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Jeff Liebermann Jeff Liebermann is offline
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Default OTA tuner sensitivity

On Sat, 31 Dec 2011 15:42:18 -0800 (PST), klem kedidelhopper
wrote:

What frustrates me is that except for the OSD "bar graph" signal
indicators
on most digital sets today, I really can't tell what the actual signal
strength of a particular station is anymore.


Some TV's and converters have diagnostic displays that shows some
details. When you disclose exact model numbers of the receivers and
converters that you're testing, it might be possible to find the
diagnostic page.

It used to be so easy. I
would
connect up my old Sadelco analog meter to a cable or antenna coax and
simply read the carrier level. Now that we have two different types of
TV
broadcasting systems to deal with all my equipment is obsolete.


Baloney. My antique Sadelco 719B meter (the one with FOUR 9v
batteries), still works. It indicates the signal strength of the OTA
digital stuff just fine. It won't demodulate the audio, but the
signal strength is still usable. What model Sadelco are you using?

1. Has anyone noted consistent instances where one tuner is noticeably
"hotter" than the other? That is to say one set that will perform with
a
weak signal where the next being fed the same signal might break up?
This
slight difference in the front ends, which might never be detected on
cable
could affect antenna users in fringe areas like myself. In fact I
don't
know if I ever would have noticed this if I hadn't been running two
different sets in the shop at the same time).


Nope. That's because, like you, I'm using a tower mounted amplifier.
With such an arrangement, the RX sensitivity is almost totally
determined by the amplifier noise figure. You could compare a high
quality receiver with a piece of junk, and they would be about the
same sensitivity. Now, there are some things that will make a
receiver worse, such as digital noise in the receiver front end,
overload by adjacent channel stations, ability to deal with
reflections, etc. Hard to tell from here.

2. If it's economically feasible I would like to be able to read
signal
level directly on a test instrument. This would be useful on antenna
jobs
as well as cable distribution systems. Is there such an affordable
instrument available for this purpose? Thanks, Lenny


I wouldn't mind one of those myself. I used to own one of those
government subsidized converter boxes (Zenith DTT901), that had an on
screen diagnostic page. All CECB certified converters are required to
have an on screen signal strength meter. However, there's a catch.
Most converters do not show signal strength. They show "signal
quality" which is usually calculated from the BER (bit error rate) of
the decoded DTV signal. This is somewhat related to signal strength,
but can easily be trashed by adjacent channel junk, internal digital
noise, reflections, etc.

Another possibility would be to purchase a laptop or PC based ATSC
tuner, and use that as the receiver. With luck and diligence, you
might be able to find some kind of open source diagnostic program that
can be used as a tester. At a minimum, something that dumps PSIP data
from the station.

There's plenty of test equipment available:
www.ebay.com/sch/i.html?_nkw=digital+tv+signal+finder+-satellite
but most of them look rather lame.

Better:
http://www.horizonhge.com (in UK)


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Jeff Liebermann
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