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Reviews For: MFJ-939 automatic antenna tuner

Category: Antenna Tuners/Matching Networks

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Review Summary For : MFJ-939 automatic antenna tuner
Reviews: 43MSRP: 159.95
Plug & Play! You won’t even know it’s there . . . MFJ-939I/K/Y automatically tunes your antenna as you tune your radio. SWR is just always low.

Tunes your coax fed or random wire antennas 1.8-30 MHz from 2 Watts QRP to full 200 Watts SSB/CW.

Matches 6-1600 Ohms (SWR up to 32:1) -- that’s a 50% wider matching range than competing products that are less capable and higher priced . . . and it’s made in the USA.

Highly intelligent, ultra-fast tuning!
As you’re ragchewing, contesting or DXing, the MFJ-939 is learning your antenna and the way you operate and storing all this in its 20,000 memories. The more you use it, the more it learns.

Measure & Compute = Instant Match
MFJ-939 uniquely measures your antenna’s complex impedance (R, X), computes the L-network and snaps in needed components for instant matching.

AdaptiveSearch determines a sub-set of all solutions that can provide a safe match and searches only that subset giving
you an ultra fast match. Others search slowly through all solutions.

InstantRecall first checks its memory to see if you have operated this frequency before. If so, tuning is instantaneous and you’re ready to go!

MFJ VirtualAntenna Memory
MFJ exclusive VirtualAntenna Memory system gives you 8 antenna memory banks of 2500 memories each.
You can use an antenna switch to select up to 8 antennas and assign each antenna its own 2500 memories!

4 Times More Solutions and Faster!
MFJ has 256 values each of capacitance and inductance for 131,072 matching solutions giving you a finely tuned very low SWR. That`s 4 times the 32,768 solutions of competitors using only 128 L/C values each!
Don`t be fooled by competing products claiming fast search times -- if you have a quarter of the matching solutions, of course,it takes less time to finish but it`s not faster.
MFJ`s faster speed comes from advanced technology and software algorithms not from fewer solutions.Audio SWR Meter
An Audio SWR meter beeps when SWR <1.5, 2, 2.5, 3. Alarms if >3. Audible & Visible Diagnostic messages.

Heavy-Duty Components
Heavy-duty L-network: 10 Amp/1000V relays, RF duty silver mica caps won’t burn up. Safe, reliable, continuous 200W SSB/CW.

As Small as Your Radio
Tiny 6 1/2W x 2 7/8H x 8 3/8D”. 2.4 lbs. SO-39s, random wire ant. & gnd posts.

Never Obsolete . . . Super Versatile
Truly Plug & Play! No settings, only one cable to plug in! Order MFJ-939I, Icom; MFJ-939K, Ken; MFJ-939Y, Yaesu. Specify Yaesu: FT-100/450/950/ 857/897/1000MP/9000/2000 or other.

Never Obsolete!

If you get a new transceiver, simply order a new Plug and Play cable.

Super Versatile! Works with ALL older rigs, classic transmitters, Flex, Elecraft, Tentec, QRP, others. Auto tune antenna -- touch tune button on any MFJ-939I/K/Y for any rig.

2-Year NoMatterWhatWarranty
Product is in production
More Info:
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
W2LEW Rating: 2023-08-29
Very Satisfied Time Owned: 0 to 3 months.
I was skeptical about anything made by MFJ ever since I had some bad experiences their products back in the 80s
I recently Purchased a little Icom 718 for backup/portable use and needed a small inexpensive tuner. I decided to take a chance with the MFJ 939I which comes already set up for the Icom. I'm glad that I did, because the Tuner is working just as advertised, and has exceeded my expectations. Just press the tune button on the 718, and the power drops to 10W, and it tunes in a couple of seconds. Bravo MFJ
K6SDW Rating: 2023-06-17
Well done MFJ Time Owned: more than 12 months.
UPDATE: After 3 years of fateful service my 939i died requiring it be sent to MFJ for repairs. This was the Fall of 2022 and it took MFJ 4 months to repair tuner. Finally, and $90 later, my 939i is back in service. Since I can only run an EFHW dipole, without the 939i, I probably would not be on the air.


I bought the 939i because my ICOM 7300 doesn't like my endfed antenna......I am a bit disappointed in the 7300.

Yes, I have to hit the tune button when QSYing but once the tuner has tuned to a band/frequency it remembers this setting and takes 1 - 2 seconds to retune.

Good job MFJ, maybe this is an indication the company is taking QC seriously.


Finish on mine is excellent
KB2TC Rating: 2023-06-17
Works well - never need to touch it Time Owned: 0 to 3 months.
I purchased this to suplement my IC 7300. i use long wire antennas and this makes it easy - simple connection and controlled via the radio - Simple.
KI5NYJ Rating: 2021-11-29
Easy and Amazing Time Owned: 0 to 3 months.
I paid $200 direct from MFJ. Save a little by going through DX, HRO, GP, etc. Bought because I could not get decent SWR with my 7300 and GAP Titan, despite GAP's saying it would be below 2. Even with the 7300's autotuning, I could not get 40 and 80 below 6 (I'm guessing here, it was high but not off the scale). Tried to resolve issues with GAP, lackluster customer service but the product is solid. Anyhoo, with the 939I between the 7300 and the Titan, I am getting at most 1.2 on all HF and 6m bands including 160. Even where the SWR was pretty good (1.5, etc.), the 939 did even better. Using the cable (choose your radio brand!!) it gets power right off the transceiver. Tunes in under 1 second, and I can push full 100w through it. Cool dials, flashing lights, and meters? NOPE. No need. :) '73
K2WPM Rating: 2021-08-24
Great Time Owned: more than 12 months.
I build wire antennas, lots of them.
Rarely used a tuner.
But this little puppie makes life a lot easier.

Update / edit 8-24-21

I forgot to mention I have used this tuner, off and on, for over five years. Used it with Yaesu 450D and with IC-7300. Small and light, easy to bring portable. I just press the tune button on the 7300 and easy peazy.
K6GBW Rating: 2021-07-27
Solid Performer Time Owned: 0 to 3 months.
I just got a Yaesu FTDX10d and built a brand new ZS6BKW antenna. The radio tuned almost everything but struggled a bit with the top of 80 meters and would not tune 15 or 10 meters at all. I had this MFJ-939 but it was for an Icom. No problem, I just reconfigured the jumpers and added a new cable. I also did a hard reset on it to avoid any issues with old settings. Now I can tune up 3.500 to 3.999 with a 1.2 or better SWR. 15 and 10 also tune fairly easily. 40 and 20 are almost comedic it tunes so fast! It just makes a little click and its done! About the only down side to this tuner is that there is no meter and the various beeps and button presses require you to read the manual and learn it before you can really get the most out of it. But in the end, I feel confident that my new radio won't get zorched (that's a technical electronic word) be exposing it to questionable SWR.
N6DXX Rating: 2021-07-24
works perfectly for me Time Owned: more than 12 months.
I have owned the MFJ-939 for over 3 years and used it on both Icom and Kenwood transceivers. My antenna is a non resonant Off Center Fed Dipole which presents a wide range of impedances to the tuner. The tuner matches everything from 80 to 10 meters to well under a 1.5 SWR. Once in memory a frequency is tuned up in an instant. Very impressive performance! I love the one touch tuning too. I could not be happier with its performance.

Tony, N6DXX
N2CYY Rating: 2021-03-15
Great Tuner! Time Owned: 0 to 3 months.
This tuner works great with my IC -7300! Using the supplied cable you can operate it either via the tuner itself or via the front panel of the 7300. Because of comprise antennas, I needed a tuner that could match a wider range than the internal 7300 tuner. The 939i is doing everything I had hoped for. Enabled me to work new bands on my vertical and g5-rv jr, as well as, really opened up the usable bandwidth on 80/75M. Well done MFJ!
VE3LTP Rating: 2020-12-19
Great Value - Single Most Useful Station Accessory Time Owned: 0 to 3 months.
Any one starting out or having to use compromise antennas should buy this tuner first and then see what is left in the budget for a transceiver.
I could not get out at all before using this tuner. It has worked so far on all the bands that are open with amazing results with a very limited antenna.
Tunes quickly and efficiently. Easy to use with appropriate interface cable. I rate it as a super value for money.
It is always a good idea to read the manual. If you power cycle the tuner too quickly you will corrupt the memory. No where near to being a deal breaker.
KC3OLR Rating: 2020-09-24
939Y works out of box with a new Yaesu FT-891 Time Owned: 0 to 3 months.
Plug n play 939Y comes with MFJ's Yaesu 950/450/891 cable per MFJ site, mine says /847 instead of /891. Connected 8 pin connector to radio TUN, coaxes and separate DC power supply (unlike the Icom version reviewed below). Ignored the radio's TNR Function. Powered on, then pressed Tune for about 2 seconds while sending carrier in AM mode at 5 watts until it finished tuning. Tuner chugged for a few seconds, beeped once and SWR green light came on. Changed band and sent carrier again, it automatically tuned it again without pressing any buttons. 1.5 reached in seconds on an 50" indoor vertical (collapsed MFJ-1979) with no base loading coil, that was sending swr near the right edge of the FT-891's scale beforehand while talking, on 20m. It couldn't be simpler, though you'll have to switch back to SSB and raise power if you intend to QSO, then return to AM mode and < 20w at any new frequency you chose - the tuner did not work automatically from speech, just a carrier, but this is before any frequencies were stored in memory. What's left is to see how well it works on bands besides 20m, and its reliability. The FT-891 fits perfectly on top of the 939Y.