> The 642s were provided with either UHF or N connectors > depending on the customer request.
Murphy's Law says the matching feedline lead from the outside world will have the other type connector. > The cable lengths were selected at the factory to meet the > VHF frequency requirement and unless the TX RX spread was > more than 600 KC the cable lengths were the same on both > the TX and RX Side. Which is probably a ball park method... the lower frequency cable should be a bit longer... the specific length dependent on the band/frequency. > "Wacom Products Modified RG-214 Double shielded" on it, it > is an untinned double shielded cable Are the shields the same exact material makeup... or is one copper and the other something else? > which will provide the necessary isolation although there > is a large segment of the forum participants that feel that > untinned double shielded cable is vulnerable to low level noise ....not the untinned part... the part with dissimilar sheild materials is the problem generator. In short vulnerable no, possible PIM generator yes. > and that duplexer interconnects should used silver plated > double shielded RG-214 or RG142 MilSpec cable. Double shielded coax is a nice thing but not always a must have. There have been times when I've used lower spec cable on purpose... Doesn't even have to be silver plated but the double shield materials used should be similar metals without known dissimilar metal gremlins > The Type N terminated interconnects on the 642 duplexer > supplied by Wacom for 145.29/144.69 were 12.5 inches including > the connectors, tip to tip. I've actually seen that duplexer... :-) the receive leg would be longer if you could knats behind it on really good test equipment. I have a near duplicate duplexer on 145.470 and the rx leg is about 1/4 inch longer than the tx cable length. > The optimum length for cables terminated with UHF connectors > might be slightly different because the UHF connectors and > chassis jacks are probably not a true 50 ohms at VHF frequencies. Depends on who spec'd and made the UHF Connectors. I know a group of Certified (looney) RF Engineers who say UHF Connectors are a train wreck and another (also looney) Engineering group who have spec'd them on serious lab test gear for operation well past 500 MHz with no real impedance bumps. Go figure... > Lloyd Alcorn at Wacom, when he was preparing duplexers for > customers dealt with this empirically (a fancy name for > trial-and-error) by making up interconnects in quarter inch > increments and selecting the length that looked best > on a tracking generator. ... and it's a real snooze to deal with the first time out. But sometimes that's the way things have to work out. After a while you keep a lot of near x-length cables around to dial things in. > Bruce > K7IJ cheers, s.
