Unfortunately just because you use the same method, doesn't mean the
results are any good. For example if the testing methods because of using
different mixing methods generates it's own IM into the picture, it will
greatly affect the results. A radio with lousy IM distortion, will show up
bad, but a radio that has great specs, will suffer terribly, making the
user think that the better radio is really not that much better, when the
truth is that there is a huge difference. You can't measure a signal to
millivolt accuracy if your test instruments are +- .1 volt in accuracy.
At 06:57 PM 3/3/2003, Ron Notarius WN3VAW wrote:
>The important point is not that the ARRL has chosen their own method of test
>methods and procedures -- which is not to say that Jim is wrong (if
>anything, I agree with him)
>
>The important point is to make sure that the ARRL uses the SAME test methods
>and procedures on ALL equipment they evaluate. While this makes it
>difficult to do an "apples to apples" comparison between ARRL tests and
>others... by the way, which others?... it does make it easy to do an "apples
>to apples" comparison between similar equipment that the ARRL has evaluated.
>
>73, ron wn3vaw
>
>"It's a beautiful day in the neighborhood... won't you be my neighbor?"
>Fred Rodgers, "Mister Rogers Neighborhood," SK, 27 February 2003
>
>----- Original Message -----
>From: "Jim Reid" <jimr.reid@verizon.net>
>To: <tentec@contesting.com>
>Sent: Monday, March 03, 2003 6:43 PM
>Subject: Re: [TenTec] Argonaut V ARRL Review 3rd and 2nd IPs ?
>
>
>Stuart, K5KVH, wrote, in part:
>
>
> > The ARRL web site has a section on testing by their lab
> > and how it differs from that of accepted manufacturer's tests.
>
>Thank you for the lead, Stuart. I have just been there and
>read the complete method, procedure and examples of
>how they do the 2nd and 3 rd order IP tests.
>
>I was shocked!!! Why do they choose to differ completely
>from industry standard? They use audio meters to measure
>RF performance??? That is nuts. The proper way it is done,
>and the way it is done is completely described in the January/
>February issue of the ARRL's own QEX magazine in a very
>detailed article by Ulrich Rohde, page 21 the piece begins;
>actually the 2nd part of a two part paper by him.
>
>The correct test measuring instrument, as used by Rohde,
>and every one else is the RF Spectrum Analyzer where the
>IM products can be seen and accurately measured in both
>frequency and amplitude. Rohde illustrates with a simple
>block diagram, his Fig. 30 in the Jan/Feb article. His
>actual test equipment arrangement is shown in his Fig. 32,
>and the procedure used to measure several rigs --
>a couple of Rohde & Schwartz rcvrs, the XK2100L and
>the EK985, and a slightly modified Yaesu FT-890 (the
>"standard" front end switching diodes were replaced by
>Rohde with PIN diodes, a practice Rohde strongly urges
>be done with all diodes preceding the mixer stages;
>he used MI204 PINs in the tested 890).
>
>He describes the correct Spectrum Analyzer test method
>procedure in the two concluding pages of his current article.
>
>My suspicion is that this is exactly the procedure followed in
>the Ten Tec engineering labs; it is certainly NOT the procedure
>performed by the ARRL labs, if they follow the procedure they
>say they do using audio test meters!
>
>BTW, the reason I am so sensitive to this issue is, that so
>far as I know, I wrote the first paper ever in which the
>intermodulation product performance of linear devices
>is analytically discussed and measured: see the September
>1965 issue of "The Microwave Journal". The complete
>transfer characteristic spectrum of a linear device is
>analyzed via a Taylor Series expansion; the expansion
>terms define both the frequencies and amplitudes of all
>harmonic and intermodulation "error" products arising from
>the "near" linear transfer process. In our case of receivers,
>the near linear process we are after is from the RF signal
>entering the antenna terminals of our rigs, to the output.
>Rohde's article is an excellent treatment of how to do this
>using 21st century measuring/generating equipment.
>
>I also am sure, that in the Ten Tec engineering department,
>that Doug Smith's hybrid coupler is used for combining the
>test signals to the test apparatus; they ARRL labs do not,
>per their own procedure (they use a simple two port
>combiner (MCL ZSFC 2-6). Rohde also seems to imply,
>in his referenced article, disagreement with the ARRL
>test procedure/method (see bottom paragraph, page
>30, Jan/Feb. '03, QEX).
>
>Well, I have let off my steam! Won't change the ARRL lab
>procedures, for sure. I believe the ARRL test results
>may have validity only for comparative relevance between
>rigs they have tested, but I seriously doubt the absolute
>accuracy, or even typical accuracy of the reported results
>to the procedure being used there.
>
>73, Jim KH7M
>
>
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>
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Cecil
KD5NWA
|