Thanks. I believe the repeater owner is buying a Z-matcher to put in the line (I had nothing to do with that). We were thinking of tuning at least the first bandpass cavity (nearest the TX) for minimum reflected power, but we already know the cable lengths are critical and had no way to deal with that, so it's been left as-is except for retuning.
If I have to go back to the site, I'll retune it while connected, although I looked at the results after doing each cavity and it all looked to be right on the money except for what I'd call excessive PB Loss. Bob M. ====== --- Gary Schafer <[EMAIL PROTECTED]> wrote: > I thought something was wrong when you reported 120 > db deep notches. > You should tune it with all cavities hooked up as > recommended. > > You could try tuning the input cavity for minimum > reflected power and also > put a second wattmeter on the output of the last > cavity to watch for maximum > forward power. Then retune the notches again on the > tracking generator as > the last thing. But the transmitter is always going > to see somewhat of a > reactive load and you have to be careful to find the > proper balance of > forward power and low reflected power. The > transmitter may not necessarily > put out maximum power at lowest swr. > > With some transmitters you need to try different > lengths of cable between > the transmitter and duplexer. The reactive load that > the transmitter sees > sometimes will not let it perform properly. Trying > different lengths of > cable changes the reactance that the transmitter > sees and you will find one > that makes it happy. A length that works on one > transmitter may not work the > same on the next transmitter. > > Don't forget to use the proper jumper cable length > on the wattmeter too. It > and the wattmeter section needs to be a 1/2 wave > length total so that when > you remove the wattmeter the transmitter sees the > same load as when the > wattmeter was in line. > > 73 > Gary K4FMX > > > > > -----Original Message----- > > From: [email protected] > [mailto:Repeater- > > [EMAIL PROTECTED] On Behalf Of Bob M. > > Sent: Friday, April 20, 2007 2:00 PM > > To: [email protected] > > Subject: Re: [Repeater-Builder] Wacom VHF > 4-section BpBr Duplexer > > > > Thanks. We'll have to go measure them. It's all > RG214 > > coax, and they look to be about 12-15 inches long, > > with PL259s everywhere. > > > > One error in the data I posted earlier: the notch > > depth is only 90dB, not 120dB. I had the reference > > level of the spectrum analyzer at -30dBm when I > was > > looking at the notch, which was 6 divisions down > > (60dB). The marker also said -89.9dBm, so I > mistakenly > > added the -30dBm reference to that and came up > with > > -120dBm. Wrong. > > > > Each cavity had 39dB notch, no error there, so by > > adding 6dB per cable, that brings it up to 45dB > times > > two, or 90dB, which is exactly what I was seeing. > The > > spec is 85-90dB rejection so it would appear to be > > working just fine. > > > > Bob M. > > ====== > > --- DCFluX <[EMAIL PROTECTED]> wrote: > > > > > Each cable in the phaseing harness that is cut > > > correctly will result > > > in an additional 6dB of rejection each. The > cables > > > should be 1/4 > > > wavelength electrically, so you will need to > look up > > > the velocity > > > factor of your cable and use it to calculate the > > > lengths. The lengths > > > should be to the center of the tee, which should > > > also be calculated in > > > to the equasion if you can find the velocity > factor > > > of the t. > > > > > > Sinclair takes the aproach of eliminating the T > and > > > using special > > > connectors that work like a T with the coax > going in > > > the sides. This > > > can be emulated by using thin coax like RG-223 > and > > > drilling some holes > > > in the side of the connectors. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
