A Video Amplifier for boosting the output level of satellite receivers.
(and anything else that needs a bit more oomph!)
Most ATV stations use domestic satellite receivers for frequencies above 1GHz. They are cheap and easy to buy but have one serious drawback, low video output level. This isn't due to a deficiency in the receiver, it is because the modulation index of amateur TV transmissions is much lower than domestic TV uses. A lower modulation index means less video is recovered from the incoming signal.
Almost all receivers have a built-in level controls which are adjusted by their manufacturer to give the correct output level for a standard satellite input signal. In some cases this control can be advanced far enough to lift ATV signals to the same output level but most receivers will need this design adding to assist them. There is a penalty to pay for winding an amplifiers gain up, given that the gain x bandwidth is a constant, the bandwidth is proportionately narrowed which results in poorer picture quality. Adding extra gain, such as this device does, will always be a better solution.
By using a split and isolated supply, the input and output capacitors normally used in this kind of amplifier are eliminated. Bandwidth goes from DC up to more than 10MHz.
The PCB is small enough to fit upright inside most satellite receivers. Connect "A" to the old video output point and use "C" or "D" as the new output point. The two outputs can be loaded simultaneously. VR1 sets the gain, try leaving it set half-way and adjust the receivers original gain control for the desired output level. If possible, keep both controls below their maximum settings.
R1 - 1K
R2 - 220 Ohms
R3 & R4 - 75 Ohms
RV1 - 470 Ohms
IC1 - EL2020 note that ordinary '741' type op-amps will NOT work in this application!
IC2 - NMA1212
C1, C2 & C3 - 33uF / 16V
C4 - 100nF (0.1uF)
L1 - 100uH
Click HERE for downloadable PCB files.