[RFI] RF tight rooms - somewhat OT

[Roger (K8RI)]

On 5/12/2013 1:00 PM, Jim Brown wrote:
> On 5/11/2013 8:34 PM, n0tt1 at juno.com wrote:
>> My question to the group is what, in your opinion, is the
>> best/cheapest RF-tight test room he could build for himself?
>
> Roger has outlined the general concept of a proper screen room.  BUT --
> many RF interference issues are the result of poor design of the
> equipment involved, as well improper interconnections between the
> equipment and the DUT (device under test), as and can be solved by
> correcting those problems without going to the considerable expense of a
> screen room.

Jim has brought up a point I had forgotten. when working with low levels 
of measurement, be it RFI or otherwise the connections to the DUT are 
ogten as important as the DUT  and its proper adjustment.  Particularly 
measuring small component values.

I'm assuming that we are talking "good enough" an accuracy to allow 
computing values for a circuit and not high precision.

Although it'd be a bit pricey, bronze or copper window screen makes an 
excellent shield. the seams can be soldered, or sandwiched between brass 
or copper strips.  It's difficult to solder the seams neatly due to the 
expansion and contraction of the copper being heated in a relatively 
small area and screening a whole room is a whole lotta work and an 
unbelievable amount of work to solder.

If he feels he really needs shielding to do his work I'd use as small a 
room as possible.

There is one aspect not mentioned and that is the magnetic flux from the 
HV power lines.  The screen room will do nothing to alleviate that, but 
if the foil experiment works then I doubt the magnetism is a problem.
>

> The most common cause of RFI is "The Pin One Problem," followed by poor
> equipment shielding. RFI to shielded balanced twisted pair is often
> caused by Shield-Current-Induced Noise.  My website includes a lot of
> tutorial applications notes on these issues.

Studying Jim's tutorial should be well worth his time.  As I said, I 
spent a good portion of my working life doing very precise measurements, 
including RF field intensity measurements and I learned a lot from that 
tutorial.


  http://k9yc.com/publish.htm
> The Ham's Guide" is the most recent, and covers all of these issues
> except Shield-Current-Induced Noise (SCIN).  See the separate
> audio-related tutorials for SCIN, which is mostly a problem with
> microphone wiring for professional sound systems, but could be a factor
> with instrumentation that uses shielded twisted pair.
>
> 73, Jim K9YC
>
>

73

Roger (K8RI)
>