They used a R&S®ZVH Cable and Antenna Analyzer to visually see the null at a freq. Put a T on it then a termination on one side and the cable on the other and left the end of the cable open. Basically a distance to fault measurement, I think.
Wow that is nice. I cut my teeth on the HP 8510. With the S-Parameter test set it weighed over 200lbs in the flight case
A brief story since you mentioned circulators.
A carrier and a group of tech's that will remain nameless was having trouble commissioning an analog cell site. This would have been about 88 if I had to guess. They had replaced LDF on the tower, had the climbers and riggers up numerous times and yet the combiner fault was displaying on computer and shutting down the PA module. They claimed it would not transmit long enough to get a reading of reflected energy on the analog watt-meter integrated into the combiner circuit.
The boss didn't want be to give these brain surgeons instructions on how to key the radio in maintenance mode so off I went to the town with the test set in Piper Cheyenne with a cargo door so the above referenced test gear would fit in the aircraft.
I pull up onsite and they expect me to start unpacking my gear. In fact the local manager was combative from the get go since before I pulled all that crap out of the van (the 8510 and case) I wanted to have a look. I quickly keyed the radio then ran my hand across the circulators, expecting to find a mistuned cavity and know where to start my work. Low and behold the output load was hotter than a firecracker after only 3 seconds of about 120w. I pulled the jumper and peered into the N female attached to the 1 5/8 airline. The connector was assembled wrong and the centerpin was recessed. I pointed it out and told them to remake the connector and all should be OK.
Test set never unpacked, lunch at the waffle house and home in time for happy hour. I don't think the boys at the cell site had as pleasant a day.