When I bought my second Yaesu FT857D it was to use in the car. I bought the first one because I wanted a bit more power when portable than my Yaesu 817 allowed. I had used my Icom IC706 MKIIG and found it wanting when portable. The problem is the Icom draws too much current both on receive and transmission and when used from a low battery voltage it goes loopy and starts to self oscillate. The problem is in the DSP circuit but turning DSP off does not fix the issue. In the shack the Icom is superior but in a field or on a hilltop the FT857 wins hands down as my battery lasts longer and long after the Icom has died it is still going, way down to around 9.2 volts I have still managed contacts on HF.
I bought the second 857 because I wanted an easy to tune antenna for mobile HF operations and the Yaesu is designed to work with the Atas 120 antenna. There are better screwdriver antennas than the Atas but none work on a single button push like the ATAS does with the 857.
I had trouble finding somewhere to mount the antennas on my Land Rover Discovery and settled for a home made mounting bracket inserted into the runners for the roof rail. This worked fine for my VHF/UHF antennas but I initially could not tune the ATAS at all. The addition of an earthing strap almost sorted that but I could not tune the 40 metres band.
A chance clue was picked up on air when I heard someone say they had shortened their earth strap and got an antenna they could not tune to tune up. I prepared a new shorter earth strap and swapped it over, bingo! 40m now worked. As a result I had an amazing run of great contacts with SOTA stations usually while travelling at the national speed limit on motorways (Helen was driving), which collected me plenty of chaser points I previously would have missed. However when I came to try to work a SOTA station on 20m it no longer tuned there, but every other band still worked fine.
The whole thing is a little curious and but feel sure there is an optimum length for the earth strap that will allow all the bands to be tuned, so I have a few exeperiments to do when I get time. In the meantime maybe someone will read this and explain what might be going on.