Hi Burt, > Let's hope you don't need to get inside the dipole itself. BTW what is > the diameter of the aluminum tubing used on the SD2352? The SD214 uses > 3/4in OD.
I *am* hoping! They use 3/4 in. OD on these also. The width of the folded dipole is 4.25 inches and the tip to tip (outer radius of bend to outer radius of bend) length is 34.5 inches. > You could try using 3/4 wavelength matching pieces to get the extra > length. That should be equivalent to 1/4 wave but will be more > sensitive to frequency changes. I only need to extend them by about a foot to get ideal spacing between dipoles, so 1/4 wavelength with .66 VF would be enough. > Never having seen one of those antennas (the SD2352) up close, I am not > sure of the harness configuration and how it would compare to the SD214 > that I am familiar with. Total of 8 dipoles. Impedance at end of coax coming from each dipole approximately 50 ohms. Two dipoles connect to a type N tee, so at the tee center should be about 25 ohms. From there, 1/4 wavelength RG-213 to a a factory harness 'Y' splice, coax should transform the impedance to about 100 ohms, divided by 2 at the Y so we're back to 50 ohms coming out of there. From there, approximately 66 inches RG-213 to the center Y splice of the overall harness. This coax should maintain 50 ohms, divided by two at the center Y splice = 25 ohms. There is a 1/4 wavelength of some coax coming out of there, spliced to a length of RG213 running down to the bottom of the mast. I'm assuming the 1/4 wavelength matching section is 35 ohm coax, but cannot confirm that. This description may be "clear as mud"... I can make a diagram of it later if you want. > Figuring out the failure mode is the most important first step. Then > you can go from there to possible solutions whether it is harness > replacement, repair or dig into the dipoles. I have decided no matter what I'm not putting it back up as an 8 dipole bidirectional array so I will take apart the original harness for inspection. I will also test each of the dipoles on the repeater individually to check for noise. If I do not find any problems in either of these processes, then I will have no clue what caused the problem! Paul N1BUG
