All, I have been somewhat following the discussion and think I have the correct antenna geometry and have created a NEC model in free space. See the attached power point.
Bill, WA8WG ----- Original Message ----- From: "Paul Kelley N1BUG" <[email protected]> To: <[email protected]> Sent: Wednesday, June 24, 2009 3:49 PM Subject: Re: [Repeater-Builder] SRL235-2 Bi-Directional Antenna, which direction has gain? > Yup. I completely agree with the theory of operation as you stated > it for free space in-phase dipoles and dipoles 1/4 wave from a mast > but not fed in pairs on opposite sides of a mast. It would certainly > be interesting if someone were to model this thing. > My take on it is that having two side by side dipoles fed in phase > (which they are) changes the situation. The fed in phase dipoles > largely overcome the tendency for the mast to act as a reflector. > There may be some pattern disruption from the presence of the mast. > That may be why there don't seem to be any deep nulls in the > SRL235-2 pattern, where with a free space array I would expect to > see fairly deep nulls in-line with the dipole pairs. > > But who knows... it has to be a rather complex situation. > > 73, > Paul N1BUG > > > Jeff DePolo wrote: >> Now you have me second-guessing myself. >> >> Over-simplying greatly: >> >> If the dipoles are spaced roughly 1/2 wave apart or less, it's going to >> be >> broadside to the axis of the elements (assuming the elements are fed in >> phase, which I presume they are). That's in free-space; but here we have >> a >> mast right in the middle of the two elements. >> >> If the elements are spaced somewhere in the vicinity of 1/2 wave apart, >> that >> means the mast is roughly 1/4 wave from each bay. A mast 1/4 wave behind >> a >> dipole would normally yield a cardiod pattern, with maximum gain away >> from >> the mast. So, two such cardiods back-to-back would yield an end-fire >> "figure 8" pattern. That contradicts the first analysis (broadside). >> >> Maybe time to model it... >> >> I checked a Sinclair catalog (circa 1990) and, although it showed the >> elliptical pattern, it didn't say how the antenna was oriented for the >> plot. >> I don't have Comprod docs other than what's on their web site. >> >> --- Jeff >> >>> -----Original Message----- >>> From: [email protected] >>> [mailto:[email protected]] On Behalf Of Paul >>> Kelley N1BUG >>> Sent: Wednesday, June 24, 2009 5:36 AM >>> To: [email protected] >>> Subject: Re: [Repeater-Builder] SRL235-2 Bi-Directional >>> Antenna, which direction has gain? >>> >>> >>> >>> If the Comprod is really the equivalent of the Sinclair SRL235-2, I >>> must respectfully disagree with this. The instruction sheet for the >>> SRL235-2 says the opposite, that maximum radiation would be >>> perpendicular to a line drawn as described. I can scan a page from >>> the Sinclair instruction sheet to back up this statement. >>> >>> Paul N1BUG >>> >>> Jeff DePolo wrote: >>>> If all of the elements are parallel as in your photo, then it's >>>> bi-directional. If you drew a line through one element, >>> through the mast, >>>> and through the other element, maximum radiation would be >>> along that axis. >>>> If the elements are staggered such that each bay pair is >>> rotated 90 degrees >>>> from the bay above/below it, then it's basically omnidirectional. >>>> >>>> --- Jeff >>>> >>>>> -----Original Message----- >>>>> From: [email protected] >>> <mailto:Repeater-Builder%40yahoogroups.com> >>>>> [mailto:[email protected] >>> <mailto:Repeater-Builder%40yahoogroups.com> ] On Behalf Of Jesse Lloyd >>>>> Sent: Tuesday, June 23, 2009 8:28 PM >>>>> To: [email protected] >>> <mailto:Repeater-Builder%40yahoogroups.com> >>>>> Subject: [Repeater-Builder] SRL235-2 Bi-Directional Antenna, >>>>> which direction has gain? >>>>> >>>>> >>>>> >>>>> Hi all, >>>>> >>>>> >>>>> I acquired a Comprod equivalent to the SRL235-2. Basically >>>>> the same, just heavier duty and the cabling harness is in the >>>>> boom. Anyway, which way is it directional? In the case of >>>>> this picture of one >>>>> http://www.repeater.n1bug.com/sinclairant.jpg >>> <http://www.repeater.n1bug.com/sinclairant.jpg> >>>>> <http://www.repeater.n1bug.com/sinclairant.jpg >>> <http://www.repeater.n1bug.com/sinclairant.jpg> > is it >>>>> diectional through the dipoles, or 90 degrees from them, ie >>>>> in the diection of the tower (and opposite to) in that case. >>>>> >>>>> >>>>> Thanks, >>>>> >>>>> Jesse > > > ------------------------------------ > > > > Yahoo! Groups Links > > >
