JK, Having 50 Ohm cable from each element to a T and then 35 Ohm cable will probably work. Most antennas like the DB224 have non-50 Ohm cable from each element transforming into 100 Ohm each the parallel to form 50 Ohms at T.
73, ron, n9ee/r >From: Ron Wright <[EMAIL PROTECTED]> >Date: 2008/03/06 Thu AM 06:32:31 CST >To: Repeater-Builder@yahoogroups.com >Subject: Re: [Repeater-Builder] Re: DB 212-2 Harness info. > >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: Repeater-Builder@yahoogroups.com >>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 Repeater-Builder@yahoogroups.com, "John Everson" >><[EMAIL PROTECTED]> wrote: >>> >>> --- In Repeater-Builder@yahoogroups.com, "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 Repeater-Builder@yahoogroups.com, "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. > > Ron Wright, N9EE 727-376-6575 MICRO COMPUTER CONCEPTS Owner 146.64 repeater Tampa Bay, FL No tone, all are welcome.
