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Reviews Categories | Antenna Tuners/Matching Networks | MFJ-935B Help

Reviews Summary for MFJ-935B
MFJ-935B Reviews: 11 Average rating: 3.9/5 MSRP: $199
Description: Small High Efficiency Loop Tuner
Product is in production.
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K2CAJ Rating: 5/5 Aug 12, 2018 04:29 Send this review to a friend
Works great, but buy the 933.  Time owned: more than 12 months
I've used this with a loop of soft copper tubing from the plumber's supply store: just squash the ends in a bench vise, drill holes, and clamp it in for a mostly self-supporting loop. You can hold the whole thing up on a bit of PVC in a tripod, and clamp in different diameters for different bands.
This makes a great antenna that is pretty quiet, absurdly easy to setup and take down, great for portable operation.

However, make sure you open it up before you use it and check to make sure everything is jake. Mine had one of the wires bent and it contacted the fins of the small capacitor! Bent the wire back, and everything was perfect, but I was glad I looked before I tried to use it. MFJ can have QC issues, but in my experience they are easily adjusted and you then have a solid product, as long as you remember to look in the box when you buy it.

Overall, I'd say that you're better off with the 933 because you won't need to use the meter. If you're running 100W into a loop, you don't want to be so close to it that you can read the meter when you tune it, and if you have an antenna tuner you don't need the meter anyway. Use an antenna analyzer or your transceiver to tune your loop and save yourself 20 dollars.
N2JLI Rating: 2/5 Aug 4, 2017 19:41 Send this review to a friend
Quality control problems  Time owned: 0 to 3 months
Shortly after setting up and tuning up a 21ft wire loop in the window of my apartment, I saw some flashes behind the current meter. Opening up the box I found the wire going from the sensitivity pot to the meter was shorting to one of the long screws that hold the cap plates together. Re-positioning the wire fixed the problem. I wrote an email to MFJ complaining about it and received NO response.
I'd advise taking the cabinet off and checking everything out inside before you use it.
K3JLS Rating: 1/5 Jan 16, 2017 19:43 Send this review to a friend
DOA  Time owned: 0 to 3 months
I bought an MFJ-933 for which there is currently no category. But, since it's electrically similar to the 935, I thought I'd post the review here.

I bought it from HRO in Delaware, and it was quickly shipped from their Milwaukee location. It arrived promptly and was very well packed.

That's the good news.

The bad news is that it doesn't work properly because whoever assembled the thing bent the back rotating contacts on the smaller impedance matching capacitor creating a short!

The red tag inside the unit says MR 9/16, so I guess I'll have to report this to MFJ tomorrow. I did realign the capacitor so that it no longer shorts out and will try it again with a proper copper loop.

MFJ generally makes good stuff, but it really irks me to have to repair their blunders on something that was supposedly 'tested' properly.

I'll review this again. If it doesn't work 'as advertised', it goes back.

73's - Joe - K3JLS
KW4JA Rating: 5/5 Nov 5, 2014 12:51 Send this review to a friend
Great experimental fun!  Time owned: 3 to 6 months
I bought the 935B in preference to the MFJ 1786/88 choices because I like to experiment. Also the price was half the others. First I built a 20 meter loop using 1/2 inch copper tubing ten feet in circumference. I got as far as Japan on digital. Next I found a cheaper source for copper tubing. My local plumbing supply sells 3/8 inch copper coil for only 65 cents a foot. I purchased 23 foot for a 40, 30M loop. This is the quietest antenna I've ever used on 40/30 and I worked every dx I've worked using a multi band vertical but much less noise.
My next project is to use my 23 foot loop on 20-6 meters by putting capacitance in series with the 935B capacitor. Most of my readings discourage mag loops larger than 1/4 wave or between 1/4 wave and full wave. Who says so? I'm going to try it and prove/disprove it for myself. After that I'm going to try mounting half circle sections of coiled pipe in directional beam configurations just to see what happens - a low power first to test.

The MFJ935B works great and is well built. I use mine on my roof with copper coil tubing hung horizontally and vertically using tree branches and pvc tubing. My advice to hams is experiment - worse that can happen is you fail and waste a few dollars. Who knows you might stumble upon something and invent a new antenna type. You've got EZNEC to boot so what's stopping you.

AG6YK Rating: 5/5 Oct 19, 2014 22:08 Send this review to a friend
Meets expectations  Time owned: 0 to 3 months
Let me start by saying that my unit does not appear to have any QA problems, all solder joints look good, no shorts, I bought this tuner as an interim until I decide on which mag loop I want to install permanently. It is performing much better than I originally expected!
I am using it indoors inside the shack. This requires a 1:1 current balun and reducing the power to 50W to eliminate RFI. I am running mostly PSK-31 but also some SSB. I get an excellent match to my radio and the antenna is easy to tune using receive noise and the built-in current meter.
I have had good success making contacts on 20M with a 10-foot circumference loop. I am making my own loops and I have used 10M and 20M so far.
This product does exactly what the manufacturer says it will do. It is a capacitively-coupled magnetic loop tuner intended for indoor or portable use. It requires you to provide more than one loop to cover the ham bands, but provides a simple connector to facilitate this. I have built three loops, a 4 foot, 5.5 foot, and 10 foot cirmcumferences. I am also planning on building a 9.5 foot loop and some multi-turn loops with additional capacitance to increase the range to 80M.
I cannot comment on the 10-gauge wire loops available from MFJ, I am using 3/8 OD copper refrigerator tubing and an external support.
I recommend this product to those hams who are challenged by antenna restrictions and who feel comfortable with some design and building. This is not a product for somebody who wants to buy a complete package, nor is it for the home-brew only DIYer. It is a capable antenna which is getting me on the air.
LU1DO Rating: 3/5 Nov 18, 2013 16:08 Send this review to a friend
watchout !!!  Time owned: 0 to 3 months
The review goes for a MFJ-933 ( the simplest of the loop tuners)
Hams , beware of this product!!! Sorry to start like this, but I must inform that my tuning capacitor produced strange noises on my transceiver. Before transmitting, I opted to open this unit and was amazed at what I found.... between the capacitor plates I saw a small aluminium "lock" thin as a hair. This small metallic piece was erratically shortening the plates hence making noises while on receive.
So, if you buy one of these toys, before attempting anything, do yourself a favor and open the top, take a good torch light and carefully inspect if you find anything loose.
Not doing this check, could turn into a costly repair of your transceiver.
Itīs a pitty that somebody gets payed to attach a sticker on the bottom as if controlled...
WF8O Rating: 5/5 Oct 5, 2013 12:05 Send this review to a friend
FB Loop Tuner  Time owned: 0 to 3 months
I have had this tuner for several days. It has tuned a 95" circumference loop if 1/4" flexible copper tubing to 1:1 match at 7 watts from my Elecraft K1. Well made excellent fit and finish! Signals from this tuner are virtually the same as from my endfed dipole. Very nice!!
PD0T Rating: 4/5 Mar 1, 2012 01:46 Send this review to a friend
Great for magnetic loop starters  Time owned: 0 to 3 months
I recently purchased this tuner and don't regret it at all. The build quality is not great but ok. I would like to have more sturdy loop terminals and the placement of the SO239 connector could get into your way sometimes. But it works extremely well. So far I made a few PSK31 QSOs on 10m using a 1m long, 15mm copper pipe loop with only 5 Watts.
Of course due to the narrow bandwidth nature of loop antennas, the "sweet spot" for resonance and matching can be sometimes hard to find. Also if you're living in a building with lots of steel around you it will still pick up lots of noise. So placing your antenna on the balcony would be advisable.

The bottom line is:
This is the ticket to start experimenting with magnetic loop antennas. Get it!
KDMSKY59 Rating: 3/5 Feb 8, 2012 15:58 Send this review to a friend
compromise but it works  Time owned: 0 to 3 months
The best thing about the MFJ 935B is it's quieter than most antennas as you probably already know. Here's the downsides: Whatever loop diameter you are using may tune one or two bands within it's range but not the third so you need to change the location of the tuner making tuneup unpredictable.
My 12 foot long 10 guage loop tunes 30M but not 20M. My 10 foot tunes 30 and 17 but usually not 20 (SWR over 2:1) unless I move it around to a sweet spot in my yard. Yeah it's like that.

The connection points on the rear of the tuner are only 3/16 inch so they are not heavy duty. At one time one of the connection rods rotated which shorted out the capacitor and the unit would'nt tune. If you want to construct a heavy duty loop you'll need to weld it to small lugs that fit the connectors. MFJ gives the idea this tuner is heavy duty. It's not a tank but rather a Corolla at a Mercedes price.

If you like experimenting this tuner is fine. Expect to spend 90% of your operating time setting it up and tuning it and 10% actually operating.

On the positive side I live in an RF dead zone. Nothing works at less than 50 watts - not dipoles, verticals, windoms, calmdoms, bazookas, wrigleys.
Still I can make contacts with this. The trick is to be tuned to the right frequency when some other station somewhere is on the air. You'll probably hear him well and he'll probably come back to you.
N3LCW Rating: 5/5 Jan 1, 2010 10:25 Send this review to a friend
It really works great!  Time owned: more than 12 months
I've owned the MFJ-936B version of this tuner for 2 years now. It really does work and it works very well, and if you can get it outside or near a window it will do great.

I tried it first on 20M with a 13ft length of wire formed into a loop. Tuned it up on 14.070 and was amazed to hear loud PSK signals. I copied DX signals from South America that I could not detect with my 20M attic dipole. I had excellent reports on transmit also. The loop is much quieter than an indoor dipole or wire antenna but it still will get noise if you operate in a noisy environment.

Use the largest loop as close to 1/4 wave as possible and the efficiency of the loop will be much better.

Also consider a two turn loop if you are restricted for space. Be sure to have a few inches space between the turns.

Another little secret: you can work 80M with a 32ft circumference wire loop as long as you add a high voltage capacitor (doorknob cap, or HV air variable) in parallel with the loop terminals on the tuner. Try a 150pf capacitor for starters. This extends the tuning capacity and you will be able to use the tuner lower in frequency than previously thought. A 1/8w loop at 80M is very effective especially if you can get the loop outside. Keep the loop vertical and you can operate with the tuner on a small table a few feet above the ground.

Using this tuner eventually gave me magnetic loop fever and I've built many and use them exclusively at this CCR restricted QTH.

I think this tuner is an MFJ winner and am surprised it hasn't caught on yet.

Andrew N3LCW
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