHYY-DT||13 kW output power before|
|Approved for 20 kW|
|CHANNEL 34||WCAU-DT||480 kW output power before|
|Approved for 700 kW.|
If you get the impression by glancing through the above listing that the DTV Transition resulted in a number of real-world limitations that the FCC and their “experts” didn’t foresee, you would be correct!
These misguided power calculations require fast corrective action. Normally, it would take months and months to obtain power change modification from the FCC. This time the Commission acted as fast as two days. An all time record.
For emergency engineering services:
Call: (609) 883-9866
Web site: www.biroengineering.com
PRINCETON, N.J. 08543