I'm on a quest to find the proper termination for my Beverage on Ground antenna (BOG) My MFJ-259 is just not accurate up near 500 ohms. I see two different styles of TDR a pulse and a square wave. The square wave is neat in that you can watch the square wave get square as you adjust the termination and the pulse about the same you watch the reflection disappear when you get the proper termination.
Is there any other reason to pick one over the other?
Also, Is the output impedance important? I see many set to 50 ohms, using four drivers with series 220 ohm resistors. Then I see other circuits that add additional series resistance for 75 ohm, 100ohm, and
120 ohm, etc. So if my antenna is actually 250 ohms, do I need to raise the output impedance of the pulse driver?Some use a 74AC14, which would be fine, but if I build it, is there a fast edge chip that will run at 4.5 volts or even 3 volts. I understand the layout is important to the fast edges.
Thanks, Mikek
Here's a square wave generator,
Here's a pulse generator,