Towertalk
[Top] [All Lists]

[Towertalk] LPA designs

To: <towertalk@contesting.com>
Subject: [Towertalk] LPA designs
From: stevek@jmr.com (Steve Katz)
Date: Fri, 15 Nov 2002 14:29:49 -0800
Interesting, Josh.

I've been a real believer for many years that one can never evaluate the
performance of any antenna, if it's the only one he has.  Any antenna is
"terrific," when it's the only one in the farm.  After all, propagation has
allowed many of us to make international contacts using light bulbs for
antennas, or, as in the case of W6ISQ's recent QST writeup, a shielded
Cantenna dummy load fed with double-shielded RG214.  I wonder how much that
radiates?  Not much.

Here at my company we have an RF anechoic chamber built by Rantec
Engineering and guaranteed to provide a minimum of 120 dB shielding at 1
GHz, when the door's closed and all interlocks are in place.  Yet, with the
door cracked open one inch I can use my cellular telephone in there.  Of
course, the local cell site is about 200' away, across the parking lot.

Without standards of comparison, we're all wondering in the wilderness.

What wins in the pileups does help tell the story for sure, but what tells
it more clearly is when you win against your neighbors.  Literally.  I have
several hams within one mile of me, in a flat terrain area so we're all on
very equal footing.  In shootouts when we're all involved at once, it is
truly interesting.

WB2WIK/6


> Its an old design - it had little sales
> appeal -  the T 620  log yagi 6 el only for 20 meters .
> 
> The theory goes that the 4 el LOG CELL
> that has 4 el has 6 dbd  - the LOG CELL is the driver - then add
> director and reflector -  the boom is
> small at 27 ft -  I have very high winds
> so I dont want a huge boom.  At any rate
> it will meet my needs -  I have great
> respect for Pete K4EWG consumate operator on CW and has all homebrew
> transceiver and amps and antennas.
> antenna modeling aside - NOTHING compares to real world testing
> of antennas at same height at same QTH !!!!!
> 
> I expect it to run with any 30 foot boom
> monobanders -   Chuck at Tennadyne
> AND Pete K4EWG say it will easily
> run with 48+ foot boom monobanders -
> The only real test is to compare antennas
> , both installed at same height and QTH .
> 
> Chuck says it is much better than the T 12
> on 30ft boom ON 20 meters.
> 
> We will see how it rates " Real World "
> 
> below is message from Chuck at Tennadyne
> Interesting reading       josh n7xm
> 
> 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
> 
>   ----- Original Message ---
> 
> Josh n7xm
> ----- Original Message -----
> From: "Steve Katz" <stevek@jmr.com>
> To: "'xppq'" <xppq@pyramid.net>
> Cc: <towertalk@contesting.com>
> Sent: Friday, November 15, 2002 1:38 PM
> Subject: RE: [Towertalk] LPA designs
> 
> 
> > Hi Josh,
> >
> > I didn't know Tennadyne even made a 20m-only log yagi.  The only
> antennas
> on
> > their website are the T6 through T12 and one VHF-UHF model, nothing
> > monoband.
> >
> > I don't think a 3/8-wavelength boom yagi can have 10.5dBd gain, either;
> > however, you might have to look at "how" they rated it.  I note a lot of
> > manufacturers, including Force-12 and Tennadyne, give references of gain
> > based on total gain (including ground gain) for an antenna mounted at a
> > certain height above earth, like 1 wavelength.  When you sum that, a
> small
> > beam can certainly have so much gain when installed at a favorable
> height.
> >
> > WB2WIK/6
> >
> > "If everything seems under control, you're just not going fast enough."
> -
> > Mario Andretti
> >
> > > -----Original Message-----
> > > From: xppq [SMTP:xppq@pyramid.net]
> > > Sent: Friday, November 15, 2002 1:38 PM
> > > To: Steve Katz
> > > Subject: Re: [Towertalk] LPA  designs
> > >
> > > I have TENNADYNE  6 el log yagi
> > > monobander for 20m on 27 foot boom.
> > > ON ground , hope to install up around
> > > 100feet once my new tower is installed
> > >
> > > Tennadyne says 10.5 dbd GAIN !
> > > Very few hams will agree with that!
> > > Boom length being what it is.
> > >
> > > I am told it is considerably better than
> > > the T 12
> > >
> > > What ya think?
> > >
> > > Josh N7XM   Nevada
> > > ----- Original Message -----
> > > From: "Steve Katz" <stevek@jmr.com>
> > > To: "'xppq'" <xppq@pyramid.net>; <towertalk@contesting.com>
> > > Sent: Friday, November 15, 2002 11:13 AM
> > > Subject: RE: [Towertalk] LPA designs
> > >
> > >
> > > > I think the responsible manufacturers don't make any ridiculous
> claims
> > > about
> > > > gain.  Tennadyne, for example, rates the T6 (12' boom, 6L 14-30 MHz)
> at
> > > > 5.1dBd and BW = 57 degrees, and it's very much bigger brother T12
> (30'
> > > boom,
> > > > 12L 14-30 MHz) at 6.5 dBd and  on 20m.   Yet, the signals emanating
> from
> > > > these antennas are frequently stronger than signals from similarly
> > > located
> > > > stations using bigger stuff.  Why that is, is the question.
> > > >
> > > > I don't have the answer.
> > > >
> > > > -WB2WIK/6
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > "If everything seems under control, you're just not going fast
> enough."
> > > -
> > > > Mario Andretti
> > > >
> > > > > -----Original Message-----
> > > > > From: xppq [SMTP:xppq@pyramid.net]
> > > > > Sent: Friday, November 15, 2002 10:28 AM
> > > > > To: towertalk@contesting.com
> > > > > Subject: [Towertalk] LPA  designs
> > > > >
> > > > > Peter  K4EWG  has a great LOG YAGI
> > > > > monoband design -  his GAIN estimates
> > > > > differ from many other "experts"  -
> > > > > but bottom line Pete knows his stuff
> > > > >
> > > > > josh n7xm
> > > > >
> > > > >
> > > > > --- StripMime Report -- processed MIME parts ---
> > > > > multipart/alternative
> > > > >   text/plain (text body -- kept)
> > > > >   text/html
> > > > > ---
> > > > > _______________________________________________
> > > > > AN Wireless Self Supporting Towers at discounted prices,
> > > > > See http://www.mscomputer.com
> > > > >
> > > > > Wireless Weather Stations now $349.95. Call Toll Free,
> > > > > 888-333-9041 for additional information.
> > > > > _______________________________________________
> > > > > Towertalk mailing list
> > > > > Towertalk@contesting.com
> > > > > http://lists.contesting.com/mailman/listinfo/towertalk
> > > > _______________________________________________
> > > > AN Wireless Self Supporting Towers at discounted prices,
> > > > See http://www.mscomputer.com
> > > >
> > > > Wireless Weather Stations now $349.95. Call Toll Free,
> > > > 888-333-9041 for additional information.
> > > > _______________________________________________
> > > > Towertalk mailing list
> > > > Towertalk@contesting.com
> > > > http://lists.contesting.com/mailman/listinfo/towertalk
> > > >
> > > >
> > >
> >
> >
> 

<Prev in Thread] Current Thread [Next in Thread>