Line stretchers/shrinkers were also built by Kings Connectors (I have five of them) but I don't see them in their catalog any longer. They modified a female N barrel to mate with the shoulder of a male UG-21 that permits the barrel to thread in and out of the UG-21, effectively varying the length of the device. There is a total range of about 1/2 inch, so if you center the stretcher before inserting it in the line, all you get is about 1/4 inch of range either way. That range applied to an interconnect at 1.2 gig is useful to correct an impedance mismatch. AT 440, there is not sufficient range to make a correction but will tell you which way you want to alter the cable length to effect a correction when viewed on a Bird 43 at the duplexer output. At VHF, a 1/4" correction is not sufficient to nudge a Bird 43, but you can see it on a Bird 4381 digital meter. In any event, the stretchers are not an exact way to measure the optimum cable length because the stretchers are air line devices and have a different velocity propagation constant from coaxial cable. The same matching issue prevails on the receiver side, but in most cases, the noise floor at the site would mask any improvement that cable matching would produce at the receiver. I don't think as a discrete measure that optimizing transmitter to duplexer cables results in any improvement for the listener, but in concert with the myriad of other measures you take to optimize system performance, it's worth doing. A little bit here, a little bit there - it adds up. In a message dated 6/30/2007 3:11:19 A.M. Pacific Daylight Time, [EMAIL PROTECTED] writes:
Ian, I owe you an apology for my comment about striped tower paint in response to your 'Line Stretcher' post. I never thought of using such a tool on a short line between a transmitter and duplexer. I was thinking such was used in AM broadcast delay lines with phased towers, and never though of using such to correct such minuscule variations as might be found in a VHF or UHF duplexer and it's connection to a radio transmitter. I wonder how many dB of improvement might be achieved optimizing such minor differences and what kind of a jump in S Meter readings folks on the receiving end might realize? 73, Steve NU5D ************************************** See what's free at http://www.aol.com.
