Spectrum analyzer

Hi there!
Is there a possibility to add more reference traces to the spectrum analyzer? On the “real instruments” (e.g., R&S) I often have dark noise traces as a reference, then a “previous measurement” as a reference, and then the current live trace, potentially even more.
Also, it would be useful to have the vertical scale in Vrms/rtHz, and still displayed logarithmically. Sure, I can always convert the dBm back, but… that’s more inconvenient/error-prone.
– Sebastian

Hello Sebastian, thank you for posting to the LI forum!

We have 3 different products currently available - Moku:Go, Moku:Lab, and Moku:Pro. Each share many of the same instrument and software features. The Spectrum Analyzer’s do have a reference trace feature that can be used on our iPad app or Desktop app that gives a “previous measurement” reference as well as the current trace. To enable the reference trace you just need to select the channel by tapping on the trace and holding to bring the extra options menu (or right-clicking on the Desktop app) like in the screenshot below. Moku:Go and Moku:Lab allow 2 of these reference traces and Moku:Pro allows up to 4.

We do have a few different unit options including Vrms/rtHz. To enable this you’ll need to tap the Units in the top right and select Vrms, then enable the PSD units slider to get rtHz. In the “Frequency” settings drawer you can switch between linear and logarithmic scale as well.

Which reference trace features do you find the most useful when using other Spectrum Analyzers? We are constantly updating our existing instruments with new features as well as adding new instruments every so often. This is possible due to the software modularity of the FPGA we use in the Moku family so you don’t need to buy a new set of hardware to get these new features or instruments, the device will grow and upgrade with you!

I am also curious which of our Moku products you are using or if there is one you would like to test out? If you have any other questions I am happy to help.

Yes, to clarify, I’m talking about the spectrum analyzer on the Moku:Lab. As you say, it has one reference trace – it would be immensely useful to have more than one. And while indeed one can set the units to Vrms/rtHz, the vertical display is then in linear units, i.e. just as can be seen in your second picture, the noise floor cannot really be resolved, it basically sits on the 0µV/rtHz level. This would be different if the vertical scale would be shown logarithmically, then one could see the e.g. nV/rtHz noise floor. Unfortunately, this is only possible right now by switching to dBm units – which personally I find more inconvenient to work with.
BTW, I see on your second picture that the screen goes to -5µV/rtHz, which is unphysical :slight_smile:

Yes you are correct the vertical scale cannot be displayed in log scale, but I will convey this feature along with the multiple traces to our client team.

It is possible to see the nV/rtHz range as the vertical scale is adjustable and has a minimum resolution of 10 nV/rtHz. We also have some automatic measurements to determine noise level and peak SNR that you may find helpful!

I also want to support both feature requests.

Before I ordered my Moku:Pro, I was in contact with Liquid Instrument’s sale. I suggested adding a trace feature or at least an additional reference trace. When I received my device, I was quite happy to see the reference feature actually being implemented. However, the more traces the better. Usually, I record 6 or more traces to compare them. We have a spectrum analyser in our lab that we barely use because it only has two memory traces. Therefore, I would really appreciate it if you extend the reference feature to store more than only one trace - the more the better.

I am usually using dBm units. However, in my institute, the unit preferred by most of the people is Vrms/rtHz. In the gravitational wave community, this unit is basically the standard.

Hi Sebastian and Dennis,

I just wanted to point out that you can setup the spectrum analyzer units to be dbV/rt Hz. While this is not exactly what you are seeking; its probably better than using dBm/rt Hz.



Thanks, Paul. Yes, this I found, but sadly my brain doesn’t seem to work in dBV :slight_smile: