You can actually model the conductor losses in a Yagi (or quad for
that matter) using NEC. You will find that the difference between
aluminum tubing and a perfect conductor is typically a very small fraction
of a dB. Its certainly not 3dB. In fact if anything the efficiency of
a yagi is probably a bit better than a quad given the large surface
area of the tubing relative to that of the wire that is usually used to
build a quad.
73 de Mike, W4EF.................................................
----- Original Message -----
From: "Bill Wall" <billwall@eyecon-solutions.com>
To: "Jon Ogden" <na9d@speakeasy.net>; "xppq" <xppq@pyramid.net>;
<towertalk@contesting.com>
Sent: Saturday, November 16, 2002 4:51 AM
Subject: Re: [Towertalk] IS Boom length the HOLY GRAIL ?
> Hi Jon;
> Consider the full wave Quad has about 1.8 db more gain than a 1/2 wave
Yagi.
> The Quad is quieter on receive and does not hear rain static. The
efficiency
> of the average 3 el Quad is in the 90% + category. The 3 el Yagi is about
> 50%. Put 1000 watts on the Quad and you have apprx. 900 watts. Put 1000
> watts on the same Yagi and you have aprrx 500 watts out. The power is lost
> in resistive heat.
> A few years ago Lew Mccoy W1ICP published an article in CQ magazine about
> this. Boom length is gain, but there are other things that are more
> important like, takeoff angle, frontal lobe pattern and so forth.
> Bill Wall KC4UZ Antenna Mart
> ----- Original Message -----
> From: "Jon Ogden" <na9d@speakeasy.net>
> To: "xppq" <xppq@pyramid.net>; <towertalk@contesting.com>
> Sent: Saturday, November 16, 2002 12:26 AM
> Subject: Re: [Towertalk] IS Boom length the HOLY GRAIL ?
>
>
> > I totally question the veracity of anyone that claims a cubical quad
with
> > the exact same dimensions as a yagi has more gain. It's just not true.
> > Force 12 dispels this myth on their website.
> >
> > 73,
> >
> > Jon
> > NA9D
> >
> > on 11/15/02 10:03 PM, xppq at xppq@pyramid.net wrote:
> >
> > > Below in a communication from CHUCK at Tennadyne
> > > I am soon to install a T 620 - his is a 6 el LOG YAGI for 20m only (
> > > discontinued model)
> > > on 27 foot boom - it has 4 el in LOG cell, and director and
reflector.
> > > It is NOT a big antenna and I expect it will survive my very windy
> > > location - It will be approximately 100 ft above ground.
> > > I have no wild expectations myself - if it compares
> > > with monoband yagi on 30 foot boom - so be it !
> > >
> > > the text below is from Chuck at Tennadyne -
> > > I welcome feedback from the Tower Talk BRAIN TRUST
> > > on this matter:
> > >
> > > josh n7xm nevada
> >
>
> --------------------------------------------------------------------------
> ----
> > > --------------------------------
> > >
> > >
> > >
> > > Josh, in general, and within limitations, they're correct. One must,
> however,
> > > compare apples with apples, and not with oranges. Now, apply the
> psychology
> > > of all of this, don't forget that people will tend to tell you what
they
> > > want/need to believe. The Cubical Quad, for instance, has different
> gain than
> > > a Yagi given the same boom length. A 2-element Quad for instance,
using
> a
> > > reflector and an 11 ft boom has 1.1 dB more gain than a 3-element Yagi
> on a 20
> > > ft boom (W2PV). The 3 element Quad with an 18 ft boom is another 1.24
> dB
> > > higher, how do the gurus explain that away? However, with the T620
you
> start
> > > with a 'driven element,' the Log-Cell itself, that has a gain of 6.3
dBd
> while
> > > the DE for a Yagi is 0.0 dBd. Ultimately, the LCY parasitics do not
> yield
> > > quite as much of an improvement over the DE as the parasitics of the
> single
> > > element do, but it's very close.
> > >
> > > In controlled measurements on our test range, when we had one, my LCY
> with a
> > > 31 ft boom came in .13 dB higher in forward gain than a 6-element Yagi
> on an
> > > 80 ft boom, the latter was a design straight from the ARRL Antenna
Book
> and
> > > optimized for overall performance. There'll always be those that
"know
> > > better" and I wouldn't worry about the self-anointed antenna gurus,
just
> cream
> > > 'em in the pileups and smile, as I did when I had my own T620 (31 ft
> boom) at
> > > 101 ft. I've had too many engineers tell me that they were far too
good
> an
> > > engineer to have made such a mistake............but they did. The
test
> range,
> > > by the way, is a far more critical judge of an antenna than any
> on-the-air
> > > performance checks I've ever been part of.
> > >
> > > 73 Chuck - KA1PM
> > > TENNADYNE
> > >
> > >
> > >
> > >
> > > --- StripMime Report -- processed MIME parts ---
> > > multipart/alternative
> > > text/plain (text body -- kept)
> > > text/html
> > > ---
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> >
> > -------------------------------------
> > Jon Ogden
> > NA9D (ex: KE9NA)
> >
> > Citizen of the People's Democratic Republik of Illinois
> >
> > Life Member: ARRL, NRA
> > Member: AMSAT, DXCC
> >
> > http://www.qsl.net/na9d
> >
> > "A life lived in fear is a life half lived."
> >
> >
> > _______________________________________________
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>
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