This handy prescaler divides input frequency by 1000. It takes maximum input frequency of 3.5GHz and converts it into 3.5MHz that may be measured using standard frequency meter.
Posted on Thursday, October 7, 2010 • Category:
Antennas
This is an UHF band TV antenna preamplifier circuit With 15dB gain to build easily. It is formed based on BF180 UHF Transistor. The first stage is an band pass filter constructed by the C1, CV1, L1, L4, C7 and C3, the second stage is a base-common voltage amplifier with low input impedance to match. Build the L1 ~ L4 as air core coil to obtain high Q-Factor. After assembling, pack it into a proper metallic box and connect the ground of the circuit to the box to reduce noise effect.
Posted on Wednesday, October 6, 2010 • Category:
FM Transmitters
RF amplifier with 25W of power for 88-108MHz FM transmitters.
Posted on Wednesday, October 6, 2010 • Category:
FM Transmitters
The important part of the circuit is formed of the Colpitts type oscillator. C3,C4,C5,C6,CD1-CD2 and L1 determines the frequency. BF982 and dual gate MOSFET are active parts in oscillator. When the input impedance of the MOSFET gate inputs are high, LC tank is not affected. However transistors force the LC tank and cause phase shift. Two driver stages are added to isolate the antenna from oscillator. First stage (BF199) amplifies the low signal of the oscillator and works as a constant load. The second stage (BFR90) amplifies the signal going through the antenna some more. A short copper wire can be used as an antenna here. Attaching a large antenna to this circuit is unnecessary because the output power is low.
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