UHF is more robust than VHF (was Re: Digital TV receptionproblem)
Sat Jun 20 22:07:09 EDT 2009
My experience is that, even though the "signal-strength meters"
indicate that the Channel 7 DTV dignals are substantially weaker than
the Channel 42 signals (displayed strength of ~68 for Channel 7 vs ~94
for Channel 42), the VHF signals are less variable in intensity and
hence less subject to pixellation and audio dropouts. For users of
indoor antennas (like me) the downside is that the large VHF rabbit
ears are more intrusive than the UHF loops. I read that WHDH has
applied to double its ERP on Channel 7 (presumably by diplexing its
main and about-to-be-installed auxiliary VHF DTV transmitters).
Assuming that change is granted, it may be the best approach. I had
said to a friend that the diplexed transmitters, the transmission
line, and the VHF antenna should easily be up to the task, since WHDH
analog transmitted at about 300 kW ERP whereas if WHDH digital doubles
its power on Channel 7, its ERP will be about 60 kW. My friend's
reply: "Then you haven't heard that analog power was peak and digital
is average, so it doesn't necessarily follow at all that 60 kW digital
is less than 300 kW analog." Does anybody have a conversion formula?
Dan Strassberg (email@example.com)
----- Original Message -----
From: "Peter Q. George" <firstname.lastname@example.org>
To: "Boston-Radio List" <boston-radio-interest@lists.BostonRadio.org>;
"Rick Levy" <email@example.com>
Sent: Saturday, June 20, 2009 6:53 PM
Subject: IMHO: UHF is more robust than VHF (was Re: Digital TV
Personally, I think WHDH-TV would be better off on UHF Channel 42 than
on VHF Channel 7. For DTV signals (in this area), UHF propagates
better than both VHF-lo and VHF-hi. I was also told, by another
engineer, that during the analog days of color TV, UHF provided a much
robust signal for color transmission than VHF could ever do. He
compared the color of the old WGBH-TV (Channel 2) and WGBX-TV (Channel
44). He found he prefered the color on 44 better than 2. So, I'm
wondering if the reason for UHF's better quality color analog pictures
is the same reason why UHF is a better fit for DTV than VHF could ever
be. I would not be surprised if WHDH-TV just might turn off Channel
7's DTV signal and stay with 42. It will still "map" to 7-1 and 7-2.
It's a no brainer.
Peter Q. George (K1XRB)
"Scanning the bands since 1967"
--- On Sat, 6/20/09, Rick Levy <firstname.lastname@example.org> wrote:
> From: Rick Levy <email@example.com>
> Subject: Digital TV reception problem
> To: "Boston-Radio List"
> Date: Saturday, June 20, 2009, 5:46 PM
> Quoth Maureen Carney,
> I now have another strange issue - the box picks up WHDH on
> both 7 and 42
> and shows it twice (using virtual mapping to 7.1 & 7.2
> for channel 42). So
> if I am sequentially going through the channels it will go
> 6.1, 7.1, 7.2,
> 7.1, 7.2, 10.1 and on. Anyone else picking up
> It's not your equipment. WHDH-DT is currently
> simulcasting on channels 7
> and 42. After filing an urgent application last
> Monday to revert
> temporarily to 42 (in addition to operating on 7), they
> received permission
> on Tuesday to do so, and switched 42 back on again.
> You are evidently not
> among the viewers unable to receive 7 despite
> rescanning. The station
> reportedly had *lots* of calls over the weekend, prompting
> the FCC
> Rick Levy
> Broadcast Signal Lab, LLP
> Cambridge, Mass.
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