MFJ RF Isolator Balun MFJ-915 Choke For Ham & CB Radio HF Antennas

easy to install , helped greatly

Does absolutely nothing. Waste of money and time.

Worked fantastic. In y opinion it was a good choice.

I’ve got 1 in my shack and 1 outside connected to my G5RV. I am very happy with the performance off this balun. If using outdoor in the weather, then you must seal the balun.

The simplest possible isolation choke - a bunch of toroids strung on a length of coax, inside a piece of plastic sewer pipe for physical protection. Thus, its insertion loss is very low, and there is no chance for mis-winding, etc., during construction. MFJ is notorious for poor quality control, and I've read of a few of these needing repair by purchasers, but I've bought 3 so far and all were mechanically and electrically good (no loose screws,no loose glued endcaps, and no sign of poor soldering to the connectors inside when I did electrical tests.Test #1: very low DC resistance end-to-end on center and shield and not shorted either. Test #2: running over the entire HF band up to 30 MHz, testing them with an antenna analyzer and a 50 ohm resistive load, they show essentially no reactance (1:1 SWR or very close). As you get into the low VHF, things start to fall apart a bit (usable up to maybe 6 meters as I recall). A Balun Designs isolator, built with a single wound toroid, did just about as well. Another brand, (which I won't mention) with a single wound toroid of the same design, started misbehaving between 7 and 14 MHz. I'd not use that one above the 20 meter band, and it was marginal there (1.3:1 or more SWR, JUST DUE TO THE ISOLATOR, from its reactance.Finally, using a portable antenna notorious for feedline RF, (always changing SWR as I touched the radio, etc.) - an MFJ-915 at the radio stopped that (and likely would have stopped RF burn too, if my power levels were high enough for it to be a problem).Yes, it's MFJ - but it is so simple that even THEY (usually) can't screw it up!NOTE: the SO-239's on each end are mounted inside the end-cap, and stick though a drilled hole. Thus, they are somewhat recessed. Depending on the PL-259's on the end of your cables, it can be a little bit of a tight fit, getting them fully tightened. None I've found are too bulky to tighten (which would require some reaming of the end-cap hole to fix), but a couple were close, so MAYBE it could happen with some really large ones with big knurled rings.

I used this to in prove the tuneup on a Windom short antenna. It worked as expected. Others have complained about the build quality. Mine was just fine. I am going to miss MFJ.

It does what it is supposed to do. I have never had stray RF leak past this device, and I have used several of them. The only complaint I have is that one was shipped to me with a missing screw on the connector, so it was a bit loose. These cannot be disassembled, so I just used it that way. It doesn't affect the electrical characteristics of the device, it's just poor QC.DX Engineering makes a similar device that is built into an aluminum case, and its build quality is higher. But it also three times the price. For a good choke on budget, this is a good choice. For high power applications (e.g., 1kW or more), I would go with the DX Engineering part.