Tuner Systems and Video Amplifiers

1
Tuner Systems and Video Amplifiers

• Portions of the following are covered
• Chapter 12
• Chapter 13
• Chaptor14

2
Tuner Systems and Video Amplifiers

• Development of I.F. signals Sound I.F. carrier
  is 41.25 MHz. Picture I.F. carrier is 45.75 MHz.
• The picture carrier for channel two is 55.25 MHz.
• What will the channel 2 oscillator frequency be?
  . 55.25 MHz 45.75 M?H?z 101 MHz
• Does this oscillator frequency work for the sound
  I.F. carrier? 101 MHz 41.25 MHz _________
• What is the difference frequency dveloped
  between the picture and sound I.F.
  carriers?___________
• What is the oscillator frequency for channel 2?
  _____

3
Tuner Systems and Video Amplifiers

• TUNER TYPES 1.) Early systems used a
  continuously variable inductance. 2.) A ganged
  switch and drum method followed. 3.) Varactor
  Tuners 4.) PLL (frequency synthesis).
• Pushbutton varactor requires a voltage reference
  to each switch.
• PLL type varactor uses a VCO.
• UHF tuners implement tuned lines (shorted stubs)

4
Tuner Systems and Video Amplifiers

• I.F. amplification
• Video detector
• Video amplifier 3 d.c. coupled voltage
  amplifiers driving a power amplifier to CRT
• Takeoff points Ex. AGC, sound.
• D.C. restoration required due coupling
  capacitors blocking d.c. reference. DC clamp
  (reinsertion) at CRT.
• Frequency compensation roll off inherently exist
  at low and high ends of response. Low loss
  develops poor contrast and unstable sync.

5
Tuner Systems and Video Amplifiers

• High frequency loss reduces picture detail.
• Cause distributed capacity.
• Remedy peaking coils as part of the collector
  loads. this will introduce an additional reactive
  load that will vary with frequency and provide
  compensation.