JK, The coaxial sections coming off each antenna element is 35 Ohm coax at odd multiples of 1/4 wave length.
What this does with antenna element at 50 Ohms then 1/4 wl down the 35 Ohm cable it looks close to 100 Ohms looking into this cable. Then you take 2 of these ant elements/35 Ohm coax in parallel and you get 50 Ohms at this junction. If have 4 elements do the same for the other 2 and then make another to join these 2 again using 35 Ohm 1/4 wl coax. The length of the 50 Ohm coax going from the tx/rx to this antenna input does not matter for SWR or impedance. Only concern would be length and loss of 50 Ohm cable. 73, ron, n9ee/r >From: Jeff Kincaid <[EMAIL PROTECTED]> >Date: 2008/03/05 Wed PM 11:24:35 CST >To: [email protected] >Subject: [Repeater-Builder] Re: DB 212-2 Harness info. > >OK John, just making sure. I'm not familiar with the configuration of >the antenna, but what you are saying makes sense. I'm confused by the >idea that the length doesn't matter, because that would imply that >everything is 50 Ohms throughout, which doesn't seem to be the case. > >'JK > >--- In [email protected], "John Everson" ><[EMAIL PROTECTED]> wrote: >> >> --- In [email protected], "Jeff Kincaid" <jeffk@> >> wrote: >> > >> > I think this is just sloppy word choice, rather than a lack of >> > understanding, but I've seen it a couple of times now so let me >> clear >> > it up in any case. Regarding velocity factor, it's a factor, so you >> > want to multiply it. Subtraction is not a part of the equation. >> > >> > Say your free space length is 100 inches, and your velocity factor >> is >> > 88%. Your length in cable is then 88 inches: >> > >> > 100 x 0.88 = 88 >> > >> > Regards, >> > Jeff >> > >> > --- In [email protected], "John Everson" >> > <johneverson@> wrote: >> > > >> > > So if I understand correctly, the length of the 50 ohm sections >> is >> > > irrelevant, as long as they are equal? Also, is my previous >> > > assumption that the matching stub is just made of 35 ohm cable >> cut to >> > > 1/4 wavelength at the operating frequency minus the vel. factor >> > > correct? >> > > >> > > Thans again for the help. >> > > John >> > >> Hello Jeff. >> >> You are correct. It was a poor choice of words on my part. I >> understand the theory of velocity factor. I am still not sure about >> the lengths involved with the harness. If the 50 ohm sections from >> the loops to the "tee" can be any length, (as long as they are the >> same) doesn't that affect the impedance at the tee? I will assume the >> impedance at the feedpoint of the loop is 200 ohms. If we use half >> wavelengths of coax between the loops, the feedpoint impedance will >> be repeated at the end of the cable to the tee. Is this correct? If >> so, when the loops are connected to the tee, we should see 100 ohms, >> then, the matching section brings us to about 50 ohms. >> >> Is this correct? Or am I out to lunch? >> >> Is the matching section a quarter wave? >> >> I need to dig out the antenna handbook and refresh. That is for >> certain. >> >> Thanks. John >> > > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
