Transcript

Radiated Emissions Testing Overview

Today, we’re going to be testing the Volt’s radiated emissions. These tests measure how much electromagnetic energy the Volt emits at certain frequencies, and there are limits for this for the FCC and also for worldwide standards.

This set of equipment is designed for these tests that we’ll be connecting over the next several days. The spectrum analyzer and EMC analyzer can measure very precisely the amount of emissions that are coming out of the Volt. We have other equipment that will measure the Volt’s immunity to RF fields that we’ll do in the next few days.

The Screen Room Setup

We have the Volt inside a screen room. These emission limits are very small, so to make precise measurements, we have to have the Volt inside an RF-shielded room. This screen room is designed with a Faraday cage, and it prevents outside EM fields from coming in and prevents anything in here from getting out. So this is an RF-quiet room so that we can measure just the emissions from the Volt and nothing else in the environment.

We have the Volt as the device under test, and we have for the first set of tests a bi-conical antenna, which is rated for 30 to 300 megahertz for this first series of tests. In the screen room, we have copper shielding to prevent any other noise from getting in and also RAM material to prevent reflections so we have a more accurate test.

We have an isolated feed-through to supply AC power to the Volt within the room, and this AC power is filtered as part of the screen room environment.

30 to 300 Megahertz Test

We’re powering the Volt up, and we are going to measure its emissions, first toward the low-frequency band of 30 megahertz to 300 megahertz. So we’ll come over, and we’ll close the screen room door.

Now with the door closed, that’s an isolated environment, and that bi-conical antenna comes through the feed-through port into the spectrum analyzer. We will turn on the continuous sweep. Here, the spectrum analyzer is showing the equivalent volts-per-meter field.

We’re showing the CISPR 22 limit, which is very similar to the FCC Part 15 Class B limit, which is very low because that’s designed for consumer electronics. The Volt actually would be a Class A device, which has more relaxed limits, but we’re gonna test to the more strict limits so we can see what we get.

So here we have a limit, it’s roughly 40 microvolts per meter equivalent field, and the spectrum analyzer has the calibration code, which is for that antenna to convert the received voltage into a field strength measure. We’re using a three kilohertz resolution bandwidth here, and you can see with the sweep that the Volt is underneath the limit.

We had sweep from 30 megahertz to 300 megahertz, and this is a 5 dB per division scale, and we can see we’re at least 15 dB underneath the limit at 30 megahertz. This 40 megahertz component is the Volt power supply, from the switching power supply in the Volt, but it’s still well within the limit, 15 dB underneath the limit. And then as we go up in frequency, these small spikes are digital emissions from the Volt, and it is well, well underneath the limit up to 300 megahertz.

So the Volt has passed the first set of radiated limits, the 30 to 300 megahertz limit, in accordance with FCC Part 15 Class B and CISPR 22, the limits.

300 Megahertz to One Gigahertz Test

Now we’re going to complete the radiated emissions test for the Volt. We are now going to test from 300 megahertz to a gigahertz. To do that, we have a different antenna.

Inside the screen room, we’ve swapped out the bi-conical antenna for a log-periodic antenna. This antenna is designed for EMC tests from 300 megahertz to a gigahertz. The antenna is pointed directly at the Volt, the device under test, and the Volt is already powered through the coupling port inside the screen room that allows 120 Volts to come into the screen room.

Now the Volt’s powered, we begin the sweep. We are sweeping from 300 megahertz to one gigahertz, and this white reference line is the limit of the frequency for CISPR 22, while also in harmony with FCC Part 15 emissions limits in this range. We can see that the Volt is underneath the limit over the entire range.

So the Volt has passed the emissions limits from 30 megahertz to 300 megahertz with the other antenna, and then in this test, we completed the emissions testing up to a gigahertz, and the Volt has passed both.