On 5/12/2013 1:00 PM, Jim Brown wrote:
On 5/11/2013 8:34 PM, n0tt1@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)
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|