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Video Enhancer & Y/C Separator • S-video from your VCR • Adaptive digital comb filtering • Edge enhancement by JIM ROWE Are you planning to transfer some of your VHS videotapes over to DVD, via your computer? If so, you need this project. It’s not only an edge enhancer to sharpen up the picture but also a Y/C separator, which converts the composite video from your VCR into S-video so you get a higher quality transfer. T HE VIDEO SIGNALS from an analog VCR are not only in composite video form but are also fairly limited in luminance (Y) bandwidth, due to the limitations of VHS recording. In fact, the luminance bandwidth is typically no more than about 3MHz, which corresponds to a horizontal resolution of about 240 lines. This is only about half the luminance bandwidth and resolution capability of DVD video discs. These can usually provide a luminance bandwidth of about 6.4MHz, or just on 500 lines of resolution. As a result, when you’re transferring video from a VCR onto DVD via your 30  Silicon Chip PC, you may get better results by applying some judicious video enhancement or “sharpening”. It’s true that this also tends to degrade the video signal-to-noise ratio but most people feel that the overall picture quality is improved – provided that the sharpening isn’t overdone. In practice, your eyes can best judge how much enhancement is worthwhile and how much is “too much”. Sharpening techniques There are two broad ways of providing this type of video enhancement. The most commonly used method is to apply “high peaking” to the video, so that the higher video frequen- cies are boosted and the effective horizontal resolution improved. This method certainly works but it also tends to produce visible “ringing”, or multiple trailing edges after vertical transitions. The other way of providing enhancement is to detect the vertical transitions in the video signal, then differentiate and amplify just these transitions to provide what is effectively an edge enhancement or “sharpening” signal. A selected amount of this sharpening signal is then added back into the video signal, to “steepen” the original transitions (ie, decrease the risetimes). This method is a little harder to do but it does give better results. That’s why we’re using it in this new Video Enhancer project. Note that regardless of which technique is used, the enhancement processing should only be done on the luminance (Y) component of the video signal. That’s because this is the video component that conveys the picture contrast and detail information. There isn’t much point in trying to sharpen the chrominance (C) components and siliconchip.com.au Fig.1: block diagram of the Philips TDA9181 Integrated Multi-standard Comb Filter. It contains all the circuitry necessary for Y/C separation. in any case, this tends to produce various kinds of annoying colour distortion. In short, the chrominance components are best left alone. Y/C separation Most traditional video enhancers use fairly simple analog filtering to separate the Y and C components before they enhance the luminance. However, this type of filtering is very much a compromise, as it results in some distortion of the chrominance. It also actually reduces the effective luminance bandwidth, which cancels out much of the potential benefit of any enhancement. Because of this problem, we decided to use a better method of Y/C separation in this design: adaptive digital comb filtering. This provides greatly improved separation of the luminance and chrominance information, without distorting the chrominance or artificially reducing the luminance bandwidth. In short, it provides better results all round! But that’s not all. Comb filter Y/C separation has another important benefit: it allows the Enhancer to act as a composite video to S-video converter. By feeding the Enhancer’s output signals to your PC’s MPEG encoder in S-video form, you get a better quality signal transfer than takes place with composite video. So that’s the rationale behind our new Video Enhancer & Y/C Separator. It uses edge enhancement rather than simple high peaking, it has imsiliconchip.com.au proved Y/C separation using digital comb filtering, and it also functions as a composite video to S-video converter for better transfer quality into an MPEG encoder. It also features a composite video output, for use with an encoder which doesn’t have an S-video input. The comb filter IC Perhaps the most interesting part of our new Video Enhancer is the adaptive digital comb filtering, used to separate the Y and C components of the incoming video. This processing is all performed inside a single highperformance IC – the Philips TDA9181. This device is described by Philips as an “Integrated Multi-standard Comb Filter”. As well as operating on PAL signals, it can alternatively be configured to separate NTSC signals. Fig.1 shows what’s inside this rather impressive IC. At first glance, it looks a bit complicated because, as well as the comb filtering circuitry, the TDA9181 also contains input and output signal selection switching. It’s shown here with the internal switches in their correct positions for Y/C separation. The incoming composite video enters the TDA9181 at pin 12 via a capacitor. It’s then passed through a clamp circuit, to set the DC level of its sync pulse tips, and then fed to a low-pass filter. This filter removes any frequencies which are high enough to cause aliasing when the video is sampled for the comb filtering. This sampling is performed at four times the colour subcarrier frequency (Fsc) – ie, 4 x 4.433MHz or 17.732MHz. As a result, the low-pass filter’s cutoff frequency is still quite high at about 7MHz, which is well above any likely luminance components (especially in VCR video signals). After low-pass filtering and 4Fsc sampling, the video signals pass through two delay lines connected in series. These each provide a time delay of two line periods (2H or 128µs), so there are three video output streams from the delay line section: (1) the original undelayed video signal; (2) a 128µs (2H) delayed version; and (3) a 256µs (4H) delayed version. All three video streams are then fed into the adaptive comb filter, which analyses them and adds/subtracts them in a dynamic “adaptive” way to “comb apart” (or separate) the Y and C information. The fine details of comb filtering are a bit too complex to explain here but you’ll find more information in the TDA9181 data sheet (just Google in your browser) if you want it. After separation, the Y and C signals are each passed through low-pass “reconstruction” filters, to remove any sampling artefacts. They then emerge from pins 14 and 16 respectively, when the internal switching is set as shown. In order to perform this impressive job of Y/C separation, the TDA9181 needs to be fed with two reference signals. The first is a “sandcastle” (SC) pulse signal, which is fed in via pin 7 and used mainly to gate the video input clamp circuits. If fully stepped August 2004  31 32  Silicon Chip siliconchip.com.au Fig.2: this diagram shows the full circuit details for the Video Enhancer. IC2 functions as the Y/C separator. siliconchip.com.au August 2004  33 The rear panel of the unit carries four sockets: (1) composite video input; (2) composite video output; (3) S-video output; and (4) power. sandcastle pulses are not available, colour burst gating pulses can be used instead (and that’s what we do in this design). The second reference needed is a colour subcarrier signal, which is used to lock the TDA9181’s internal sampling clock to four times the colour subcarrier frequency (ie, 4Fsc or 17.73MHz). This reference signal is fed in via pin 9 and can have a frequency of either Fsc or 2Fsc, provided the chip is informed which is being used by taking control pin 8 either low or high. In this design, we feed in a reference signal at Fsc and tie pin 8 low. Circuit details Fig.2 shows the full circuit of the Video Enhancer. As shown, the incoming composite video from the VCR or some other source is fed in at CON1. It is then fed to IC1a which is half of a MAX4451 dual op amp, used here as a video input buffer. The output of this buffer stage is then fed to the input of IC2 (TDA9181) via a 100nF coupling capacitor. It is also fed to one side of analog switch IC10c and to the input (pin 2) of IC3, an LM1881 sync separator chip. IC3 is used to derive the various sync and timing signals from the video: ie, composite sync (CS-bar), vertical sync (VS-bar) and a basic colour burst gating signal (BG-bar). These signals are then passed through Schmitt inverters IC6a-IC6d, to both invert them logically and “sharpen” them up. We’ll look more at the outputs of IC6a-IC6c later but for the present, note that the BG pulses from IC6d are “trimmed” in length to correspond more closely to the actual PAL colour 34  Silicon Chip burst length of 2.5µs. This trimming is done using a pair of RC differentiator circuits (390pF & 12kΩ and 47pF and 10kΩ), each feeding one input of XOR gate IC4c. The trimmed BG pulses are then fed to pin 7 of IC2, to provide the “sandcastle” reference signal. They’re also used to gate analog switch IC10c, which allows the buffered video input signal from IC1a to pass through to transistor Q1 only during the colour bursts. Q1 is used to amplify the gated colour bursts, which appear across its load circuit, as formed by L1 and the parallel 330pF capacitor. These amplified bursts are then fed via a 10nF capacitor to diode D1 and a 100kΩ resistor, which clamp the negative burst tips to ground potential. They then go to pin 12 of XOR gate IC4d, which is used here as an inverter. IC4a, IC4b, IC5b and transistors Q2 & Q3 are used to generate a 4.433619MHz clock signal for IC2, locked to the colour subcarrier bursts of the incoming video. IC4a is the oscillator and uses crystal X1 as its main frequency reference. Its output is then buffered by IC4b and fed to the D (data) input (pin 12) of flipflop IC5b. As shown, the amplified and squared-up colour bursts are fed to IC5b’s clock (CLK) input and this allows IC5b and transistors Q2 & Q3 to act as a gated phase detector. It compares the phase of IC4b’s output with that of the gated colour bursts. The resulting DC error signal from Q2 & Q3 is then fed through a loop filter and a 100kΩ decoupling resistor to ZD1, a 12V zener diode used here as a varicap. As a result, ZD1’s capacitance is au- tomatically varied to keep IC4b’s output in lock with the colour bursts. As well as gating IC10c, the trimmed BG pulses from IC4c are also used to gate analog switch IC10d. This switch is used as a DC level clamp on the separated Y signals which emerge from pin 14 of IC2, via a 1µF coupling capacitor. As a result, the separated Y signal fed to buffer stage IC1b has its sync tip level clamped firmly to ground potential. Video enhancement All of the circuitry we’ve looked at so far has essentially been used to convert the incoming composite video signals into S-video – ie, into separated Y and C (luminance and chrominance) signals. And that’s about it as far as the C signals on pin 16 of IC2 are concerned. As shown, they are now simply passed through a low-pass RC filter and then fed through wideband output buffer and cable driver stage IC9b. This stage operates with a gain of two, to compensate for losses in the 75Ω output terminating resistor. The Y (luminance) signals don’t have it quite so easy, because it’s these that we operate on for video enhancement. In this case, the Y signals appear on pin 7 of IC1b and are then fed in three different directions: to analog switch IC10b; to pin 5 of IC7b (via a 51Ω resistor); and to pin 2 of IC7a via a 510Ω resistor. Delay lines Pin 5 of IC7b is also connected to earth via one of two delay lines, as selected by switch S1. Both delay lines are made from 50Ω RG58/C/U coaxial siliconchip.com.au cable, with their “far” ends shorted so that any signals which propagate along them are reflected straight back again. The cable lengths are carefully chosen to give a down-and-back “round trip” delay time of 27ns when the 2.67m length is selected or 35ns when the 3.47m length is selected. What’s the idea of this? Well, the action of the delay line is to generate an opposite polarity version of the Y signal from IC1b but delayed by the selected short period of time (ie, 27ns or 35ns). This delayed opposite-polarity version is added to the original Y signal at pin 5 of IC7b, so all signal changes which last longer than the selected delay time will be cancelled out. As a result, only relatively rapid transitions will escape this cancellation and so IC7b’s output consists of a series of short positive and negativegoing spikes, representing only these faster transitions. These spikes can be considered as a kind of “differentiated” version of the Y signal and they become our enhancement signal. Following IC7b, the enhancement signal is fed to IC7a where it is mixed with the original Y signal from IC1b. Potentiometer VR1 acts as the enhancement level control. The enhanced Y signals from the mixer (IC7a) are then fed to IC8b, which re-inverts them to compensate for the inversion in IC7a. At the same time, diode D7 clips any negativegoing enhancement spikes, to make sure they don’t act as fake extra sync pulses. Fast electronic switching Now we come to analog switches IC10b and IC10a, which are used to select either the original Y signal direct from IC1b or the enhanced signal from IC8b. These switches are controlled in complementary fashion, because inverter IC6e feeds the gate of IC10a with an inverted version of the control signal fed to the gate of IC10b. So IC10a is “off” when IC10b is “on” and vice-versa. Basically, IC10a and IC10b form an electronic SPDT switch, which allows us to select either the original Y signal or the enhanced version. The selected signal is then fed to the Y signal output buffer (IC9a). The reason for this switching is that we don’t want to disturb the critical sync pulses or colour bursts on the siliconchip.com.au Parts List 1 PC board, code 02108041, 198 x 157mm (double sided – see text) 1 ABS plastic instrument box, 225 x 165 x 40mm 1 47µH RF choke (RFC1) 2 220µH RF chokes (RFC2,RFC3) 1 miniature 4.8mm coil former, base & shield can 1 F16 ferrite slug to suit coil former above 1 short length of 0.25mm enamelled copper wire 2 SPDT miniature toggle switches (S1,S2) 1 4.433MHz crystal, HC/49U or HC/49US (X1) 1 U-shaped TO-220 heatsink, 19mm x 19mm x 9.5mm 2 PC-mount RCA sockets, yellow (CON1,CON3) 1 4-pin mini DIN socket, PCmount (CON2) 1 2.5mm concentric power socket, PC-mount (CON4) 1 6.2m length of RG58/C/U 50Ω coaxial cable 6 100mm-long nylon cable ties 1 1kΩ 16mm-diameter linear pot (VR1) 1 small skirted instrument knob to suit VR1 4 PC terminal pins, 1mm diameter 6 6mm-long self-tapping screws (for board mounting) Semiconductors 4 MAX4451ESA dual wideband op amps (IC1,IC7,IC8,IC9) 1 TDA9181 multi-standard Y/C comb filter (IC2) 1 LM1881 sync separator (IC3) 1 74HC86 quad XOR gate (IC4) 1 74HC74 dual flipflop (IC5) 1 74HC14 hex Schmitt trigger (IC6) 1 74HC4066 quad analog switch (IC10) Y signals as part of the enhancement processing. As a result, we use fast electronic switching to feed “undoctored” Y information through to the output when any of this critical information is present and only make the enhanced Y information available during the active parts of the video lines. 1 LM7805 +5V regulator (REG1) 1 LM7905 -5V regulator (REG2) 1 BC548 NPN transistor (Q1) 1 PN200 PNP transistor (Q2) 2 PN100 NPN transistors (Q3,Q4) 1 12V zener diode (ZD1) 1 3mm green LED (LED1) 1 3mm red LED (LED2) 1 1N5711 Schottky diode (D1) 5 1N4148 or 1N914 diodes (D2D6) 1 BAW62 high speed diode (D7) 2 1N4004 1A diodes (D8,D9) Capacitors 2 2200µF 16V RB electrolytic 2 100µF 16V RB electrolytic 2 10µF 16V tantalum 1 4.7µF 16V tantalum 1 2.2µF 16V tantalum 1 1µF 16V tantalum 1 220nF MKT polyester 4 100nF MKT polyester 15 100nF monolithic ceramic 1 10nF MKT polyester 4 10nF monolithic ceramic 1 1nF disc ceramic 1 470pF disc ceramic 1 390pF disc ceramic 1 330pF disc ceramic 3 47pF NPO disc ceramic 1 39pF NPO disc ceramic 1 33pF NPO disc ceramic 1 3-30pF trimmer (VC1) Resistors (0.25W, 1%) 1 1MΩ 4 1kΩ 1 680kΩ 1 680Ω 2 100kΩ 1 620Ω 1 39kΩ 11 510Ω 2 27kΩ 1 470Ω 2 22kΩ 1 220Ω 1 15kΩ 2 100Ω 1 12kΩ 4 75Ω 5 10kΩ 1 51Ω 1 2.2kΩ 4 24Ω The signal that’s used to perform this switching is generated from those sync and burst gating outputs from IC6a-IC6c which we looked at earlier. As shown, these outputs are combined in a simple 3-input OR gate using diodes D2-D4 and a 22kΩ resistor to ground. This produces a switching signal which is high during any of the August 2004  35 Fig.3: install the parts on the PC board as shown here (top copper shown). The red dots indicate where component leads and “feed-throughs” have to be soldered on both sides, if you don’t have a board with plated-through holes. critical sync and burst gating periods and low at all other times. As a result, IC10b is turned on during the critical periods, while IC10a is on at all other times. At least that’s what happens when switch S2 is in the “On” position. However, if S2 is set to “Off” instead, the Y switching signal line is pulled to +5V (via a 1kΩ resistor), preventing it from going low during 36  Silicon Chip the active video line periods. In this case, IC10b remains on continuously, while IC10a remains off and so only “undoctored” Y information is fed to output buffer IC9a – ie, the enhancement is disabled. Inverter IC6f and transistor Q4 are used to drive LED2 from the Y switching signal line. This means that LED2 is only turned on when the switching line is at low logic level, corresponding to those times when IC10a is turned on to pass the enhanced Y signal. As a result, LED2 functions as an “Enhancement Enabled” indicator. Output buffer stages The Y and C signal output buffer stages based on IC9a and IC9b are virtually identical. Both stages have a simple RC low-pass input filter. IC9a’s filter is there to remove switching transients, while IC9b’s filter is included simply to match the delay and phase shifts in IC9a’s filter. The outputs of both stages are fed to the S-video siliconchip.com.au All the parts except for the two front-panel switches mount directly on the PC board. Be sure to coil the delay lines up neatly, so that the lid will later fit on the case. output socket (CON2) via 75Ω back terminating resistors. The alternative recomposited video output signal for CON3 is generated by feeding the separated Y and C output signals to the non-inverting input of buffer stage IC8a via 1kΩ mixing resistors. As with the other two output buffers, IC8a operates with a gain of two, to compensate for the loss in its 75Ω back terminating resistor. Power supply All of the circuitry in the Video Enhancer operates from either +5V or ±5V rails. The power supply is really quite simple. As shown, power is derived from a 9V AC plugpack supply and this feeds half-wave rectifier diodes D8 & D9. The resulting DC rails are then fed to 3-terminal regulators REG1 siliconchip.com.au & REG2, which produce the regulated +5V and -5V rails. The 2200µF and 100µF capacitors provide supply line filtering and decoupling, while LED2 provides power indication. Construction Despite the circuit complexity, the construction is straightforward, with all parts mounted on a single PC board. This board is coded 02108041, measures 198 x 157mm and fits snugly in a standard low profile ABS instrument box measuring 225 x 165 x 40mm. Note that the board is double-sided, with the top copper used partly as a groundplane. However, unless this board is supplied with plated-through holes, you will have to fit short wire “feed-throughs” (or links) at various locations on the board, to connect the copper pads on each side. You’ll also have to solder some of the component and IC leads to both sides of the PC board or in some cases, to the top copper only. That’s not as daunting as it sounds. To make it easy, all the wire feedthroughs and “top solder” points are marked with a red dot on the parts layout diagrams – see Figs.3 & 4. As shown in the photo, the two lengths of RG58/C/U coaxial cable used for the enhancement delay lines are coiled up together and secured to the top of the PC board using nylon cable ties. It’s a bit of a squeeze but they do fit in. Before fitting any parts to the board, inspect it carefully with a magnifying glass to make sure there are no etching defects or solder plating problems. It’s much easier to find and remedy these August 2004  37 Table 1: Resistor Colour Codes o o o o o o o o o o o o o o o o o o o o o   No. 1 1 2 1 2 2 1 1 5 1 4 1 1 11 1 1 2 4 1 4 Value 1MΩ 680kΩ 100kΩ 39kΩ 27kΩ 22kΩ 15kΩ 12kΩ 10kΩ 2.2kΩ 1kΩ 680Ω 620Ω 510Ω 470Ω 220Ω 100Ω 75Ω 51Ω 24Ω at this stage than later on. Begin the assembly by fitting the four input and output connectors along the rear edge of the board. That done, if your board doesn’t have plated-through holes, fit the small number of short wire “feed-throughs” at the positions indicated. There aren’t many of these but they are best done now to make sure you don’t forget them. Next, fit the four PC board terminal pins that are used to terminate the connections to the coaxial delay lines. These fit in the front right of the board. The resistors, diodes and capacitors can all now be installed. Table 1 shows the resistor colour codes but it’s also a good idea to check each value using a digital multimeter before installing it on the PC board. Take care to ensure that the diodes and electrolytics go in with the correct polarity. Take care also to ensure that the correct diode is installed at each location. In particular, note that D1 is a 1N5711, D7 is a BAW62 and D8 & D9 are 1N4004s. The remaining diodes (D2-D6) are all 1N4148s. Don’t forget to solder any leads marked with a red dot on the wiring diagrams to the top copper as well as underneath. Once these parts are all in, install 38  Silicon Chip 4-Band Code (1%) brown black green brown blue grey yellow brown brown black yellow brown orange white orange brown red violet orange brown red red orange brown brown green orange brown brown red orange brown brown black orange brown red red red brown brown black red brown blue grey brown brown blue red brown brown green brown brown brown yellow violet brown brown red red brown brown brown black brown brown violet green black brown green brown black brown red yellow black brown trimmer capacitor VC1. This should be installed with its flat side towards crystal X1 as shown. That done, you can wind the 4.433MHz peaking coil (L1) – see Fig.5. This consists of just 20 turns of 0.25mm enamelled copper wire, wound close together at the bottom of a miniature 4.8mm OD former. Note that the former is fitted with an F16 ferrite slug for tuning. It is then fitted to the board with the coil connections adjacent to the 330pF capacitor. A matching shield can fits over the coil assembly and is secured by soldering its tags to the bottom copper. The three RF chokes (RFC1-3) and quartz crystal X1 can go in next. Note that the 47µH RF choke is used as RFC1 and that a short length of tinned copper wire is used to earth the shield can of X1 and to make sure the crystal is held firmly in place. The two crystal leads are soldered to the underside copper only. The four transistors (Q1-Q4) can now be installed, followed by 3-terminal regulators REG1 & REG2. Again, take care to ensure that the correct device is used at each location and that it is oriented correctly. Push each transistor as far down onto the board as it will comfortably go before soldering its leads. 5-Band Code (1%) brown black black yellow brown blue grey black orange brown brown black black orange brown orange white black red brown red violet black red brown red red black red brown brown green black red brown brown red black red brown brown black black red brown red red black brown brown brown black black brown brown blue grey black black brown blue red black black brown green brown black black brown yellow violet black black brown red red black black brown brown black black black brown violet green black gold brown green brown black gold brown red yellow black gold brown Table 2: Capacitor Codes Value 220nF 100nF 10nF 1nF 470pF 390pF 330pF 47pF 39pF 33pF μF Code 0.22µF 0.1µF .010µF .001µF   –   –   –   –   –   – EIA Code 224 104 103 102 471 391 331   47   39   33 IEC Code 220n 100n   10n    1n 470p 390p 330p   47p   39p   33p The two regulators lie flat against the PC board. Before mounting them, you will need to bend their leads down through 90°, so that they will go through their respective solder holes (and so that the metal tab on each device lines up correctly with its mounting hole). That done, REG2 (7905) can be installed and bolted down directly against the board copper using a 10mm x 3mm machine screw and nut. REG1 (7805) is mounted in similar fashion but must also have a 19mm x 19mm Ushaped heatsink sandwiched between it and the PC board. The device leads should be soldered siliconchip.com.au only after REG1 and REG2 have been bolted in position. Note that all three pins of REG2 must be soldered to the top copper, while only the centre pin of REG1 needs this. Mounting the SOIC-8 Devices Installing the ICs The leaded DIP ICs should now be fitted to the top of the board, taking the usual care to prevent them being damaged by overheating or electrostatic charge. Be sure to earth yourself while you’re handling these ICs and use an earthed soldering iron when you’re soldering their leads. Note again that some of the IC leads need to be soldered to the top copper as well as underneath, as shown by the red dots. The final ICs to fit are the four MAX4451ESA chips (IC1, IC7, IC8 & IC9). These are in SOIC-8 SMD packages and mount on the underside of the board – see Fig.4. As shown, all four mount with their chamfered side towards the rear of the board. Take care when soldering them in place, so that you don’t overheat them or leave solder bridges their between pins. The best way to approach the job is to first lightly tin the IC pads using a soldering iron with a fine-pointed tip. You can then “cement” each device in position using a tiny spot of epoxy glue before soldering their leads. Hardware & delay lines The next step in the assembly is to install the Enhance Level potentiometer (VR1). To do this, first cut its shaft to about 9mm long, then push the pot all the way down onto the board and solder its terminals. By contrast, the two switches aren’t directly mounted on the board. Instead, you should install five 30mm lengths of insulated hookup wire at the switch positions – three for S1 and two for S2 (left and centre). The free ends of these wires are then later soldered to the switches, which mount directly on the front panel. Fig.4: the four MAX4451ESA dual op amps are all mounted on the underside of the PC board, as shown here. Make sure you install them the right way around. end of each cable, gently fan out the screening wires and carefully remove about 3mm of the inner dielectric to reveal the centre conductor. Now bend the screening wires on each cable back down again, twist them around the bared inner conductor and solder the connections – ie, the Coil Winding Details (L1) Delay lines You are now ready to prepare and fit the two coaxial cable delay lines. Begin by cutting off two lengths of RG58/C/U coaxial cable, one 3480mm long and the other 2680mm long. Next, carefully remove a 5mm length of the outer sleeving from both ends of these cables and unplait the screening braids at these ends. That done, on one siliconchip.com.au Fig.5: follow this diagram to wind the 4.433MHz peaking coil. It uses 20 turns of enamelled copper wire and is fitted with a tuning slug. shielding braid is soldered to the inner conductor at one end of each cable (see Fig.2). Once the solder joints have been completed (and have cooled), wind a short piece of insulating PVC tape over these ends to protect them from damage. Moving now to the other end of each cable, again fan out the braid wires and remove about 3mm of the inner dielectric to reveal the centre conductor. At these ends though, the individual shield wires are simply twisted together on each cable, to form the earth leads. The next step is to solder these inner and outer wires of each cable to the terminal pins on the PC board – see Figs.3. As shown, the connections for the shorter delay line (DL1) go to the pins on the left, while those for the longer line (DL2) go to those on the right. In both cases the centre conductor goes to the left. After soldering the cables, fit 100mm-long nylon cable ties through the six pairs of 3mm holes around the edge the board. Each cable tie should be fed down through its inner hole and then back up through the outer hole, to give two ends of equal length. They will then all be in a “U” shape, ready for you to loop the two delay line cables around inside them. Because the cables are fairly stiff and bulky, you might find it easier to August 2004  39 There are just three front panel controls: an enhancement on or off switch, an enhancement level pot, and an enhancement rise time switch. use narrow strips of gaffer tape to hold each loop in position, before winding on the next loop above it. At the very least, it will reduce the frustration level to a dull roar. When the end of the shorter cable is reached, you can form each cable tie into a loosely closed loop. This helps hold all the twin cable loops in place while you thread through the last part of the longer cable. Finally, when this is in place too, you can tighten up the cable ties in stages as you tidy up the cable loop layers. Make sure that the delay line loops pack down into a compact shape that will fit inside the Video Enhancer’s case. This is a rather fiddly operation, but take it steady and keep your cool because it can be done – as you can see from the photos. After the cables are in place and tied down securely to the board, you can fit the last components to the board itself. These are the two LEDs, which mount in the front lefthand corner. Both LEDs are fitted with their longer anode lead towards the left, with the green Power LED on the left and the red Enhance LED on the right. Initially, the LEDs should be mounted vertically, with their bodies about 16mm above the board. Once they’re in position, bend their leads forward by 90° about 9mm up from the board, so that they will later mate with their matching holes in the front panel. Final assembly Now for the final stage of assembly. If you purchase a complete kit, the case will be supplied pre-drilled and with screen-printed lettering. If not, then you’ll have to drill your own holes in the front and rear panels. Use the panel artwork (it can be downloaded from the SILICON CHIP 40  Silicon Chip website) as a drilling guide if you do have to drill the holes yourself. You’ll need 12mm holes for the RCA sockets and the 4-pin mini-DIN socket, a 9mm hole for the power input connector CON4, 7mm holes for the front panel switches and pot, and 3mm holes for the two LEDs. By the way, for the larger holes, it’s best to drill small pilot holes first and then carefully enlarge them to size using a tapered reamer. Once the panels have been drilled, you can attach the artworks, then fit the two toggle switches to the front panel. That done, you can make the connections between these switches and the PC board, by soldering the ends of the five wires you fitted earlier to the appropriate switch lugs. Just be careful not to burn the delay line cables with the hot soldering iron barrel while you’re doing this. It’s now just a matter of installing everything inside the case. First, slip the front panel over the LEDs and the pot shaft, and loosely fit the pot nut to hold the assembly together. That done, fit the rear panel over the RCA sockets and lower the complete assembly into the bottom half of the case. The board is then secured in place using six short self-tapping screws – three along the front of the board and three along the rear. There’s really no need to fit screws in the remaining four holes, although you can do so if you wish. Once the board assembly is in place, you can tighten up the pot nut to hold it securely in position. Finally, push the knob over the pot shaft and you’re ready for the smoke test! Checkout time Connect a 9V AC plugpack to CON4 and apply power. The green Power LED should immediately begin glowing; if it doesn’t, switch off immediately and look for the cause. You may have wired in the LED with reversed polarity or fitted one of the power diodes or electrolytic capacitors the wrong way around. You can check that the power supply is working correctly by measuring the DC voltage at the righthand output pins of both REG1 and REG2. You should get readings of +5V and -5V respectively (within a few tens of millivolts). Now feed some composite video from a VCR (or camcorder) into CON1 and use an oscilloscope or a DMM with an RF detector probe to measure the AC voltage across diode D1 (between L1 and IC5). This will allow you to adjust the tuning slug in coil L1 – just tune the coil for a peak in the diode voltage, to obtain the maximum gain in burst amplifier Q1. Once L1 has been peaked, the only remaining adjustment is to set trimmer VC1 so that the subcarrier oscillator is correctly locked to the video colour bursts. This isn’t hard to do if you have a frequency counter and/or an oscilloscope. If you have a counter, connect its input to the output of IC4b and read the oscillator’s frequency. If it isn’t exactly 4.433619MHz, adjust VC1 until you get this reading consistently. If you have an oscilloscope (but no counter), connect it to the junction of the 100kΩ, 22kΩ and 2.2kΩ resistors, just to the right of zener diode ZD1. If the oscillator is correctly locked, you should see a small sawtooth signal at a DC level of about +2.5V. If not, adjust VC1 until you do get this. If you have neither a scope nor a counter, set VC1 to the centre of its range and try connecting the S-video output of the Video Enhancer (CON2) to the S-video input of your TV or projector. You should see nice, clear pictures, indicating that the unit’s colour subcarrier oscillator is locked to 4.433619MHz and that everything else is working correctly. If not and the pictures are distorted and flashing with various colours, try adjusting VC1 slowly until the pictures do stabilise and become clear. That’s it – fit the lid on the case and your new Video Enhancer and Y/C SC Separator is ready for action. siliconchip.com.au