I guess most people have some kind of small antenna analyzer that has a TDR kind of function.
I have not warmed up to them yet as the results I see seem to be "all over the place". Maybe I just don't know how to use them yet. My goto TDR is homebrew - using an analog scope. Here is one design pretty similar to what I am using: A very simple TDR from W2AEW – PierpaLab.com <https://pierpalab.com/2022/04/30/a-very-simple-tdr-from-w2aew/> I put a switch on it to slow down the rep rate as an option since some of my "stuff" is pretty long. It works wonderfully to check feedlines and beverages. I have one beverage that has transformers and feedlines on both ends and I can see the difference between open/short/terminate on the "far end" (which is physically in the shack). 73 Tree N6TR On Mon, Apr 3, 2023 at 10:11 AM Frank W3LPL <[email protected]> wrote: > Another highly recommended tool is a Time Domain Reflectometer. > Tt easily detects any abnormalities in my 8-circle and 4-square > arrays and stacked HF Yagi arrays and switches. > > Other than my hand held antenna analyzer, my hand held TDR is my > most often used and most valuable tool for proving that the performance > of my antennas and feedlines has not changed from prior measurements > and identifying and isolating faults before they cause partial or > total failure. A TDR can detect, diagnose and locate feedline and > antenna faults from the comfort of your ham shack. > > Affordable TDRs are often available on eBay. Some antenna > analyzers have rudimentary TDR capabilities but I've never used > an antenna analyzer with TDR capabilities comparable in > performance to a TDR. > > Long before moisture causes coax failure, it causes the impedance > of the coax to change, a potentially big problem in a phased array > or stacked Yagis. A TDR easily detects and locates the problem > before it causes a failure. > > An antenna analyzer can also detect that moisture has caused > an impedance shift in coax cable. Place a dummy load (with the > same impedance as the coax) at one end of the coax cable. Sweep > the antenna analyzer frequency. As you do a frequency sweep the > VSWR and impedance should not change. If it does, moisture is > probably eating away inside your coax. > > 73 > Frank > W3LPL > > > > > > ----- Original Message ----- > From: "Dennis W0JX via Topband" <[email protected]> > To: "topband" <[email protected]> > Sent: Monday, April 3, 2023 4:42:37 PM > Subject: Re: Topband: High Impedance RX Antennas > > There is an old saying "The enemy of good is perfect." You will be driven > crazy by chasing down every slight variance from the ideal. That being > said, it is important to check out the obvious areas where flaws can create > big problems. Indeed, the feedline coax, typically RG6 CATV line, is a > major contributor to array performance problems. The cheap, big box cable > is covered with PVC and that stuff hardens and tightens up over the years. > This allows water to enter the shield and the water easily migrates for > long distances, creating a high resistance. Spend the money upfront and buy > quality cable that is flooded. > The idea of using cable that has a solid copper conductor has merit. But > even with that, a bare copper conductor will oxidize over time. I find > myself cleaning these conductors on an annual basis with the eraser end of > a pencil (recommended by Lee K7TJR). > I have also had F connector failures on my combiner box and on a common > mode choke. Sometimes the imported female connector center contact just > fails for no reason. The alternative Amphenol connectors are very expensive > at about $8+ each but I am considering replacing the connectors with these > higher grade parts. > Also, the so-called "water-proof" compression connectors are often not. > The connection must be waterproofed effectively. Also, condensation from > humidity can be a big problem. Here is northeast Ohio, the environment is > humid for the majority of the year. I have poured water out of a 75 ohm > preamp that was sheltered in a good enclosure! > These complex phasing arrays are by no means plug and play. Each > installation will be unique depending on layout and surrounding objects. > There are three tools necessary to get them and keep them working: 1.) a > good portable signal source to feed the antenna preamps (I use an Elecraft > XG-3 with a home brew impedance transformer at the input); 2.) a portable > transceiver to measure signal out of the system at various points (My KX3 > does a great job); and an accurate antenna analyzer to measure impedances > and to measure feedlines and phasing lines for the proper electrical > lengths. N6RK is right. There can be considerable difference in RG6 > impedance so you need to check it out. > > 73 Dennis W0JXMilan, OH > _________________ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _________________ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector > _________________ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
