Part of our Building Your First Ham Radio Station guide.
I run a Yaesu ATAS-120A on my Jeep, fed by an FT-891, and it has become one of my favorite pieces of gear. If you want HF in your vehicle without a fistful of monoband whips and a manual tuner, this antenna is hard to beat. Here is an overview of what it is, how it works, and why I have been so happy with mine.
What the ATAS-120A is
The ATAS-120A is Yaesu’s Active Tuning Antenna System, a motorized mobile antenna. Instead of swapping resonators or fiddling with a separate tuner for each band, the antenna itself physically retunes. A small motor inside adjusts the length of the radiating element to find the lowest SWR on whatever band you are on. It is sometimes described as a screwdriver-style antenna for that reason.
The clever part is how it is controlled. There is no separate control cable. The radio sends microprocessor-controlled voltages up the coax to drive the tuning motor, so a single coax run does everything. You just press the tune button on the radio and let the antenna find its match.
Bands and specs
The ATAS-120A covers the 40, 20, 15, 10, and 6 meter bands, plus 2 meters and 70 centimeters. A few key numbers:
- Bands: 7, 14, 21, 28, 50, 144, and 430 MHz
- Height: roughly 4.6 to 5.2 feet (it changes as the element tunes)
- Weight: about 2 pounds
- Maximum power: 120 watts SSB/CW
- Impedance: 50 ohms, with a matched SWR under 2:1 given a proper ground or counterpoise
One important note: the ATAS-120A only works with Yaesu radios that support the ATAS system. That includes my FT-891 as well as rigs like the FT-991A, FTDX10, FT-710, FT-857D, FT-897D, and the newer FTX-1, among others. It will not do its automatic tuning trick on a non-ATAS radio.
Grounding is everything
This is the single most important thing to understand about the ATAS-120A, or really any HF mobile antenna. It works against your vehicle body as its ground plane, so the quality of your mount and bonding makes or breaks the performance. My mobile antenna mount and grounding guide covers the general principles in more depth.
You want a solid mount with good electrical contact to bare metal, not just to painted surfaces. Yaesu specifically warns against magnet mounts, because they often do not give the motor a good enough ground path to tune reliably. On a Jeep, bonding the various body panels, the hood, and the tailgate back to the frame with grounding straps can make a real, measurable difference in how well the antenna tunes and gets out. If your ATAS ever struggles to find a match, poor grounding is the first suspect.
How it performs for me
Paired with the FT-891 on my Jeep, the ATAS-120A tunes quickly and gets me on the air across 40 through 6 meters with almost no fuss. The convenience factor is enormous. Change bands, tap tune, and I am matched and ready in a few seconds. For mobile POTA and casual operating from the trail, that speed matters.
Like any short mobile HF antenna, it is a compromise compared to a full-size antenna, especially on the lower bands where physics simply demands more length than a 5-foot whip can provide. You will not out-perform a big home antenna. But that is not the point. The point is capable HF from a vehicle, on many bands, with a single antenna and no manual tuning, and at that job the ATAS-120A excels.
A couple of things to watch
- Because it has a moving motorized element, keep an eye on it in ice and heavy snow. Ice building up on the tuning section is worth clearing before you tune.
- It needs that good ground plane, so it is happiest mounted on a vehicle. You can adapt it to base or portable use, but only with a proper mount and a substantial counterpoise or radial system.
- Respect the 120 watt limit and the duty cycle. It is a mobile antenna, not a contest-grade base antenna.
Bottom line
If you have a compatible Yaesu radio and want fuss-free multi-band HF from your vehicle, the ATAS-120A is a fantastic option. Get the grounding right, and it rewards you with fast tuning and genuinely useful performance. On my Jeep with the FT-891, it has earned a permanent spot, and I would recommend it to anyone building out a mobile ham setup.