Bypass ALL DC pins with the LC type feed thrus installed in the metal box.

  *
  |  __O    Thomas C. Sefranek   WA1RHP@ARRL.NET
  |_-\<,_   Amateur Radio Operator: WA1RHP
  (*)/ (*)  Bicycle mobile on 145.41, 448.625 MHz

http://hamradio.cmcorp.com/inventory/Inventory.html
http://www.harvardrepeater.org

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Jinx
> Sent: Saturday, April 05, 2003 6:21 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [PIC]:Blocking RF
>
>
> I made up a number of F628 circuits that have been installed (not
> by me) in small planes, and all seemed to be well until a couple of
> the pilots reported back that, when using the radio, now and then
> the PICs acted as though one of the circuit switches had been
> operated. The symptoms indicate that noise is getting into at least
> Portb4 and being interpreted as a switch closure. I've not yet been
> able to get to the either of the circuits to physically check how they've
> been installed, mainly because they're overseas. It couldn't have
> been the ones just up the road that went funny could it !!
>
> All circuits are in closed aluminium cases bolted to the plane's
> chassis and I recommended that grounded screened cable be
> used for signals (about 2m long) and power lines. The cable
> plugs into a 9 pin D. Portb4, like other inputs, already has pulldowns,
> ceramic caps, Zeners and Schottkys on it. Portb4 is the first
> tested in a switch checking loop, which is why I'm assuming (oh-oh)
> that's the reason for the faulty operation
>
> The radios causing the problem are 5W @ 100-150MHz. I've sent
> the installer some ferrite beads to see if that cures it, and someone
> has suggested winding the cable once or twice around a ferrite ring.
> Maybe it needs a ferrite + choke as well, or something similar to
> the surrounding ferrite on a printer cable
>
> If anyone has comments that would be appreciated
>
> TIA
>
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