I have completed the "Squeakie" 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 (purple in colour) 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 "Squeak": When the sensitivity control is adjusted right to the edge just before self-oscillation, the circuit achieves maximum sensitivity. A tiny amount of RF causes clicking, and stronger RF drives the 555 timer into a higher-pitched audible squeak or shriek through the speaker.
- I used a traditional landline telephone handset speaker (100 to 150 ohms) that actually work better and offer several functional advantages over a standard 8-ohm speaker for this specific circuit. The reason being: 100-to-150-ohm telephone speakers are specifically engineered to be highly sensitive to vocal/mid-range audio using very little electrical power. They will cleanly reproduce the faint, early "clicking" and low-power squeaks at the very edge of the meter's threshold, extending the usable sensitivity of the device.
I will definitely play around with the "Squeakie" when I find the time. It is now onto completing the Passive RF Field Strength Meter and putting it into a cabinet.
Images: Click on images for larger view.
