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.
This thing are helpful for radio fans, engineers and new people.
They can check how strong signal is in different area.
They also can use it to make their antenna better and check if radio is working good.
It also measure signal from different radio station.
Circuit Working:
Parts List:
| Category | Description | 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.
People who make model airplane use it to check if signal from transmitter is going good.
With this FS meter we can fast know if problem is in transmitter or in receiver.
This circuit uses only one active part which is one transistor called T1.
This transistor is part of bridge circuit and it works like controlled resistor.
Antenna is connected to base of T1.
When radio signal voltage goes up at base of T1 then transistor start conduct and make bridge unbalanced.
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.
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 gives more gain than without capacitor.
Remember AC and DC things when build common emitter amplifier.
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:
- Place T1 transistor on PCB.
- Connect antenna wire straight to T1 base.
- Make T1 work like controlled resistor.
- T1 is part of bridge circuit only one side.
- Now connect resistors and capacitors to make full bridge.
Connect Resistor R3:
- Join resistor R3 in line with meter and T1 which is emitter to collector.
- They to connect in series together.
Add Potentiometer P1:
- Put potentiometer P1 in circuit.
- Before turning ON transmitter set P1 to zero with meter.
Meter Setup:
- Be sure meter is connected with right polarity with + and – correctly.
Finish Bridge Circuit:
- 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.
- This help check signal strength correct.
Power Source:
- Give power that matches the circuit and parts need.
- Use steady power which is not too high or low.
Test It (Examine):
- Turn ON transmitter and watch meter.
- Meter will move when signal strength changes.
Adjust Circuit:
- If result is not good then change some parts or values.
- Try different resistor or capacitor until it is working good.
Safety First:
- Be careful with electric things.
- Always follow safety rules.
Choose Part Values:
- Pick resistor, capacitor and potentiometer values that fit the design.
Antenna Setup:
- Put antenna in right place.
- Connect antenna good for better signal.
Grounding:
Important Tip:
- If we not know about electronics then ask someone who know.
- Also we can read more from books or trusted website.
Conclusion:
This Simple RF Field Strength Meter Circuit is very useful.
It help to place antenna to find signal problems and check RF rules.
Design depends on how sensitive we want and at what frequency.
Always work with RF device with care and safety.