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Picture quality with decreasing signal level

This shows the variation of analogue signal quality with falling signal level for a 1993 vintage Sony SLV-E7 VCR used as the receiver. The receiver is running without any boosters. Improvements in receiver design mean a typical receiver of the last era of analogue transmission (2005-2010) could be expected to give similar results with an input about 3dB lower.

Analogue showed the variations in quality even in a single still, and would still operate under far poorer signal levels than digital, aking it better for showing the performance changes over such a wide and often out of spec range. Even when analogue terrestrial TV transmission is a distant memory, the principles still hold - it is the level of the aerial signal that determines the quality of the results. You can compare these results with another experiment that used boosters to keep the level going into the receiver at broadly the same level, eliminating the noise performance of the receiver. The comparison shows that boosters cannot compensate for a poor signal level from the aerial. A moderate gain booster would improve the noise figure of this receiver up to modern standards (this was the original purpose of a booster), but that is only really useful in the extreme low-level situations (like the lowest image here, with an input at 14dBuV) where even after the booster the picture borders on the unwatchable.

launch level
attenuation Picture Picture (100%, closeup) amps Rx input level
59 0 0 58
59 20 0 37
59 20+12 0 25
59 20+6+12 0 20
59 20+6+12+6 0 14
Finally, it's important to remember that it is possible to have too much as well as too little signal. Observe the patterning in the sky.
59 0 22+22 104


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

experiment demonstrating boosters don't compensate for aerial deficiencies

Improving noise figure with boosters


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  
  2. (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