At these incredibly low signal levels a very good screened room is required. Even in the 70's I was using a copper enclosure to measure sensitivity levels within a double screened room. Extraneous radiation from the test equipment itself disturbed our measurements. We had to fit blanking plugs to unused outlets on various bits of gear. This is not for the home lab.
David G3UNA > > From: Don Wilhelm <[EMAIL PROTECTED]> > Date: 2007/10/01 Mon PM 03:53:59 BST > To: elecraft@mailman.qth.net > Subject: Re: [Elecraft] Sherwood on ARRL Testing Methodology > > As measurements become more precise, it becomes more and more important > to recognize what Bill is pointing out. A slight difference in test > setup can result in a different result. These measurements are done at > the sub-microvolt level and it does not take much to create a difference. > > Test equipment must be calibrated, and the calibration tolerance should > be known. Traceable calibration is one thing, but the tolerance limits > of that calibration are also important - not all calibration labs are equal. > > Even with calibrated equipment and the same test setup, two different > equipment operators may yield two different results. As an example, > consider an instrument having a display for readout (like an > oscilloscope), the trace has a finite width, and one operator may place > the cursor on the midpoint of a trace width while another may place it > at one edge yielding two different values - how much they differ depends > on the resolution used, brightness of the trace, scale illumination, how > well the display was focused, etc. > > One good step in the right direction would be to report the region of > uncertainty for all measurements. For me, that is a piece of information > that becomes more critical as the measured values become smaller. The > ARRL lab may do that calculation in-house (I haven't asked), but they do > not state it in their published reports. > > So for now, when I see comparison data between two receiver that vary > only by a dB or so, I usually figure that is close enough to ignore the > difference (I usually do consider 3 dB or more difference to be > significant). > > 73, > Don W3FPR > > Bill Tippett wrote: > > snip... > > It's also dangerous to assume Elecraft's measurements > > will be identical to ARRL/Sherwood. There are often differences > > due to different test methodologies, people and equipment. > > > _______________________________________________ > Elecraft mailing list > Post to: Elecraft@mailman.qth.net > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > ----------------------------------------- Email sent from www.virginmedia.com/email Virus-checked using McAfee(R) Software and scanned for spam _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
