[opendtv] Re: CBA and Microprose team up on NTIA DTV Boxes
- From: Richard Hollandsworth <holl_ands@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Thu, 22 May 2008 14:50:56 -0700 (PDT)
Funai argued against mandatory Analog Pass Thru feature, saying
it would degrade sensitivity (only if you designed it wrong!!!),
and indicated that affected users could readily install their
own RF Splitters or A/B Switches (see item 49):
http://www.ntia.doc.gov/ntiahome/frnotices/2007/DTVFinalRule_2e.htm
I don't know what happened wrt argument to RETAIN NTSC in the
existing demodulator chips, although they argued to make MTS/BTSC
Stereo output optional....
Surely it COST MORE to modify chips to DELETE these functions.
BTW: In AvsForum Antenna thread, I've looked at many different
post-Feb2009 situations....MOST of them will have some NTSC stations.
APT would also be useful for second TV's attached to Whole Home
distribution systems, such as UHF TV2 output on DISH HD-DVR.
======================================
If you use an RF Splitter to feed a Converter Box and your old TV
there is a 3.5-4.0+ dB loss of sensitivity.
If you use a A/B Switch, it's under about 0.5 dB.
[BTW: Radio Shack 15-1968 is a R/C A/B Switch.]
The Thomson DTT76850 tuner is used in some Converter Boxes.
A few (too few) came with the OPTIONAL Analog Pass Thru (APT)
feature enabled....which is an RF Splitter and low-gain Preamp:
https://gullfoss2.fcc.gov/prod/oet/forms/blobs/retrieve.cgi?attachment_id=923119&native_or_pdf=pdf
The low-gain Preamp reduces the effect of the conventional tuner
Noise Figure (typ. 8-10 dB) so overall Noise Figure is 8 dB (max).
Given a thermal noise floor of -105.9 dBm (at 100-deg F) and 15.2 dB
required SNR, theoretical ATSC sensitivity would be -90.7 dBm.
With 8 dB NF, this is reduced to -82.7 dBm, barely meeting
CECB sensitivity requirement of -83 dBm. [Not much wiggle room!!!!]
Another approach would be to use PIN Diode switches
to select either CH3/4 CECB output or Antenna input.
However, in order to meet FCC Output to Input isolation requirements,
a low-gain Preamp would still be needed.
Both approach puts a drain on the Energy Star power budget.
Making it hard for APT to work in a CECB with power "OFF".
Most are selected via menu entry when "ON".
holl_ands
======================================
"Hunold, Ken" <KRH@xxxxxxxxx> wrote: Perhaps you might need an analog tuner
after next February, but I'd
venture a guess that the vast majority of other users would have no need
for another NTSC tuner and would benefit from the few extra dB of
sensitivity.
A few of the CECBs have the smart antenna interface. There used to be
some comparison spreadsheets posted, but I can't find them now. The RCA
unit has the interface, and there are others. Unfortunately, there
aren't many smart antennas available. More chicken-and-egg, I guess.
Ken
-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx]
On Behalf Of Craig Birkmaier
Sent: Wednesday, May 21, 2008 9:28 AM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: CBA and Microprose team up on NTIA DTV Boxes
At 9:10 AM -0400 5/21/08, Hunold, Ken wrote:
>I'd rather see a smart antenna interface (which I can't add myself) and
>more smart antennas. I'm using such a setup now, and while I don't
>need all the capabilities of the smart antenna in my
>high-signal-strength location, I did see a difference at home.
I'd rather see an integrated analog tuner, like those in EVERY new HDTV
capable receiver sold in the U.S. today. It was sheer stupidity to
remove (or disable) these tuners from the NTIA DTV box specifications.
By the way, the NTIA specs do allow for a smart antenna interface,
however I have not seen this feature in any NTIA approved box.
Regards
Craig
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