Simple RF Field Strength Meter Circuit

To begin with, this Simple RF Field Strength Meter Circuit show how to make device to measure radio wave!

Radio and mobile phone both use radio wave and this signal we cannot see, also this thing are helpful for radio fans, engineers and new people.

Also, they can check how strong signal is in different area and they can use it to make their antenna better and check if radio is working good; as it also measure signal from different radio station.

Circuit Working:

Parts List:

Components	Values	Quantity
Resistors	10k 1/4 watt	1
	1.5k 1/4 watt	3
	Potentiometer 1M	1
Semiconductors	Transistor BC547	1
	Diode OA79	1
	1mA Meter	1
	ON/OFF Switch	1
	Battery 3V	1
	Antenna	1

This small circuit can measure how strong signal is from a transmitter, also people who make model airplane use it to check if signal from transmitter is going good.

With this FS meter, we can quickly identify whether the problem is in the transmitter or the receiver because the circuit uses only one active component, a transistor called T1.

Also, this transistor forms part of a bridge circuit and works like a controlled resistor, while the antenna connects to the base of T1.

Moreover, when radio signal voltage goes up at base of T1 then transistor start conduct and make bridge unbalanced and then current goes through resistor R3, meter and transistor path which is emitter to collector.

How to use it: Before turning ON transmitter we need to move P1 and set meter to zero.

Formulas:

This circuit is simple common emitter amplifier and in this amplifier input and output both share same transistor emitter.

Here, is how to understand this type of circuit:

Voltage Gain (Av):

Formula for voltage gain is:

Av = −Rc / Re

This work if capacitor is big and it short Re for AC signal.

Input Impedance (Zin):

To find input impedance:

Zin = Rb

Mostly base resistor Rb decide it.

Output Impedance (Zout):

Output impedance depend on Rc and transistor:

Zout = Rc / (β + 1)

here,

• β is current gain of transistor.

Voltage Gain with Bypass Capacitor:

If we put capacitor across Re so Re is short for AC, then:

Av = −Rc / Re

This design provides more gain than a circuit without a capacitor, but remember to consider both AC and DC conditions when building a common emitter amplifier.

Hence, to get right gain and to get good matching check all values are right.

How to Build:

To build a Simple RF Field Strength Meter Circuit below mentioned are the connection steps to follow:

Get Components Ready:

• First, find and collect all parts needed from above.

Put Transistor T1:

• Next, place T1 transistor on PCB and then connect antenna wire straight to T1 base.
• Then make T1 work like controlled resistor, as T1 is part of bridge circuit only one side.
• Now connect resistors and capacitors to make full bridge.

Connect Resistor R3:

• After that, join resistor R3 in line with meter and T1 which is emitter to collector, as they connect in series together.

Add Potentiometer P1:

• Put potentiometer P1 in circuit and before turning ON transmitter set P1 to zero with meter.

Meter Setup:

• Also, make sure we connect the meter with the correct + and − polarity.

Finish Bridge Circuit:

• After that, add all needed parts to complete bridge so it stay balanced when no signal.

Important Step Before Power:

• Before we turn ON transmitter then adjust P1 so meter shows zero and this help check signal strength correct.

Power Source:

• Give power that matches the circuit and parts we need and use steady power which is not too high or low.

Test It (Examine):

• Then turn ON transmitter and watch meter and this meter will move when signal strength changes.

Adjust Circuit:

• If result is not good then change some parts or values and also try with different resistor or capacitor until it is working good.

Safety First:

• Be careful with electric things and always follow safety rules.

Antenna Setup:

• Put antenna in right place and connect antenna good for better signal.

Grounding:

• Do grounding proper which will help to stop unwanted signal or noise.

Important Tip:

• If we not know about electronics then ask someone who know and also we can read more from books or trusted website.

Conclusion:

To conclude, this Simple RF Field Strength Meter Circuit is very useful as it help to place antenna to find signal problems and check RF rules.

Also, design depends on how sensitive we want and at what frequency, so wlways work with RF device with care and safety.