Cheap Cables

I picked up a box of 3-foot and 6-foot BNC cables. The cables are marked as RG58. Overall construction of the cables look good as they have molded ends on the BNC connectors. Unfortunately good looks is where it ends. Electrically the cables suck. A good example raised its ugly head today. I was checking a function generator and connected it to my HP 5335 frequency counter. Ran through a few frequencies to make sure the calibration of the generator was reasonable. Higher frequencies no problem. When I went to 1 KHz the counter would not lock onto the signal. I connected the generator to my oscilloscope and observed a nice 1 KHz sine wave. Playing around with the counter I engaged the filter switch and got a correct measurement of 1 KHz. Looks like I am getting noise in the input on lower frequencies that prevents the counter from locking onto the desired signal. I placed a few clamp-on ferrite chokes on the cable and that also took care of the problem. I then replaced the cheap BNC cable with one I made from LMR240 ultra flex. Problem went away without any filtering.

Moral of the story. Buy good cables they will save you headaches in the long run.