[600MRG] Fw: Re: Discontinuance of the USCG DGPS Service

[Murray Greenman]

You guys also need to consider not just the source, but where the noise 
is entering the receiver path.

It's been my experience (when using an active whip antenna) that a 
significant cause of noise is radiation of noise from the cable feeding 
the actual antenna. Consider that the receiver is 'earthed' to the house 
mains supply 'earth', which carries a lot of noise from appliances. 
Applying filters to the appliances will only be of limited benefit.

The best solution is the use of a seriously good common mode filter on 
the antenna coax cable. The cable on the antenna side of the filter 
should be securely earthed to a separate and very good earth, ideally 
the ground mat used for the transmitting antenna. In this way, the coax 
will be 'quiet' as it approaches the antenna, and can't therefore 
radiate noise into it.

A further improvement can be made by using galvanic isolation between 
the antenna and the receiver, right at the receiver, to remove the mains 
earth noise from the antenna cable altogether. But the first step must 
be to quieten and ground the cable at the antenna end.

The solution is not so obvious with loop antennae, which are less 
susceptible, or with large receiving antennae, but it's a point worth 
considering.

73,
Murray ZL1BPU
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