Folks,
To get the definitive information on this topic, please go to
www.arrl.org/forum. Look for the “Technology”
category and then scroll down to “Equipment Testing.” Look for the three
postings from ARRL Lab Manager Ed Hare.
Regards, Joel
Joel R. Hallas, W1ZRTechnical Editor, QST
ARRL,
the national association for Amateur Radio™
----- Original Message -----From: Bill Tippett Date: Thursday, September 1,
2011 8:37 amSubject: Re: [TenTec] ARRL ReviewsTo: tentec@contesting.comCc:
hans@pa1hr.nl> W3ULS wrote:> > >With the changes ARRL has made in reporting
IMD3 for > receivers, all you have> to do is subtract 8-10 dB to get very close
to Rob Sherwood's > findings. No> biggie.> > The actual IMD difference
is ~12 dB which is the > difference > in noise bandwidth between 3 Hz (spectrum
analyzer) and 50 Hz > (approximate BW of the human ear) using [10 log(BW1/BW2)]
or > 12.2 > dB. I'm afraid it IS a biggie if someone looks at PA1HR's >
unfootnoted listing and concludes the FT-5000 is head and > shoulders > above
other rigs. It is not, as can be seen in Sherwood's > table. It > simply has
the benefit of being tested using *new* methodology > versus > other rigs using
the *old* methodology, and there is not even > any > indication of when the
measurement methodology was changed!> > One of the major benefits of
any published test data is > comparability, and ARRL's older data (I'm not sure
of the exact > date > of the methodology change) is definitely not directly
comparable > to > current data. Unfortunately I believe Peter Hart of RSGB's >
RadComm > is now using the same IMD measurement methodology so his data is >
also > not comparable over time.> > >IMHO, Sherwood and his work are admirable,
even irreplaceable. > Yet I think> he is overly critical of the ARRL and its
lab procedures, given > the fact of> the ARRL's large overhead that must be
paid for and the good > work they do> overall. They beat the FCC in the U.S.
Court of Appeals for the > District of> Columbia, for example, which is no
small accomplishment. So I > can live with> a little less rigor in the testing
area as long as Rob Sherwood > (and Peter> Hart) are around to offer their
opinions.> > I'm certainly not critical of everything ARRL does for >
us. However when published comparisons are made of their data > without so
much as a footnote detailing the differences in > measurement methodologies,
then criticism may be justified. The > average person reading these comparison
listings may be > seriously > misled if they simply take them at face value.
I'm copying this > to > PA1HR so hopefully Hans will consider footnoting the
differences > in > measurement methodologies, and perhaps Joel W1ZR will tell
us > exactly > when ARRL's methodology changed.> >
73, Bill W4ZV > > _______________________________________________>
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