It was a -1502 that we were using. Unfortunately, our experience with TDR's involves much simpler (non-phased) antennas which tend to display a rather pronounced 'end' at the cable (either a short or an open) and when you see something else at the end you can bet that there is either a connector or antenna issue. With the phased array of the -224, we were seeing a fairly wide band of 'noise' which, as you say, tells us nothing. particularly without a comparison.
I'm not sure what other equipment Dan has available from the FAA site, but I suspect that everything we need is probably available. I would like to have a look at your return loss sweep so we'll have something as a comparison. I suspect that years of weather and neglect have taken their toll on the phasing harness and the dipoles and I really think (unless the experts here say otherwise) that the best bet would be a new antenna. The membership is gonna love me! Mike WM4B _____ From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of nj902 Sent: Saturday, May 26, 2007 11:04 AM To: [email protected] Subject: [Repeater-Builder] Re: VSWR Issues When you say TDR, if you are referring to an instrument such as a Tektronix 1502, there probably isn't going to be a definitive TDR "image" for you to compare to. TDR's do an excellent job of determining the length of a transmission line or the distance to an open or short. Because they do this with a fast rise DC pulse, they don't fully characterize your antenna system in the frequency domain. Also, even a partially functional antenna will put enough noise [RF] onto the transmission line that it is difficult to identify issues with a TDR. Most antenna system testing today is done with instruments that use swept frequency techniques. These will produce plots of return loss vs. frequency or distance to fault [computed from the frequency domain sweep by use of an inverse fourier transform] A handheld analyzer such as an Anritsu Sitemaster or a R&S FSH3 is an ideal tool to use for this purpose, however these tests can also be performed using a spectrum analyzer with a tracking generator and a return loss bridge or with a properly equipped HP8920. If that is the type of test you conducted or if you have one of these instruments available to conduct further tests, I have some return loss test sweeps which show what a properly operating DB224 looks like that I could send you for comparison. ---------------------------------------------------------- --- In Repeater-Builder@ <mailto:Repeater-Builder%40yahoogroups.com> yahoogroups.com, "Mike Besemer \(WM4B\)" <[EMAIL PROTECTED]> wrote: " ... The next step was to put a TDR on the line. Everything appeared to be okay up to the antenna, but the termination point (antenna) looked pretty ragged. What does a DB-224 (or similar) antenna look like on a TDR? ..."
