Friday, December 09, 2011

Mains filter, results

I told you I would write about the mains filter performance after the little VDR issue (blast off).

Well... did it worked?.....did it?......! Can't win all the time!

I'm sure the mentioned filter would work in minor interferences from mains, so the filter will be put in line with the transceiver power line (it's 230V AC powered).

I am not the first one to have issues with switching power supplies since by their nature they are an RF source and this one is a beast, 4A at 20V, normal laptops are have half the rate in current, I guess this computer is not very economical in power consumption.

When removing interferences that you suspect are from a power line there is some simple stuff one can do:

*Put a power line filter: Didn't worked in my case. If the power is DC sometimes a simple capacitor in parallel or an inductor in series will do the trick (low pass filter), capacitors "don't like" voltage change so do the inductors with current.

*Invert the power plug terminals: This will work if the source problem is unbalanced (power line wise)

*Some ferrite cores around the power cables. I've used this method wen using the Si570 RF generator close to some testing boards and it works (Now when using the Si570 I power it up from a separate power supply).

*Build a Faraday cage: Will work as long as that any "air" space in the gaps is smaller than the interfering wavelength... but for my case I suspect the interference is getting in from the antenna cable since the FT-102 it's self is build in a metallic "Faraday cage". I discarded the hypotheses of the interference getting picked by the antenna since it's 10m away, never the less further tests will be removing the antenna cable and the microphone.
I didn't tested yet was to put the laptop power supply inside the filter cage and earth blindage exiting the power cable or even moving to another plug (it's to far away for connecting the laptop to the screen monitor).

*Put and isolation transformer (230V/230V): That is expensive and I would prefer to put again the small computer previous used that I know causes no interference.

Well...the saga will continue....I will test more this weekend.

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