Hi folks I have heard that the military will not allow BNCs on RF connections because the bayonet connection on the outside shell allows the ground side of the cable to vary (wiggle) and be noisy. BNCs appear to be used for data and low freq but TNCs are specified for RF use.
Some years ago a local club was having trouble with their homebuilt duplexor that used BNC connectors on the cable connections. The duplexor became noisy intermittantly. Move the cables and it would quiet down for a few days but would always return. I suppled them with equivalent TNC connectors for the duplexor and they never had trouble again from that source. The standard PL259/SO239 combo has an impedance of approximately 35 ohms. If the insulation is removed from the SO239, the impedance is close to 50 ohms. I did see a Japanese wattmeter (I think it was Yaesu) that had insulatorless SO239s on it. One problem with the PL259 that I have not seen mentioned is that it is not weatherproof and the ground connection is problematic at best. It is very easy to tighten the shell and then find it loose because the "teeth" on the PL259 were not bottomed into the notches in the SO-239. Just my 2c for what it is worth. Burt VE2BMQ>> Eric Lemmon wrote: > Allan, > > That's a good question! Both "N" and "BNC" connectors vary the dielectric > thickness, and the spacing and diameter of the center and shield elements, > so that the swept impedance seen by a Time-Domain Spectrometer (TDR Test > Set) shows no variation in characteristic impedance through the connector. > When a "Constant-Impedance" connector is installed <CORRECTLY> in a > transmission line, its presence will not be revealed when swept with a TDR > Test Set. > > The infamous PL-259 plug, when mated with the matching SO-239 jack, is far > from constant impedance. Even the most basic TDR Test Set can detect the > impedance "bump" where UHF connectors are used. Where the impedance is not > constant, unwanted parasitic oscillations can occur, which means that > intermodulation and spurious signals have a fertile breeding ground. > > Moreover, the ideal RF transmission system comprises cable and connectors > that present a uniform 50-ohm impedance, without any significant bumps or > dips. This cannot be achieved with RF connectors that do not have constant > impedance. > > 73, Eric Lemmon WB6FLY > > > -----Original Message----- > From: [email protected] > [mailto:[EMAIL PROTECTED] On Behalf Of allan crites > Sent: Thursday, March 22, 2007 7:57 PM > To: [email protected] > Subject: RE: [Repeater-Builder] LMR feedline revisited and revised! > > I sure would like to hear what you all mean by " constant impedance ". > Allan Crites, WA9ZZU > >
