Use and Construction of A Noise Sniffer

Antenna Sniffer (fig. 1):

Checking For Noise On A Wire (fig. 2):

Two types of noise sniffers can be made. The first is made from an old piece of antenna lead-in. The second type is made from a personal type radio/cassette player.

The first is ideal for checking for noise in the instrument panel while the second is better suited for locating noise in the engine compartment. For the antenna lead-in style sniffer, refer to Figure 1. The two-inch section of coaxial cable with the black coating and braided shield stripped back becomes the antenna when the sniffer is plugged into the radio's antenna socket. It can then be used to find noise in and around harness wiring. Simply plug in the noise sniffer and probe around suspected areas (see Figure 2). For best results, turn the RADIO volume up and probe from several different angles. The noise will be heard on the speakers once the noise sniffer is near the wiring harness which is producing the noise.

Equipment Needed:
^ Personal AM/FM radio with headphones.
^ Four feet of 75 ohm antenna coaxial cable.
^ One-half inch heat shrink tube the same diameter as the coaxial cable.
^ A drill and drill bit the same diameter as the coaxial cable.
^ Book of matches or hair dryer.
^ Soldering iron and solder.

Assembly:
1. Strip 1/4" of insulation from each end of the coaxial cable.
2. Place the heat shrink over one end of the bare wire, Fasten the heat shrink to the wire by heating it (match or hair dryer).
3. Disassemble the radio and locate the antenna.
4. Disconnect the antenna and fasten the bare end of the coaxial cable to the antenna mount. A soldering iron may be needed.
5. Feed the coaxial cable to the exterior of the radio. Drill a feed hole if necessary.
6. Reassemble the radio.

To use the sniffer, tune the radio to an AM station. It can now be used in the same manner as the previous noise sniffer, but with the noise being heard through the headphones.

Once the problem area is isolated, wrap the harness in that area with a braided shield and attach the shield to a known good ground. If the noise persists, continue checking for other noisy wires.