We asserted last time that the existing amplifiers in the current test set up might be used to generate the higher stress levels if the test distance was reduced from 3 meters to 1 meter. As a reminder, we argued that testing at 1 meter means testing takes place in the near field as is the case for the threats faced by medical equipment (nearby cellphones etc.). Using the same amplifiers would significantly lower the investment (by about half a million dollars) required by the test house
Note that the medical manufacturer still has to face the fact that his equipment needs to pass at the higher stress levels, so no gain for him other than he does not have to indirectly pay for the test manager’s half a million dollar investment in new amplifiers.
Now, it is true that there are issues with 1 meter testing that offset the power savings in military and automotive testing. The key issue with these two types of test is cross-coupling between the antenna and the ground plane. The ground plane is a raised metal sheet grounded through a low impedance path. The cross-coupling reduces the effective gain of the antenna, so you need more amplifier power. However, we are not advocating the use of a ground plane, so this particular issue goes away.
In the next blog I will make the case that the test waveforms should truly represent the waveforms emitted by nearby threats. This will, of course, require special test instruments and this will offset the savings made by not replacing the amplifiers
–Thomas Mullineaux
