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--- emi_testing [2019/02/26 16:42] – jrseti
+++ emi_testing [2023/10/28 18:36] (current) – external edit 127.0.0.1
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 =====NOTES=====
-From Roy, in an email Feb 22, 2019:
+**From Dave Deboer, Feb 22, 2019:**
+Hi - there certainly are standards and standard techniques.  We used to have a wideband conical antenna — I can have a look.  Multiple discones are often used.  Of course, we do have our feed to use.   You could use it at room temp and turn off everything you can on the feed used to take the measurements (as opposed to a cooled feed you may wish to measure).  I’d suggest this approach.
+The measurements occur in a screen to guard against outside RFI, but also because the RFI from the DUT (device under test) bounces around and eventually will get into the measurement system (it is an echo chamber).  Ideally mode stirrers are used so that you don’t get standing waves that can produce nulls.  You could measure twice, once with a big piece of metal in a corner and once not.  You want to measure with the DUT on (of course) and then off with a reasonably well known source at various frequencies across the band (ideally a comb generator, but could transmit a set of tones out from a signal generator transmitted out of a reasonable antenna (a few simple dipoles fashioned for a few bands would be a start).
+I think sufficient for our purposes would be to use a room temp feed and then maybe a tone/dipole combo every octave across the band.  I will look and see what antennas we may have here that could help.
+**From Roy, in an email Feb 22, 2019:**
-<pre>
 I spent the second half of the '70s doing almost nothing but EMI testing and remedial design on products to get them to meet FCC regulations. I also set up a number of EMI chambers for companies I consulted with to enable them to do their own testing and compliance design.
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 So, I think it would be more fruitful to focus on directly measuring the feed equipment and discuss how to reduce the interference at the source.
-</pre>
+**From Franklin, Feb 22, 2019:**
+Roy, I agree with everything you said.
+However, there's some other stuff going on, where we've been discussing doing EMI testing on some new devices that are soon to be brought into the ATA facility.  In the past there has been a shocking lack of process, for example no emi testing before introducing new equipment.  In two cases I know about, the new gizmos are going to be mounted outside in the field among the antennas.  Seems like there should be some sort of EMI qualification before introducing new stuff among the world's most sensitive receivers, and broad-band receivers to boot.
+There is some desire to institute a more rigorous process.
+So Jon is trying to understand what he can do.  He has access to a spectrum analyzer and screen room at Minex, which are major parts of what's required.  They don't seem to have any appropriate known-gain antennas.  A significant problem is that he lacks the background to know how to proceed.
+I think you can help them on this.  One way would be for you to teach them how to make use of the tools they have.  Alternately, it might be more appropriate to simply contract out for EMI testing at a local EMI test lab.  Once you visit Minex and see what they have, work with Jon a bit, etc, I suspect you can figure out the best way for them to proceed.
+Among the many little issues... They have no "spec".  There is a standard that astronomers use, ITU rec 769.  (I'll send you a copy.)  I read it quickly and while its something one could certainly use, it is not particularly suited to our situation.  For example, the standard seems use very wide measurement bandwidths.  In SETI we often look at 1Hz wide frequency bins, so this standard doesn't seem particularly appropriate for SETI.