single magnetically deflected beam, so there is no requirement to generate the scanning signal. Equalizing pulses The absence of equalizing pulses to facilitate interlace was defended at the start of the BBC service on the grounds that it only caused a lack of interlace with field synchronizing separators of the integrator type, and that there were, even at that time, numerous other circuits which gave completely accurate interlace without equalizing pulses. The question was raised again from time to time, but a series of tests, conducted during 1952 in cooperation with the British Radio Equipment Manufacturers' Association, confirmed that there was no general need for equalizing pulses. Spot wobble On some larger TV screen sizes, the scanned lines were not fat enough to give 100% coverage of the CRT. The result was a lined picture with darkness between each horizontal scanned line, reducing picture brightness and contrast. Larger screen sets often used a spot wobble oscillator, that slightly elongated the scanning spot vertically at high frequency to avoid this line separation effect without reducing horizontal sharpness. Spot wobble was also utilised when making telerecordings of 405-line programmes. Experimental colour transmissions During the late 1950s and early-to-mid 1960s, some experimental colour broadcasts were made in the UK with the 405-line system using NTSC colour encoding (this encoding was a 1953 enhancement of the original 1941 NTSC monochrome standard, added to the NTSC standard so that it could also provide for colour broadcasting). The subcarrier frequency was 2.6578125 MHz (525/2 times line frequency) with an "I" signal bandwidth of 500 kHz and a "Q" signal bandwidth of 300 kHz. Tests with PAL, SECAM and other NTSC subcarrier frequencies were also attempted. Some of these broadcasts were on UHF (also an experimental technology at the time), while others were carried over the regular VHF network outside of normal broadcasting hours. United States 405-line field-sequential color system After the U.S. adopted the NTSC 525-line monochrome standard for commercial broadcasting in 1941, subsequent efforts were made to upgrade the standard so that it could also accommodate a "compatible" colour broadcasting system. Eventually these efforts would prove successful, but because repeated attempts had consistently produced unsatisfactory results, in 1950 the United States Federal Communications Commission (FCC) officially approved for commercial broadcast an alternate 405-line broadcasting system which the Columbia Broadcasting System (CBS) had developed over the past decade. This system was a field-sequential colour system which