| 摘要 |
A filter in the UHF antenna circuit rejects the IF frequency. This filtered signal is applied to a double tuned low pass filter comprising series inductors and a DC blocking capacitor. Inductors to ground are designed to maintain an impedance of 50 ohms at the input and output. Inductors maintain a constant bandwidth over the tuning range. The tuning is effected by variable capacity diodes connected to ground through coupling capacitors presenting a very low impedance at the tuning frequencies. The tuning control voltage is applied to the circuit through isolating resistors.
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