Hi Paul Did I hear my name mentioned??? Maybe just ESP:-)
Some time ago the ISP I originally used merged with anther. I had files on another ISP (rocler.qc.ca) but dropped it due to a dispute concerning SPAM filtering. All my files that I kept have been moved to my own domain website (gorum.ca) where I have better control over it. The old NEDA packet files are on another site that I use. The folded dipole clone info is at: http://www.gorum.ca/fdipolev.htm or download fdipolev.gif from the gorum.ca site. (Sometimes the link gets redirected to sedoparking.com which I have trouble getting rid of.) 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. You do have it right that there is a matching piece of 125 ohm coax (RG-63/U) inside the dipole. This makes the impedance of each dipole 50 ohms. 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. That takes care of the impedance but you first must match the phase of the rf signal at each dipole. Failure to consider the phase matching will result in a really messed up vertical pattern (unless you are very very lucky). Matching the phase simply means that the electrical wavelength along each feedline path to each dipole has to be as close to equal as possible. They don't have to be any particular wavelength, just so long as they are all equal electrically. Saying this is easy, measuring the wavelength is not easy and requires some speciallized test equipment. I don't know how others measure electrical wavelength, possibly using a network analyzer (which I don't have). What I use is an old HP803A VHF RF Bridge fed with a signal generator and a spectrum analyzer as a null detector. The other essential component of this setup is a "Z-Theta Chart" which looks sort of like a Smith Chart. See: http://www.gorum.ca/z-theta-8x11.gif On the chart, the resistance and reactance components of the impedance are plotted on the inside of the chart and a line drawn between them will intersect the relative electrical wavelength around the perimeter. The wavelength can be measured to better than 0.002. There is an HP application note that explains the process in detail. I could scan it if anyone is interested. The wavelength on the feedlines of each of the dipoles is measured and the shortest one selected. The other feedlines are then shortened by the necessary incremental length to make them all electrically equal. Of course this has to be done as a first step before paralleling the feedlines. That is my experience. Others may have different ways to achieve the same end result. Burt VE2BMQ N1BUG wrote: > Me again. I just got "handed" a potential project. > > I am looking for information on the phasing harness for Sinclair VHF > 4-bay dipole arrays with the coax inside the mast. I want to know > types of coax and lengths so I can understand the matching. I could > use info on both the bidirectional and cardioid versions, but > especially cardioid. The harness lengths must be different in order > to cram it inside that mast. Burt? Or anyone can shed some light on > this? (I was thinking Burt had some info on a web site somewhere, > but I can't seem to find it) > > I am aware of the 125 ohm quarter wave section inside Sinclair > dipoles, but want to know about the rest of the harness. > > I am wanting to attempt the difficult or, maybe, impossible... I am > trying to figure out if it would be possible to use dipoles from an > SRL235-2 to rebuild what is believed to be and SRL214, and at the > same time convert the antenna from bidirectional to cardioid > pattern. I would be constructing my own harness. I think this might > be possible, if I can find out how the phasing harness for the > SRL214/cardioid version was made. > > Any info out there? > > Paul N1BUG > > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > >
