non magnetic coax

This doesn't make any sense. There is nothing magnetic about coax, unless it's in a coil creating a magnetic field, which isn't the coax's fault.

Hope This Helps! Rich

I think RG142 has a silver plated - copper coated steel center conductor. Maybe his application is in an MRI?

ble?

A tinned shield would have some nickel in it, right?

e?

Perhaps Belden types 7805 or 7805R? They apparently have a solid copper center conductor instead of stranded copper-clad steel.

Cheers, Tom

ble?

You should try holding a magnet near normal RG-174/U sometime.

unfortunately nearly everything is magnetic. Most cables have steel conductors that are strongly magnetic. Even if they have no steel, many cables and connectors (everything that is gold-plated) have nickel adhesion layers below the gold. I am doing ferromagnetic resonance experiments, in these I can see the absorption from the cables. Our samples are very thin films (around hundred nm), so even a very thin metal film left from machining will cause a signal as big as the sample. Many people have problems with ferromagnetic resonance caused probably by the dielectric of microwave connectors, even though nobody really knows the reason.

Daniel

Hello Tom,

thanks for the idea.

Daniel

I don't know, do you know a source for that info?

I just checked out an example of semi-rigid coax, and the one I looked at used copper for the outer conductor and silver-plated copper (SPC) for the inner.

Unfortunately, when I checked out RG402 and RG405 - the semi-rigid coax that you can buy from most broadline distributors - all the manufacturer's data sheets that I could find used silver-plated copper-clad steel wire for the inner conductor (also known as silver-plated copper weld SPCW). Many of Micro-coax's semi-rigid cables use the same centre conductor, but they do seem to use silver-plated copper centre wires in at least some of their cables - I didn't dig deep enough to find out why.

Semi-rigid cable is nice stuff, but expensive, and if you can't get it from a distributor you quite often have to buy quite a lot more than you need.

If you called up a local manufacturer of semi-rigid cable and told them what you needed and why you needed it you might be able to get a big enough free sample out if them to enable you to check out the approach.

e?

Belden 9221

e?

Yup I needed this to run RF to our optical pumping apparatus. Belden

George Herold

thank you all for your help, I've ordered both 9221 and 7805, I'll post the results soon.

Daniel

Well, it didn't take long for my ignorance to get corrected. ;-)

If you learn something new every day, does that mean I can go back to bed now? ;-)

Thanks! Rich

able?

ss

:-) I have a friend that often says, "Any day you learn something new is a good day." I have lots of good days, and I'm thankful for them. Well, OK, especially the ones where the learning isn't too painful or costly.

Cheers, Tom

Well, I must admit I wasn't very confident, having seen copperclad steel cores. But it never occurred to me that that was what the OP was probably referring to.

Thanks for the correction. :-)

Cheers! Rich

In french we say "je vais me coucher moins niaiseux a soir", which roughly translates to "I'm going to bed less dumb tonight".

Hello All,

both the Belden 8705 and the 9221 (75 Ohm) cable are nonmagnetic and work well.

Thanks again for all your ideas

Daniel

l cable?

nless

lt.

bed

Slightly off-topic: another friend pointed out an interesting property of RG-174/U -- the type with the center conductor of copper- clad steel strands. Most coax shows attenuation (in dB/unit length) proportional to the square root of operating frequency, at least where the frequency is high enough that skin depth is smaller than the thickness of the conductors and low enough that dielectric loss isn't significant. But because the copper on the center conductor of the RG-174 is so thin, about a mil, and because skin depth in the magnetic steel core is extremely small, the copper loss--and therefore the attenuation--is nearly constant over a range of frequencies up to roughly 10MHz. This can occasionally be an advantage.

Cheers, Tom

Oh, is the 8705 50 ohm? That would be nice.

George Herold