crimso
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Butternuts. Dirty little secrets 1 & 2.
quote:
In the ensuing pages we'll look at several widely advertised vertical antennas for which claims are made that could have come straight out of Dreamland.
http://www.bencher.com/pdfs/00363ZZV.pdf
http://www.bencher.com/pdfs/00804ZZV.pdf
quote:
NOTE: What is not radiation resistance is LOSS resistance that does us no good at all. EFFICIENCY IS MERELY THE RATIO OF THE
ANTENNA'S RADIATION RESISTANCE TO ITS TOTAL FEEDPOINT IMPEDANCE, or 35 ohm/85 ohm = 41% in this case.
quote:
Here, then, is our dirty little secret to calculate the probable efficiency of an antenna; You need to know only it's radiation resistance and
feedpoint impedance. Not that any information that has been available to the general public for nearly a century can be called "secret."
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1/Sep/2009, 2:27 pm
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26fb010
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Re: Butternuts. Dirty little secrets 1 & 2.
its shocking how they get away with that crap, they are making false claims and surely there is a trading standards issue there. can they be sued for it? cb antennas are the best bull, look at the piece of wire in a tube (antron 99)!!! i wish i`d had the idea first, i would be on my 70 foot yacht now in the carribean surrounded by busty wenches and bath tubs full of champagne..lighting cigars with $100 notes..
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2/Sep/2009, 8:53 pm
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simon26OD004
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Re: Butternuts. Dirty little secrets 1 & 2.
interesting reading, and they are correct aswell, the ARRL antenna handbook I've read certainly backs them up.
As for the wild claims made by antenna manufactures, I'm sure they could be taken to trading standards if you wanted to, but at a guess you would have to prove scientificly that they were padding out their figures.
I may be wrong, but the last time I saw an A99 box, it had 9.9dB gain claimed on it. What does 9.9dB gain actually mean? Jack diddley squat, it means nothing at all. dB's are a measure of gain, but it is a relative measurement, dB on its own doesn't actually make any sence. dBd means gain over a dipole, dBi means gain over an isotropic radiator, dBm means gain over a millivolt etc. etc. Just putting 9.9dB gain on the box is just a marketing tactic used to make numties think its a high gain antenna when it isn't, and a way around trading standards laws I expect. A more accurate gain for the A99 would be 9.9dBwps (wet piece of string).
If you look at the sirio antenna website you will see that they are now putting much more believable and accurate gain figures on their spec sheets. Hopefully more manufactures will follow suit soon.
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2/Sep/2009, 11:29 pm
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crimso
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Re: Butternuts. Dirty little secrets 1 & 2.
quote:
simon26OD004 wrote:
I may be wrong, but the last time I saw an A99 box, it had 9.9dB gain claimed on it.
The A99 claims a 9.9 dBigain, so is a theoretical gain, also that is claimed against a DC earth.
If you read the infomation on it, it claims to be a variable mutual transconductance tuned antenna. ask a dealer who advertises these what it means in terms of a DC earth.
I think they are one & the same thing, as a shunt fed antenna is DC fed to achieve the desired impedance. And my guess would be that this is the dBi gain they are measuring, not the radiated power measured against the power fed to the antenna.
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3/Sep/2009, 10:05 am
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John193
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Re: Butternuts. Dirty little secrets 1 & 2.
Back in 2003 I talked the RSGB to back me in a trading standards lawsuite with Sirio they settled for costs plus goodwill sum! and all agreeed to specify the relative db figure on uk sales ie isotropic or dipole. It does work but it took me a lot of time and effort and hundreds of letters if anyone else wishes to have a crack then I know a good trading lawyer but you will have to cover all costs up front until you win, IF!
dbm is decibels per square meter and is a relative measure of field strength, the decibel range used in voltage unit measurements is relative to .707v ie 1 db and is generally expressed as dBV and called VU for short (Voltage Units). Just so we don't get accused of misleading info by any lurking antenna manufacturer lol.
John193
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24/Sep/2009, 7:59 am
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