Interference Problems - Interphase Twinscope Operation Manual

Interference Problems

Interference can come from several sources. The most common of these are:
1) Other nearby depth sounders operating at the same frequency.
Interference caused by nearby depth sounders operating on or near the same frequency as the Twinscope will
typically appear as "rabbit tracks" that march up and down the screen. Reducing the gain will help minimize this
problem.
2) Radiated interference from the boat's electrical system (alternator, distributor and spark plugs) or from nearby
equipment that radiates electrical noise.
Radiated interference caused by the boat's engine can usually be identified by observing the Twinscope with both
the engine running and turned off. If the interference disappears when the engine is turned off, it is safe to assume
that the engine is the source of the interference.
3) Conducted interference usually occurs when the Twinscope shares a 12VDC power lead with other noisy
equipment (i.e.; bilge pumps, motors, refrigeration systems, autopilots, etc.)
This type of interference can usually be eliminated by using the same techniques used in the automotive industry to
eliminate interference to car radios, CB's, etc. The following actions may be required:
1) Reduce the SENS setting to minimize interference.
2) Make sure your boat uses resistor type spark plugs and plug wiring.
3) Install a suppressor on the center lead of the distributor.
4) Install an alternator filter to smooth the alternator's output signal.
Interference may also be caused by radiation from other nearby equipment and can be detected by turning off all other
equipment and observing the Twinscope display as each suspected source is turned back on. This type of
interference can usually be eliminated by moving the Twinscope away from the source and checking to ensure that
the interfering source is properly grounded.
Interference causing the display to be unstable, to pulsate or periodically change size is usually caused when another
piece of equipment shares the same 12 VDC power leads from the battery. This problem is especially severe when
equipment requiring large current surges (i.e.; autopilots, refrigerators, or bilge pumps) share the same power leads.
Minimize this type of interference by running the Twinscope's 12VDC power leads, or those of the interfering
equipment, directly to the battery.
Alternately, you may find it helpful to install a separate dedicated power supply battery that is used only to run your
electronic gear (e.g.; fishfinders, VHF radios, radar units, etc.). If your unit shuts off during low voltage situations,
such as when cranking your engine starter, you may want to install an isolator switch with an "A/B" type of battery
system. An "A/B" system allows you to run your electronic gear on one battery, while the starter and alternator are
hooked up to the other battery.
Your authorized marine electronics dealer is familiar with the methods of reducing electrical interference and is
qualified to assist you should a problem persist.
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