RE: [amsat-bb] Arrow II antenna -- why no gain figures given?

[<alan_bloom@xxxxxxxxxxx>]

I've always heard that the gain of an optimized Yagi is proportional to boom length, not the number of elements.  Gain_in_dB ~= constant + 10*log(boom_length)  For example, a 5-element Yagi is about double the length of a 3-el, so if the 3-el is 7 dBd then the 5-el should be about 10 dBd.

Al N1AL


> -----Original Message-----
> From: owner-AMSAT-BB@amsat.org [mailto:owner-AMSAT-BB@amsat.org]On
> Behalf Of KC6UQH
> Sent: Wednesday, November 17, 2004 10:21 PM
> To: Gary Mayfield; AMSAT-BB@amsat.org
> Subject: Re: [amsat-bb] Arrow II antenna -- why no gain figures given?
> 
> 
> I suspect that ground reflections do not contribute much to gain measurments
> with the antenna pointed up, as you would when working a satellite. Rule of
> thumb for a yagi is 0 dBd for just a dipole (one  element ) 3 dBd for two, 6
> for four 9 for eight...............etc. The more elements, the greater the
> chance that the full gain will not be relized due to losses in the elements.
> Spacing can change this number by 2 dB and also reduce the bandwidth of the
> antenna. As the gain goes up the area of coverage goes down and by
> determining the beamwidth, angles of the 1/2 power points, (1/2 S Unit on a
> good receiver) can be another way to determine antenna gain.
> 
> Art ,KC6UQH
> 
> ----- Original Message -----
> From: "Gary Mayfield" <gary_mayfield@hotmail.com>
> To: <AMSAT-BB@amsat.org>
> Sent: Wednesday, November 17, 2004 5:27 AM
> Subject: RE: [amsat-bb] Arrow II antenna -- why no gain figures given?
> 
> 
> >     Not practical to have gain figures on a handheld antenna.
> >     Not useful info.
> >
> > which struck me as strange -- obviously I've run into yet another
> > thing I don't know about antennas (which happens pretty much every
> > time I do anything involving antennas -- nothing new there.)
> > Obviously they're likely to be close enough to the ground for the
> > ground to interfere with things, but does it really mess things up
> > that badly?
> >
> > Does anybody have approximate figures on their performance?
> >
> > --
> > Doug McLaren, dougmc@frenzy.com, AD5RH
> >
> >
> > Doug,
> >
> >      The ball park numbers folks have given you are 
> probably pretty good.
> > Remember most of the Arrow numbers you are getting are 
> measured where the
> > other antenna numbers are "advertised"!
> >
> >      This actually makes very good sense.  A great deal will depend on who
> > is holding the antenna, and how are they holding it.  Is it a large or small
> > person?  Is that person wearing potentially reflective clothing?  Is it a
> > wavelength above the ground?  Is it parallel to the ground?  The list goes
> > on and on making comparision very diffucult.  As an ex antenna range / EMI
> /
> > EMC / RFI / Radar Cross Section guy I will add that (with the exception of
> > one antenna made by the Hughes corporation) I have never seen an antenna
> > who's advertised gain figures weren't inflated from what we actually
> > measured.
> >
> >      Logic says the properly optimized, designed and built narrower band
> > antenna will always have more gain than the wideband antenna with the same
> > boom length.  If you find a way around this the world will beat a path to
> > your door.
> >
> > 73,
> > Joe
> > ----
----
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