Re: NEC-LIST: Small antennas: can they me multiply resonant?

Just a "simple" reminder -- *accuracy* versus *precision* -- the former being
in accordance with excellent Practice and Standards (even if not high
*precision*
measurements, but with 'verifiable' limits) while the latter may be extremely
careful measurements, with lots of decimal points AND the stats to support it,
but based on a corrupt standard, or a basic 'misteak', -- or not based on
fundamentally acceptable Standards -- a Big difference in mentality and
credibility
-- one can 'bet' on Accuracy but Beware of Precision only--

Example from the old days, an engineer measuring insertion loss of an
1-5/8 inch coax connection with a high *precision* bridge setup (unbolting,
rebolting, unbolting the flanges -- carefully, 20, 50 times, to get an estimate
of the Standard Deviation [precision] of his measurements) and finding about
3-1/2 dB (!) "loss" to a few milli-dB's (very high *precision* measurements) but

*totally* inaccurate (NO *accuracy*) as he made a vital 'misteak',
forgetting to insert the coax "bullet" each time, thus connecting the centre
conductors), getting capacitive coupling only, and not recognizing his blunder
after the first or second run, 'blindly recording 'data' this, at about 1 GHz.
(Don't 'bet' on the 3.518 dB loss reported).
(Turns out, he had an excellent lesson about the "Difference" between the two
definitions). AND, varying the frequency of such measurements will frequently
expose such errors.

Antenna measurements being far more difficult than measuring closed coax,
waveguide (non-radiating) insertion loss; in general, one cannot be toooo
careful with the twin aspects of precision and accuracy with 'aerials'......

"Please, guys, Never bring me 'narrowband, single-frequency results', look a
little wider, and do some 'tire-kicking' (misteak) explorations".......

K6BLG

alan.boswell_at_baesystems.com wrote:

> Chip
>
> You say you have made measurements with 'acceptable' precision. I assume
> the precision is acceptable to you, but you would benefit if it's also
> acceptable to potential customers. Maybe it is, maybe it isn't. What I
> said is not a personal opinion, it is what any antenna engineer would tell
> you. You would not expect to buy a pound of apples measured on scales with
> untraceable calibration, antenna measurements are done to the same standards
> in the real world.
>
> 73s
>
> Alan
>
> -----Original Message-----
> From: Fractenna_at_aol.com [mailto:Fractenna_at_aol.com]
> Sent: 08 January 2003 17:53
> To: nec-list_at_gweep.ca
> Subject: Fwd: NEC-LIST: Small antennas: can they me multiply resonant?
>
> Return-path: <Fractenna_at_aol.com>
> From: Fractenna_at_aol.com
> Full-name: Fractenna
> Message-ID: <a2.31b2b0af.2b4dbf05_at_aol.com>
> Date: Wed, 8 Jan 2003 12:51:01 EST
> Subject: Re: NEC-LIST: Small antennas: can they me multiply resonant?
> To: nec-list_at_gweep.com
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> In a message dated 1/8/2003 7:31:38 AM Pacific Standard Time,
> alan.boswell_at_baesystems.com writes:
>
> >
> > Chip
> >
> > I have not seen any gain measurements for fractal antennas so cannot
> > comment
> > on validity or otherwise. But I would characterise a traceable
> measurement
> > as one in which the quantities are measured with instruments whose
> > calibration is traceable to an international standard by an established
> > quality control procedure.
> >
> > In professional antenna engineering the strategy is to feed a measured
> > amount of rf power to the antenna and to measure the radiated field (power
> > density) at a set of points around the antenna, sufficient to calculate
> the
> > total radiated power. Then the gain is equal to the directivity (i.e. the
> > pattern gain) less the efficiency factor, and the efficiency is the
> > radiated
> > power divided by the power accepted at the terminals. Gain can be
> measured
> > within about 0.5dB above 1GHz and about 1-2dB below 30MHz by this
> approach.
> >
> >
> > Antenna measurements techniques are summarised in "IEEE standard test
> > procedures for antennas", ANSI/IEEE Std 149-1979, and the terms used
> > internationally are defined in "IEEE standard definitions of terms for
> > antennas", IEEE Std 145-1993.
> >
> > Anyone offering a new antenna for general acceptance has a good chance of
> > success if the gain and efficiency are measured to professional standards.
> > I don't know if this has been done for fractal antennas in particular so
> > maybe you could point me to some references.
> >
> > All the best,
> >
> > Alan
> >
> >
> >
>
> That's a wonderful process, and I am familiar with the metrology. But
> frankly, I don't care about what you call 'traceable' methodology.
>
> With acceptable precision, the measurements I make from relative dipole
> differentials, using S12, are more than adequate, and I have sufficient
> confirmation from outside customers--who make their own measurements--that
> we
> see apples to apples.
>
> I presume you would also disagree with a Wheeler cap method for efficiency
> (that is, when applicable).
>
> In any case, it is important for others to understand that what you and Doug
>
> are discussing is not a question of validity, but whether one can only
> believe a result if done at the highest priced facilities, such, as you
> know, exist at BAE systems.
>
> That's beyond my interest of discussion.
>
> 73,
> Chip N1IR
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