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NTSC-to-PAL Converter Use this converter to watch NTSC programs in full colour on a PAL-standard TV set or video monitor. It is easy to put together because it is based on an assembled PC board and a standard video modulator module. By JOHN CLARKE These days there are quite a few video program sources which produce an American NTSC signal instead of the PAL standard signal used in Australia, New Zealand and much of Europe. These sources range from video disc players, NTSC VCRs and 18  Silicon Chip cam–corders and last, and perhaps most important, signals from some satellite TV channels. If you have tried it, you will probably realise that many PAL standard TVs and video monitors will actually work with an NTSC signal but it will always be in black and white instead of colour and the picture will probably not be the full screen height. This is not the most satisfying way to view a video program so the availability of this NTSC-to-PAL Converter pro­ject at a reasonable price is good news. Of course, some upmarket TVs can accept and display NTSC signals in colour but they are in the minority and some are quite costly. The unit described here is designed to be used for view­ing purposes only. It cannot be used for recording from NTSC to the PAL format. The unit is built into a small plastic case with audio and video input and output RCA sockets on the rear panel. Fig.1: this scope shot depicts a colour bar video signal. The top trace is an NTSC signal showing the negative going line sync pulse, the short colour burst and then stair-cased chroma and brightness video information. The second trace is the bypass output from the NTSCto-PAL Converter, while the lower trace shows the video signal after conversion to PAL. Fig.2: this shot shows the NTSC colour burst signals on the top trace and the PAL colour burst signals on the lower trace. The precise NTSC colour burst frequency is 3.579545MHz, while the PAL colour burst frequency is 4.433619MHz. These oscilloscope traces show that the NTSC-to-PAL converter does change the colour burst frequency. Features • • • • Fig.3: this shows what happens with the NTSC-to-PAL Converter when it is given a frame rate of 60Hz. It can be seen that the conversion process does not change the frame frequency The output is also avail­able as an RF modulated signal at VHF channel 0 or 1. Front panel controls are the power on/off switch and the NTSC-PAL/ Bypass switch. Inside there is little to the circuit since the conver­sion is all done on a small pre-built module. We have added a modulator and power supply to complete the converter. Before we go too much further, we should briefly explain what the terms “NTSC” and “PAL” actually mean. Contrary to what some smart alecks like to say, NTSC does not stand for “never twice the same colour”. Rather, it stands for National Television Sys- Uses a pre-built NTSC-PAL converter module Video or RF modulated output Bypass or NTSC-PAL conversion option Allows viewing of NTSC programs in colour on a PAL TV Warning! This NTSC-to-PAL converter does not alter the 60Hz frame rate to 50Hz. This means that some TV sets or monitors will not lock onto this frequency and will continuously roll. To test whether your PAL TV or monitor can be used with the NTSC-to-PAL converter, simply test it on an NTSC signal. It should produce a stable picture in black and white. tem Committee of the USA. This was the body that set the American colour TV standard in the first place. The “never twice” epithet alludes to the fact that the NTSC system has problems maintaining the correct colour due to drift in the circuitry. PAL stands for “phase alternate line” and refers to the changing phase of the colour burst signal on each alternate line of the picture. PAL is a German (Telefunken) development. How does it work? The NTSC and PAL video formats are similar in a number of re­spects. The NTSC horizontal line frequency is 15.750kHz while PAL operates at 15.625kHz. The sync levels and widths are also similar and a colour burst signal occurs after each line sync. By the way, the easy way to remember these line frequencies is to take the product of the number of picture lines, multiply by the field (or frame) rate and then divide by two. For NTSC, we multiply 525 lines by 60 Hz and divide by two to obtain 15.750kHz. Similarly, for PAL, we multiply 625 lines by 50Hz and divide by two to obtain 15.625kHz. It is because the line frequencies for May 1997  19 PARTS LIST 1 NTSC-PAL Converter (available from Av-Comm Pty Ltd) 1 PC board, code 02303971, 102 x 117mm 2 adhesive labels 132 x 28mm 1 plastic case, 140 x 110 x 35mm (Jaycar Cat. HB-5970) 1 ASTEC UM1285AUS 0/1 video modulator (DSE Cat. K-6043) 1 12VAC 500mA plugpack 1 TO-220 heatsink, 30 x 25 x 13mm 1 SPDT toggle switch (S1) 1 1kΩ horizontal trimpot (VR1) 3 panel-mount RCA sockets 1 DC panel socket 1 8mm ID grommet to insulate DC socket 1 400mm length of hook-up wire 1 3mm dia. x 6mm screw and nut 1 3mm dia. x 9mm screw and ut 1 3mm x 3mm spacer (TO220 insulating bush) 4 self-tappers to mount PC board 6 PC stakes Semiconductors 1 7805 5V regulator (REG1) 4 1N4004 1A diodes (D1-D4) 1 12V 400mW zener diode (ZD1) 1 3mm LED (LED1) Capacitors 1 1000µF 16VW PC electrolytic 2 470µF 16VW PC electrolytic 1 47µF 16VW PC electrolytic 3 10µF 16VW PC electrolytic Resistors (0.25W, 1%) 1 1kΩ 1 180Ω 1 560Ω 1 100Ω Where To Buy The Parts The major parts for this design are available as follows: (1) NTSC-PAL converter module plus main PC board: Av-Comm Pty Ltd, PO Box 225, Balgowlah, NSW 2093. Phone (02) 9949 7417; Fax (02) 9949 7095. Price: $89 plus $5 p&p. Cat. K1300. (2) Astec UM1285AUS 0/1 video modulator: Dick Smith Electronics. Cat. K-6043. (3) Complete kit: Jaycar Electronics. Price: $149.50 plus $8 p&p. Cat. KC-5223. 20  Silicon Chip Fig.4: the circuit consists of the NTSC-to-PAL converter board, a standard video modulator and a power supply (D1-D4 and REG1). The NTSC video input signal is applied to the converter board and it delivers a converted PAL output. This output can be taken direct and is also used to drive the modulator. both formats are so similar that many PAL TVs and video monitors will display an NTSC picture. However, some older sets may not be able to lock onto the higher frame rate of NTSC (60Hz) and so will display a rolling picture. If your set is among these, you can’t use this NTSC-to-PAL Converter. Fig.1 shows a colour bar video signal. The top trace is an NTSC signal showing the negative going line sync pulse, the short colour burst and then stair-cased chroma and brightness video information. The second trace is the bypass output from the NTSC-PAL Converter, while the lower trace shows the video signal after conversion to PAL. This demonstrates the different colour bursts of the NTSC and PAL formats. The phase of the PAL colour burst changes by 180° on every alternate line and this reversal cancels out drift in the circuits to maintain accurate colour locking. This is where the PAL signal derives its name: Phase Alternate Line. Fig.2 shows the NTSC colour burst signals on the top trace and the PAL colour burst signals on the lower trace. The precise NTSC colour burst frequency is 3.579545MHz and the PAL burst is 4.433619MHz. These oscilloscope traces show that the NTSC-to-PAL converter does change the colour burst frequency. Fig.3 shows what happens with the NTSC-to-PAL Converter when it is given a frame rate of 60Hz. It can be seen that the conversion process does not change the frame frequency. To sum up, the converter changes the colour burst signal but it does not change the number of picture lines or the frame rate. Circuit details The circuit for the NTSC-PAL Converter is shown in Fig.4 and it is about as simple as you get, bearing in mind the complex function it performs. It comprises the NTSC-PAL board, a video modulator and a power supply. The NTSC-PAL board comprises a number of inscrutable proprietary chips. It is an irregularly shaped board 73mm along its longest dimension and 46mm wide. The input, output and power connections to the board are made via a 5-pin header. The video input is coupled to the NTSC-PAL converter board via a 470µF capacitor. Similarly, the output signal is also coupled via a 470µF capacitor. Trimpot VR1 attenuates the video output before applying it to the video modulator via a 47µF coupling capacitor. The modulator input in- Fig.5: install the parts, including the NTSC-PAL board, on the main PC board as shown here. cludes a clamping circuit which sets the video level at around 2V. The 1kΩ resistor provides a discharge path for the 47µF capacitor. The video modulator produces an RF output on VHF channel 0 or channel 1. This option is selected by linking the channel input to ground for channel 0 or leaving it open circuit for channel 1. Power for the circuit is derived from a 12VAC 500mA plug­pack. Diodes D1D4 rectify the voltage and a 1000µF capacitor filters it to produce about 20V DC. Zener diode ZD1 provides RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ No. 1 1 1 1 Value 1kΩ 560Ω 180Ω 100Ω 4-Band Code (1%) brown black red brown green blue brown brown brown grey brown brown brown black brown brown 5-Band Code (1%) brown black black brown brown green blue black black brown brown grey black black brown brown black black black brown May 1997  21 Fig.6: this is the full-size etching pattern for the PC board. a regulated +12V supply to the video modulator via a 180Ω resistor. This limits the current to the 6.2V zener diode inside the modulator can. A 7805 3-terminal regulator (REG1) provides +5V to the NTSC-to-PAL Converter and drives the power indicator LED via a 560Ω resistor. and breaks in the copper pattern. You may need to drill out two holes; one for a 3mm screw to mount the NTSCPAL module and one for mounting REG1. Also check the hole sizes for the modulator earth mounting lugs and the four corner mount­ing holes for the PC board. Fig.5 shows the wiring details. Install the resistors first, followed by the diodes. Note that there are two types used: the 1N4004s which have a black body and the smaller zener diode, ZD1. Next mount the four PC stakes, followed by REG1. This mounts horizontally on a small U-shaped heatsink and is secured using a 3mm screw and Construction As already mentioned, the NTSC-toPAL Converter is based on a pre-assembled module. We mounted it on a PC board coded 02303971 (102 x 117mm). It is housed in a plastic case measuring 140 x 110 x 35mm. Begin construction by checking the PC board for shorts between tracks nut. Bend its leads so that they fit into the holes provided on the board. The capacitors can be inserted next, taking care to orient them with the correct polarity. LED1 is mounted with sufficient lead length to enable it to be bent over and inserted into the front panel hole. The video modulator can be mounted next. Solder the earth tags to the PC board and insert the four wires into the holes provided. You will have to decide whether you want the modulator to provide an RF signal on channel 0 or channel 1. The NTSC-PAL module is mounted with its 5-way pin header inserted into the main PC board. It is supported on a spacer using 3mm screws and nuts into the one mounting hole. Now fit the adhesive labels onto the front and rear panels and drill out the holes for the RCA sockets, DC socket and RF out socket on the rear panel. On the front panel, drill and file out the holes for the power switch, LED and Convert/Bypass slider. Attach the DC socket, RCA sockets and switch onto the panels and then complete the wiring, with the panels and board secured in place on the baseplate of the case. Note that if a metal panel label is used, the DC socket must be insulated from it with a rubber grommet otherwise the labelling will short one side of the AC power supply to ground via the RCA sockets. Testing The unit can now be tested. Apply power and check that there is 12V across zener diode ZD1 and that +5V is present at the output of 3-terminal regulator REG1. If these checks are OK, you can connect the converter to a standard PAL Fig.7: you can use these full-size artworks as drilling templates for the front and rear panels of the case. The larger holes are made by first drilling the hole with a small pilot drill and then carefully reaming them to size. NTSC TO PAL CONVERTER + + CONVERT BYPASS POWER + + VIDEO IN VIDEO OUT 22  Silicon Chip + AUDIO IN + + RF OUT 12VAC IN The PC board fits neatly inside a low-profile instrument case measuring 140 x 110 x 35mm. Note the small U-shaped heatsink fitted to regulator REG1 (top photo). Power comes from a 12V AC 500mA plugpack. audio/video source such as that from a VCR. This done, slide the Convert/ Bypass switch to Bypass, connect the RF output to the TV antenna input, and tune the TV set to channel 0 or 1 (if the RF output is used). VR1 is set to give the cor­rect contrast range and to prevent overmodulation. You are now ready to test its operation on an NTSC signal source. Switch the front panel slide switch to the “Convert” setting. The Hue and saturation trimpots on the NTSC-to-PAL module may then need adjusting for best colour and contrast. You may also need to adjust the height on the TV set so that there are no black strips at the top and bottom of the picture. Bear in mind, however, that when you switch back to a PAL signal (Bypass mode), you will need to readjust the height control to avoid SC vertical overscan. May 1997  23