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| Reviews Summary for MFJ 912 4:1 W9INN Balun Box |
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Reviews: 13
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Average rating: 4.4/5
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MSRP: $69.95
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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.
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More info: http://www.mfjenterprises.com/products.php?prodid=MFJ-912
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write your own review of the MFJ 912 4:1 W9INN Balun Box.
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W1KQ
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Rating: 5/5
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Oct 19, 2009 07:54
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MFJ-912 4:1 W9INN Balun
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Time owned: more than 12 months
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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.
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N4UED
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Rating: 5/5
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Jun 9, 2009 13:58
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GREAT BALUN FOR THE BEST PRICE,QUALITY!
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Time owned: more than 12 months
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I HAVE OWNED THESE BALUNS SINCE I WAS A NOVICE IN 1988.
THE ONLY THING IS THAT YOU MUST SECURE THE BALUN TO A STUCTURE SUCH AS A BOARD IF MOUNTING OUTSIDE.
ALSO WATER SEAL IT AND STOP ARGUING ABOUT THE BALUN.
REPLACE THE SCREWS OR LUBURICTE THEM WITH A QUALITY SEALANT IF YOU ARE GOING TO LEAVE IT AND NEVER LOOK AT IT AGAIN.
IF YOU ARE GOING TO BRING THE LADDERLINE TO THE BRINK OF YOUR HOUSE, JUST ATTACH THE BALUN TO SOMETHING TO SUPPORT IT.
MINE HAS WORKED GREAT FOR SO MANY YEARS.
1500 WATTS IS HANDLES WITH EASE.
YOU WANT BE DISAPPOINTED.
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K8KAS
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Rating: 3/5
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Mar 20, 2009 10:12
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MFJ at its best
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Time owned: more than 12 months
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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.
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W5VK
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Rating: 5/5
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Aug 7, 2008 15:24
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Works fine
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Time owned: more than 12 months
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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.
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N3DOK
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Rating: 4/5
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Apr 5, 2008 13:46
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MFJ Explains it in the Manual
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Time owned: more than 12 months
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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.
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KW4N
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Rating: 5/5
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Apr 5, 2008 12:19
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Fine Product at Good Price
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Time owned: more than 12 months
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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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K8KAS
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Rating: 3/5
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Jan 12, 2007 14:53
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Crappy Hardware
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Time owned: more than 12 months
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I owned one for two years, works fine at 1500 watt power levels. However in good old MFJ fashon all of the nuts/bolts rusted and were impossiable to loosen. I spent time with a Dremal Tool cutting them away and then went to Ace Hardware and replaced them with brass for about $2 bucks. What a joke, what would this add to the cost to use a non-corrosive brass nut and bolt. It's made to be mounted outside right? MFJ what a joke.
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N4CEB
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Rating: 5/5
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Jan 12, 2007 13:19
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balun is a balun
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Time owned: 6 to 12 months
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Whats the difference?...a 4:1 balun is a 4:1 balun...it is actually a impedance transformer meant to transform a ladder line from high impedance to 50Ohms. I love mine...it handles full power and transforms my 200 ohm line to 50 ohms for a 1:1 match.
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SAHLBOM
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Rating: 3/5
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Jan 2, 2007 13:11
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NOT a Current Balun
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Time owned: 0 to 3 months
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A dealer sold me the MFJ-912 W9INN Balun as a current balun, but it is definitely configured as a VOLTAGE balun. MFJ's spec doesn't say either way.
For a detailed test of current versus voltage baluns see the experiments at the end of Roy Lewallen's article at:
http://www.eznec.com/Amateur/Articles/Baluns.pdf
I see no reason anyone would want a voltage balun for an antenna application. It certainly isn't a good match for my 272' loop antenna fed with ladder line.
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W4EPA
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Rating: 5/5
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Feb 12, 2006 07:21
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Great performer!!
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Time owned: more than 12 months
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Have used this balun for over 7 years. Used with a 260 foot dipole, 12 guage wire up at 55 feet in center and 30 feel on sides and 67 feet of 450 ladder line feeding from the balun to the dipole. The balun is located under the house eaves and grounded with 10 guage wire to a ground post.. From the balun to the rig I use 28 feet of RG8 coax to eliminate the rf in the shack. This to a Palstar 1500 tuner and a Kenwood 950sd rig.
The Balun when grounded at the balun location not the rig eliminates any rf in the shack and seems to balance the 450/50 ohm match well. So this 260 foot dipole works well on all bands from 10 to 160. Some difficulty on 15 but get great reports on all bands. Does collect fire ants though. (Figure why?) What a great hobby and what a great way to meet some great people.
73 All. Jim W4EPA Social Circle, GA
NOTE: Antenna works great Has been dubbed a WAG system that works (Wild A-- Guess antenna!!!!!)
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