What's the gain of this antenna?

As far as I know the manufacturer has not published any gain figures. One does not get this kind of antenna to achieve gain. Its purpose is to provide a good signal in a compact package for mobile use. Also, its automatic tuning function only works with certain Yeasu products (e.g. the FT857). The ATAS 120A might theoretically have a slight dBi or even dBd gain on UHF and VHF depending on the quality of the counterpoise (grounding). However on HF amateur bands (7/14/21/28/50 mhz) it should have negative (less) gain compared to a halfwave dipole as it is essentially a compromise vertical that is shorter than 5/8ths or a quarterwave, with loading coils to compensate for the lack of electrical length. However with a good counterpoise (groundplane provided by bonding connections to the vehicle) reports indicate that it gives excellent mobile results (compared to other mobile verticals) when used in a vehicle.

I'm reading that the radio tunes the antenna. I'm about to buy the 857d BUT!! do you need to but the antenna tuner made by yaesu for this To work

Most of the below answers are confusing. FT857D DOES NOT have a built in tuner. If you have a good resonant antenna no tuner is needed. There are some antennas that can tune themselves via various methods and resonance is obtained at the antenna not the radio. Almost any antenna tuner at the radio can tune many non-resonant antennas. Yaesu specifically makes a tuner that attaches to the outside of the radio but almost any automatic (I recommend) tuner will work. Ground your radio and have a good counterpoise for your antenna. Most of my antennas are resonant at frequency (most efficient) but an auto tuner is wonderful for mobile HF operation especially at the lower frequencies (ie. 160-80M) and you keep your eye on the road. JUst remember to initially tune at 5-20 watts. The yaesu antenna is not an efficient antenna but it is convenient. N8LB

Will the atas-120a tune 80 meters

No, only down to 40 meter band. Google ATAS-120a to get the one-page operating guide in pdf format. It includes the operating range in the specs section.

Tough question: I intend to use this antenna as base station on my 5th floor condo HOA (inside of window) will the inside house ground be sufficient ?

As a DC ground, yes it will work. You may want to add the ATBK-100 radial kit to improve the ground plane or add homemade radials to expand the ground plane. Hope this helps - 73s de KC5AJS

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Reviews

J**S

Calidad de antena

22.12.2025

B**R

Ok, I am TOTALLY convinced...

Due to the local HOA (wife) I can't put up what most would call a "REAL" antenna. So, I read a few reviews, watched YOUTUBE videos and took the chance and spent some hard-earned cash on a mobile antenna. THIS IS NOT A WASTE OF MONEY!!! BEST idea I ever had! As you can see, it's on a wrought iron fence. Not sure if that makes the difference, but I'm able to use a Yaesu FT-891 at 100 watts for a very good contact on 10M FM to the east coast from San Diego, WARC bands not a problem. IN SHORT, If I can hear the other station, I can talk to them. The ATAS-120A is fantastic! (Yeah, not the surface area one would seem to need, amazes me how well this little thing works!) On the fence about buying it? I'd suggest it. Not sure if it's the fence for grounding, the ground plane which there really isn't one, or what it is, but I'm lovin' it!

5.03.2024

C**S

Great antenna

This thing is awesome. I have mad3 contacts from Hawaii to the east coast, Brazil, Canada, Australia on ssb and have gotten farther out on ft8. I have it mounted on my van and have a ground strap from the mount to the door.

14.09.2025

B**Y

Perfect FIT

Works well as advertised 10-40 meters with my ft891.

2.10.2024

R**S

Just great!

Best mobile antenna I've ever had.

1.05.2025

B**D

Broke after a few years of use

I bought this antenna and used it as a base for a few months. I put it away after moving to a New house and it sat for a few years. I recently put HF in my 2nd Tahoe and thought this antenna would work great with my 857d. Antenna broke about 3 months after installing it. It will no longer tune or move at all. Pretty expensive antenna for it to break after a year of use.

17.08.2021

B**Y

SWR is inaccurate

When linked to my FT-891 the frequency scan does indeed zero in on a very low SWR, however when compared with two different SWR meters the actual SWr is about 6 to 8. totally unusable.

7.02.2026

B**N

Work great for a apartment

Must have ground feed lines

9.02.2021

ASIN	B004UM9UL4
Best Sellers Rank	#1,206 in Radio Antennas
Customer Reviews	4.3 4.3 out of 5 stars (77)
Date First Available	March 31, 2011
Is Discontinued By Manufacturer	No
Item Weight	0.01 ounces
Item model number	ATAS-120A
Manufacturer	Yaesu
Product Dimensions	37.3 x 2.4 x 3.3 inches

Yaesu ATAS-120A 40 Meter through 70cm Auto Tune Motorized HF/VHF/UHF Antenna For FT-857D, FT-450DandFT-897D ATAS-120

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