> -----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
