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Improving noise figure

An amplifier can improve the noise figure of the receiver, provided it has a lower noise figure than the receiver itself. The 1993 vintage Sony SLV-E7 VCR has poorer noise figure than I would expect of later equipment.  This was the original purpose of a booster. It still applies to some classes of equipment - a TV card working inside a PC for instance may be noisy not by design but by the environment it has to run in. 

In the days of valve (tube) UHF tuners which had a dreadful noise performance this could be very worthwhile. However, for more recent kit the improvement is only really available where the signal is so far below spec that even after the booster the picture still borders on the unwatchable.

This is an extreme case, of trying to work at a signal level of 14dBuV, 46dB below the PAL minimum level. Two boosters, providing a combined gain of 44dB, lifts the signal to nearly the correct level. Although less bad than without boosters, the picture is not really of a watchable quality.

launch level
(dBuV)
attenuation Picture Picture (100%, closeup) amps Rx input level
(dBuV)
59 20+6+12+6 0 14
59 20+6+12+6 22+22 59

 

Picture quality with decreasing signal levels 

real aerial measurement of DTT performance with decreasing signal levels + adding booster

experiment demonstrating boosters don't compensate for aerial deficiencies

 

Selecting and siting your TV aerial

Aerial system components

Why DTT is different from an analogue install

 

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  1. DTG R-Book 5, available on http://www.dtg.org.uk/publications/books/r_book5.pdf  
  2. http://www.maxview.ltd.uk/trd_inampsta.htm (July 2005)
  3. noise floor is sqrt(4kTBR) where k is Boltzmann's const (1.38 x 10-23), T is absolute temp (about 293K indoors), B is the channel noise bandwidth (8MHz for UK UHF TV) and R is the termination of 75 ohms. Then multiply by 1000000 to express in uV, take 20 log10 of this to get 10dBuV and add the 3.5 noise figure.
  4. 60dBuV minimum, 80dBuV maximum into 75 ohms if you want to be pedantic.

M E g A L i T h i A
Text and photographs RM 2005 unless otherwise credited