PSN-L Email List Message

Subject: Re: it happened again
From: ChrisAtUpw@.......
Date: Wed, 26 Jul 2000 00:35:15 EDT

Dear John Tacinelli,

>  Well it jumped again tonight, right on schedule.  Fortunately I was right 
> there listening to KOLM radio, 1570 AM.  It jumped exactly as they went off 
> the air.  It must be their carrier signal during the day that keeps it in 
> place and then when it goes off the signal changes.  Unfortunately, my 
> homemade aluminum foil box shield did not work.  At least not enough.  

    Thin tinned steel sheet, folded with overlaps at the corners and then 
soldered is by far the most effective enclosure. It provides magnetic as well 
as electrostatic shielding. The easiest way is to put non corrosive flux on 
the fold faces, pop rivet them together and then use a big flame and a stick 
of solder. Aluminium sheet doesn't make very good electrical contact at the 
overlaps for very long.

    A few thoughts. Is your amplifier itself well shielded? Before you start 
spending real money, try making a filter in a long tin box with a few ferrite 
radio frequency chokes and small capacitors. 1520 KHz should filter out 
without too much difficulty. Do you use coax cable to link the coil to the 
amplifier? You need something like URM70, which has a stranded core and a 
heavy braided copper sheath. You might try putting the amplifier in a steel 
cake tin? If this works, add ventilation with a sheet metal cutter....


    Chris Chapman

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Larry Cochrane <cochrane@..............>