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 > > >
