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Old 28-Jun-2014, 4:04 PM   #17
tripelo
Senior Member
 
Join Date: Jan 2010
Location: Dallas, TX
Posts: 127
Tuner Sensitivity & Multipath

Quote:
Originally Posted by rabbit73 View Post
The problem is, the tuners in TVs and boxes can vary a lot in sensitivity, and ability to handle multipath problems
If using a preamplifier, the sensitivity of the tuner is not very critical. Sensitivity is mainly determined by the noise figure of the tuner. In most cases when using a typical preamp, the noise figure of the system approaches the noise figure of the preamplifier alone. Thus, the preamplifier is the main determinant of sensitivity.

One could take a poor sensitivity tuner and add a good preamplifier and probably exceed the sensitivity of the best available tuner alone.

Multipath is a serious concern, and not all tuners handle multipath equally. Better noise figure and S/N ratios can help multipath reception but only in a very incremental way.

The multipath capabilities of a tuner are determined by the demodulator chip (usually a system on a chip). In the 2009 generation of set top boxes there was appreciable variation in capability to handle multipath.

Presumably, the very latest generation demodulators have improved multipath capability. There is some evidence that suggests LG’s recent generation LGDT-3305 is improved with respect to multipath mitigation.

A way to compare receivers for multipath reception is to use a configuration similar to rabbit73’s, except to test:

- With a good preamp in line.
(To minimize effects of differing noise figures in the units under test)
- Against channels with known multipath problems.

As you know, there are several other factors that are important for a good tuner:

- Resistance to overload
- Selectivity
(ability to reject signals that are not specifically related to channel-of-interest)
- Others

Most critical factors were fairly standardized (probably due to NTIA set top box requirements). Noise figure and multipath capability are usually critical for fringe reception, with noise figure essentially controlled via the choice of preamplifier.

Quote:
Originally Posted by Stereocraig View Post

Why should I shell out dough, to compare a TV's performance?
You do have a point. But, having so far not seen much evidence of such tests:

It appears that manufacturers' do not have interest in publishing such helpful data. It also seems unlikely the current situation with technical specifications will improve.

With ATSC 3.0 well on the way, and almost certain to displace current ATSC (8VSB) with some form of OFDM, one might guess that R&D in the current ATSC will soon dry up.

If one wants the data/info, then someone has to pay the price and do the work.

.

Last edited by tripelo; 28-Jun-2014 at 9:57 PM. Reason: Remove: 'best' In: 'way to compare'
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