To measure radiated power to 95% certainty, ETSI standards allow a +/-6dB
tolerance, although most Test Houses can get to within 3dB. I built a reference
dipole and bazooka balun for 400 MHz for tests: I was amazed when we calibrated
it at the Russian Test establishment equivalent to NIST or NPL to get answers
within 1.5dB of what it should theoretically give. Pure luck!
73
Peter G3RZP
========================================
Message Received: Nov 14 2013, 02:23 PM
From: "David Kirkby" <david.kirkby@onetel.net>
To:
Cc: "amps" <amps@contesting.com>
Subject: Re: [Amps] UHF connector discussion For Dummies
On 14 November 2013 13:41, <TexasRF@aol.com> wrote:
> Dave. not everyone has access to this $100,000 software.
Agreed.
> As a result, we do
> what we can with what we have to work with.
Agreed. BUT doing "what you can" should not extend to publishing a
gain figure that is inaccurate, with no justification for how it is
arrived at. Would you think it reasonable to publish a design for a
LNA, with a claimed gain and noise figure you can't measure of have
anything else to justify it?
It should be clear that particular individual does not know what he is
doing, the fact the gain is quoted in dB, with no reference.
My concerns about amateur antennas extends to the person who was
(probably still is), writing the "Antenna" column in RADCOM. He does
not have an ****ing clue what he is doing, but still writes things.
When I reported a number of issues to the RSGB, it took over a year to
get a response, but finally they conceded I was right, but still did
not want to publish any corrections.
On a similar topic, there was an article about forces on antennas in
RADCOM. All forces were measured in kg, despite it is basic school
physics that force is measured in Newtons, and not kg. There is a lot
of **** in the amateur radio press.
> So, the published gain is off 3
> dB
Well, depending on whether you work in dBi (as professionals tend to)
or dBd (as amateurs tend to), it is either 2 or 4 dB off. The gain is
around 7 dBi or 5 dBd - a far cry from the claimed "9 dB".
> it is still a good way for a ham to improve his 70cm station performance
> for very low cost.
The peak radiation is not on the horizon either. It is tilted up in
the air by about 15 degrees, so the gain for terrestrial use will not
be realized.
> I see that design as neither weird nor wonderful; just an idea that might be
> helpful to others.
But in my opinion, one should not invent gain figures. Let's assume I
publish the design for a colinear with a claimed gain of 6 dBd (8.15
dBi), and his antenna has a claimed gain of 9 dB. What should a ham
build? You may so both, but that is not practical if funds are
limited.
> I wonder how one of the Diamond or Comet antennas of this type would stack
> up?
Having worked in the antenna industry professionally, I know many gain
figures are exaggerated, and many SWR figures are just plain wrong
too. It relies on the fact that especially at higher frequencies, and
for things like WiFi, few people have the test equipment to measure
anyway.
My last employer would sometimes buy antennas from a competitor, but
when I tested them on a VNA they were well outside the SWR spec. My
employer was ok with that, and would just ship them out with the same
claimed spec. It seems the norm. As a chartered engineer, it is not
the way I work.
There was a particular antenna made by some company (forget who just
now - I might dig it out later), with a claimed gain of x dB. It was
an aperture antenna, so it is possible to put a theoretical limit on
the gain based on the size of the aperture. That gain was exagerated
by several dB. It just seems the norm in the antenna industry - at
least at the amateur and low-end pro stuff.
> 73,
> Gerald K5GW
Dave, G8WRB.
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