> -----Original Message----- > From: Repeater-Builder@yahoogroups.com [mailto:Repeater- > [EMAIL PROTECTED] On Behalf Of Barry C' > Sent: Friday, February 16, 2007 10:59 PM > To: Repeater-Builder@yahoogroups.com > Subject: RE: [Repeater-Builder] Re: Antennas that work both in commercial > and amateur > > > > > >From: "Gary Schafer" <[EMAIL PROTECTED]> > >Reply-To: Repeater-Builder@yahoogroups.com > >To: <Repeater-Builder@yahoogroups.com> > >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: Repeater-Builder@yahoogroups.com [mailto:Repeater- > > > [EMAIL PROTECTED] On Behalf Of Barry C' > > > Sent: Friday, February 16, 2007 6:15 PM > > > To: Repeater-Builder@yahoogroups.com > > > Subject: RE: [Repeater-Builder] Re: Antennas that work both in > >commercial > > > and amateur > > > > > > > > > > > > > > > >From: "Laryn Lohman" <[EMAIL PROTECTED]> > > > >Reply-To: Repeater-Builder@yahoogroups.com > > > >To: Repeater-Builder@yahoogroups.com > > > >Subject: [Repeater-Builder] Re: Antennas that work both in commercial > >and > > > >amateur > > > >Date: Fri, 16 Feb 2007 17:33:49 -0000 > > > > > > > >--- In Repeater-Builder@yahoogroups.com, "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 >
A shift of 2% may produce a noticeable drop in gain in an antenna system but not for the reasons you seem to be expressing. The water seems to be getting a little muddy here and it is becoming a little difficult determining as to what you are comparing your reasoning to. Some times you seem to be discussing multiple element antennas and other times a single element antenna. Maybe you could give us an example of a particular type of antenna and tell us why the gain drops on that antenna when frequency is changed. 73 Gary K4FMX
