RF interference

Archiver

Hello all,

I am a beginner with Basic Stamps and am using one (OEM II) to
interface between 4 RF transmitters and a serial LCD screen. My
systems work great separately, but together there are some
problems. (we've all heard that before!!)

When the system is connected, the transmitters are marginally
functional. This seems to be caused by the proximity to the Stamp. I
was hoping for ideas to recify this situation. The project is in a
fairly small plastic enclosure. I realize EMI/RFI has a lot to do
with my problems, but I did not expect this so I need some way
to "fix" it. (in a hurry, of course, project is due in one week)

Should I shield the stamp with copper or aluminum? Is there a
technique for that for it to be effective? Is there anything else I
can do?

Any suggestions would be great, let me know if I need to provide more
info...

Thanks,

Patti

Archiver

Hi Patty
What I know about RFI come from working with satilite receivers and catv
equipment so take it for what its worth.
First I would separate each transmitter in a metal Can by itself all
grounded together and connected to the P/S ground.
Second if there are any wires longer than a couple of inches, use
shielded wire and connect the wire shield to ground.
Third use a very good, well filtered power supply or maybe even use
batteries.
If none of this does any good try a different stamp. I have had some that
seem be overly sensitive to environmental noise.
I dont know what these suggestions will do to the transmitter range, any
grounded metal object in close proximity will tend to short a certain
amount of RF energy or changing the radiation pattern in one direction or
another. You will have to experiment to find the best balance.

On Sat, 10 Nov 2001 03:59:55 -0000 patti@p... writes:
> Hello all,
>
> I am a beginner with Basic Stamps and am using one (OEM II) to
> interface between 4 RF transmitters and a serial LCD screen. My
> systems work great separately, but together there are some
> problems. (we've all heard that before!!)
>
> When the system is connected, the transmitters are marginally
> functional. This seems to be caused by the proximity to the Stamp.
> I
> was hoping for ideas to recify this situation. The project is in a
> fairly small plastic enclosure. I realize EMI/RFI has a lot to do
> with my problems, but I did not expect this so I need some way
> to "fix" it. (in a hurry, of course, project is due in one week)
>
> Should I shield the stamp with copper or aluminum? Is there a
> technique for that for it to be effective? Is there anything else I
>
> can do?
>
> Any suggestions would be great, let me know if I need to provide
> more
> info...
>
> Thanks,
>
> Patti
>
>
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Archiver

Hi Kevin & Patti, I missed Patti's original entry but have a few
suggestions: (1) The ARRL RFI Book is very helpful as is (2) The ARRL Radio
Amateur Handbook. Also bypass all power supply leads coming into the Stamp
with a high quality ceramic 0.01 mfd disc capacitor and also consider using
RF chokes in series with the supply leads. Enclose the stamps with copper
clad PCB material and solder together to create a shield around sensitive
devices. Review how the devices are oriented to the RF circuits and
antennas. The above texts are very helpful for that. Locate a gray haired
ham operator that builds equipment to help you. Good Luck, Burt