Image: Passive RF Field Strength Meter
Let's build a Passive RF Field Strength Meter (Part 1) available HERE.
I have completed the Passive RF Field Strength Meter.
Herewith a few notes:
- This field strength meter is for use on HF and VHF. It has it's limitations in using it on VHF with a handheld putting out 3 - 5 Watt RF power. The more RF Output Power the stronger "Squeaks" you will get.
- The ideal cabinet for the meter is either metal or aluminum. I used a 3D printed cabinet which I lined with aluminum tape on the inside to screen the components against stray RF.
- Use a decent RX antenna on the RF Field Strength Meter. It will improve sensitivity and range.
- I installed a ground wire that I hold in my hand. I found that the RX is much better with the ground wire making contact with my hand. If you use a metal or aluminum box I still recommend a ground wire as an "earth". Hi Hi!!!
- Keep your wires in the box as short as possible to prevent interaction with possible stray RF or Capacitance.
- The sensitivity (tuning) control is adjusted to achieve maximum sensitivity but also to keep the meter between 01 and 60.
- You can use the tuning control when moving further or closer away from the RF Field Strength Meter to "calibrate" the meter.
An RF field strength meter is a helpful tool that measures the intensity of radio frequency (RF) electromagnetic fields in the air. If you build, tune, or experiment with antennas, it gives you a practical way to see how much energy your antenna is actually radiating.
What It Does
Detects Radiation: It picks up wireless signals through a small antenna without needing a direct physical connection to your transmitter.
Compares Signals: Most hobbyist meters show relative strength. They tell you if your signal is getting stronger or weaker as you make adjustments.
Finds Nulls and Lobes: You can walk around an antenna to map out where the signal goes.Why You Need One for Antennas
Verify Output: It confirms that radio frequency energy is actually leaving your antenna element and going into the air.
Tune for Maximum Gain: As you tweak an antenna match or adjust lengths, a higher meter reading indicates improved radiated power.
Check Directionality: You can test directional antennas (like a Yagi) to compare front, side, and rear signal strength.
Troubleshoot Noise: It helps track down unwanted RF leaks, common-mode current on feedlines, or local electromagnetic interference.
In my humble opinion the RF Field Strength Meter is not strictly necessary in a radio shack, but it is a helpful optional tool for tracking stray RF and checking basic antenna radiation without having to by expensive test equipment.
Images: Click on images for larger view.
