Aluminium..Copper... Coil Screening

[pwdrive]

Would anyone know if copper can be used in place of aluminium for screening RF coils given the same distance from the outside of the RF coil to the screening can?

Lawrence.

[Kalee20]

Should work, as long as it is similar thickness (well, minimum 60% of the aluminium thickness strictly).

Conductors work as screens because any changing magnetic field causes eddy currents which cancel the field on the remote side of the screen. As long as the screen thickness is a fair bit more than the skin depth at the frequencies of interest, it'll work well.

[Yorkie]

I've seen quite a few pics of vintage radios in which the IFTs etc, were screened with copper.

[pwdrive]

Should work, as long as it is similar thickness (well, minimum 60% of the aluminium thickness strictly).

Conductors work as screens because any changing magnetic field causes eddy currents which cancel the field on the remote side of the screen. As long as the screen thickness is a fair bit more than the skin depth at the frequencies of interest, it'll work well.

Thanks kalee, I am thinking of using copper foil, it's for the shortwave Regenerodyne project that hopefully I will be working on again once the new workshop is finished, I want to do away with range switches if possible so the idea is to make each coil range as a plugin unit similar to that used in the HRO, my metalworking facilities are limited so I want to make the coil pack enclosure box in thin plywood with plywood compartments seperating each coil the created compartments will be lined with copper foil as it is easy to solder the various sections of the copper lining together and earth them, the front panel of the coil pack will be aluminium and also be earthed I can get thin phosor bronze strip to make the chassis side of the contacts, these will be arranged as individual contacts over the top of the plugin coil pack mounted on a composite bar of paxolin or some such material, the contacts on the actual coil pack will be plated studs/rivets etc. which will protrude at the correct hieght from the top of the coil box to make contact with the phosphor bronze spring contacts. If copper foil is not suitable I have an old copper hot water cylinder I can cut to get copper sheets out of.
All subject to change of course..

Lawrence.

[pwdrive]

I've seen quite a few pics of vintage radios in which the IFTs etc, were screened with copper.

Yes, Philips Superinductance? the coils will be for shortwave David, the coils in the coilpacks for the HRO are individually screened (aluminium) and that receiver covers up to 30 Mhz so hopefully the idea will work for what I have in mind.

Lawrence.

[Skywave]

Having seen the insides of bits of test equipment from the U.S.A. manufactured during the 1930's, copper for screening seems to have been quite common, there and then.
I don't think you'll experience any problems using copper instead of aluminium. If anything, copper should be superior, since you can solder any joints and make reliable earth connections: these are a bit difficult to do with aluminium (today's understatement!) as you will be aware.

Al.

[Andy M0FYA]

I have a number of vintage (30s and 40s) signal generators and wavemeters where the whole of the inside of the (wooden) cases are lined with copper foil.

Andy

[Refugee]

I think we are down to the cost of copper here.
Armored power cables are sometimes made of aluminum if the world price of copper goes sky high.
Aluminum is cheaper than copper and the star washers used to get good contact have improved since aircraft started getting made out of aluminum due to the weight saving.
If you have the copper to hand you had might as well use it.

[pwdrive]

Copper it is then, when that Mongolian copper mine comes on full stream I don't think there will be a shortage of copper, copper foil would be ideal for me as it is easy to cut and shape and takes solder readily, all this is subject to change if I ever find some off the shelf aluminium boxes of the right shape and dimensions.
At the moment all I can do is yap about it due to all the house diy stuff, the new radiator in the new workshop decided to run cold last night so I am off bubble hunting sometime today, plumbing = wetness....
I'm going to shut both rad. valves down and release the pressure with the bleed valve then remove it and fit a bsp fitting in it's place connected to a hose dumped in a bucket and de bubble the flow and return pipes in turn as that's where the bubbles are so far as I can make out.

Lawrence.

[pwdrive]

Just checked out double sided copper clad boards, typically 12" x 8" = £5 (ish) so that might do as I could fabricate that as a compartmentated open front box which could fit into an aluminium fronted diy plywood box for the coil packs.

Lawrence.