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TV Signal Amplifier circuit


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Please help. I am curious about some of the components in this circuit. They are in particular L1 and L2. The circuit description says nothing about them but this, L1 and L1 Diameter: 5mm / Wire: 0.5mm / Spiral: 8. If anybody knows anything about this please inform me. Also, I would like to know which resistor I can swap with a pot to make it a variable gain amp rather than the fixed 20db?? Thanks in advance.


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L2 resonates with C5 and C4 near the center of the TV band. A 75 ohm resistor would probably work as well. L1 is a "peaking coil". It is self resonant near the upper edge of the band and is there to raise the high frequency gain. You cannot put a pot in this circuit because the leads have to be very short and this is a high frequency circuit. The ratio of C5, C4 could be changed, keeping the total constant, to change the gain. FYI: the total is (c5*c4)/(c4+c5).

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