Well the 125 ohm quarter wave info sounds reasonable. That would imply the actual impedance of the folded dipole is in the vicinity of 300 ohms.
I think my strategy at this point is to test each element by itself. I'll have to actually put each one on the repeater and check for noise as that's the only way I know to see if they are noisy in duplex operation or not. If all the elements test good, I will rip apart the factory interconnection harness to see if I can find anything wrong with the Y splices. Meanwhile if anyone else has any insight on exposed dipole arrays going noisy within a short time after installation, please chime in. I would really like to understand the issues with this. Paul N1BUG Chuck Kelsey wrote: > Sounds like something in the harness went intermittent. To get at the inner > element connection, you'd need to cut the shrink tubing on the outside of > the element. That should gave you access to the connection point of the > 125-ohm matching section that is spliced to the RG-213. You could then pull > that out. However, if each element plays alone with no noise, I'd leave the > element wiring alone and check the harness that connects the elements > together. > > All that said, I've never worked on a Sinclair. I'm going by info that I > believe to be correct as to what is inside the element. > > Chuck > WB2EDV > > > > ----- Original Message ----- > From: "Paul Kelley N1BUG" <[email protected]> > To: <[email protected]> > Sent: Monday, May 18, 2009 6:58 PM > Subject: Re: [Repeater-Builder] Sinclair dipole array premature failure > (noisy) > > >> That's what I thought Chuck. Thanks! I haven't yet decided whether I >> want to rip the heat shrink tubing off an element and disassemble it >> to see what coax is inside, which is why I asked. >> >> I was sort of contemplating whether it might be possible to replace >> all that coax with RG-214 in an attempt to build a noise free >> harness. But if there's a matching section, I'm sure the return loss >> without it would be really ugly. >> >> Paul N1BUG >> >> >> Chuck Kelsey wrote: >>> There is a 1/4 wave impedance matching section of coax (125?) inside the >>> element. The matching section is stagger tuned from the element itself. >>> That's why it is more boadbanded and why you see two return loss dips. >>> >>> Chuck >>> WB2EDV >>> >>> >>> ----- Original Message ----- > >>> >>>> I wonder if anyone knows what (if any) gimmick Sinclair used to get >>>> such broad SWR bandwidth on these dipoles? The exposed portion of >>>> the coax on each dipole is RG-213, 50 ohms... but I'm wondering if >>>> they may use some quarter wavelength (or ???) of some other >>>> impedance on the part hidden inside the dipole, especially since >>>> these things exhibit a clear double dip SWR curve (one dip near the >>>> low end of the design range, 138 MHz, and another dip near the upper >>>> end, 174 MHz, with a somewhat reactive bump in between). >>>> >>>> 73, >>>> Paul N1BUG >> >> ------------------------------------ >> >> >> >> Yahoo! Groups Links >> >> >> > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > > -- Paul Kelley, N1BUG http://www.n1bug.com
