There are two VERY different issues being addressed here.
First, you should define what a "Bright House" cable is so that we
understand YOUR question. Is it coax, or is it some other kind of cable?
What is the spectrum and power level?
Second, let's look at Dick's comment re: trash from DTV stations in
Portland. I don't have experience with DIGITAL TV stations and spurs,
but I DO have experience with spurs and trash from analog TV (and two-
way systems) in downtown Chicago. There, ALL TV and FM transmitters are
on either Sears or Hancock, two very tall buildings within about 1.5
miles of each other. Some transmitters are multiplexed into a common
broadband stick (mostly FM), but most have their own dedicated antenna.
In addition, there are lots of 2-way rigs, although I'd heard that the
number of 2-way rigs there has fallen over the years.
When I was actively involved in ham repeaters (about 25 years ago), the
VHF trash was so bad that a VHF receiver probably saw a noise floor on
the order of millivolts. Both the broadcast antennas and 2-way antennas
use 1-2 bay antennas for low-band TV (Ch2-6) and FM, and 3-4 bays for
high band (Ch7-13). This makes them relatively omni in the vertical
plane, as compared to UHF antennas, which typically have 12-16 dB of
vertical gain. That difference puts more signal in the downtown area
under these VHF antennas.
Power levels for TV broadcasting depend on where you live. In the
eastern half of the country and in major metro areas in the west,
licensed transmitter powers are typically 3-10 dB lower than in the wide
open areas of the west. There are also some factors related to antenna
height. The biggest high band VHF antennas in Chicago typically are
getting 100-316 kW ERP (that ERP includes feedline and combiner losses
and antenna gain). Low band Vs in Chicago are down around 50 kW.
You can see details for transmitter powers and antennas anywhere in the
US by visiting this FCC site
http://www.fcc.gov/mb/audio/
and asking for a TV or FM Query, plugging in your Lat/Lon coordinates
and a radius that you'd like to consider.
Up to now, the vast majority of broadcasters have run their digital rigs
at significantly lower power levels than their licenses permit. Two
reasons. First, the electic bill. Second, many digital licenses are on
channels adjacent to the analog channel, 99% of viewers are watching
analog, and the ratings surveys weren't counting digital viewers.
Running the digital channel QRP minimizes interference to the analog
channel, which is where the revenue is.
As to that 20 dB increase in Portland -- I'd first ask how they measured
it? Were there a couple of good cavities and/or band pass filter in
front of the measurement device so that it's front end wasn't getting
blown away by the fundamentals of these transmitters?
I'd also ask about the linearity of the transmitters (and how they're
being driven/tuned). A house I rented in Chicago for 20 years was 3
miles from Hancock, and I had a nice FM/TV yagi on the roof that put
lots of signal into my Technics ST9030 FM RX (very bulletproof analog
tuned front end). In all the time I lived there, I heard an FM spur only
once, and it disappeared within an hour or two.
BTW -- 20 dB is 100 times the power.
73,
Jim Brown K9YC
On Sat, 19 Apr 2008 17:35:53 -0400, kd4e wrote:
>Since they just ran a Bright House cable next door in our
>*very* rural neighbohood (10 acre lots) to a pole that is
>about 120 feet from the house should we anticipate a rise
>in RFI?
>If I we to allow them to run the cable to our house would
>that increase RFI?
>> First a comment.. This subject DOES impact ham radio, for in a larger
>> city with multiple Digital TV stations, which are normally "megawatt"
>> stations, the noise floor for VHF repeater inputs rises accordingly,
>> for digital pulses are full of spectrum noise!
>>
>> In Portland, Oregon with channels 2, 6, 8, 10, and 12, and not all
>> converted yet, it rose 20db! This translates out to a factor of some
>> 120 times the origional noise!!
>>
>> Dick, CET (I'm licensed TV tech!!)
>--
>Thanks! & 73, doc, KD4E
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