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
