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Reviews For: MFJ-936B

Category: Antenna Tuners/Matching Networks

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Review Summary For : MFJ-936B
Reviews: 17MSRP: 259.95
The MFJ-936B is a specialised small wire loop tuner for portable/home use. It has built-in SWR and RF antenna current meters for tuning. It turns virtually any wire loop into a high efficiency transmitting magnetic loop antenna. Depending on its length, and this can be 5ft, 10ft or longer, it is possible to cover two or more amateur bands. You can operate up to 150W, no ground, radials or counterpoises required. The wire can even be simply draped around a bookcase. The MFJ-936B has a carry handle built into the side. There is a detachable PVC mount that bolts onto the top of the case. Into this can be placed a PVC frame cross (MFJ-57) for mounting a 20-15m or MFJ-58 for mounting a 17-10m antenna, alternatively you can use insulated wire such as PVC coated multristranded copper wire to form an antenna. You can tune any shape loop - circle, square rectangle, any odd shape. A quarter wavelength wire shaped as a circle is the most efficient though. A 10ft wire formed into a loop operates 20-15m, 5ft for 17-10m, 24ft for 30-40m.
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# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
NG2Q Rating: 2023-09-18
Great for what it does Time Owned: more than 12 months.
I have owned this loop tuner for several years and never had any issues. I have used it to tune copper loops to coax loops and it tunes them all very well. This is GREAT for FT-8 when I can park it on the frequency and not have to jump around like on SSB to tune it. I also have the MFJ-1788, which I like a little better since I can tune it inside the shack. I have it mounted on a cart, with the copper loop mounted on a piece of PVC and I can wheel it out to my patio. No kidding, this thing gets out At one time, I had it mounted on the cart, with a rotator on the bottom and was able to null out other loud stations and bring up the station I wanted. Research mag loops, they can be your best friend.
LNXAUTHOR Rating: 2021-12-22
works FB Time Owned: 0 to 3 months.
found a NOS NIB 936B... these mfj units are all about the same inside, using an mfj-19 butterfly variable air cap... the 936b only has two wire connectors in the rear, unlike the 936c, which has UHF connectors for coax

went to the local home improvement store, and for less than $25 built a pvc frame and 13-foot 10ga loop for 20M (mfj wants a lot more for its pvc antennas); hint: drill a hole in each of three pvc end caps and use a shock cord thru to create a support loop for your wire or copper tubing

i didn't know what to expect, but it worked great! on the first outing w/my 705 made 1,500km contacts using 10W

this will be a fun tuner to use to do experiments in antenna building... no power required, and the two meters obviate the need for an analyzer
G4KIN Rating: 2020-07-30
Surprisingly delightful Time Owned: 0 to 3 months.
Bought the mfj 936b however I realised it was overkill with a current meter.
Initially I used 13 ft of micro bore copper 10mm but 8mm would have handled better . mounted it on a lock-down special diy wooden stand . I was a bit hesitant at first after reading all the warnings (particularly after watching the movie "Philadelphia Experiment" however the tuning I found surprisingly straight forward having spent my early years with a "dip and load" mindset . I tuned up with 5 watts once I had the hang of the tuning and moved on to 10 watts where I decided to stay.
The build of the unit is atrocious the outer case looks like it had been painted with a stucco brush and then bent into the box shape due to the paint stretch marks on the bends .
The matching control has 2mm play on the knob although It might not be the shaft but just a loose grub screw! There is a slight hand capacitance but I put that down to my foil hat !
It is,nt my main twig but it looks like I will use it quite a lot at my beach trailer.
The smaller version would have done I suppose. I did try to bring it to resonance with the aid of a sark antenna analyser but it was a tad long winded so I stuck with the 5 watts RF. I have dug out my old antenna noise bridge and try it out to bring the tuning as near as damn it but I guess peaking the noise on the radio via the tuner controls is pretty much the same!
I am going to try heavy fence wire as a loop its not copper but I thinks it will be ok .
I am going to try the wire around the bookcase as per the adverts if I can get my xyl to give me a hand to get it out into the back yard ..

its a fun thing but it works ...
I do have some Mag loops 2 home brewed and an MFJ one which I managed to save from a guy before he jumped off the bridge . at the moment this is my flavour of the month. By any other name its a Military loop and my next "experiment is ready to go using a 40ft diamond shape with the sides pulled out hanging on a 6 mtr fibreglass pole .
I use data modes quite a bit rtty psk and it will be okay for that just sitting on one freq.
I do have some heavy qrn at this qth as I live next door to the funeral parlour drilling and hammering all the time. the loop is quieter.

AC7CW Rating: 2019-11-23
Never Again Time Owned: 0 to 3 months.
I hate MFJ stuff. I swore off it long ago but, unfortunately, I could not find a loop tuner from any other source. I screwed in a PL-259 plug. The socket that MFJ installed gripped the center conductor so tightly that when I disconnected the coax it pulled the plug apart. I'm sure they got a really good price on those sockets, go MFJ!! I gave away all my Chinese stuff and this loop tuner just to be rid of all of the problems.
AF2DX Rating: 2018-04-03
Can't get any better Time Owned: more than 12 months.
I purchased the 936-B a few years back.
I sold the unit because I purchased the MFJ mag loop but I did miss it and purchased another MFJ 936-B
This tuner I feel is a bit better then the $500.00 MFJ LOOP because you can cut a wire for each band.
I made a slight mod to the terminals just to keep the ends of the copper loop away from the tuner box.
With my new FT 891 a few weeks ago I worked ON4UN and received a 579 with some QSB,Alaska,Finland and Washington State and this was all indoors.
I still play around with mag loops but I like being able to carry the tuner to my outdoor operating spot.
Tuning for a low SWR is not that bad when you get used to it
I use only copper tubing,5/16th OD with terminals soldered on the ends.
Really nulls out QRN and it is a dream for antenna restricted hams with no room
G4VZV Rating: 2018-01-15
Excellent Time Owned: more than 12 months.
Excellent device where you cannot use outside antennas, or for portable use. It is a magnetic loop in all but name. What you're buying here is the tuning system for a loop and you can indeed use any conductive material as the loop. Use wire, use copper tubing ,aluminium strips the heavier duty the better, I've used this device at home and portable and used wire to 1 inch diameter copper tubing. It works like a dream low noise, simple , so so easy to use and tune up the loop. Results: Amazing ....i mean amazing for example the 20mts band loop of total length 7 feet produces QSO's all over Europe and sometimes much further. Lookat my QRZ page or DXNews page under my call for images and log book recorded QSO's (G4VZV) It's a joy to use ....MFJ this is a winner !!!!
SP9NLI Rating: 2018-01-07
Great portable solution Time Owned: 0 to 3 months.
I've been messing around with this tuner for two months now and find it really excellent.
At first I feared that some of the comments here were right saying that the SWR-meter was useless showing huge reflected current when the antenna is matched.
Actually, it is not the case, when the tuner shows a mismatch, it means that the matching capacitor needs adjusting.
Once I figured out how to bring do reflected needle down to zero with each and every loop I put on it, the whole tuning process is fast and easy.
The SWR and power meter seems perfectly calibrated, so I give it 5 stars despite finding one of the matching capacitor's blades slightly bent and short-circuiting the signal at some point.
A great solution for portable QRP operation.
AE7TO Rating: 2016-07-21
Great Travel Antenna Time Owned: more than 12 months.
I bought the MFJ-936B a couple of years ago so I'd have something better to do than watching TV when in the hotel on business trips . The first thing I learned is that this thing is tricky to tune, as many others have said. And it must be re-tuned if you change frequency by more than about 10 KHz. Eventually I learned how to consistently get SWR below 1.5 by using an antenna analyzer. After an initial "earball" tune for max static on the radio, I VERY gradually home in on low SWR by alternately adjusting the Tune and Match knobs while watching the analyzer (overshooting each knob slightly past the lowest SWR) until the match is acceptable. I have also attempted to use MFJ's "manual screwdriver" (with a telescoping whip) as a travel antenna. That setup works well outdoors, and is easier to tune. But it isn't practical indoors, where the ceiling interferes with extending the whip. My 13 foot circumference loop, on the other hand, works indoors and out. So I'm back to using the loop (13 feet of soft copper 3/8" OD tubing that I can coil into a suitcase). By the way, I don't use the Current meter for tuning because the analyzer works fine. But the cross-needle SWR meter is very handy. Saves me from packing a separate meter.
K1OYQ Rating: 2016-02-22
It works very well! Time Owned: 0 to 3 months.
I picked one of these up used and experimented with it for about a week. I started out with a loop of #12 wire and found that to be just about useless (as expected). I then tried RG-58 coax and noticed a big improvement right away. Then I tried low loss RG-8 coax (shield only) and noticed a significant improvement. I haven't tried 1/2 inch copper tubing yet, but I'm sure that will be even better then the aluminum shield on the RG-8. I made three loops out of the RG-8 (13ft, 9ft, and 4ft). All of these loops worked well and I made CW and SSB contacts on each using 5 to 50 watts. The true test came during the ARRL CW DX contest and I used the 13ft loop on 20M. I worked most of the EU and a lot of SA stations with 5 watts with an FT-817. My next test will be an A/B comparison of the loops vs Buddipole antenna. The downside of this tuner is that the SWR meter is about useless. As far as I can tell it does not provide any useful information. In fact the SWR meter shows huge reflected current when the antenna is tuned properly (max current on the MFJ current meter and low SWR on the rig). I'll have to research this a little more (meter connected backwards?). That is why I gave it a 4. I would recommend the MFJ-935B vice the 936B. I do not recommend using the top 3/4" PVC support on the 936B for antenna support for the 13ft or larger loop due to the stress from the weight. It is ok for the 9ft or less loops. The loops exhibit the same directivity as a dipole which can be useful during operations. This antenna tuner has now become a part of my Go-Kit of emergency and portable antennas.
AH6OY Rating: 2015-05-05
Works Time Owned: more than 12 months.
While travelling if you are going to stay in a tall hotel room this tuner works fantastic. G2SZU / KH6ZU used my tuner downtown Waikiki and worked a chum in England 579. This was from the long path side of the building. I think a combination of height and buildings magnetic field help setup good working conditions. Keith was arranging the 13' wire loop strung horizontally so that a portion was 1" off from the metal balcony railing. I also have a feeling since current regulations for safety concerning high rise balcony railing require the railings to be welded to the concretes rebar that it gives the antenna a great shot at tying into the whole buildings height to help radiate signals and receive better.

So pretty much the loop plays better at height oriented horizontally. Rigging low and vertical you have sharp nulls and don't get out as good. Bought the tuner to fight noise and have for a portable backup. Works fantastic for a loaner to visiting friends.

Caution is the unit is not sturdy concerning the rear connector lugs. Twisting hard on the wing nuts can torque the inside components loosening and bending components. My case causing this malfunction was using copper waterline tubing unsupported and it flopped from side to side. Damage was repairable but the unit could be improved by making it with insulated standoffs instead of connections just going through gaps in the rear of the case. The tuner can give an RF bite if you touch the case. It didn't help matters that when receiving the tuner new it had a loose screw floating around inside I had to install. Like they say, you get what you pay for and that's pretty much a crap shoot.