Electronic projects

you are here: home page :: projects :: Tools & measurement :: measuring devices :: Field-strength meter

Field-strength meter

Circuit diagram

Original source:
I saw this circuit in an old issue of "73 Radio Electronics". I built it, but it didn't work well, so I changed a few components to get better sensitivity.

This is a very straightforward circuit. The first stage acts as a crystal receiver. Use a germanium detector diode (like 1N34, but AA119 is much more common in Europe), a silicon one won't do. The frequency is determined by L and C. For the FM band and VHF, wind a coil 5mm in diameter, 6-8 turns of coated wire 1mm thick. You can always vary the frequency by spacing the turns a bit looser or tighter. C is much less critical. Something around 100p is preferable, though.
The second stage is based around the versatile 2N3819 JFET high-impedance amplifier. With the 470k potentiometer you can adjust sensitivity of the circuit. The trimmer is used to zero the meter. Use any old 50mA or slightly smaller ammeter from the junk box.

You can't expect great performance from such a simple detector-based meter. Sensitivity is just adequate enough to get a basic idea of the power that your transmitter is capable of.

Possible uses:
Use the field-strength meter to find out when a transmitter is operating at optimal power. It can be very handy when aligning stages (like in case of the 4W transmitter) or experimenting with different antennas.

author: 73 Radio Electronics
web site: http://www.electronics-lab.com
project categories:
folder Audio (49)
folder Power & high voltage (43)
folder Radio (23)
folder Light & LED (31)
folder Tools & measurement (40)
folder Telephone (18)
folder Automotive (10)
folder Microcontrollers (12)
folder Sensors & control (47)
folder Timers & oscillators (40)
folder Miscellaneous (26)

StumbleUpon button

Share this page
Bookmark and Share
project subcategories:
All subcategories
testing equipment
measuring devices
other tools

similar projects:
Capacitance Meter
Digital Radar Speedometer
Digital Remote Thermometer
Digital Voltmeter
Electromagnetic Field Probe with Meter Output
Field-strength meter
Led display digital Voltmeter
Linear Resistance Meter
Picoammeter circuit with 4 ranges

recently added projects:
Doorbell for the Deaf
High Quality Intercom
Combinational Conjuring Trick
Ultrasonic Dog Whistle
Quiz Circuit
LED Torch
Insect Repellant
Speaker Microphone Circuit
Magic Wand Conjuring Trick.

most popular projects:
Led display digital Voltmeter
500W low cost 12V to 220V inverter
Low pass filter - Subwoofer
High And Low Voltage Cut Off With Time Delay
Metal Detector
2N3055 Power Amplifier
Basic UPS Power Supply
200W audio amplifier
LED Torch
100W RMS Amplifier

DIY Electronics Projects

Promote Your Page Too