I’ve been using Yaesu’s ATAS-120A since 2007. It’s an “easy button” for their mobile HF radios. I bought a Scorpion mobile HF antenna in 2021. I hadn’t been on HF in several years, which meant that I didn’t have an immediate comparison against my ATAS. Even if I had logged as much data as possible, and on the same car, the solar cycles were certainly different between the two purchase times! The ATAS has seen many mounting locations on three different cars. Today, it’s mounted to a roof rack and the Scorpion is mounted to a trailer hitch. Many hams, including myself, have been curious to know how a high-mounted ATAS performs when compared to a low-mounted Scorpion.
Eventually, I connected the ATAS and Scorpion antennas to the same antenna switch. Not only would the switch allow me to adapt to whether the Scorpion was mounted or at home, it also allowed me to make back-to-back comparisons between the two antennas. Neither mounting method is ideal, but the ATAS is higher with the roof below it. How do they compare? It’s tough to hear which antenna receives better on 20m-40m, but fellow hams tell me that my 40m signal definitely is stronger on the Scorpion!
I saw an “ATAS vs. Little Tarheel“ comparison by Mike, K8MRD. He used Weak Signal Propagation Reporter, better known as “WSPR” (spoken as “Whisper”), to make some unscientific comparisons. Why are the tests unscientific? He did his tests with each antenna mounted to the same mount, which was good; however, the transmission and receive testing was done during different time frames between the antennas. That means that band conditions and available stations could have changed without notice. My own testing featured different mounts and locations due to the drastic differences between the ATAS and Scorpion antennas.
Testing took about an hour for each band, even with a streamlined approach to transmitting in two 2-minute sessions and then listening for 10-minute sessions. Each session had to be at least ten minutes long to avoid capturing map data from the previous session; then the data could only be captured in one-hour segments. Given the time differences between each antenna test, it’s possible that band conditions changed enough to skew my results. So, I will report the results as being “general.”
“Generally” speaking, the Scorpion outperformed the ATAS-120A by a 15% margin on 20m (14.097 MHz) and a 75% margin on 40 meters (7.040 MHz). Using this spreadsheet image as an example, green shading highlights the “winning” antenna, red shows the “loser,” and white indicates negligible results, differences of 2 dB or less. While a signal-to-noise ratio (SNR) of 2 dB may not be negligible to some, I decided to observe some “wiggle room” to account for minor atmospheric changes. That’s totally scientific, right? 😉
The Scorpion’s SNR was between 3-15 dB greater than most of the ATAS-120A’s readings on 40m. The ATAS was heard better by only three stations on 40m. The difference was 2 dB or less for ~21% of reporting stations. Testing on 20m told a different story. The Scorpion still performed better overall, but the margin of victory was not as wide. The Scorpion “won” the transmit session with 35% of stations compared to the ATAS-120’s 21%. I counted the remaining 44% as “negligible.” Received signals was surprisingly “negligible” between the antennas on both bands. I was not surprised when the Scorpion won, but I used bold font to show when the ATAS came out on top to highlight my own surprise.
I didn’t interpret the “weakest signal” data quite the same as K8MRD. He presented the possibility that his ATAS performed better because it had received weaker signals, not necessarily because it was the weaker antenna. In my case, both the ATAS and the Scorpion received signals as weak as -33 dB. However, my “farthest” and “closest” data was based upon the farthest and closest signals that both antennas received for a more direct comparison. The Scorpion received a -26 dB signal from Antarctica, 14,000 km away. However, I did not include that in my comparison since the ATAS didn’t receive that signal at all, perhaps simply because AB8O didn’t transmit during the ATAS session.
I have not found a clear answer to why the ATAS won with certain stations other than a short-term band condition change in the direction of a specific station. Regardless, it appears that a large screwdriver antenna does provide an advantage over a small one, particularly on the lower bands. K8MRD’s testing did a good job of illustrating that the ATAS-120A performs just as well or better than a small model from Tarheel. I am continually pleased to have an ATAS on my car full-time. However, I think my testing has shown that “bigger [can be] better.” That sentiment will apply even more if I ever decide to add an amplifier to my station. My Scorpion antenna can accept more power than I would ever try in a mobile setting. Scorpion is no longer in business, but I wouldn’t hesitate to consider large model by Tarheel Designs or Tarheel Antennas (not the same company) if I was shopping today.
I did learn one unexpected lesson during my testing: My ATAS is a new replacement and this was its first time operating in rainy conditions. I found myself experiencing high SWR at some point. Later, I had high SWR on the Scorpion, too! “Do I have water leaks at the weather seals?” Everything worked fine later when the rain subsided. Later, I had high SWR again, this time in dry conditions. It occurred to me that the two antennas were interacting with and detuning each other even though only one was connected to the radio at a time.
I’ve operated plenty with both antennas on the car, but my weekend of testing may have been the first time that I had both antennas mounted and tuned to the same band. “Who does that?” Apparently, “This fool does!” 😀 It can be easy to forget that everything is “near-field” in a mobile environment since the antennas are mostly out of sight. Coincidentally, I think I’ve had unexplained SWR problems in the past that may have been caused by this mistake. I’ll resolve future conflicts by tuning the non-use antenna to its highest frequency when it’s disconnected.
Most of my daily driving is done without the Scorpion mounted. So, this is a rare conflict. Regardless, I’m content to run with both antennas when I have HF goals to pursue. See the images below for a better look at my test results.
Unscientifically Submitted, 😉
Scott
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