SWR of antennas on my new tower were too good because of high coax losses.The coax cables were as follow:
25′ jumper of RG213 on top
100′ of LMR600 to the bottom of the tower
120′ of LMR240 to a switch on the next tower
150′ of LMR240 to the shack.
The loss of 30m (100′) cable at 30 MHz is 1.2db for RG213, 1.4db for LMR240 and 0.45db for LMR600. So the total loss on 10m was about 4.5db, or about 65% of power stayed in the coax.
I dreaded digging ditches for the new coax because of some 100 buried radials for 160 and 80m verticals. In the end, I used a pickax, carefully checking for radials. Lots of work.
Almost all LMR240 was replaced by LMR600 clone, and now the total losses on 10m are < 2 db, or > 65% goes to the antenna. The losses are 1.5 db on 20m and 1 db on 20m, pretty reasonable. Reducing the losses further would require using hardlines, which are quite difficult to handle.
As the real LMR600 is quite expensive, initially I bought a few sections of used LMR600 and LDF 4-50 at hamfests. Some of them showed high losses because of oxidatated crimp connections, and a connector in LDF 4-50 fell off. A new LMR600 clone by Shireen had lower loss than all the used coaxes, and installing crimp connectors by W5SWL turned out to be pretty easy.