[BC] Re: Split level combine and the loss of the analog-only transmitter

[Mark Humphrey]

On 4/9/07, Xmitters at aol.com <Xmitters at aol.com> wrote:
> If I lose my analog-only transmitter and the Analog + HD transmitter
> survives, Is the FCC going to let me run the allowed HD power as dictated by my
> full-power RF mask, or are they going to want me to reduce the HD power to the
> appropriate level consistent with the amount of analog power I'm putting out at
>  the time?

Good question.   I checked the FCC website, it appears that you must
conform with the iBiquity hybrid specifications, as directed in this
document:

http://hraunfoss.fcc.gov/edocs_public/attachmatch/DA-03-831A1.pdf

iBiquity's hybrid mask is referenced to the analog carrier, so my
interpretation is that you must reduce the digital carriers if you
lose the analog-only transmitter.

However, it's interesting to consider that some stations using
separate analog and digital antennas might be several dB out of
tolerance with the mask if signals are measured in the field.

One of the Philadelphia HD stations has been using a master antenna
(wrap-around panel design with a near-omni pattern) for analog and a
slightly-lower side-mounted antenna for digital.  These antennas are
mounted on a 12-foot face tower and I'm on the back side.  When I
measure their mask, the digital sidebands about 10 dB lower than
normal.  I haven't taken field measurements on the opposite side of
the tower yet, but would expect the opposite effect: several dB of
digital "enhancement".

Mark