Noise supression  

Re: Noise supression

hi jeremy
can you be a little bit more precise:
❓ ❓ ❓

first: in which frequency range do you get the interferences (lf / sw / vhf / uhf - modulated as am or fm ?) ?
do the interferences appear as soon as you switch on the printer ?
do you encounter more interferences when the printer prints ?

btw. in which area of the world are you located ?
what about your power grid ?

Re: Noise supression

Thanks for your reply Jeff, as soon a machine is switched on interference starts and changes as printer goes through its cycles. Radio is on fm. I am in the UK so would have though power was clean. There is no tv interference. Jez

Re: Noise supression

ok, there are several sources of interference where our prusa might provide unwanted radio signals:

1. the switching power supply
2. the rambo board
3. every cable attached to the rambo board, especially the ones for the stepper motors.
4. the lcd board
5. the usb cable

💡 just to explain: every switching of currents produces harmonics. the more powerful and accurate the "switch" is, the higher the harmonics could be.
and with "switch" i mean not only mechanical switches, every transistor unit inside the printer (even the million on-chip ones inside the cpu) can cause such harmonics that reach into the radio range. if the switching of the current appears itself with a certain frequency, the produced higher frequency is n times higher, while n will be an integer. for rectangular switching behaviour the most important harmonics are the odd ones (3x, 5x, 7x... and so on).

💡 now this happens in nearly every machine... it's up to designer to avoid that the produced high frequencies doesn't get transmitted. but that's not always easy and comes with some costs.
in europe we have several standards that need to be followed before you get an approval to sell them... and furthermore, in the most countries, we have a liability for interference... so if you interfere with your neighbours radio and he complains about it, you have to pay for the measures to avoid or reduce these interferences. this could be nasty (and expensive) if your neighbour is some kind of public service that uses radio for their operations (like police, fire service, emergency ambulance etc.).

ok, thats enough for a short roundup of the background.

➡ as mentioned above, the designer could take several measures to avoid emitting the high frequencies. and the manufacturer is responsible that these rules are followed. in case of the kit: you are the manufacturer .

there are two major methods:
- filters
- shielding

inside the power supply of our prusa, there should be a so called "line filter" which avoids that produced high frequency will be fed into the power grid. sometimes these filters aren't designed very good... and fitting their components sometimes is skipped, due to cost reasons, because they are not really necessary for a successful operation of the device.

first thing i would do is to check if the interferences are produced by the power supply. so i would swap it temporarily with a standard computer power supply, capable to deliver more than 12 amp at its 12v output.

if the interferences still remain:
open the rambo and start to disconnect several devices. i would start with the z-motors.
i expect that the amount of radio interference will drop at some point.
if it doesn't and the prusa still emits severe interferences, if none of the external components are attached (steppers, lcd, endstops, heatbed, hotend, pinda ....), the measures we have to take can be much more costly (see "3rd" below)...

now if you've encountered the major source of interference, you could take further measures.
1st you can provide additional filters, such as ferrite filters for round cables and/or for ribbon cables.
2nd you can shield the cables (i guess the ones for the steppers will have a major effect).
3rd you can shield the whole rambo board (which means: replace the plastic housing with a tinplated one).

ok, i think thats enough for a roundup.
if you figured out which component provides the most interferences, we can discuss the measures against it in detail.

Re: Noise supression

That's a very detailed explanation Jeff, thank you again. I will start to tackle the problem later when I have done some more printing. I have only had the printer operating for a couple of weeks but like to have the radio on in the workshop but most of the printing happens at night. I have some ferrite doughnuts for my rc projects and also wondering if I could sheild any areas with aluminum foil. I aim to build an enclosure for temperature control and fume extraction so I can print ABS, perhaps I could sheild the whole machine ?. Regards Jez

Re: Noise supression

.... I aim to build an enclosure for temperature control and fume extraction so I can print ABS, perhaps I could sheild the whole machine ?. Regards Jez

➡ that's the ultimate way: build the enclosure with a faraday cage 😀 😆
then you can still enjoy radio-5-live or radio-2, even when you're printing. 😛

by the way, i guess the main pollution source are the cables for the steppers, so shielding them (don't forget to ground the shield at one end (not both)) would improve the radio reception at your workshop notable.

Re: Noise supression

Radio 4 ! 😀

Re: Noise supression

The print bed and print head are being pulsed (PWM). Maybe the printbed with the traces is sending out the RF noise. It does have a good amount of current to broadcast with.

Re: Noise supression

The print bed and print head are being pulsed (PWM). Maybe the printbed with the traces is sending out the RF noise. It does have a good amount of current to broadcast with.
yeah, possible... but a little bit unlikely because a) jez get's the radio interferences as soon as he switches on the mk2 and b) the pwm for hotend and printbed is at a very low frequency, as you can see by the led that indicates the current flow at the printbed.