Not even a little. You're explaining basic theory that I don't have any trouble with.
It does, however, seem less magical now that you've got the impedences right. Jeff --- In [email protected], Ron Wright <[EMAIL PROTECTED]> wrote: > > Jeff, > > As some have stated the coax coming off the DB212-2 dipoles is 50 Ohms. These two are connected to a T connector and these 2 will be in parallel making 25 Ohms. > > The 35 Ohm coax, special for this application, forms what is called a coaxial transformer. Transformers can be used to convert to other impedances and coax can be used for this in RF. > > So a piece of 35 Ohm piece of coax at 1/4 electrical wavelength converts the 25 Ohms to 50 Ohms. This is the coaxial transformer. > > Hope this helps. > > 73, ron, n9ee/r > > > > > >From: Jeff Kincaid <[EMAIL PROTECTED]> > >Date: 2008/03/06 Thu PM 04:39:40 CST > >To: [email protected] > >Subject: [Repeater-Builder] Re: DB 212-2 Harness info. > > > > >So the elements are 50 Ohms? It does help to know that. :) > > > >But you seem to be calling for some kind of magical 35 Ohm coaxial > >transformer. > > > >Jeff > > > >--- In [email protected], Ron Wright <mccrpt@> wrote: > >> > >> 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 <jeffk@> > >> >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" > >> ><johneverson@> 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. > >> > > > > > > > Ron Wright, N9EE > 727-376-6575 > MICRO COMPUTER CONCEPTS > Owner 146.64 repeater Tampa Bay, FL > No tone, all are welcome. >
