That may be where I got it, not sure. It seems to make sense and it seems to work where I have tried it, at least no known problems using it. Maybe all this discussion on cable length will settle the issue for good. Thanks. Sid.
--- In Repeater-Builder@yahoogroups.com, Russ Hines <r...@...> wrote: > > Sid, I think I found your formula. Look on page 62 of: > > http://www.repeater-builder.com/antenna/pdf/ve2azx-duplexerinfo.pdf > > BTW, my guess was wrong. Length is expressed in inches. > > 73, Russ WB8ZCC > > On 8/13/2010 1:44 PM, Russ Hines wrote: > > Hmm, the formula is a bit off, but... 30 x 32.785 = 983.55. I'll also > > bet length is expressed in feet. > > > > Looks eerily like someone wants you to cut a one-wavelength piece of > > coax cut at the mean repeater frequency. > > > > Just a guess. > > > > 73, Russ WB8ZCC > > > > On 8/13/2010 11:38 AM, Sid wrote: > >> > >> I have a note in my file that I do not recall where it came from > >> relative to cable length between the duplexer and the TX or between > >> the duplexer and additional filter. Length = (30)(32.785)(vf/freq). > >> 30 is for 30 degrees, vf is velocity factor, freq is the average of > >> the pass and reject frequencies. If too short add 180 degrees. Don't > >> know if this is good info or not. The article would be appreciated. Sid. > >> > >> > >> --- In Repeater-Builder@yahoogroups.com > >> <mailto:Repeater-Builder%40yahoogroups.com>, Nate Duehr <nate@> wrote: > >> > > >> > > >> > On Aug 5, 2010, at 11:20 AM, Kevin Custer wrote: > >> > > >> > > Allan Crites and I are currently in discussion which will be used > >> as the basis of a RB web article that will explain exactly what is > >> happening, why it happens, and why an 'optimized' cable length can be > >> used to transfer power ending up with the stated loss of the duplexer > >> and have little reflected power toward the transmitter - so long as > >> the duplexer is tuned properly and exhibits good return loss on the > >> frequency it's designed to pass. > >> > > >> > There's already a great book on that topic, it's called the ARRL > >> Antenna Handbook, and the chapter on transmission lines covers it in > >> more detail than anyone will ever need to know in the real-world, > >> who's not a practicing RF Engineer. > >> > > >> > That book if read cover-to-cover, is also damn good for insomnia. > >> Or at least it'll keep you distracted while you can't sleep! :-) > >> > > >> > -- > >> > Nate Duehr > >> > nate@ > >> > > >> > facebook.com/denverpilot > >> > twitter.com/denverpilot > >> > > >> > >> >
