Unless you are talking about a phasing harness for two antennas, "trimming coax" IS NOT how you get the swr down. In fact, all it does is full your meter. The fact is SWR is generated by mismatch between the ANTENNA, and the coax and radio. The only way to get swr truly flat is to make the antenna itself flat
Let's say you had ?? feet, maybe 20 feed of feedling, with a mismatch. Let's say you had a connector every foot--foot an a half. You would find that as you move your SWR meter to each connector, THE READING WILL CHANGE. Does this mean the SWR changes? No, the different readings are generated entirely by the mismatch condition itself
To put this more simply, if you had a TRULY matched antenna system, that is, "flat," you could move the meter ANYWHERE along that coax and it would read the same
In other words, trimming coax is a crutch.
There are two conditions in systems of these types:
1...The antenna can be RESONANT, but this does not mean the SWR is flat. This is because the impedance of a resonant antenna is NOT necessarily 50 ohms!!!
2....Therefore once the antenna is resonant, the impedance must be matched to the coax AT THE BASE OF THE ANTENNA by means of inductance/ capacitanc (LC) network of some type.
This is the ONLY correct way to set up an antenna system.
I used to use a "screwdriver" antenna from 160M through 10M, Metron 1KW amplifier.........all legal on amateur radio
................similar to this photo off the net
View attachment 1715053144
These, in their original form, and where they got this name, is that they used an old B&D rechargeable screwdriver motor to run the coil in and out of the housing. The large white object is the add on 160M coil, the small white object is a matching network goes onto the base -to- coax connection
"Long before" distracted driving was such an issue (and traffic was a little lighter LOL) I had tape markers on the housing for the band markers. I could tune the thing and change bands while driving.
Worked all over the world, Australia, Japan, England, Germany, Spain, and the Soviet. A few others I've forgotten, and one morning, the Orkney Islands