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.
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.