The following photos and captions tell how to modify a Yaesu ATAS-120a Screwdriver Antenna to accept a small spring between the whip and the top of the main coil. It does not effect tuning and it gives some flexibility as it makes it easier to change out the whip sections or to connect a long wire to the coil in place of the whip. At the present time, I think the ATAS-120a is quite possibly the best buy for the money on the market to put on a Yaesu FT-857d. I have heard and read many good and bad experiences. So far, my experience has been all good as have the vast majority of the comments I have read. Yaesu seems to have cured the main complaint of the older ATAS-120 in the newer version. with the installation of a weather boot on the top of the antenna coil. The modification I describe here, IMO, will increase the water resistance of the boot by making a compression of the boot where the spring attaches to the coil.
However, there are several problems that Yaesu either has not considered or has no desire to change. The first is the flexibility of the whip they include with the coil. It is thin and made of soft stainless steel with a tendency to bend easily and stay bent. I found that the whip could easily be straightened with without tools but it would soon bend again. Also, I found that the main coil was really rigid and was in constant danger of being broken by a tree limb when mounted high on the vehicle. I cured the first problem with the mod described in this photo gallery. I am still working on modifying a large antenna spring for UHF connectors to allow for some give to the coil assembly if it impacts a rigid object such as a large tree limb or too small garage door opening.
The spring that I chose is a readily available small spring that was manufactured for many years by Antenna Specialists for their CB and commercial antennas. The Antenna Specialists K-126 Standard Replacement Spring is the spring I chose for mounting to my ATAS-120a. It is still manufactured so it can be purchased new. While I used an Antennex whip, the Antenna Specialist whip is also a high quality whip that will work well for this mod. The spring has also been copied by many other manufacturers for similar antenna designs and should be readily available at many garage sales and hamfests. It has a 1/4 x 20 stud for mounting the spring to an antenna and a stud with set screw on top to accept a whip.
If you decide to make this modification, you do so at your own risks! If you are unsure of your abilities with tools, don't attempt the modification. Find someone who you trust who has known abilities. This mod has worked very well for me, but I must add that I take no responsibility for how it will work for you. Remember, you are modifying a $300.00 antenna and the warranty could be voided by the mod. In my case, the possible loss of warranty is more than outweighed by the better survivability of the antenna in my rural environment.
Whip Spring Project (html)
Base Spring Project (html)
My Mobile Installation (html)
Whip Spring and Base Spring (pdf)
Remote Tool Box Lid Opener (under construction)