ZS1I Blog: Let's build the Modified "Squeakie" RF Field Strength Meter

I was not satisfied with the functioning and build of the veroboard "Squeakie" Field Strength Meter described in Part 2. I decided to ask AI for Dead-Bug construction outlay listed below. I however changed the following components: 1. D1 = I used a unlabeled Germanium Diode instead of the 1N4148 or 1N914. 2. Potentiometer = I used a 50K instead of a 25K.

The Germanium Diode is far more sensitive then the other two diodes while the 50k Pot is all that I had on hand. The 50k needs a sensitive hand when tuning but it works fine.

The Dead-Bug style construction is preferred instead of the Veroboard build. One can keep the leads of the components short to prevent stray RF and Ground Loops from causing unwanted issues.

I 3D printed a new larger project cabinet as to easily fit items in the cabinet.

Well here is the verdict: This unit works far better than the one I constructed on the veroboard. I will rip the first "squeakie" apart and build another type of RF Field Strength Indicator in the coming weeks.

Finally: If you experiment with antennas the "Squeakie" and Passive Field Strength Meters are a must have in your test equipment arsenal if you do not have a good antenna analyzer and other state of the art test equipment. The Modified "Squeakie" is far more sensitive then the Veroboard "Squeakie" version, although the audio output is much lower and softer. I tested it using a VHF handheld and by moving 3 meters away from the unit. It however works as described by Peter VK2YE. Great and useful project!

AI Feedback:

Here is your complete, comprehensive construction manual and Bill of Materials (BOM) for Peter Parker’s (VK3YE) RF Squeakie Field Strength Meter, optimized exclusively for error-free Dead-Bug construction on Linux Mint.

📋 BILL OF MATERIALS (BOM)

Component Identifier	Component Value / Type	Quantity	Purpose / Notes
IC1	555 Timer IC (DIP-8 package)	1	The core audio oscillator chip.
D1	1N4148 or 1N914	1	Silicon switching diode (RF detector). Must have a clear polarity band.
R1	15 kΩ Resistor (1/4W or 1/8W)	1	Limits bias voltage to the potentiometer.
R2	47 kΩ Resistor (1/4W or 1/8W)	1	Feeds rectified DC into the 555 trigger circuit.
R3	100 kΩ Resistor (1/4W or 1/8W)	1	Connects between Pin 7 and the Pin 2/6 bridge network.
Sensitivity	25 kΩ Potentiometer (Linear)	1	Fine-tunes the diode right up to the conduction threshold.
C1	1 µF Electrolytic Capacitor (16V+)	1	Smooths the main 9V power rail inputs.
C2	4.7 nF Ceramic Capacitor	1	Filters out RF ripples, leaving clean rectified DC.
C3	10 nF Ceramic Capacitor	1	Decouples Pin 5 (Control Voltage) to ground for stability.
C4	10 µF Electrolytic Capacitor (16V+)	1	Blocks DC voltage from reaching the speaker/buzzer.
C5	100 pF Ceramic Capacitor	1	Small timing capacitor determining the high audio pitch.
LS1	High-Impedance Piezo or Small Speaker	1	Acoustic output transducer.
PCB Base	Single-sided Copper-Clad Board	1	Size: 50 mm x 50 mm. Acts as the system ground.
Power Source	9V Battery & Battery Snap	1	Power source.

🗺️ VISUAL ASSEMBLY SCHEMATIC (BELLY-UP ASYMMETRIC MAP)

text

===================================================================
VK3YE "SQUEAKIE" FSM - COMPLETE DEAD-BUG LAYOUT WITH ALL COMPONENTS
===================================================================
View: Flipped 555 IC (Belly-Up, Notch facing LEFT)
Floor: The solid copper-clad circuit board base is all GROUND [FLOOR]
===================================================================

     +----------------------- 9V BATTERY (+) ----------------------+

     |                                                             |
     |          +------------------[ R1: 15k ]----------------+    |
     |          |                                             |    |
     V          |                                             V    V
  [PIN 8]       |       +-[ POT: 25k ]+                    [C1: 1uF (+)]
   (VCC)        |       |             |                        |

     |          |       | Leg 3       | Leg 1                  |
     |          |       | (Right)     | (Left)                 |
     |          |       |             V                        |
     |          +-------+          [FLOOR]                     |
     |                                                         |
     |                  +--- Leg 2 (Center Wiper)              |
     |                  |                                      |
     |                  V                                      |
     |           [ NODE A (AIR) ] <==== ANTENNA                |
     |                  |                                      |
     |                  V                                      |
     |           [1N4148 DIODE (D1)]  (Anode to Cathode ->)    |
     |                  |                                      |
     |                  V                                      |
     |           [ NODE B (AIR) ]----+                         |
     |                  |            |                         |
     |                  |            V                         |
     |                  |       [C2: 4.7nF]                    |
     |                  |            |                         |
     |                  |            V                         |
     |                  |         [FLOOR]                      |
     |                  |                                      |
     |                  +-------------[ R2: 47k ]----------+   |
     |                                                     |   |
     |     ======================================          |   |
     |    |     555 TIMER IC (BOTTOM VIEW)       |         |   |
     |    |     Notch/Dot is on the LEFT side    |         |   |
     |    |                                      |         |   |
     +--->|   [PIN 8]   [PIN 7]   [PIN 6]   [PIN 5] |        |   |

     |    |    (VCC)     (DISC)    (THRES)   (CTRL) |        |   |
     |    |      |         |         |         |    |        |   |
     |    |======|=========|=========|=========|====|        |   |
     |    |      |         |         |         |    |        |   |
     |    |   [PIN 1]   [PIN 2]   [PIN 3]   [PIN 4] |        |   |
     |    |    (GND)    (TRIG)    (OUT)     (RESET) |        |   |
     |     ======================================          |   |
     |           |         |         |         |           |   |
     +-----------|---------|---------|---------+           |   |

                 |         |         | (Bridge Wire)       |   |
                 V         |         +---------------------+   |
              [FLOOR]      |                               |   |
                           +========[ WIRE BRIDGE ]====+   |   |

                           |                           |   |   |
                           V                           V   V   V
                     [PIN 2/6 BRIDGE NODE] <---------------+---+

                           |             |
                           V             V
                     [C5: 100pF]     [R3: 100k]

                           |             |
                           V             V
                        [FLOOR]       [PIN 7]

                                         [PIN 5] ----> [C3: 10nF] ----> [FLOOR]

                                         [PIN 3] ----> [C4: 10uF (+)] -> [SPEAKER]

 -> [FLOOR]

Use code with caution.

🛠️ STEP-BY-STEP ASSEMBLY MANUAL

Phase 1: Mechanical Foundation

Prep the Floor: Use steel wool to polish your 50 mm x 50 mm copper board until it is bright clean.
Mount the IC: Add a drop of superglue to the top face of your 555 IC. Glue it upside down in the middle of the board so its pins point up. Make sure the notch or index dot faces to the left.
Anchor the Circuit: Locate Pin 1. Bend it all the way down until it lays flat against the copper board floor. Solder it securely to the copper. This is your main ground reference and structural anchor.

Phase 2: Wiring the Power and Core Audio Loop

Reset Jumper: Run a bare wire jumper connecting Pin 4 to Pin 8 across the top of the chip. Solder them together.
Trigger Bridge: Run a bare wire jumper connecting Pin 2 to Pin 6. Solder them together.
Audio Timing Stack: Solder the 100 pF capacitor (C5) directly from the Pin 2/6 wire bridge down to the copper ground floor. Keep its legs short.
Discharge Link: Solder your 100 kΩ resistor (R3) directly between Pin 7 and the Pin 2/6 wire bridge node.
Pin 5 Stabilizer: Solder your 10 nF capacitor (C3) directly from Pin 5 straight down to the copper floor.
Output Audio: Connect the positive (+) leg of your 10 µF capacitor (C4) to Pin 3. Solder the negative leg of C4 to your speaker or piezo element. Connect the other side of your speaker directly to the copper ground floor.
Power Filter: Solder the positive (+) side of the 1 µF capacitor (C1) to Pin 8, and the negative (-) leg straight down to the copper floor.

Phase 3: Creating the Isolated RF "Air Nodes"

To prevent RF leakage, these nodes must hang in mid-air and never touch the copper ground board below them.

Assemble Node A (In-Air): Solder these three items together in a free-floating joint suspended above the board:
- The center wiper leg (Leg 2) of the 25 kΩ Potentiometer.
- A short stiff piece of wire (approx 10-15cm) acting as your Antenna.
- The Anode (unbanded end) of the 1N4148 diode (D1).
Assemble Node B (In-Air): Solder these three items together in a separate free-floating joint:
- The Cathode (banded end) of the 1N4148 diode (D1).
- One end of the 47 kΩ resistor (R2).
- One leg of the 4.7 nF capacitor (C2). Take the other leg of this capacitor and solder it directly down to the copper floor.
Hook RF to the Engine: Take the free hanging leg of the 47 kΩ resistor (R2) extending out from Node B, bend it over carefully, and solder it straight onto Pin 7 of the 555 IC.

Phase 4: Final Potentiometer and Battery Links

Pot Ground: Solder Leg 1 (left pin when looking at the knob) of the 25 kΩ pot to the copper floor.
Pot Supply: Solder one side of the 15 kΩ resistor (R1) to Leg 3 (right pin) of the pot. Connect the other side of this resistor to Pin 8.
Hook Battery Rails: Solder your 9V battery strap's black wire (-) directly to any bare spot on the copper floor. Solder the red wire (+) directly to Pin 8.

🚀 INITIAL CALIBRATION & FUNCTION TESTING

Turn on the circuit.
Slowly rotate the 25 kΩ Sensitivity Potentiometer. At one side of its rotation, you should hear a high-pitched squeal from the speaker.
Rotate the knob backwards slowly until the squealing slows down into discrete clicks, and then drops into absolute silence. This transition edge is your sweet spot. Leave the knob right at this threshold.
Key up your handheld transceiver (HT) on low power a short distance away. The rectified RF entering through Pin 7 will instantly spark the 555 into life, producing a loud, high-pitched audio tone that shifts in frequency as you move closer or further away.