>From: "Gary Schafer" <[EMAIL PROTECTED]>
>Reply-To: [email protected]
>To: <[email protected]>
>Subject: RE: [Repeater-Builder] Re: Antennas that work both in commercial
>and amateur
>Date: Fri, 16 Feb 2007 19:31:17 -0500
>
>
>
> > -----Original Message-----
> > From: [email protected] [mailto:Repeater-
> > [EMAIL PROTECTED] On Behalf Of Barry C'
> > Sent: Friday, February 16, 2007 6:15 PM
> > To: [email protected]
> > Subject: RE: [Repeater-Builder] Re: Antennas that work both in
>commercial
> > and amateur
> >
> >
> >
> >
> > >From: "Laryn Lohman" <[EMAIL PROTECTED]>
> > >Reply-To: [email protected]
> > >To: [email protected]
> > >Subject: [Repeater-Builder] Re: Antennas that work both in commercial
>and
> > >amateur
> > >Date: Fri, 16 Feb 2007 17:33:49 -0000
> > >
> > >--- In [email protected], "Barry C'" <[EMAIL PROTECTED]>
> > >wrote:
> > >
> > > > >
> > > > I presume its some sort of stacked arrangment , in chich case it
> > >will make
> > > > that gain at resonance ,
> > > >
> > >
> > >Yes, the ASPB602 is four stacked dipoles, just like the DB224. My
> > >point again is that resonance is NOT a requirement for an effective
> > >and efficient antenna. The wider frequency coverage for this antenna
> > >is likely because the dipoles are fabricated from 3/4 in. OD tubing
> > >instead of 3/8 in. tubing.
> >
> > or as in many cases of commercial sticks its almost a dummy load in
> > reactance ( think about it)
> > I must admit brandishing model number does no good as I am not familiar
>,
> > its been a long time since I was at broadcast school so I am unlikly to
> > change methodology now :)
> >
>
>A collinear antenna is not as wide band as a dipole antenna because each
>element of a collinear is fed from the previous element. When changing
>frequency there is a phase shift at the end of each element. That phase
>shift is cumulative and by the time it gets to the higher elements the
>phase
>shift can be significant. That destroys the pattern of the antenna and thus
>the gain.
>
>With a dipole antenna all the elements are fed from the same source so you
>don't have that same kind of phase shift from element to element and the
>pattern remains more intact with a shift in frequency. Yes there is some
>phase shift in the phasing/feed lines to the dipole elements that
>eventually
>disrupts the pattern of the antenna and thus the gain. But this type of
>antenna can be operated over a much wider range than a collinear type.
>Swr on the antenna only becomes a problem when it gets high enough that the
>transmitter can no longer be matched or it is excessive and caused
>excessive
>feed line loss. By using fatter elements it provides for a broader Swr and
>makes matching easier.
>
>Does any of this fit with your "methodology"? :>)
>
>73
>Gary K4FMX
>
>Thanks for trying to teach "how to suck eggs"
The dia of a radiator has to be incresed to a noticable portion of the
wavelength in use to appreciably increas useable bandwidth , an excursion of
2%/Frq does produce a noticable drop in response and gain , just because
the swr is acceptable does not the thing a decent radiator , I suggest you
spend a day on a rabge some time and do some tests , when I have some time I
will pursue it further but atm I have to finsih sorting out the next $
generation project.
B
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