Kitz Forum
Chat => Tech Chat => Topic started by: Weaver on October 04, 2015, 12:37:50 AM
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Does anyone know where I could get a RFI-screened type metal mesh box? With three large(-ish) holes for bundles of cables, and a door or lid for access. DSL cables, Ethernet cables and DC cables go in.
It's to put three small DSL modems in, as an experiment to see if physical screening could help DSL performance. I have no idea if it's going to be effective. It's just an experiment.
I have no idea where to get one from, nor any idea as to how to Google it. I've tried all kinds of Google search phrases with no luck.
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http://www.amazon.com/Design-Ideas-Mesh-File-DE34279/dp/B0000TQFHI
http://www.amazon.co.uk/Silver-Super-Strong-Magazine-storage/dp/B0099OY8BU
https://www.google.co.uk/search?q=metal+mesh+box&tbm=isch&tbo=u&source=univ&sa=X&ved=0CEMQsARqFQoTCPq9m9ycqMgCFYJYFAodp9oFPQ&biw=1440&bih=807
http://www.themeshcompany.com/products/Bargain-Off-Cut-Scrap-Box-304.html
http://www.themeshcompany.com/products/RFI-shielding.html
https://www.google.co.uk/search?q=rfi+shielded+box+uk
http://cpc.farnell.com/1/3/rfi-shielded-enclosures
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@dray - wow, what a hero, thanks v much for that lot! ;D
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Unfortunately no luck at all from that generous list. I had gone over some of that ground before.
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Can't see it helping really.
In fact its very unlikely that radiated interference is being picked up within the ADSL modem, it'll pretty much all be conducted interference on the copper pairs* - bonding no doubt introduces some crosstalk between pairs but there's not a lot you can do about that. If its local interference (ie within the property) then you'd be far better off trying to suppress the source than ameliorate the effects.
If you still want to try it then I'd recommend butchering an old microwave oven to test it out as the insertion loss between the inside & outside is fairly impressive. Hell you could even butcher a new microwave oven - Aldi sell them here for £30 so there's bound to be some on fleabay or Amazon (or Freecycle if you have a group nearby) :D
*the main cause of which is MF transmitters inducing the interference in the first place but after that its conducted interference.
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@rizla - that's a good tip about the microwave oven.
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Do bear in mind that you will most likely have to use a hole-saw to go through some "stuff" that varies from oven to oven. ie use a decent filter for mouth/nose & ideally do it outside your house with wind blowing the right way etc.
Most microwaves will have a substance which looks/feels like polystyrene around the oven (before you get to the earthed metal). Take precautions for this as it isn't polystyrene - some of the commercial microwave oven stuff (which used to operate at 800MHz, doubt they still do that) was basically asbestos.
Most microwaves have a fan which only turns on when the "electronics" are getting hot. You can probably use that to vent any heat generated by the modems - just wire it "always-on" :)
You definitely want to go find the crimp connections for the magnetron & disconnect them - someone will turn it on if you don't :D
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ISTR reading that microwave ovens also tend to contain a large high voltage capacitor, that can do serious mischief even long after the power has been removed. Similar, perhaps, to the way big old CRT TV tubes used to hold onto the EHT charge?
I have never attempted to dismantle a microwave oven but I'd want to do some research on above before I did, and discover whether it is fact or fiction...
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The magnetron will require something in the order of 4-5kV (4000-5000 volts) to operate so there will be a voltage multiplier circuit with EHT caps. If there's no discharge path then they will retain charge for hours - there's no doubt plenty of google hits showing how to safely discharge them but unless you actually turn the magnetron on then there won't be any charge in them.
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No need to worry about me and the microwave oven just yet. I'd probably have to get out of bed to do such surgery, so given the general state of my health and usual abilities, it isn't going to happen unless I can get a crazy friend of mine to pitch in. :-)
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Use a large Biscuit Tin as a Faraday Cage. !
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Can't see it helping really.
In fact its very unlikely that radiated interference is being picked up within the ADSL modem, it'll pretty much all be conducted interference on the copper pairs* -
There are plenty of internal devices in the house that can interfere with the modem and LCD TV's monitors and Plasma TV also HDMI to VGA converters are the worst but it all depends on how close the modem is to the internal disturber.
My advise if you can is to move the modem well clear of the offending device not just a few inch's but like 4 or 5 meters away.
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Use a large Biscuit Tin as a Faraday Cage. !
This must be one of the best suggestions.
It might work, or it might not. But either way, on the assumption the tin should be empty, it's an excuse in the interests of scientific research, to eat a large tin of biscuits. Might even be tempted to try it myself. :)
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Use a large Biscuit Tin as a Faraday Cage. !
This must be one of the best suggestions.
It might work, or it might not. But either way, on the assumption the tin should be empty, it's an excuse in the interests of scientific research, to eat a large tin of biscuits. Might even be tempted to try it myself. :)
I'm sure Weaver could find a tin of Scottish shortbread :) it might even be empty :P
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Perhaps it should be four empty tins of Scottish shortbread, as Weaver has three modems and one router. :-\
Then there is the decision as to how many drilled perforations, to allow satisfactory air-flow to disperse the heat of operation from the devices.
Last but not least, each of the four Faraday cages will need to be bonded to a good signal earth (and not the mains supply earth) by a short, heavy duty, cable.
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@burakkucat - quite so.
I do need to get a separate heavy earth connection in the office for general duties of this kind.
Just a tiny improvement would gain me a 3 * 0.25 Mbps d/s speed increase, as I am close to the 2272 sync rung on each one of the modems. One was indeed syncing briefly at 2400 earlier this week then back to 2240 which it is now holding at the usual target SNRM of 6dB and no errors reported. The biscuit tin / microwave oven thing is just for the sake of science, to see if any improvement is there to be gained.