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Author Topic:   Isolating interference
PamlicoSound posted 04-22-2008 11:48 AM ET (US)   Profile for PamlicoSound   Send Email to PamlicoSound  
I have an Interphase Sonar/Depth Sounder and a Standard VHF. When both are operating, I hear the squelch break on the radio unless turned way up as if the sounder is interfering. Suggestions for isolation?
They are on a bridge together, so the cables share a chase to get from below.
Chuck Tribolet posted 04-22-2008 07:40 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
If Interphase wasn't making the noise, Standard couldn't
receive it.


Fill us in on what cable goes where. The VHF has (at least)
power and antenna, the sounder has (at least) power and
transducer.


Separate the cables? esp. the transducer cable from the
VHF power and antenna cables.

And put twists in both power cables. One twist per foot
is probably good enough, a little more wouldn't hurt. But
first figure out if they already have a twist inside the
sheath.

And ask Interphase. They may have some specific suggestions
about your model.


Chuck

jimh posted 04-22-2008 09:04 PM ET (US)     Profile for jimh  Send Email to jimh     
To tell if there is interference, tune the radio to a weak but steady signal, such as you might get from a distant weather radio broadcast. Leave the squelch control at full-off, or minimum squelch, or maximum radio sensitivity.

Now turn on the Sounder. If you then hear noise modulating the weak signal, you have interference.

With the Sounder verified as the source, next determine the path for the interference to enter the receiver:

--via the power leads
--via the antenna lead
--via the antenna itself

Disconnect the antenna from the radio. Open the squelch. Set the noise to a reference volume. Turn on the sounder. Does the noise go up? If yes, the noise is entering via the power heads. Install some chokes on the leads to the sounder as close to the sounder chassis as possible. If the noise does not go up, the interference is not via the power leads.

Reconnect the antenna. Separate the power leads and the transducer leads of the sounder from any wiring to the radio and antenna. Check for change in interference. If the interference changes, the path was probably via the cables. If the interference stays, the path was probably via the antenna itself.

If the interference is via the cables, separate them. Check with the sounder manufacturer about shielded cable.

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