Included in the photo are duplicates of the shunt coil and common mode current choke that I use on my mobile with all my various gearmotor and monobander HF antennas as seen in this link photo of the underside of my mobile.
On occasion I have built shunt coils and common mode current chokes similar to the samples shown, for other hams to install on their mobiles.
You may question how my shunt coil performs, installed at the feedpoint of the antenna, and mounted in a enclosure...
Living in a place where winter puts in a yearly appearance , believe me when I say that you need a enclosed shunt coil, as the accumulation of snow and ice on a exposed shunt coil, is guaranteed to be detrimental to the shunt coil, and the SWR of your favorite HF antenna.
BTW...my shunt coils are terrific performers, going about doing what they do best...keeping the SWR in check across the band of a favorite HF monobander antenna, or the various HF bands of a gearmotor antenna.