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t . IUHlllfUUf .l UIU.I · llftUUfU .t HUH 1.l f l l UHF shenanigans with a VCR Many Australians want to watch UHF broadcasts from SBS and other services but their TV receiver does not have a UHF tuner. If they have a VCR this problem is readily solved. Are you one of the many people who want to have a look at SBS or other UHF TV broadcasts? Foiled because your TV does not have an inbuilt UHF tuner? Well look again because if you have a videocassette recorder you can tune to UHF and watch the broadcasts on your old TV. This fact is seldom alluded to in the instruction manual that comes with every VCR but it is a handy facility particularly if your VCR has a remote control and your TV doesn't. Consider a very common situation in Australian homes. The family TV set is a Rank model from the 6 SILICON CHIP early days of colour but it does not have a UHF tuner. In the last couple of years though, the family has purchased a VCR and uses it mainly for " time-shifting" programs or watching rented tapes. Surprisingly, the family has not twigged to the fact that their VCR can be used as the tuner for their TV and they can then use their VCR remote control to select the stations they watch. Setting up the VCR The way to set it up is as follows. Connect the antenna lead-in directly to the VCR and connect the VCR RF output lead to the antenna input of the TV. With a tape playing in By LEO SIMPSON the VCR, or using the VCR's own test pattern, tune the TV set to receive the VCR program. With older VCRs this generally means tuning the TV set to channel 3 or 4, according to a switch setting on the rear of the VCR. In more recent VCRs, the RF output is usually switchable between channel O or 1 and so the TV set should be tuned to one of these latter stations. The set-up just described is exactly as set out in the VCR instruction manual. But suppose you want to use the VCR to select the stations you watch on the TV. To do this the VCR must be in the "Standby" or "Operate" mode and the VCR/TV switch must be set to the VCR mode. This allows you to select the stations you watch with the VCR remote control while the TV set can be left permanently on the VCR setting (ie, Channel 0, 1, 3 or 4, depending on your set-up). In fact, most VCRs are supplied ready tuned to local VHF stations in the area where they are sold so it is usually not necessary to go through a tuning procedure. How does the VCR manage to deliver all station programs via its RF output? Essentially, its own inbuilt tuner picks up the stations you want and converts the program to composite video and audio signals. These are then re-modulated onto its RF output (at Ch 0 or whatever) and then delivered to your TV set's antenna socket where it goes through the whole process of detection again. Recording and watching The only time your VCR cannot be used to act as a remotecontrolled TV tuner is when you want to watch a program on one channel while recording a program on another channel. In this situation the VCR must be in the record mode and the VCR/TV switch must be set to the TV mode. This allows all the signals from the TV antenna to be fed directly to the tuner of the TV set. Now suppose you want to watch SBS broadcasts on channel 28 (or The TV/VCR switch i~ hard to find on many machines. On this older Philips machine it is one of many behind a flip-down door. On the National machine on the opposite page, the TV/VCR switch is near the REWind button. 45 as it is in many areas). Simply set the VCR in "Operate" mode, set the VCR/TV switch to VCR and refer to your owner's manual for the instruction on how to tune to UHF stations. Remember though, in most areas you will require a separate UHF antenna or a combined VHF/UHF antenna if you are to have satisfactory UHF reception. So if you wanted to watch UHF programs but have been loath to replace your old VHF only set, this is the solution. And if you don't yet have a VCR, this could be the excuse you needed to buy one. Next month, SILICON CHIP will publish construction details of a high gain UHF antenna which will cover bands 4 and 5. A stacked bowtie design, it will be less prone to aircraft "jitter" than conventional Yagi designs. ~ Horizontal jitter problem with VCR I have recently purchased a VCR and am generally pleased with it but it does present a problem when playing some rented tapes. With these tapes the TV picture has severe horizontal jitter at the top and on one severe case the picture was completely black at the top half. A number of people have suggested that this is a fault in the VCR and it should be corrected under warranty. What do you think? • This fault is commonly referred to as "flag-waving" and can be caused because the TV set's horizontal sweep circuit timeconstants are too long to suit the VCR sync pulse waveform. The solution is a fairly routine modification that would be familiar to most TV servicemen. In your case though, you imply that the picture is quite satisfactory for most of the time and it only plays up with some tapes. While that may suggest that the fault is in your VCR it is highly likely that it is not. Instead, the VCR RF output is probably overloading the tuner of your TV set. In fact , we're betting that your set is a late model Philips with a "Fringe" button. This button can be pressed to give better reception on weak signals. If you have a look at the control behind the door on the front of the set, the Fringe light should not be illuminated when the VCR station is selected. If it is automatically selected, you should reprogram your set so that the light is off in VCR mode. This instruction is buried in the instruction manual and has caused more than one unnecessary service call. As a general rule, if TV sets have a local/distant antenna setting they should be set up for "local" reception when used with a VCR. DECEMBER 1987 7