MFJ MFJ-918 User manual

MFJ-918, MFJ-2919, and MFJ-2920
1.5 kW, 1.8-30 MHz Ferrite Bead Balun
Introduction: Without a balun, the outer surface of your coax shield provides a common-mode
path for transmitted RF to flow from the antenna down to your operating location. Here, it can
disrupt or damage sensitive electronics and, if severe, may even change the antenna's radiation
pattern, distort your transmit audio, or cause a painful RF burn. On receive, the process is
reversed, with stray locally generated carriers and "hash" traveling up the cable to the feedpoint
to raise the noise floor and cover weak signals.
Description: The MFJ-918, MFJ-2919, and MFJ-2920 are designed to replace the feed-point
insulator on wire antennas and provide balun protection. Rugged stainless steel eyebolts provide
the superior pull-strength needed to support a full-sized 160-Meter dipole, and the top eyebolt
accepts a center-support halyard to reduce wire strain. Two #14 stranded copper-wire pigtails
solder directly to the antenna wire for reliable conductivity. On the inside, high-permeability ferrite
beads are installed over RG-303 Teflon coax to ensure high power handling, maximum
suppression, and minimal signal loss. Thick-wall chemically welded PVC construction guarantees
long life under adverse environmental conditions, and a high-quality Teflon-insulated SO-239 at
the base provides a secure connection for your coax. Three versions are available:
[ ] MFJ-918: A 1:1 ratio 50-Ohm current balun designed to minimize losses and deliver superior
suppression over the entire HF range.
[ ] MFJ-2919: A 4:1 ratio transmission-line transformer style balun designed for 200-Ohm loads.
[ ] MFJ-2920: A 9:1 ratio transmission-line transformer design for 450-Ohm applications.
Installation:
Drip Loop
Antenna Wire
Pigtail 3-4
Turns
4-5 Turns
Solder in Place
Form
[ ] Loop 4" of wire through each eyebolt, then wrap back and twist 4-5 turns for a secure hold.
[ ] Form a drip loop in the pigtail, then wrap 3-4 turns around the antenna wire.
[ ] Solder the pigtail and antenna wire together, making sure solder flows down into the strands.
Be sure to form good drip loops -- these keep water from running into the enclosure, ensure pull
forces are supported only by the eyebolts, and prevent overheating the PVC during soldering.
Also, when possible, attach a nylon halyard to the top eyebolt to provide extra center support.
Orient the base of the balun down so water can drain from the weep hole located next to the
connector. A coat of clear nail polish or lacquer reduces oxidation of solder connections.
Important Warning: To prevent accidental death or serious injury, never install an antenna
where it can contact power lines. Also, to prevent dangerous RF burns, keep energized
antenna surfaces out of reach to humans and animals.

LIMITED 12 MONTH WARRANTY
MFJ Enterprises, Inc. warrants to the original owner of this product, if manufactured by MFJ
Enterprises, Inc. and purchased from an authorized dealer or directly from MFJ Enterprises, Inc.
to be free from defects in material and workmanship for a period of 12 months from date of
purchase provided the following terms of this warranty are satisfied.
1. The purchaser must retain the dated proof-of-purchase (bill of sale, canceled check, credit
card or money order receipt, etc.) describing the product to establish the validity of the
warranty claim and submit the original or machine reproduction of such proof of purchase
to MFJ Enterprises, Inc. at the time of warranty service. MFJ Enterprises, Inc. shall have
the discretion to deny warranty without dated proof-of-purchase. Any evidence of
alteration, erasure, or forgery shall be cause to void any and all warranty terms
immediately.
2. MFJ Enterprises, Inc. agrees to repair or replace at MFJ's option without charge to the
original owner any defective product under warrantee provided the product is returned
postage prepaid to MFJ Enterprises, Inc. with a personal check, cashiers check, or money
order for $7.00 covering postage and handling.
3. This warranty is NOT void for owners who attempt to repair defective units. Technical
consultation is available by calling the Service Department at 662-323-0549 or the MFJ
Factory at 662-323-5869.
4. This warranty does not apply to kits sold by or manufactured by MFJ Enterprises, Inc.
5. Wired and tested PC board products are covered by this warranty provided only the wired
and tested PC board product is returned. Wired and tested PC boards installed in the
owner's cabinet or connected to switches, jacks, or cables, etc. sent to MFJ Enterprises,
Inc. will be returned at the owner's expense unrepaired.
6. Under no circumstances is MFJ Enterprises, Inc. liable for consequential damages to
person or property by the use of any MFJ products.
7. Out-of-Warranty Service: MFJ Enterprises, Inc. will repair any out-of-warranty product
provided the unit is shipped prepaid. All repaired units will be shipped COD to the owner.
Repair charges will be added to the COD fee unless other arrangements are made.
8. This warranty is given in lieu of any other warranty expressed or implied.
9. MFJ Enterprises, Inc. reserves the right to make changes or improvements in design or
manufacture without incurring any obligation to install such changes upon any of the
products previously manufactured.
10. All MFJ products to be serviced in-warranty or out-of-warranty should be addressed to:
MFJ Enterprises, Inc.,
300 Industrial Park Road
Starkville, Mississippi 39759 USA
and must be accompanied by a letter describing the problem in detail along with a copy of
your dated proof-of-purchase.
11. This warranty gives you specific rights, and you may also have other rights which vary
from state to state.