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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.
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N4CEB Rating: 5/5 Jan 12, 2007 13:19 Send this review to a friend
balun is a balun  Time owned: 6 to 12 months
Whats the difference?...a 4:1 balun is a 4:1 is actually a impedance transformer meant to transform a ladder line from high impedance to 50Ohms. I love handles full power and transforms my 200 ohm line to 50 ohms for a 1:1 match.
SAHLBOM Rating: 3/5 Jan 2, 2007 13:11 Send this review to a friend
NOT a Current Balun  Time owned: 0 to 3 months
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:

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.
W4EPA Rating: 5/5 Feb 12, 2006 07:21 Send this review to a friend
Great performer!!  Time owned: more than 12 months
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!!!!!)
K6XR Rating: 5/5 Feb 12, 2006 07:00 Send this review to a friend
Grounds the system  Time owned: more than 12 months
I have used the w9inn balun for several years and I have spoken personally to w9inn (he has passed on)and he explained to me that he designed the balun and gave the rights to MFJ. He stated that it was a voltage balun and that when grounded from the ground lug, it grounded the whole system. that is the only ground I use and it works fine with 450 ohm ladder line to an EDZ for 20 meters. I use both a manual tuner, the mfj 986, the mfj 974hb, the mfj-993, and elecraft T1 with it and no problems with any of them. The Balun works well. I compared it with the Radio works current remote balun and could tell no difference in performance.
AC0DV Rating: 4/5 Feb 12, 2006 03:01 Send this review to a friend
Got rid of RFI  Time owned: 0 to 3 months
Just installed this balun for a 290' full wave horizontal loop. (Loop Skywire)

I have a "voltage" balun inside my MFJ 949E tuner... for balanced line.. but I got RFI when using it... and everything I read says a current balun is better... so I opted for this balun and 10-15' of coax from outside my window to the rig. (And it's heavier duty than the tiny balun inside the tuner.)

Seems to work great... although I moved it today and put it into a plastic container since it's not waterproofed.

Concerning the ground lug... I'm not sure what the manual or the last reviewer was saying... the manual says: "Both sides of the balanced line have a continuity to ground so grounding the box will ground the system".

The last reviewer says:

"There is a ground nut on the Balun wich makes is possible to ground the whole antenna system from that point - but i did not -i diddent want my coax to be the direct carrier of ground currents from the tuner and rig, so i gounded the rig instead. IÂŽam very satisfied and recommend it."

What is the difference? What does he mean by "ground currents from the tuner and rig"?

From the rig the coax should be grounded... no? And so the ground would be through the coax up to the balun? So if you ground at both points is that not BETTER? Better RFI reduction?

Or am I missing something about "grounding the system?"

--Keith -- AC0DV
OZ1HTH Rating: 5/5 Nov 9, 2004 01:20 Send this review to a friend
Does the job  Time owned: 0 to 3 months
I have used the MFJ 912 balun for a month and it does a great job. First of all, its NOT waterproof, and got to be mounted under the roof or where its not exposed direct to rain. I my case that was not a problem (there are holes to fit screws in), its well crafted and specially i like the two big ceramic insulators cause they gives you a very good and safe connection of the ladder line. The coax fits on to the SO239 connector. I have about 4 meters of 50 Ohms coax and 20 meters of US-Wireman 450 Ohms ladderline and in the end of that a 40 meters vertically feed Delta loop, and its working perfectly. No TVI/RFI at all, no matter what band iŽam working on from 40 meters up to 10 meters. No indication of losses is registred, and having a good "ragchew" at full power doesent make the balun warm or changes the SWR.
There is a ground nut on the Balun wich makes is possible to ground the whole antenna system from that point - but i did not -i diddent want my coax to be the direct carrier of ground currents from the tuner and rig, so i gounded the rig instead. IŽam very satisfied and recommend it.
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