Sometimes noise generated from within the motor compartment of a tractor or auto can be very difficult to trace down. One of the best ways is with the use of a RF Sniffer. A simple one can be made easily and quickly.
Here are the steps to construct the sniffer:
- Use an 18' length of either RG/58 or RG/8x stranded center coax. The 18' length should provide enough length to allow reaching all areas needed.
- On one end, solder a PL-259 connector.
- On the other end trim back 12" of the outer rubber covering and the shield. This will leave 12" of foam exposed.
- Trim off 10"of the foam, leaving the center strand exposed.
- Twist the strands of the wire together to form a tighter wire.
- Using a broom handle or similar sized round tube, wrap the exposed wire around the handle forming two loops.
- Tightly twist the excess wire back around the beginning of the wire, to prevent loops from undoing.
- Remove the broom handle from the windings.
- Spread apart the loops so that they are not touching each other.
- Construction of RF Sniffer is now completed.
When completed, it will look similar to this picture:
A more enhanced version that will eliminate most interference or radiation of coax line can be constructed by adding a 5 or 10 watt, 50 ohm resistor in line and soldering the other end to the coax shield in this picture:
Here are the steps to actually use the sniffer:
- Connect the end of the coax with the PL-259 connector to the radio.
- Turn radio on, and the volume up enough to be able to hear the noise when you are outside of vehicle.
- Start and run vehicle engine.
- Move the loop end of the coax around the motor compartment, over motors, etc., being careful not to touch any thing. CAUTION: Be careful around fan motors to avoid fan blades.
- When the noise level increases, the item that the loop is over is the part causing the noise to be generated.
- This part may be needed to be filtered, grounded, or shielded ( depending on the part ) to cure the noise problem.
- Repeat process to locate all the sources of noise.