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

[Xmitters@aol.com]

In a message dated 4/20/07 12:50:42 PM Central Daylight Time,
broadcast-request at radiolists.net writes:

<< On Monday 09 April 2007 02:19 am, Xmitters at aol.com wrote:  >
  > I'm wondering about the FCC and theoretically allowed operating conditions
  > during emergency operation of a Harris split-level combined transmitter
system.

   Since you qualify it as "emergency operation" it may fall under the
emergency
   operation rules, though there are none for HD/IBOC.

  > 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?

   Clearly, for non-emergency operation the digital power must be reduced
   to maintain the mask, but, if the operation is declared and justified
   as emergency operation, and there are no rules for what you ask
   specificly, it's a good question !
   Reasonable and prudent men would allow the full power HD level, but the
   Commission is full of lawyers, who are not known to be reasonable,
   nor prudent.
   My suspicion is that there won't be an answer until after there is a test
case.

  > Second question: What would happen at the analog and digital receiver
  > locations with regard to reception, when I lose the 13 kW analog-only
transmitt
  > er and
  > the  analog + HD (4 kW analog 170 Watts HD) transmitter remains on the
air?
  > (we will ignore the losses in the HD/Analog RF combiner for the sake of
  > simplicity)

   Probably nothing !
   Maybe the HD coverage would improve slightly, and the analog obviously
   worsen, but I doubt it.

  --
  Cowboy >>

Cowboy:

Thank you for the reply. I'm thinking that the HD power level allowed while
analog power is reduced due to a failure, that the FCC might look at the
situation based on the licensed power level. So if you're a 50 kW FM, 
HD cannot be
greater than 500 watts never, ever.

I had a slightly comparable situation at a 50 kW AM station where I worked,
before IBOC had been born yet. We had an RCA 5 kW that would not meet the NRSC
mask, based on the 5 kW power level. I don't remember how the conclusion was
made, but it was decided that the 5 kW RCA actually met the NRSC mask if you
compared the measurements to our 50 kW carrier. Ergo, we met NRSC compliance.
Had we been licensed for 5 kW, we would not have met NRSC compliance.

I suspect that the FCC would use similar logic in determining how high the HD
carriers could be under conditions of reduced analog power. As you pointed
out, we will have to wait for a test case :-) I would guess that the potential
for increased interference under this hypothetical would be restricted to
ourselves.


Jeff Glass, BSEE CSRE
Chief Engineer
WNIU WNIJ
Northern Illinois University