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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
G6DLJ Rating: 2020-03-28
Poor finish but works fine Time Owned: 0 to 3 months.
Purchased the MFJ-939i version from a UK radio dealer near Heathrow Airport (a well know grey importer!) . On opening the box I was surprised to see a lot of missing paint on both folder corners. The dealer told me this how MFJ kit sometimes comes these days and they seem to fold the case after it’s been painted. I’ve since heard stories from other amateurs that MFJ are sometimes noted for their poor exterior finish and minor problems such as sticky knobs, the joke is you need to finish off building their products when you get them ????

It didn’t work with the IC7100 Tuner/Call button out of the box but I suspect that’s because I was using the supplied DC power cable when in fact power was already being supplied from the Icom cable, my fault for not reading the instructions which are surprisingly comprehensive (you have to print them yourself but that’s par for the course these days).

So far its worked well with my 40M endfed and will even match down to 160M and up to 50MHz. It seems very simple and quick in operation. The 929 looks to be similar electronics with the addition of an antenna switch, connector for a wire antenna and built-in SWR metre with the option to manually tweak L and C.

So, pleased with the electronics and operation, disappointed with the finish.
KB1OQ Rating: 2020-02-14
Easy setup with my IC-718! Time Owned: 0 to 3 months.
Don't be intimidated by the long owners manual if you have an ICOM. The manual tells you to set jumpers inside the unit but that is not needed if you get the ICOM version (they are already set). You do not need the power cable because the tuner gets its power from the radio just fine through the interface cable. You do have to go into the 718's initial setup menu and change the tuner to "4". You really do not have to touch the tuner at all after that. Leave it on and it will power up and down with the radio. You activate it by pressing the "TUNER" button on the 718. THAT'S IT! I can now work every band but 12M. The tuner could not tune that for some reason. I can live with that. I did not try 160M. Feel free to email me if you have any questions. My antenna is an MFJ-1984MP end fed.

Highly recommended!
AA4UC Rating: 2020-02-10
Replacement Tuner Much Better Time Owned: 0 to 3 months.
I just received my MFJ-939Y in the mail from HRO and the first thing I notice taking it out of the box is the sound of several lose parts rattling around in the enclosure. Back it goes! I will update this review after I get the new one assuming it also doesn't have blatantly obvious quality control issues.

Update 2/10/2020... Replacement arrived and no issues with this tuner so far. Tunes my loop on 160-10 meters in a couple of seconds. Works much faster than similar LDG units. Frankly I'm shocked!
G8FXC Rating: 2019-08-11
Pretty Good! Time Owned: 0 to 3 months.
It would be silly to deny that MFJ sometimes have quality control problems, but when they get it right they do produce some nice products at good prices. I run an IC-7300 at home and have been getting along on a combination of a manual MFJ VersaTuner plus the built-in auto tuner in the radio. But I was getting fed up with slow, manual tuning and decided to try an auto-tuner. I was tempted by the MFJ-929, but ended up going with the 939 to save some money.

It arrived in good condition and I plugged it up to the 7300, keeping the VersaTuner in the feed chain to the antenna for SWR metering and antenna switching. I connected a fairly short random wire via a cheap unun and hit the "tune" button. It found a reasonable match quite quickly, though not as fast as the adverts suggest.

My first day of operation was a bit frustrating - when it got a match, it was very good, but it often seemed to lose the match and go through a retune which could take quite a long time. Eventually, I admitted defeat, read the manual, understood how it really works and it has been reliable ever since. Unlike the 929, this tuner only has three buttons and has to cram a lot of functionality into them - you really do have to RTFM before you try to use it!

Two points - my shack it on the upper floor of our house and the RF ground is long. I use an MFJ 931 Artificial Ground to make it look shorter - and that is critical to the 939. It does not seem to matter so much on the higher bands, but if I tune up on 80m and transmit without the ground resonated, all hell breaks lose! As soon as I hit the ATU with a hundred watts, it goes into repeated tuning cycles. Provided the artificial ground is resonated first, the 939 is able to get a close to perfect match that holds indefinitely.

I've seen questions on the net as to whether of not these MFJ auto-tuners can operate on 6m - the spec is only up to 30MHz. I can confirm that the 939 is able to resonate most things on 6m, but it does lose some functionality. It contains instrumentation including a frequency counter and an antenna analyser which drive the IntelliTuner function and reduce the tuning time. It seems to be this instrumentation that is only rated up to 30MHz. On 6m, the tuner reverts to a basic "dumb" tuner - every time you hit the "tune" button, it goes through a full search looking for a match - which can take several seconds. Further, since the frequency counter cannot measure the carrier frequency on 6m, it is unable to store the solution in memory, so it will always go through the full tune cycle. Even so, it is still pretty impressive - this morning my 939 has allowed me to have a QSO on 80m, another on 40m and a couple on 20 followed by pinging up the 6m repeater in the next town - all on about forty feet of wire running from the shack window to the tree in the corner of the garden!
AB5IE Rating: 2019-05-24
Instructions somewhat vague and operation is a little funny ... Time Owned: 0 to 3 months.
Bought the pre-configured "A" version with the cable for my Alinco DX-SR8, which I use for rag-chewing on 40 and 75 meters. I operate mostly QRP/weak signal using Elecraft KX-2s and Yaesu FT-817/818s ... so higher power communication not my usual quest.

The MFJ-939A actually out tunes on 75/80 meters, (with a Hustler 6-BTV as my load), my manual MFJ tuners, the LDG tuner with FT-817/818s and the internal tuner on KX-2s (which will normally tune everything from a wet rope to a nail). That is, matches with less than an SWR of 1.5:1. I can't get that close on the other tuners. There are some frequencies that are an especially peculiar load, and the tuner has to "scratch it's head" for a while ...

Main complaint is the fuzzy and "hit or miss" instructions. And, I don't like setting parameters by how long you press a button. I'd rather MFJ include some more buttons to toggle between tuner bypass, tuner on and "sticky mode", etc. ...

At only $149.00 street price, this is a good value and despite it's quirks, I'd recommend it, as it really does a good job, (usually), matching your transmitter to challenging loads.

G6ATJ Rating: 2019-04-12
Fantastic simple matchinging Time Owned: 0 to 3 months.
%%%%I had the mfj948 manual tuner which i burnt out after connecting to an endfed via 9:1 unun! Minimum swr at ANY frequency was 8:1 (as expected).
I bought the 939 and connected and hey presto! It works so quickly and tunes all bands 80 - 6 including warc with VERY low swr ( <1.5 ). I love it! I do like a manual tuner....something very satisfying about turning two var. caps to get that needle down to near 0, but auto tuner saves so much time when chasing DX.
Ic7300 + 939i + endfed longwire: A winner!

Earlier 5-star review posted by G6ATJ on 2019-04-12

I had the mfj948 manual tuner which i burnt out after connecting to an endfed via 9:1 unun!
Warily, I bought the 939 and connected and hey presto! It works and tunes all bands with VERY low swr ( <1.5 ). I love it!
Ic7300 + 939i + endfed longwire.
W6UXB Rating: 2019-04-01
For MFJ tuners its pretty good Time Owned: 6 to 12 months.
I have had mine for awhile now, I use it with a radio that the tuner does not support so I have to hit the tune button while keying the rig, not as bad as it sounds it tunes very fast but will stop at a 1.5 SWR you can hit the tune button again and it probably will go down to 1.3 SWR and when you hit the tune again it toggles between the 2 settings, my antenna is better than that across most of the bands I use so only use it when I get on my resonant edges!
K6ERF Rating: 2019-03-31
Efficient Tuner Time Owned: 0 to 3 months.
I use this tuner with the Icom IC-7000 & IC-7300.
I have previously used the LDG IT-100 tuner which is good and reliable. This MFJ-939 loads extremely fast on all my antennas, about 10 times the speed of the LDG. The loading is just about instantaneous. Several antennas that the LDG could not match are easily matched with this tuner. Overall I'm very pleased with the performance.
KD5JZN Rating: 2017-11-20
Good for the price Time Owned: 6 to 12 months.
I've run the MFJ939 with my TS2000 for about a year now. The tuner works just fine 90% of the time. It will match my OCF Windom within a second or two , with the rare occasion that an end of my antenna is touching the metal roof. Otherwise the tuner works flawlessly with either the TS2000 or the IC706MK2G{ once I reset the internal jumpers}.
Is it, or do I expect it to be perfect for the $150 price? Of course not, you do have to approach this hobby with a slice of common sense and realize that you get what you pay for. Overall. this tuner preforms well for the price...
WD8U Rating: 2017-07-20
MFJ great service Time Owned: 0 to 3 months.
I got a new IC-7100 and wanted an automatic tuner for it. So I bought a mfj 939I..
Had some problems with it...but after a few emails
with there support (Richard) got another one to me Fast! It works great with the IC7100..
They stand behind there products and provided me with a Fast solution,, with out effort on my part.. I am very satisfied with there service and product,,,The MFJ-939I tunes fast and has a wide swr range.