Gerald,
R. Kenneth Keenan's book Digital Design for Interference Specifications (Vienna,
Virginia: The Keenan Corporation, 1983) has some excellent advice for doing
developmental tests in chapter 6. He tells:
* How to do basic emissions tests using:
- An AM broadcast receiver.
- An FM broadcast.
- Or an inexpensive wide-band receiver.
* How to make basic test accessories such as a:
- Line-Impedance Stabilization Network (LISN) for conducted emissions
testing.
- Rotating folded-dipole antenna for radiated emissions testing.
The techniques/equipment that he describes will let you do *comparative*
measurements. If you have a problem because of ambients (radio, TV, pagers,
police/fire/emergency radio systems) you can easily build a simple shielded room
out of wood strips and chicken wire, being sure to overlap every seam by several
inches to provide good electrical contact and waveguide-below-cutoff effects.
You can reduce problems with standing waves by building the walls and ceiling so
that they are not parallel to one another-- a couple degrees off square will
probably be enough. If you always put the device-under-test (DUT), the antenna
and receiver, and yourself (use chalk or tape to mark the position of your feet
for making measurements) in close to the same positions you can get some pretty
decent semi-quantitative measurements using this type of shielded room, for a
very small investment in materials and time.
John Barnes Advisory Engineer
Lexmark International
author of Electronic System Design:
Interference and Noise Control Techniques
(Prentice-Hall, 1987)
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