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uhf interference on VHF 22. digital tv

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ever since june 12 which was inauguration of digital tv in sf bay area, i get STRONG (perfect reception) of channel 7 tv on channel 22.
i seem to be the only one in the bay that has this problem. i called the USCG and they havent heard of this problem.
my vhf is a fairly new Raymarine.

bruce adornato

3 Replies

  • I assume you are talking about station KGO in San Francisco. They are something of an exception in the DTV transition of June 12, 2009 in that they were on Channel 7 before the transition and remained on it afterwards. The spectrum involved is 174-180 MHz.

    VHF Marine Band Channel 22 is 157.1-MHz.

    I am curious how you were able to determine that the source of the interference is from KGO's DTV signal.

  • Another related aspect of the June 12, 2009 transition to DTV is that most television stations in the VHF band reduced their power. When KGO was transmitting in NTSC on Channel 7, their effective radiated power was probably on the order of 300-kW. After June 12, 2009, the DTV signal from KGO was transmitted with only 24-kW on Channel 7.

    Also, I am still curious how you we able to demodulate the digital television signal on a VHF Marine Band radio.

  • Pehaps Bruce has abandoned this discussion.

    I would like to point out that prior to June 12, 2009 all television stations broadcasting in NTSC were transmitting their audio using normal frequency modulation techniques, quite similar to the frequency modulation used in the VHF Marine Band Radio Service, and thus it would be plausible that a VHF Marine Band radio might be able to receive a television NTSC broadcast of the audio portion of their transmission. But after June 12, 2009, the transmission of television broadcast signals changed to the advanced television system or HDTV, and the audio portion of the broadcast signal became digitally encoded and transmitted along with the picture. It is extraordinarily unlikely, really implausible, that a VHF Marine Band radio could demodulate the audio portion of an advanced television transmission.

    I have to conclude that this report of reception of an advanced television signal broadcast by KGO following June 12, 2009 is highly unlikely. The only plausible explanation might be that there was an ongoing transmission of what was called a "Night Light" service. That refers to a transmission of an NTSC broadcast to inform viewers that a substantive change had occured and they would no longer receive any NTSC transmission. In some markets these Night Light transmissions were continued for a week or two following June 12, 2009. However, in as much as KGO remained on channel 7 both following the transition to the advanced television system, it seems implausible that they could be involved in the Night Light program.