shield and emi filter - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: November 16, 2023, 08:46:36 am
content: if you have a circuit board part with a shield over it, like a section, and its fed in through a shield, say a RC network, where should it be? If its just say a MHz filter on a op amp (something MHz). Do you want the filter right outside of the shield? inside of the shield? capacitor behind shield and resistor in front of shield?how about power rails? Lets say you have a decoupling capacitor right near the op amp. Could you just feed the power under the shield, or should you have a little capacitor at the perimeter of the shield? Say 1/10th of the decoupling capacitor value maybe?also, does anyone make through hole shield clips? they are all SMT. I can stake them with eyelets but its alot of work. it's not like its not gonna work.

author: jonpaul
author_rank: Super Contributor
timestamp: November 16, 2023, 10:36:59 am
content: Coppercone: Rebonjour, Great question:what power/freq range? prod or proto?In our FM tuner prod, used ready made shield cans like thesehttps://www.harwin.com/products/S01-806005KIT/Protos were made our own in the shop from copper sheet or tin can stock.Power was via feedthru RF bypass filters or caps like the old US mfg C-D, Centraab, Sprague.Signals were on the PCB or fed thru the shield via plain feedthru terminals.No issues at 100 MHz (FM band ) as all RF/IF was balanced.Just my experience...1973Your thoughts appreciated!Have an Absolutely fantastic day,JonPIX: Feedthru caps/filtersMy 1973 Sequerra FM Tuner 100 MHz counter (TTL/MECL) with shield/filters/beads/feedthru

author: coppercone2
author_rank: Super Contributor
timestamp: November 16, 2023, 10:58:49 am
content: i mean if a network of chips was shielded on the pcb inside of a enclosure. no real feed throughs. and with a shield that is clipped on

author: jonpaul
author_rank: Super Contributor
timestamp: November 16, 2023, 11:20:33 am
content: Unsure your question.any pix/schematic?j

author: Vovk_Z
author_rank: Super Contributor
timestamp: November 16, 2023, 11:29:15 am
content: Quote from: coppercone2 on November 16, 2023, 08:46:36 amI guess inside. You don't want high frequency signal to go out of the shield.

author: MathWizard
author_rank: Super Contributor
timestamp: November 16, 2023, 05:28:21 pm
content: I put an amplifier or low MHz oscillator circuit in tuna can once, with the cover taped on, and I don't remember didn't noticing any difference on my good scope. I know inside a perfect sphere of spread out charge on a conductor, the E field will sum up to zero. I can't remember if it exactly cancels in non-sphere's. And magnetics do something different and are way harder to shield.So if you sealed up the can tight, even with solder, what would that be like ?If you cut apart tin cans, into little rectangles, is there any reason you can't use that to make shielding cans ? If someone had the tools, they could cut/shape SMD cans too. If I knew where my tin-snips were, I might try it today.

author: coppercone2
author_rank: Super Contributor
timestamp: November 16, 2023, 05:47:37 pm
content: I saw a massive increase in resolution on half a shield before on a ground plane pcb. Copper sheetJon Paul I mean if you had a pcb that has say a gain stage on it with an op amp. Then you just shield that chip and it’s resistors. Caps, etc. so traces go under the shield. Then that connects to other circuit stuff not under the shieldI decided not to do it right now because i don’t want to put rivets for the shield holders but in general I would like to know how to do it for a pcb

author: MarkT
author_rank: Frequent Contributor
timestamp: November 18, 2023, 10:41:08 am
content: Quote from: MathWizard on November 16, 2023, 05:28:21 pmIf talking about solid conductors, the interior field is always at zero when no current is flowing. And no the surface charge is not necessarily symmetrical on a sphere as it depends on the external electric fields. The surface tangential field is always zero.With hollow conductors the charge on the inside of a metal container also distributes itself so there's no tangential field at the interior surface. The internal field depends on the internal charges, but always intersects the container at right angles.You can only impose a particular distribution of charge with an insulator like an electret, as the charges are fixed in place in an insulator.The charges/fields on the outside and on the inside are un-correlated with a conducting container (in electrostatics). Skin depth is important in the real world though, so at low frequencies fields leak through (and there are currents within the conductor wall).

author: PeteH
author_rank: Unknown
timestamp: November 18, 2023, 11:04:03 am
content: Companies like tech etch can provide custom shields which have through hold or smt mounting options. Shields are often custom, so for COTS stuff SMT is probably the most common to achieve sufficient volumes to stock.

author: coppercone2
author_rank: Super Contributor
timestamp: November 18, 2023, 11:54:27 am
content: omfg pay someone to bend a sheet metal for me?said while holding pressure on laceration

author: coppercone2
author_rank: Super Contributor
timestamp: November 20, 2023, 09:44:19 am
content: bought some EMI clips for experiments. first i will see how keystone eyelets do for fastening them to random PCB. it seems plausible to erect shields.. a nice combo to that bending machine I bought a while back for my vise.