To more accurately measure emissions from a DUT (Device Under Test), it is wise to calculate the path loss, or cable loss, from the receiving device, whether that is a LISN, a Current Clamp, or an antenna. We can do this by using the tracking generator on the EMI receiver or the Spectrum Analyser.
At work, we have an R&S ESR7 EMI test receiver with a Schwarzbeck VTSD 9561-F attenuator on the low-frequency input. This attenuator lists its frequency range as between DC and 200 MHz, with an attenuation of 10 dB. I wanted to know the loss above 200 MHz.
This process can be used to measure the attenuation of cables and attenuators, as well as the frequency response of filters. I would be cautious using this if I were looking to find the gain of amplifiers.
Basic Cable Loss Attenuation
I use the physical “Pre-set” button on the front of the Rohde-Schwarz ESR 7 before doing anything else to get the receiver back to a known state,
Spectrum Analyser View
Switch to the Spectrum Analyser View to view the frequency domain. At the moment, there is nothing attached to the input, so we will get the noise floor on the screen.
I have changed the selected input to input two, the low-frequency input. I want to measure the insertion loss of the Schwarzbeck VTSD 9561-F attenuator. This attenuator should be 10 dB from DC to 200 MHz, and it is usually connected directly to the input.
At the moment, it has been removed, and a short length of coaxial cable has been connected between the tracking generator output and input two.
The physical buttons on the front of the ESR7 will need to use the ‘input/output’ physical button to change the input and to access the controls for the tracking generator.
I have set the Source Power of the tracking generator (Source RF-Internal) to 80 dBμV. (see Special Symbols used in Engineering Reports, to grab μ and other symbols). There is no need to change the power level if you don’t want to.
Start frequency 9 kHz – Stop frequency 250 MHz
To normalise the tracking generator power level, to allow us to see attenuation we will need to go “Tracking > Source Cal”
Once that has run, you will select “Normalise”
Disconnect the link wire and insert the cable or attenuator you want to measure the loss of.
now you can see the path loss through the additional cable or device
While you can save this data directly to a USB stick, I will need to manually move it off, by using the marker
