TDR
Pictures from W4ZT
Taken with the
Riser Bond 1205C TDR on 10/10/2003 and uploaded to the computer using
wave-view. The feedline is an old piece of 1/2 inch heliax which runs
from inside the house up to the four 2-meter dipoles near the top of the
tower. The return loss measurements (dbrl) don't mean anything with a
complex termination on the end of the cable. The velocity factor (VOP
- Velocity of Propagation) was adjusted to get the proper length of the
RG-58 which was a known length. Note that the VOP is NOT 66% but 59% (this
difference is typical and you find the VOP different for many different
pieces of coax).
This picture
has cursor 1 at the instrument; the first pulse on the left side. Cursor
2 is 25 feet out to the right where the 25 ft piece of RG-58 joins the
1/2 inch heliax. A small "S" bump in the waveform is there.
Here cursor
2 is at the end of the heliax where it joins the matching harness for
the 4 dipoles.
Cursor 2 is
at one of two unknown bumps in the feedline. This one looks like a connector
about half way up the tower. I don't remember a connector in that coax
but there could be one there.
Cursor 2 is
at the beginning of an elongated disturbance which doesn't look like a
connector. I don't know what it is. It may be a bad splice, a bad place
caused by lightning, or something else. One day I will have to figure
that out.
This is the
over-all picture with the gain turned up so you can see the bumps in the
feedline clearer.