Wayne, RG-55/U coaxial cable might not be your best choice. That cable came into being more than a half-century ago, as MIL-C-17/26, and was canceled late in 1969. The RG-55B/U had two silver-plated copper braid shields, a solid polyethylene dielectric, and a solid copper center conductor that was silver-plated. It had a HMW polyethylene jacket.
Be very careful that you do not confuse RG-55A/U with RG-55B/U cable. The B version has double tinned-copper shields in place of the A version's silver-coated copper shields. In 1969, RG-55B/U was officially replaced with MIL-C-17/84, also known as RG-223/U. In mid-1993, RG-223/U was declared inactive for new designs, and its replacement was MIL-C-17/194, also known as M17/194-00001. Unfortunately, the current specification for MIL-C-17/194B calls for a one-mil polyester barrier tape that has an aluminum layer in contact with the outer shield. Some users of this latest version have reported that the aluminum/silver junction is a potential noise source, so keep that in mind, My choice for jumper cables on a cavity duplexer is RG-400/U, not to be confused with the LMR-400 cable. RG-400/U has a stranded copper center conductor that is silver-coated. It has Teflon dielectric, two silver-coated copper braid shields, and an FEP jacket. It looks and performs exactly the same as RG-142/U cable, except that the latter has a solid steel center conductor. There are several Internet sites that sell RG-400/U cable by the foot. I also suggest using silver-plated crimp-type connectors, rather than nickel-plated connectors, to avoid intermodulation problems. Jumper cable at the duplexer should be completely free of dissimilar-metal joints, for best performance. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of vk4cya Sent: Thursday, January 10, 2008 1:22 AM To: [email protected] Subject: [Repeater-Builder] cavity duplexer Hello to the group, I have just joined the group. The local radio club that I'm in is putting together a cavity duplexer a lot like the one in the July 1972 issue of QST. We are going ahead leaps and bounds but we have came across a problem. It is suggested that we use RG55/U coax on the cavities, but the problem is that I can't find anyone in Australia selling that type of coax. So, is there anyone that could help me in suggesting what else could be used? I have found a couple of sites on the net that have RG55/U but in roll form. We are looking for around 2 metres of it only. Any help would be most great Thanks Wayne vk4cya
