[opendtv] Re: VHF vs UHF coverage
- From: Richard Hollandsworth <holl_ands@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 22 May 2009 09:03:11 -0700 (PDT)
If you look at enough coverage maps in FCC database, you'll soon see that the
allocated DTV power
is 12 dB lower than the allocated NTSC power in order to match current coverage
on the same freq.
NTSC power has always been measured and specified as PEAK power, whereas DTV
power
is always measured and specified as AVERAGE power. Peak power for DTV is about
7 dB higher
than average power. DTV also has a performance advantage of about 5 dB for a
total of 12 dB.
When comparing VHF to UHF, it does not appear you included the lower gain of
most "typical" VHF
antennas, compared to a more compact "typical" UHF antenna.
At the outer fringes, many (most?) users will use a Preamp, which will
"typically" reduce the overall
System Noise Figure by about 10 dB. However, in the Hi-VHF band and especially
the Lo-VHF
band, the Man Made Noise levels will far exceed the Thermal Noise level found
in UHF band.
Hence it benefits UHF band much more than VHF:
http://www.tvantenna.tv/papers/PFactorsV.pdf
http://www.tvantenna.tv/papers/dtv%20coverage%20and%20service%20prediction.pdf
http://www.mstv.org/docs/techinfo.pdf
http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-05-199A3.pdf
A fair comparison should also include the effect of Land Use Clutter Loss,
which is an ADDITIONAL
loss in UHF band (only) over that calculated by the ILLR (Individual Location
Longley-Rice) program:
http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet72/oet72.pdf
http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet69/oet69.pdf
http://www.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet72/oet72.pdf
And finally there is the issue of how does one fairly compare NTSC to DTV
reception
"quality", as discussed above wrt Location/Situation/Time percentages
between glitches in DTV signal vs a very ill defined NTSC "goodness".
holl_ands
===================================================
--- On Thu, 5/21/09, Dale Kelly <dalekelly@xxxxxxxxxxx> wrote:
From: Dale Kelly <dalekelly@xxxxxxxxxxx>
Subject: [opendtv] Re: VHF vs UHF coverage
To: opendtv@xxxxxxxxxxxxx
Date: Thursday, May 21, 2009, 10:50 AM
Bert wrote:
>So if the FCC said 5 MW, sounds close enough to me.<
Yup, close enough technically.
However, the huge 5 MW UHF transmission facilities (~450 kw ave.) could not
be constructed and operated with any economic viability. Even a 1 MW
facility is a back breaker for most small and medium market VHF operations.
>A mitigating factor is, however, that analog low VHF was so hammered
with EM noise that long range reception was (in my experience) severely
limited anyway. In recent years.<
This is indeed the case in some areas, particularly on the lowest LB
channels, but it is a very regional condition. Many (likely even a
significant majority) of areas are not severely limited by such problems.
Anyway, a very good analysis!
Dale
-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx
[mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Manfredi, Albert E
Sent: Tuesday, May 19, 2009 1:24 PM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: VHF vs UHF coverage
Dale Kelly wrote:
> However, my concern in this post was an assigned UHF DTV
> channels ability to replicate the stations analog coverage.
> It is necessary, in this instance, to also compare UHF verses
> low band VHF propagation. Low band VHF's generally more robust
> signal and it's ability to provide some amount of over the
> horizon coverage, can't be replicated by UHF signals.
Right, you are coming at it from the opposite side as me. I'll give it a
shot, though, using the same techniques as before.
I'll use 67 MHz for low VHF, and 615 MHz for UHF. I'll use 100 Km range,
a 300 meter transmit antenna and a 10 meter receive antenna height.
RF path attenuation, again using the Hata model adjusted for long range,
is 140.4 dB for low VHF and 156.5 dB for UHF, or 16.1 dB advantage to
low VHF.
The low VHF analog power limit is (I think) 100 KW ERP. Using your 6 dB
difference for digital coverage parity, low VHF digital output power
would have to be just over 25 KW, to match the analog station's reach.
Increasing 25 KW by 16.1 dB results in 1.02 MW required for UHF. Not
half bad, so far. That's doable within the digital power limits.
But now try lowering the receive antenna to 2 meters and decreasing
range to 80 Km, to get something reasonable as limit of indoor
reception.
Path attenuation is now 145.6 dB for low VHF and 170.1 dB for UHF, so
that you would need 7.1 MW ERP for the UHF transmitter to equal the
coverage of the low VHF transmitter.
So if the FCC said 5 MW, sounds close enough to me.
A mitigating factor is, however, that analog low VHF was so hammered
with EM noise that long range reception was (in my experience) severely
limited anyway. In recent years.
Bert
Other related posts: