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I have a pre-manufactured Faraday enclosure. It doesn't have holes in it. It does have a door on it with an RF gasket (the door must be closed in order for the enclosure to work). It has several pass-through connectors on the side--SMA, DB9 and DB25. The pins on the DB9 and DB25 connectors are capacitively-coupled to ground. This keeps RF ingress and egress from traveling through those connectors (but also stops other high-frequency signals like USB LVDS). The SMA connectors aren't coupled (otherwise they couldn't pass RF). I'd like to pass a USB signal (1.1, standard speed) from an outside host (a medical PC on which one cannot install drivers) through the enclosure to a device inside. I'm looking for a device or several devices (preferably COTS) that will do this.

You don't have to point me to a specific device, just a class of devices. Here's what I've tried so far:

  1. USB to Ethernet adapter coupled with an Ethernet to coax adapter. Doesn't work because the USB to Ethernet adapter doesn't actually use Ethernet frames (it just uses the Cat. 5e/6 pairs however it pleases)--therefore the Ethernet to coax adapter can't pass the signal.
  2. WIFI USB device server with an SMA cable instead of an antenna. These don't work because they require special drivers on the PC (also the medical PC doesn't have WIFI).
  3. A USB to IP adapter with the USB to coax adapter in item 1. Doesn't work because the USB to IP adapters require a driver on the PC.
  4. Wirelesss-USB (WUSB) dongles and hubs. Doesn't work because: a) the dongles require device drivers, b) antennas aren't removable (SMA can't pass UWB 60GHz signals anyway), c) Wireless-USB seems to be dead. All the manufacturers list their products as out-of-stock.
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    How many SMA connectors are there? Could you do a Frankenstein wire job where you pass Data+ and Data- on to separate SMA connectors? Vcc and Ground could go though the DB9.
    – Scott Chamberlain
    Commented Oct 31, 2016 at 21:17
  • @Scott Cahmberlain. There are plenty of SMA connectors. I could do what you've suggested. It's not really a COTS solution, but I can take a hack at it. Coax cables always have a grounded shield on the outside. I'm a little concerned about RF ingress on the center conductor if I make my own Frankenstein cable. I'll ask the RF engineers across the parking lot--they should be able to tell me if it'll be a problem. If the only solution is build-it-yourself, I might try moving this to the Electrical Engineering site.
    – watkipet
    Commented Oct 31, 2016 at 21:43
  • I am CE, not a EE. So I would most defiantly ask them before trying it out. You might want to give the manufacture of the cage a call and see if they make a model with a USB pass though too (if a new cage is within your budget).
    – Scott Chamberlain
    Commented Oct 31, 2016 at 21:45
  • USB-WiFi adapter, modified to use cable rather than broadcast? youtube.com/watch?v=xIO0_ELAbWw
    – DrMoishe Pippik
    Commented Oct 31, 2016 at 22:09

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With unlimited SMA passthrough connectors, the solution is straightforward. You need to make a pair of special USB cables. And I am sure there is no COTS of this sort.

You need to take two cheap SMA cables (of proper gender), cut the other end, and solder it to board similar to this one, but with USB plug. This will make the enclosure-to-host part of USB cable.

Within the enclosure you need to make another half of the cable, from two SMA to proper USB plug. If your device has the Type-B connector, just use a cut of proper end of normal USB cable. You can do the same for Type-A plug, without any interposer board.

This arrangement will also work even for HS USB communication. Only make sure that you connect SMA connectors in right way, D+ to D+, and D- to D-, and that the coax cables are of the same length.

And you will need a third SMA channel to pass the VBUS (red wire) through.

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  • Actually, there are "COTS" SMA-USB adapters that are used for signal integrity testing and certification purposes, but they cost arm and leg, like this one, hyperlabsinc.com/HL9801.aspx , or much more for a set, usb.org/developers/tools/Electrical_Test_Fixtures.jpg
    – Ale..chenski
    Commented Oct 31, 2016 at 23:55
  • If the device is self-powered, do I need to pass VBUS through? Or is it used for level comparison / device connection signaling?
    – watkipet
    Commented Nov 2, 2016 at 18:50
  • Yes, you do need to pass the VBUS through, because it is used by USB device to indicate that USB connection is made, in classic USB framework.
    – Ale..chenski
    Commented Nov 3, 2016 at 2:44

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