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Analogue TV - Quality comparisons

Experimental setup

Signal source was a DVD player (Minato G1 cheap junk from Tesco) feeding composite video into an 1990s vintage Panasonic NV-F55 VCR which was used for its modulator. While under test no signal was fed to the aerial input of the Sony, so the only signal present was the DSB output of the modulator. This was fed into the Device Under Test (D.U.T.) and then fed into the antenna input of a Sony SLV-E7 VCR (1993 vintage) The baseband output of this was fed into my ATI All-In-Wonder TV/Graphics card to do the video capture. 

A VCD 2.0 was prepared with a high-res MPG still

Original image from which VCD source was made (click to enlarge)
original received at 59dBuV

You can compare the original source from which the VCD was made with the signal as received at nominal minimum signal level above. I didn't use the tuner of the ATI All-in-Wonder as this is in the PC and therefore expected to have a poor noise figure due to interference from the PC. The frequency of the modulator was measured, with the vision carrier at 612.31 MHz, which is somewhere between channel 38 (607.25) and 39 (615.25). The Panny used a free-running modulator, so adjusting this closer is not easy, but the Sony is a able to tune between channels so this is not a problem.

launch level
attenuation amps Rx input level
-1 0 0 -2 n02dbmv
-1 20 0 -23 n23dbmv.bmp
-1 20+12 0 -35 n35dbmv.bmp
-1 20+6+12 0 -40 n40dbmv
-1 20+6+12+6 0 -46 n46dbmv
-1 20+12 L -14 n14dbmvpostlabamped.bmp
-1 20 L 1 p01dbmvpostamp.bmp
-1 20+6 L+A +19 p19dbmv-20dtap-6dbpad-labg-antifamp.bmp
-1 20+6+6 L+A +12 p12dbmv-20dtap-6dbpad-6dbpad-labg-antifamp.bmp
-1 20+6+12 L+A +6 p05dbmv-20dtap-6dbpad-12dpad-labg-antifamp.bmp
-1 20+6+12+6 L+A -1 n01dbmv-20dtap-6dbpad-12dpad-6dbpad-labg-antifamp.bmp


Picture quality with decreasing signal levels 

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