This successful trick can be used to simulate radiated emissions on the bench.
One very successful trick I use to simulate radiated emissions on the bench is to run an RF generator into an H-field (loop) probe. The best level seems to be +15 to +20 dBm. This will generate an intense RF field around the probe tip. By sweeping the probe around circuitry and interconnecting cables, I very often find I can duplicate the system failure. By identifying sensitive circuit nodes, mitigations can then be applied. I’ve solved many tough problems for my clients this way.
Normally, I’ve used the Signal Hound VSG-25A vector signal generator (to +13 dBm) or Windfreak SynthNV or SynthHD signal generators (+19 dBm or +20 dBm). All of these generators have the ability to provide 1 kHz 80% AM or 1 kHz 50% pulse modulations, which is required for the EMC test standard IEC 61000-4-3 or MIL-STD-461. I simply connect any of these to the USB port of my laptop, launch the appropriate software control, connect my H-field probe, and off we go (Reference 1).
However, there are times when I find I need a little more RF level in order to initiate the failure mode and this generally involves adding an RF power amplifier. I’ve used an RF power amplifier a few times with good success (References 2 and 3). These amplifiers were both broadband 10 to 1000 MHz with 2-3 W output, which was able to get to a desired level for failure simulation.
Tekbox TBMDA3 power amplifier
In a recent case, where I was troubleshooting a battery management system, I was able to use a new “modulating” power amplifier from Tekbox Digital Solutions (Figure 1). The model TBMDA3 is an amplifier with a frequency range of 10 to 1000 MHz, which has built-in modulation controls for 1 kHz 80% AM, 1 kHz 50% pulse, and 217 Hz 12.5% pulse. This latter modulation is used to test TDMA mobile phones.
Figure 1 The Tekbox TBMDA3 is an RF amplifier with frequency range of 10 to 1000 MHz.
Power output ranges from +34 to +37 dBm (1 dB output compression point), depending on frequency, and with gains of up to 44 dB. The amplifier sells for $879 through the U.S. distributor Saelig Electronics. It comes with two N to SMA cables and a 30-dB attenuator and is powered from 110 to 240 VAC.
For the purpose of the battery management system testing, I drove the RF power amplifier with the Signal Hound synthesizer and adjusted its output between -10 and +3 dBm, depending on the RF output required to trigger the failure mode. The modulated RF was monitored using a telescoping antenna plugged into a Siglent SSA 3032X spectrum analyzer. The RF output from the amplifier was connected to a Fischer F-33-1 current probe that I used to inject RF into the battery cable. Although, any RF current probe (Tekbox, Com-Power, etc.) could have worked well for this application (Figures 2 and 3).
Figure 3 Here is a diagram of the general test setup used for the battery management system immunity testing.
Note that both the Signal Hound synthesizer and power amplifier could introduce the required 80% modulation, but I chose to use the modulation capability of the amplifier for most of the testing. It is also important to understand that connecting an antenna to the RF amplifier is possible, when testing for radiated immunity, but this should always be performed in a shielded room or EMC chamber to avoid interference to licensed communications systems.
I’ve had a couple cases where the engineers had worked for weeks going back and forth between applying fixes at their facility and running over to the EMC compliance test lab for testing. Once I was finally called in, we generally found the sensitive circuits and applied some quick mitigation within a couple hours.
This test method is easy to set up on the bench and can quickly locate sensitive circuits. Once these circuits are identified, fixes can be tried while retesting in real time. No more running back and forth to the test lab and wasting a lot of time and money!
Note that this test technique, and more, will be described in my upcoming book, EMC Troubleshooting Immunity (Volume 3), to be available in early summer 2021. If you’re thinking of implementing your own EMC test capability, you’ll want to get a copy of Create Your Own EMC Troubleshooting Kit (Volume 1), available now from Amazon (Reference 4).
This article was originally published on EDN.
—Kenneth Wyatt is president and principal consultant of Wyatt Technical Services.