Hi Burt, > Did I hear my name mentioned??? Maybe just ESP:-)
Yes you did, Great Sinclair dipole guru! :-) I got the dipole drawing from your new web site. Thanks! That part I'm clear on, but still a bit confused on the phasing harness. > I would suggest that you don't even consider putting the harnass inside > the mast (unless Harold can tell us how Sinclair does it). Put the > harness on the outside of the mast like the SRL210A4. Uh, yeah, I hear that. I like the idea of the internal harness, but I just spent 3 hours getting the old harness *out* of the mast. I can't imagine how it was put *in* there. > To combine the impedances on a 4 bay Sinclair array is simple. Divide > the dipoles into pairs and parallel them. This gives 25 ohms. Then add > an electrical quarter wave of 50 ohm coax (RG-213/U) to transform it to > 100 ohms. Combine the matching coax from each pair in parallel to give > 50 ohms. Then you can connect your feedline at any length from this > latter 50 ohm connection. Here is a crude drawing of what I think you are saying: http://www.n1bug.com/dipoleharness1.jpg Points X and Y are the 100 ohm points created by adding an electrical quarter wave of RG-213 coming out of the 25 ohm point where two dipoles are connected in parallel. But points X and Y are physically several feet apart. That being said, I think the coax that joins those points at the final parallel junction (to connect to the feedline) would have to be a multiple of an electrical half wavelength in order to repeat the 100 ohms at the other end (thus ending up with 50 ohms when you parallel them)? If so, I'm still confused on how they did this for both cardioid and bidirectional versions of this antenna with the harness inside the mast. Required physical lengths would be different due to the different dipole spacing from the mast. One can only work with physical lengths that "fit" inside the mast (I guess?) but this seems to clash with the electrical length required for impedance matching. It's a non-issue since I have no way of getting a new harness inside the mast. With an external harness I can just coil up or loop any extra length required for matching reasons. But I'd still like to understand how they did it. :-) In any case, the phasing harness on my 210C4 was done differently. It uses a combination of RG-213/U and RG-63B/U in the harness itself. Here is a sketch of it: http://www.n1bug.com/210C4harness.jpg Here, if we assume points X and Y are 100 ohms, point Z (where the feedline attaches) would fall somewhere between 50 ohms and 78 ohms, depending on the electrical length of the RG-63B/U coax connecting them. I'm trying to look up the velocity factor of RG-63B/U (part PE, part air dielectric), but having no luck so far. All of which seems completely different from the picture at http://forum.radioamateur.ca/index.php?topic=2245.0 where there appears to be just a quarter wave section of coax off each side of point Z to the "T" for each pair of dipoles. I don't know how that was physically possible given the dipole spacing. I think we can safely assume I'm missing something here. :-) Paul N1BUG ------------------------------------ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/Repeater-Builder/join (Yahoo! ID required) <*> To change settings via email: repeater-builder-dig...@yahoogroups.com repeater-builder-fullfeatu...@yahoogroups.com <*> To unsubscribe from this group, send an email to: repeater-builder-unsubscr...@yahoogroups.com <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
