RGR on the velocity factor... By actual length do you mean the length of the entire conductor, the circumference of the loop? That could be a couple inches on VHF cavities.
No wonder the cables I made (which I cut with the help of a network analyzer at work to be right on 1/4 wavelength all by themselves) required the cans to be adjusted quite a bit after optimizing them individually. I would expect a little touch-up after putting the set together but not as much as I had to do. My supply of RG-400 and silver-plated UHF connectors (my old DB cans use UHF connectors) is running a little thin and I don't have enough to make a lot of trials-and-errors. Although we don't have a UHF-connector calibration standard and I haven't seen any available even if I could convince the boss they're needed, what I did was I made a set of N-to-N cables, which I can calibrate, and a set of N-to-PL259 cables the exact same length and cable material which I use to set the cans. I'm counting on the small differences caused by impedance bumps and change of velocity factor in the PL259 won't be critical on VHF. See any big flaws in this approach? Here's what I'm thinking. Please tell me if this sounds like a reasonable procedure: - Measure the length of the loop conductors. - Retune a couple of the cans individually for optimum using the Agilent VNA at work and my "calibrated" N-to-PL259 cable. - Make a series of single interconnection cable that take into the lopp length, corrected for the discrepancy between the velocity factor of the loops and the RG-400, plus and minus 1/2 inch or so (think that's enough?) in 1/4 inch increments. (Do you think that's a fine enough increment for 146 MHz?) - Try the different cables between a pair of optimized cans. Select the cable that requires the least tweaking for optimum performance of two cans. - Duplicate the best cable and use it between the other cans. Thanks Brad KB9BPF --- In Repeater-Builder@yahoogroups.com, Steve Allred <[EMAIL PROTECTED]> wrote: > > The loop length is figured very close it's actual length due to the fact that the velocity factor of the loop is very fast (close to 98%) because of the air dielectric, unlike cable that is much slower. > > Steve / K6SCA > > > --- On Mon, 9/15/08, Chuck Kelsey <[EMAIL PROTECTED]> wrote: > > From: Chuck Kelsey <[EMAIL PROTECTED]> > Subject: Re: [Repeater-Builder] Cavity interconnection cable length > To: Repeater-Builder@yahoogroups.com > Date: Monday, September 15, 2008, 8:47 AM > > > > > > > Trial and error or contact the manufacturer. > > Chuck > WB2EDV > > ----- Original Message ----- > From: "kb9bpf" <[EMAIL PROTECTED] com> > To: <Repeater-Builder@ yahoogroups. com> > Sent: Sunday, September 14, 2008 5:54 PM > Subject: [Repeater-Builder] Cavity interconnection cable length > > > Hello, > > > > Many writings about the optimum length of cavity interconnecting cables > > mention that the length of the coupling loops needs to be taken into > > account, but they don't get any more specific. > > > > Does that mean the length of the conductor in the loop (circumference > > if it were round) or connector-to- end length (diameter if it were > > round) or something else? > > > > I find it pretty easy to get the cables cut to a pretty precise > > electrical 1/4 wavelength but this loop length thing leaves me guessing. > > > > 73 > > Brad KB9BPF > > >
