Figure 21.41 shows a block diagram of a VCR. To avoid regular plugging and unplugging operations, the VCR is permanently connected ‘in series’ with the aerial lead to the TV receiver. When the machine is off or recording a programme other than the one being viewed, it is important that normal TV reception is not affected by the machine’s presence, so a loop-through facility is provided in the aerial booster, a small RF amplifier which is per- manently powered. Its modest gain cancels the losses incurred in the extra RF plugs, sockets and internal splitting of the RF signal within the VCR.
Most recordings made on a home VCR come via broadcast transmissions, so the machine needs a tuner and receiver built-in to select and demodu- late broadcast programmes. An effective AGC circuit is provided to ensure
a constant signal level to the recording section, and AFC (automatic fre- quency control, sometimes known as AFT, auto fine tuning) feedback maintains correct RF tuning. Some VCRs have auto-set routines, in which they tune themselves, working from a program in the control section, and set their own clock from teletext.