EM Surfer

RE: EM Surfer

javagoza — Tue, 07 Sep 2021 15:45:54 GMT

Nice update. What a good feeling when you start seeing results.[View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-3b97f9ef-ba1c-418c-8832-7a10d5b2ad1f/contentimage_5F00_3708.png:16:16]

RE: EM Surfer

Jan Cumps — Sun, 05 Sep 2021 17:45:16 GMT

I worked with the TDC you're mentioning at the end of the post: TI Ultrasonic Sensor - SPI Traffic Snooping

RE: EM Surfer

DAB — Sat, 04 Sep 2021 17:26:33 GMT

Interesting project.

DAB

RE: EM Surfer

colporteur — Sat, 04 Sep 2021 14:02:45 GMT

It has been twenty five years since I tuned the knobs on a TDR. At one point I knew the vertical propagation delay of LDF450 coax cable from memory.

My last exercise was to map 20 different models of VHF and UHF antenna's using the TDR. As a travelling road show through the high arctic, the printouts gave me some indication of expectations when troubleshooting antenna array issues. The riggers responsible for replacing bad antennas at the top of towers despised the tech that had them change-out antennas that were not bad. VSWR and TDR data gave me a perfect batting average on antenna replacements.

RE: EM Surfer

javagoza — Fri, 03 Sep 2021 09:25:22 GMT

I remember using TDR in the 80's. I was working installing ethernet networks with 10Base2 coaxial cable and thick yellow 10BASE5 ethernet cable. There was a crisis in my country and often some workers sabotaged the network installations by pricking thin sewing pins in the cables shorting the coaxial cable. They inserted the sewing pin and broke it so that it could not be seen. We had to buy a cable scanner I think from Blackbox that used TDR to make it easier to locate the pins in the cables.

RE: EM Surfer

dougw — Thu, 02 Sep 2021 19:38:54 GMT

Cool idea.

We did a project once where we started out trying to use TDR over a pretty long distance but there were too many spurious reflections, so we switched to measuring the resonant frequency of the cavity - which is insensitive to small defects.

RE: EM Surfer

genebren — Thu, 02 Sep 2021 19:10:04 GMT

This is a very interesting project. I look forward to see what results you get as you move forward.

I have always been interested in TDR, and I used and relied on it very heavily in my first job out of college. I was assigned to support the field testing of a huge and diverse communications system. The system had a little bit of everything as it covered a wide range of RF (VLF to UHF). One of the most interesting parts of the system was the direction finding subset. There were several fast deployable vehicles with single mast, tunable antenna arrays. There were 16 receiving elements that were connected through a switching matrix that included multiple, tunable delay lines. The system would use multiple elements and delays to try and match the outputs of two receivers to estimate the direction of the incoming signals. Being antennas, these systems were the frequent subjects of lightning strikes (in the high plains of the Arizona desert) and it was my job to get them back up and operating as soon as possible. I would use an HP TDR to collect measurements on the two main coaxes, and combination of delays and antenna elements (under computer controlled switching), looking for abnormalities in the line impedances. The opens or shorts created from the lightning were usually quite distinctive and I could quickly pinpoint were in the system that the failure occurred. Fun times!