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Thursday, June 24, 2010

Simple Wideband SWR Meter Circuit

This is a circuit of Wideband SWR Meter. This circuit is used as a test instrument. To use this circuit, connect the meter, take the necessary readings, then disconnect. The meter should not be left in the line permanently because it draws up 3/4 of the transmitted power, and a similar part of a received signal. This circuit uses Three pairs of 100 Ohm resistors those are combined in a bridge circuit, with the load as the fourth resistor. The diode, D1, is used to rectify a sample of the input signal, while D2 used to rectify the differential voltage across the bridge. So, the square root of reflected power can be achieved. This is the figure of the circuit;


The two output voltages of the circuit are applied to two simple galvanometers and to a ganged potentiometer. Besides that, this output voltage can be applied to digital displays, microprocessors, etc. A 5Vrms RF signal is applied to the input and A 50 Ohm load is connected to the antenna side. So 1/2W will across 50 Ohm. D1 provides 3.5V DC because At the anode of D1 have 2.5Vrms, or 3.5V peak. D2 will not produce any DC output because it see exactly the same RF voltage at both sides, and in the same phases. The meter indicate a 1:1 SWR when The forward meter move, while the reflected signal meter will stay at zero. The transmitter will indicate 1:1 SWR too because it see 2 times 100 Ohm in parallel, or 50 Ohm. while the remaining quarter gets delivered to the antenna, One quarter of the power will be dissipated in each of the resistor pairs.

When the extreme condition occurs like the load was disconnected, so the circuit has infinite SWR. D1 see half of the input voltage, and no voltage drop across them, and there is now no current in R1/R2. D2 produces the same rectified output as D1 does because it see “the other half” of the input voltage. So the meter indicate all power is being reflected because both meters deflect by the same amount, and the SWR is infinite. The transmitter indicate a 2:1 SWR because it see 100 Ohm load, far away from causing danger to any transmitter.
[Circuit source: Homo Ludens Electronicus]

Simple Low Distortion Oscillator Circuit


This is a simple design circuit with very low harmonic distortion, 2N4416 JFET is suitable to smoothly oscillate in a circuit. On application where low harmonic content is required for a good mixer circuit, JFET local oscillator is very good. This is the figure of the low distortion oscillator circuit;


This is the 20 MHz Oscillator Values
· C1 = 700 pF L1 = 1.3 mH
· C2 = 75 pF L2 = 10T 3/8″ DIA 3/4″ LONG
· VDD = 16V ID = 1 mA
20 MHz OSCILLATOR PERFORMANCE
· LOW DISTORTION 20 MHz OSC.
· 2ND HARMONIC -60 dB
· 3RD HARMONIC > -70 dB

[Source: National Semiconductor Application Note]


Simple DC or AC Voltage Indicator Circuit

This circuit is a circuit diagram is not a novelty, but it proved so useful, simple and cheap that it is worth building. When the positive (Red) probe is connected to a DC positive voltage and the Black probe to the negative, the Red LED will illuminate. This is the figure of the circuit;


Reversing polarities the Green LED will illuminate. Connecting the probes to an AC source both LEDs will go on. The bulb limits the LEDs current to 40mA @ 220V AC and its filament starts illuminating from about 30V, shining more brightly as voltage increases. Therefore, due to the bulb filament behavior, any voltage in the 1.8 to 230V range can be detected without changing component values.

Parts:
P1 = Red Probe
P2 = Black Probe
D1 = 5 or 3mm. Red LED
D2 = 5 or 3mm. Green LED
LP = 1220V 6W Filament Lamp Bulb
Source :extremecircuits.blogspot.com

Tuesday, June 8, 2010

Simple Programmable Voltage Regulator Using L200 IC


This is a simple programmable voltage regulator circuit. With this circuit we can generate a voltage according to our wishes. This circuit is based on L200 IC. This is the figure of the circuit;


Potentiometer R2 is used to fix the output voltage Vo. Following equation show value of the output voltage:

Vo=Vref (1+(R2/R1))

We can obtain a wide range of fixed output voltage by substituting the potentiometer with a fixed resistor and choosing suitable values for R2 and R1.

[Circuit source: SGS-Thomson Application Note]

Simple Precision Current Sink Circuit


This a a simple circuit for precision current sink. This circuit uses two kinds of transistor, 2N2219 bipolar transistor and 2N3069 JFET because both of them have inherently high output impedance. This is th figure of the circuit;


To provide feedback to the LM101 op amp, this circuit uses R1 as a current sensing resistor. The true current sink nature of this circuit is enhanced because the op amp provides a large amount of loop gain for negative feedback.

The output current is given by :
Io = Vin/R1
with Vin > 0 V

The 2N2219 and the 10K resistor may be eliminated, for small current values, if the JFET’s source is connected to R1.
[Source: National Semiconductor Application Note]

Simple Air Flow Detector Circuit


This is a design of simple circuit uses an incandescent lamp to detect airflow. With the filament exposed to air, a constant current source is used to slightly heat the filament. As it is heated, the resistance increases. This is the figure of the circuit;


As air flows over the filament it cools down, thus lowering it's resistance. A comparator is used to detect this difference and light an LED. With a few changes, the circuit can be connected to a meter or ADC to provide an estimations on the amount of air flow.

Part;
R1 100 Ohm 1/4W Resistor
R2 470 Ohm 1/4W Resistor
R3 10k 1/4W Resistor
R4 100K 1/4W Resistor
R5 1K 1/4W Resistor
C1 47uF Electrolytic Capacitor
U1 78L05 Voltage Regulator
U2 LM339 Op Amp
L1 #47 Incandescent lamp with glass removed (See "Notes")
D1 LED

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