There are many radio Frequency circuit diagram that I collect them. They may be useful for you. The ideas are important for the learning circuit. I am sorry that cannot confirm it works and does not know the source. If you do not like it please tell me.
Simple field strength meter
This circuit is a Simple field strength meter that chooses a specific frequency range.
It can be used from 2 meters to 160 meters.
The telescoping antenna may be adjusted to its shortest length when working at 2 meters to keep the needle on the scale.
The meter should be a 100 microamp to a 500 microamp movement. The diodes are germanium type, such as 1N34, 1N60, etc. Silicon diode will also work, but they are a bit less sensitive.
LED FM Tuning Indicator
Usually already the circuit F.M. Discriminator the majority will give an output that can modify tall and lower 0V depend on something tuning and often use drive Tuning meter at having junction universal position.
This circuit designs by use LED 3 pcs. Replace which regard as suit very with the usability. By when institute off-tune output of Discriminator change go to tall more or lower 0V make LED1 or LED3 shine respectively.
When the output of Discriminator equal to 0V LED2 stick for informing that something tuning best effective both of transistor Q1 with Q3 that use circuit model silicon PNP small signal the multi-purpose and Q2 with Q4 be model silicon NPN small signal the multi-purpose.
Depth frequency multiplier
Most of the frequency multiplier circuit using IC phase locked loop (PLL).It will increase the frequency to an integer only. But this circuit can double the frequency, in the integer to a fractional number. This circuit has an IC phase locked loop number NE565.
Circuit diagram of A frequency multiplier in depth
It changes frequency as the incoming voltage, Frequency control. That, from the IC Oscillator NE566. IC phase locked loop circuit is in the nature of Demodulator.
The output at Pin 7 and is connected to the IC op-amp 741. Which it connects in a manner of Voltage-follower circuit. To the driver IC 566 runs.
The voltage passing through the pin 6 of IC op amp, will be entered into a 5-pin of the IC 566.To control the frequency of leg 3 of the IC NE566.
The multiplication of frequency equal to R1, C1, R2, C2. For the operation of the circuit stability. Thus the value of R1 and C1 should be chosen to suit the frequency.
The input entered. Boost up the value frequency is selected by the value of R2 and C2.
Attenuate variable radio frequency
The circuit designer it to attenuate signal frequency. We can adjust the amplitude from 1 to 40 dB.
If you want to use the band UHF. We should filter it within the flame shield. And C1 to C3 type feeds true.
The line should be short as possible, and the diode is a kind of low capacity at a high-speed frequency.
The potentiometer can be installed separately, if desired, as well as R3 and Zener diode.
Background music decoder
This is a background music (SCA) decoder circuit from the input demodulated (multiplex) FM signal.
We use NE565 (Phase Locked Loop IC) to be base of this circuit, for easy and cheap.
A resistive voltage divider is used to set a bias for the input (pins 2 and 3).
The input passes through a two-stage high-pass filter, both to effect capacitive coupling and to attenuate the strong signal of the regular channel.
In all signal amplitude, between 80 to 300mV, is a need at the input, and should have an impedance of fewer than 10,000 ohms.
The Phase Locked is turned to 67khz with a 5000Ω potentiometer; only approximate tuning is required since the loop will find the signal.
The output passes through a three-stage low-pass filter to supply not importance and reduce the high-frequency noise which often joint SCA transmission.
And the output signal is in the order of 50mV and the frequency response offer to 7kHZ.
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