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Reviews Categories | Antenna parts, accessories, incl. baluns, hardware, etc. | MFJ 912 4:1 W9INN Balun Box Help


Reviews Summary for MFJ 912 4:1 W9INN Balun Box
Reviews: 16 Average rating: 4.2/5 MSRP: $69.95
Description: Use coax from antenna tuner to MFJ-912 mounted outside. MFJ-912 converts unbalanced coax to balanced transmission line (ladder).
Giant 2-core 4:1 balun wound with Teflon wire connects to high voltage ceramic feedthru insulators.
Handles full legal limit with ease. SO-239 connector.
Product is in production.
More info: http://www.mfjenterprises.com/products.php?prodid=MFJ-912
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NG0Z Rating: 3/5 Apr 27, 2014 10:41 Send this review to a friend
Not Impressed  Time owned: 0 to 3 months
I spent a little more on this unit at the suggestion of my friends at Radio City here in Minnesota to have a balun for my custom NI4L 200' dipole with a ground lug and to handle my future power needs when I add an amp to my shack.

The antenna lugs come loose inside the unit so that when you try to tighten down the antenna on the outside, the insulators and the inside end turns with it. I have had to take it apart twice to tighten them. Next time I will add better lock-washers and loctite but this should not be necessary for an $80 balun.

Furthermore, when I took it apart I noticed one of the four screws holding the metal housing together was a mismatch, which led me to believe there is shoddy quality control in the manufacture of this product.

I have had good luck with MFJ otherwise and will certainly consider an Ameritron amp down the road but can't recommend this unit.

73

NG0Z
 
KT4EP Rating: 5/5 Dec 16, 2011 07:02 Send this review to a friend
Outdoor mounting  Time owned: 6 to 12 months
Not to start an issue, but the instructions that came with this product state: "It provides a convenient method of feeding balanced transmission lines remotely without actually bringing the line into the house". And this - "..it is not water-proof, so under the eaves of the house would be a good location". Finally, the instructions come with a diagram showing the box on the outside of a house with coax going into the house to the tuner.

It's sold/billed/ promoted for exterior use.

My old MFJ tuner I bought in 1992 and my new one, both have a connection for balanced line directly to the tuner because they have 4:1 baluns inside so why use the 912 at the tuner, of course unless the tuner has no built in 4:1 device.

So... I have my 912 under the eave out of the weather, I sealed it with RTV sealant but left a few spots for air to get inside, I replaced the washers as mentioned, and it's working fine for me.
 
W1MCE Rating: 5/5 Dec 15, 2011 07:35 Send this review to a friend
Excellent when used as designed  Time owned: months
I am a retired Aerospace Engineer. I have used the W9INN balun for over 10 years with absolutely zero issues. It is not designed for outdoor installation! When installed indoors it easily handles 1 KW at a ~30:1 VSWR [that is thirty to one] using 600 ohm open wire feeders. Mine is mounted directly at the output of the tuner [Murch 2000A].
 
KT4EP Rating: 4/5 Nov 11, 2011 17:01 Send this review to a friend
follow up to last post  Time owned: 3 to 6 months
I bought stainless washers and wing nuts, replaced, used some RTV on the open areas of the box, glued the white insulator posts, and put it back up and into use. Should not have to re-work a piece of gear like that. I have bought a lot of stuff from MFJ and things do fall thru the cracks, and again, I will continue to buy their products but use EHam for reviews,
cul
ar
KT4EP
 
N4UED Rating: 1/5 Jan 10, 2011 05:30 Send this review to a friend
DONT EXPECT A LONG HAUL.  Time owned: more than 12 months
POOR DESIGN.

THE SCREWS THAT ARE SUPPOSED TO HOLD THE LADDERLINE IN PLACE WORK THEMSELVES LOOSE.

NOT JUST FROM THE LADDERLINE, FROM THE BALUN ITSELF.

THIS HAS HAPPENED TO ME TWICE.

I HAD TO HOT GLUE THE CONNECTERS TO THE METAL CABNET SO THEY WOULD NOT COME OUT.

PLEASE DONT WAIST YOUR MONEY. BUY A BALUN DESIGN BALUN.

I HAVE FOUR BALUN DESIGN BALUNS IN USE AND THEY ARE GREAT.

THANKS,

CHUCK N4UED
 
W1KQ Rating: 5/5 Oct 19, 2009 07:54 Send this review to a friend
MFJ-912 4:1 W9INN Balun  Time owned: more than 12 months
I've been using these for a few years now. One on a homebrewed Cobra dipole made with 12 AWG 12-2 Romex fed with 450 ohm ladder line and the other more recently with a 200 dipole fed with 450 ohm ladder line. I don't see a need to mark down the rating because the hardware may rust and the item is not waterproof. A little liquid electrical tape here makes it water proof. After a few New England Winters they are still going strong. Just worked K4M this morning on 40 cw...1200 watts.
 
K8KAS Rating: 3/5 Mar 20, 2009 10:12 Send this review to a friend
MFJ at its best  Time owned: more than 12 months
How could you sell something made to service outdoors and use steel hardware. I had to replace the steel bolts and nuts with brass after 6 months. It cost me a whole $3 bucks, How can you sell stuff like this for outdoor use and use crap hardware, Anyone would pay a buck ot two more to have the job done rite..OH well its MFJ right.
 
W5VK Rating: 5/5 Aug 7, 2008 15:24 Send this review to a friend
Works fine  Time owned: more than 12 months
I've used mine two years with a 135' center fed dipole with 100' of 300 ohm ladder line. It has worked OK w/ about 10' of coax to a tuner. It handled about 800 watts w/o a problem.
 
N3DOK Rating: 4/5 Apr 5, 2008 13:46 Send this review to a friend
MFJ Explains it in the Manual  Time owned: more than 12 months
Hi,
I have used the MFJ-912 with good results. I sealed the connections with Vapor Wrap. Remove Vapor wrap,metal and wire are clean. No rust. You have to use at least RG-8 or larger in coax cable. Antenna 135 ft flat top.

MFJ-912 W9INN BALUN BOX INSTRUCTIONS
INTRODUCTION
The MFJ-912 W9INN BALUN BOX is a broadband (1.8-30 MHz) toroidal balun. It
provides a convenient method of feeding balanced line transmission lines remotely
without actually bringing the line into the house.
The MFJ-912 is basically a 1:4 impedance transformer which converts an unbalanced
output to a balanced output.
The impedance present at the balun where the balanced line is attached can be extremely
high depending on the frequency of operation and the length of the transmission line. In
light of this fact, use as large of coax as possible, at least RG-8/U or RG-8X/U. Keep the
ends of the ceramic standoffs at least two inches away from any conducting surface.
Another thing about the coax is that almost all losses will be within it. The beauty of
running ladder line is its extremely low loss. There will still be impedance mismatches in
the coax and thus, high losses. Use as short a length of coax as possible, 50 feet or less.
With 50 feet or less of RG-8/U or RG-8X/U, losses at the lower frequencies are
negligible.
INSTALLATION
1. Mount the remote balun in a convenient location. The MFJ-912 is not waterproof,
so under eves of a house would be a good location. This places it out of the way of
children, but still serviceable without any trouble.
2. Connect the balanced line to the two ceramic standoffs. That is, connect one side of
the balanced line to one standoff, and the other side to the other standoff.
3. Connect the coax to the SO-239 connector on the balun.
4. Connect the other end of the coax to your tuner.
5. Tune the tuner in the normal way for minimum SWR.
6. Use the grounding wing nut at the bottom of the balun to ground of the balun. Both
sides of the balanced line have continuity to ground so grounding the box will
ground the system.
NOTE: This system requires a wide-range tuner such as the T-network MFJ tuners. If
you need a tuner, MFJ has a complete line of T-network tuners suitable for use
with the MFJ-912.
 
KW4N Rating: 5/5 Apr 5, 2008 12:19 Send this review to a friend
Fine Product at Good Price  Time owned: more than 12 months
Given to me by a ham friend(SK) I compared it to a hundred dollar unit and it does an equal job at a KW of CW on a CF Zepp of 101' and 30-10 vertical dipole...both fed with open wire line. Cable or balun did not run hot.

Instructions state to mount under an eave because the unit is NOT waterproof. Mechanically strong. Tightly wound coils on two big cores that are well wrapped. Solder joints mechanically strong
and well soldered. No extra backing plate at extra cost required for wall mounting.

It's a 4:1 VOLTAGE balun. If in doubt, take the cover off and look at the windings.

If it's a voltage balun at 4:1 your looking for, this is a fine unit at a good price. Verify this unit is appropriate for your application because in many instances a 1:1 current balun will do a better job.
73's, Dave
 
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