As indicated in a previous blog post, it seems hard to justify the rationale behind testing medical equipment for RF immunity at 3m distance. It is this greater test distance (as opposed to the 1m test distance accepted in automotive and MIL-STD testing) that is driving the high price of the replacement amplifiers. A change from the current test field strength of 10v/m @ 3m to … [Read more...]
Do I really need that signal?
We’ve been discussing signals from the perspective of their bandwidth relative to the bandwidth of the receptor and have not considered them from the EMC point of view. RF signal energy can get from the emitter to the receptor by conduction or by radiation. We’ll discuss that later. Regardless of the energy transfer process, using the FCC classification scheme we … [Read more...]
Abracadabra the Broadband Signals Disappeared
Almost all EMC engineers these days are familiar with MIL-STD-461 and its various revisions because it has influenced the procedures in virtually all present day EMC standards. The original document and the A, B and C revisions all had requirements for measuring both broadband (BB) and narrowband (NB) emissions. When MIL-STD-461 was first released (July 31, 1967), the … [Read more...]
Another Look at Broadband Bandwidth Bandwidths
The last comment I made was regarding those perfect rectangular filters that we always describe with such reverence. But as I said, they don’t exist. Taking a receiver as an example, the filter amplitude versus frequency characteristics are measured by sweeping a narrowband signal through the passband frequency range of the circuit. Typically the passband width is … [Read more...]
Part II: The Impact of the Upcoming Medical RF Immunity Revision
The test-house manager’s perspective continued: At well over a quarter of a million dollars just to replace the existing 26-1000MHz amplifier and the same again to cover 1-6GHz at 200W (will take two amplifiers), the test manager will need to justify half a million dollars for the amplifiers alone. And the total will likely rise to around $600,000 or more with other equipment … [Read more...]
Random or Coherent Signals
In the previous post, I indicated that coupled Broadband energy levels are determined by whether the signals are random or coherent. Random/non-coherent signals originate from sources that are not time related. A couple of good examples would be receiver thermal noise and DC motor brush noise. Another would be the RF environment taken as a whole. Because the individual energy … [Read more...]
Narrowband and Broadband Signals
As I indicated in the previous post, this discussion begins examining signal characteristics from an electromagnetic compatibility (EMC) perspective. But first, a few words to describe EMC. This is a relationship issue. We want all the equipment items to get along in peace and in harmony, but if one of them is a big source and the other is a wimpy receiver, they may not play … [Read more...]
Impact of the Upcoming Medical RF Immunity Revision
As indicated last time, there are two key parties with a vested interest in the outcome of the upcoming Medical RF immunity revision:The test house manager who has to justify an upgrade to his test system to the people holding the purse strings.His customer, the company wishing to sell medical equipment compliant with the revised standard.I shall add a third … [Read more...]
Are they out to get us?
I didn’t realize when I addressed the smart meter RF situation that it was turning into such an uproar. Now, on top of the RADHAZ comments, people are expressing concern about protection of privacy. It seems that a lot of people have a difficult time believing in RF hazards because they can’t smell, feel, touch, taste, etc. the lower RF energy levels and, therefore, a hazard … [Read more...]
Just when you thought it was safe to turn off the light…
Well, I’ve used my quota of words for the month of May so now I’m going to have to make the next several posts somewhat shorter. That’s what happens when you get on a really passionate topic. The last post was about smart electric meters and the un-smart way in which the power companies have tried to make their case. We all know that it falls under the heading of WIIFM . . . … [Read more...]
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