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Reviews For: MFJ-935B

Category: Antenna Tuners/Matching Networks

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Review Summary For : MFJ-935B
Reviews: 13MSRP: 199
Description:
Small High Efficiency Loop Tuner
Product is in production
More Info: http://www.mfjenterprises.com/products.php?prodid=MFJ-935B
# last 180 days Avg. Rating last 180 days Total reviews Avg. overall rating
15134.4
EI3IBB Rating: 2023-02-09
Works A Lot Better Than Expected Time Owned: 6 to 12 months.
Update 9th Feb 2023

I haven't used this loop in a long time and decided to give it a go today so I set up outside in the cold on a patio table and a cup of Tea.

Using the FT-891 and just 5 watts made contact with Ham in Belarus, on 20 Meters, 2,223 Kms. Not bad for QRP.

I was using just 2 meters of 10mm soft copper pipe bent into a loop.

Once you're tuned a couple of times you get the hang of it.

The MFJ manual recommends different loop sizes for different bands.

I'm definitely going to use this loop tuner a lot more.


****Previous Review****

I got the 935C and got some 10mm diameter copper tubing from a local hardware store, cut 4 meters, 23 feet as recommended in the MFJ Manual and formed it into a loop, I hammered the ends and drilled holes and connected it to the tuner supported by my spider beam mast. The tuner also has connectors for PL-259 so you can make loops out of Coax which would be a lot easier to bring portable but the copper loop would be more efficient.

First contact 20 Watts VE3DZ, 5300 Kms away my QTH is Ireland, I was very impressed. :-) you can see this in action on my youtube channel.

https://www.youtube.com/watch?v=GgHE2hcZzHc&t=153s

Also watch Eric's, KJ4YZI, youtube channel "ham radio concepts" he uses a 26 inch bicycle rim and a tape measure!

https://www.youtube.com/watch?v=E56wIlpfZgA&t=589s

This will make a very fast to deploy antenna for portable use or even around the garden in the Summer to have something to play with while getting some Sunshine. Those in antenna restricted locations would have a lot of use for this loop tuner.

What I plan to do is see if I can split the loop in 2 or more bits to break it down easily for transport and use some type of screw system to put it back together. Aluminium would be more rigid but a little less efficient. From what I read 6061 aluminium alloy will give best performance.

It's a shame this tuner isn't in the Antenna section of the reviews.

I will update this after I do more testing but so far I am very impressed with this tuner.

K1TWH Rating: 2020-11-19
Loop tuners are stable Time Owned: more than 12 months.
I have two MFJ-933 loop tuners sitting on brackets inside my wooden toolshed in a CC&R environment. 80M tunes a 2 turn 5' by 7' loop made of 3/8" soft copper tubing. Bandwidth is about 8 KHz which allows a single setting to function on FT8 and JS8Call. The other tuner tunes another 5' by 7' loop of 1/2" soft copper on 40M JS8. Both tuners share a common feedline. The base of the loops are perhaps 30" above earth. The 933's are stable over temperature and humidity, very little drift in resonance. While this set up is less than optimal, I have enjoyed numerous chats on both bands!
K3JLS Rating: 2020-02-15
Works Great When Repaired / Modified Time Owned: more than 12 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.

The smaller tuning capacitor was shorted out (plates touching), but it worked very well after I fixed it.

I use it indoors with a 22 foot hunk of LMR-400 on a rectangular PVC stand (40 and 30 meters). I also modified it with the Phil Salas tuning indicator (google it) so that I can transmit up to 50 watts to it and then tune until the LED extinguishes. While tuning, the radio never sees an SWR above 2:1.

The next plan is to provide tuning control over coax so that I can QSY without leaving my operating position.

Also plan to add a vacuum cap to see if I can tune it up on 80 / 75 meters. If my mods work out I'll publish them on my website.

This thing has real potential.



73's - Joe - K3JLS
K2CAJ Rating: 2018-08-12
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: 2017-08-04
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.
KW4JA Rating: 2014-11-05
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: 2014-10-19
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.
73s,
AG6YK
LU1DO Rating: 2013-11-18
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.
It´s a pitty that somebody gets payed to attach a sticker on the bottom as if controlled...
WF8O Rating: 2013-10-05
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: 2012-03-01
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!