Another newbie question (sorry). I'm using an HP 5315A Universal Counter and doing some basic experiments to teach myself.
Here is the setup: 100KHz square wave as the "A" input to the 5315A. Using a BNC-tee to connect a length of RG58A/U from "A" to the "B" input and another tee with a 50 Ohm terminator. Using the TI Avg mode and the gate time maxed at 13.4S, I read a TI of 22.5nS. Assuming I got the numbers correct, light takes 3.3356nS to travel 1M in a vacuum. 22.5nS / 3.3356nS/M = 6.745M. If I divide the measured length of the coax (3.825M) by 6.745M, I get a velocity factor of 56.7%. This is quite a bit lower than the nominal 66% I expected. So, is the difference due to: The BNC-tee connectors? My use of a 100KHz square wave instead of a PPS? The resolution of the 5315A (100nS single-shot, 1nS averaging)? Some other failing of the 5315A? It was just out of cal in Feb 2009. Something else entirely? All of the above? The reason I'm using a 100KHz square wave is that I haven't yet modded either of the Z3801A's to bring out a PPS signal where I could use it. That is on my short list. The 100KHz from a Spectracom 8140 was the closest I can get right now. Is this type of measurement useless with anything other than a PPS signal? An interesting observation - when I remove the 50 Ohm terminator, I get a much shorter TI. I assume this is due to reflections back down the coax. Joe Gray KA5ZEC _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
