I’m using the Shake RS4D (with Swarm). The documentation has a warning on using the build in WiFi:
“We do not recommend using the built-in Raspberry Shake 3 Model B’s wifi, but it is available.”
As a workaround I’m using a USB WiFi dongle but do have the following questions:
How does the interference of the build in WiFi module occur? What’s causing it (as the frequency range of the board is far below the WiFi bands)? Can it be directly measured/displayed?
Does the USB WiFi dongle require a USB extension cable or can it directly be plugged in into one of the USB ports? Also in this case I’d again like to be able to measure any effect of the proximity of the WiFi dongle to the board. I may switch to a 4G dongle and also want to be able to monitor possible interference.
I am not 100% sure on this since I’ve not investigated in depth beyond turning the transmitter on and off, and connecting/disconnecting from SSIDs, but my understanding is that even though the frequencies don’t match, there is EM energy pointed at both the board and the geophone. This is especially apparent on the EHE channel of the RS3D, which appears to react much more strongly presumably because some wave energy is polarized along the axis of this geophone.
In my limited testing, the effect of this interference is strongest when the WiFi module is active but not connected to any access point, and is periodically searching for signals. An example of this is shown below with the signal filtered to 0.001-0.05 Hz in SQLX. You can see what looks like a 2 min repeating signal sequence on EHE versus the orthogonal channels, which do not show as much perturbation.
You can recreate this in Swarm by opening up the channel you’d like to look at and changing the Zoom and Filter settings as follows (Swarm doesn’t let you set your low band below 0.01 but you can get a similar result with a 0.01-0.05 Hz bandpass):
No extension cable needed, simply moving the source away from the circuitry and geophones should do the trick. I don’t know how you might measure the effect at home, I usually use a couple of ethernet-connected units and monitor as I switch on and off the wireless chip, but I’ll get back to you if I think of something.
Thanks a lot for your extensive answer. I’ll try out your suggestions to see if I can reproduce the interference. At least it is good to know the solution is rather cheap and simple.
Regards,
Geert Jan
You’re welcome. So far I’ve not seen any interference when using a wifi dongle, which is not to say that there is none, but that it is below the noise floor of the RS.
