MFJ -941EK Instruction Manual
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MFJ -941EK Instruction Manual

Mfj tuner kit instruction manual
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Model MFJ-941EK
INSTRUCTION MANUAL
CAUTION: Read All Instructions Before Operating Equipment
MFJ ENTERPRISES, INC.
300 Industrial Park Road
Starkville, MS 39759 USA
Tel: 662-323-5869 Fax: 662-323-6551
COPYRIGHT
2013 MFJ ENTERPRISES, INC.
C
VERSION 1A

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  • Page 1 Model MFJ-941EK INSTRUCTION MANUAL CAUTION: Read All Instructions Before Operating Equipment MFJ ENTERPRISES, INC. 300 Industrial Park Road Starkville, MS 39759 USA Tel: 662-323-5869 Fax: 662-323-6551 COPYRIGHT 2013 MFJ ENTERPRISES, INC. VERSION 1A...
  • Page 2 Customers using this manual should report errors omissions, recommendations for improvements, or other comments to MFJ Enterprises, 300 Industrial Park Road, Starkville, MS 39759. Phone: (662) 323-5869; FAX: (662) 323-6551. Business hours: M-F 8-4:30 CST.

  • Page 3: General Information

    General Information: This manual contains all the information you'll need to build, calibrate, and use your new MFJ-941EK Versa-Tuner II kit. The Versa-Tuner II is actually four very useful station accessories combined into one package. The first is MFJ's wide- range 300-Watt T-network that can match virtually any HF antenna you're likely to encounter.
  • Page 4 If there's a missing or damaged item, write down the MFJ part number and contact MFJ for replacement (see Warranty page for instructions). Most parts are packed in three plastic bags -- one for small hardware items, one for pc-board components and pre-cut wire, and a third for larger parts.
  • Page 5 MFJ-941EK Tuner Kit Instruction Manual INVENTORY Begin your inventory with the hardware bag. For identification purposes, PH = Phillips Head, SM = Sheet Metal Screw, SS = stainless steel, KEP = nut with an integral lock washer, OD = Outside Diameter, and ID = Inside Diameter.
  • Page 6 MFJ-941EK Tuner Kit Instruction Manual INVENTORY Next, inventory the circuit board bag containing small pc-board components and pre-cut wire. Color codes and number codes are included to help you sort resistors, capacitors, and chokes. Qty Description MFJ Part Number 100Ω 1/4W Resistor (brown, black, brown) 100-2100 150Ω...
  • Page 7 Finally, these separate bag items are bagged seperately. Qty Description MFJ Part Number 941E Inductor and Switch Assembly 10-13003 MFJ-941E Aluminum Chassis 800-0941E MFJ-941E Front Panel Decal (pre-installed) 782-0941E Rubber Feet (pre-installed) 770-1162 MFJ-941E Chassis Cover, Black 804-0941E Assembly and Operating Manual...

  • Page 8: Circuit Board Assembly

    MFJ-941EK Tuner Kit Instruction Manual CONSTRUCTION Key Assembly Instructions: Key words are used to shorten the length of the assembly steps to one line. Find means to pull specific items from the parts inventory for installation. Identify means to look for a mark or feature that orients the part for installation. Install means to clean leads, insert them at a specified location, and bend or wrap them so the part stays in place.
  • Page 9 MFJ-941EK Tuner Kit Instruction Manual CONSTRUCTION [ ] Install 220 pF at C5 and solder. [ ] Install .01 uF at C6 and solder. [ ] Install .01 uF at C7 and solder. Find the 3-10 pF trimmer capacitor (white ceramic, ~1/2" OD, 3 pins).

  • Page 10: Side View

    MFJ-941EK Tuner Kit Instruction Manual CONSTRUCTION Find the six (6) pre-stripped 5" lengths of jacketed hookup wire: (3) Black (1) Red (1) White (1) Violet [ ] Locate three holes marked Ground on the edge of the pc board near R8.
  • Page 11 MFJ-941EK Tuner Kit Instruction Manual CONSTRUCTION [ ] Locate the pc legend for T2. [ ] On the solder side, install the brass eyelet through the T2 pad, as shown. [ ] Solder the eyelet flange in place, but do not fill the opening with solder.

  • Page 12: Pc Board Installation

    MFJ-941EK Tuner Kit Instruction Manual CONSTRUCTION PC Board Installation: Find the MFJ-941E chassis. Also, find the following hardware items: (3) 4-40 x 1/2" Machine Screw (3) 4-40 x 1/4" Threaded Aluminum Spacer (3) 4-40 Hex Nut, KEP (nuts with lock washers) Locate the three circuit board mounting holes on the bottom of the chassis.
  • Page 13 MFJ-941EK Tuner Kit Instruction Manual CONSTRUCTION Find the following coax connector items: (4) SO-239 female chassis-mount coaxial connector (8) 4-40 x 3/8" Machine Screw (8) 4-40 Hex Nut, KEP (nuts with lock washers) [ ] Install a connector at COAX 1 and tighten hardware.

  • Page 14: Groundpost Mounting

    MFJ-941EK Tuner Kit Instruction Manual CONSTRUCTION [ ] Install the split lock washer. [ ] Install the wing nut (loosely). From the larger parts bag, locate the three red plastic insulated terminal posts. Confirm that each one has a mating lock washer and nut. Install according to Diagram 7.
  • Page 15 MFJ-941EK Tuner Kit Instruction Manual CONSTRUCTION On the chassis, locate the balun transformer mounting hole (approximately 2" in front of the terminal posts and ground post). Refer to Diagram 8 below: KEP Nut Metal Washer 4:1 Balun 1-1/4" FG Washer 1/4"...
  • Page 16 MFJ-941EK Tuner Kit Instruction Manual CONSTRUCTION Refer to Diagram 9 below during meter installation. Locate the adhesive foam-tape pad adhered to the rear of the meter assembly. This pad is installed to cushion the meter bracket and provide tension. Do not...
  • Page 17 MFJ-941EK Tuner Kit Instruction Manual CONSTRUCTION Find the following parts for installation of the tapped tuning inductor: (1) Tapped Air-Wound Inductor and Switch Assembly (1) 3/8" Hex Control Nut, Panel Mount (1) 3/8" ID x 5/8" OD Flat Washer, Metal (1) 3/8"...
  • Page 18 MFJ-941EK Tuner Kit Instruction Manual CONSTRUCTION Like the Inductor switch, the Transmitter and Antenna tuning capacitors are isolated from the chassis by non-conductive washers. The Transmitter control uses fiber washers and the Antenna control uses Teflon washers. Find the following items: (2) 12-313 pF air-variable capacitors (2) 3/8"...
  • Page 19 MFJ-941EK Tuner Kit Instruction Manual CONSTRUCTION Looking at the coil assembly, you'll see that the top winding has been cut and is isolated from the remainder of the coil. This wire is used to connect the stator of C1 to the pc board. It will be pulled back from the two front retainer rods and...
  • Page 20 MFJ-941EK Tuner Kit Instruction Manual CONSTRUCTION Tuner wiring is now complete. Before going on, check all solder connections and hardware for security. The next stage is final assembly. Find the following items to complete the Antenna Selector Switch assembly: (1) 1/4" ID Heyco Nylon Shaft Bushing (1) 1/4"...
  • Page 21 MFJ-941EK Tuner Kit Instruction Manual CONSTRUCTION "A" Switch Position Common Ring Contact Selector Diagram 13: Switch Alignment [ ] Align contacts and install a 1" knob at Inductor with the pointer at "A" . [ ] Install the red plastic pushbutton at Lamp On-Off.

  • Page 22: Test And Calibration

    MFJ-941EK Tuner Kit Instruction Manual TESTING Test and Calibration: These procedures require the following items: (1) 100-Watt HF transceiver with adjustable RF-power output (1) Accurate Wattmeter (Bird with 100H slug or calibrated digital meter) (1) Accurate 50-Ohm dummy load (100-Watt rating or higher) (1) Porcelain or plastic light socket with pigtail attached (1) 40-Watt incandescent "appliance"...

  • Page 23: Power Meter Calibration

    [ ] Connect VOM leads across the Balanced Line terminals and confirm continuity. Power Meter Calibration: The accuracy of your MFJ-941E SWR/wattmeter depends on the reference standard you use for calibration. A Bird through-line wattmeter with a 100H slug (100-W) is probably the best choice. A high-quality digital meter with certified accuracy will also work well.
  • Page 24 MFJ-941EK Tuner Kit Instruction Manual TESTING The calibration procedure is conducted on 20 Meters at 14.200 MHz. For radios equipped with analog RF-output controls, start each test run at minimum power and turn it up to the prescribed level while watching your reference power meter.
  • Page 25 MFJ-941EK Tuner Kit Instruction Manual TESTING [ ] Reduce transmit power to 20W. [ ] Change the range switch to 30W (button out). [ ] View Forward scale and apply power. Set R7 for 20W (200 on 0-300 scale). Reflected Power Setup: This procedure uses the same setup, except the Transmitter and Coax-1 connections are reversed to measure reflected power.

  • Page 26: Installing Cover

    [ ] Find eight (8) 3/8" x 6-32 black sheet metal screws and install. In Case of Difficulty: As noted in the introduction, the MFJ-941E is really four station accessories in one package. If difficulty arises during testing, the problem can likely be isolated to one of them.
  • Page 27 MFJ Technical Service at 662-323- 0549 or the MFJ Factory at 662-323-5869. You will be best helped if you have your unit, manual and all information on your station handy so you can answer any questions the technicians may ask.
  • Page 28 MFJ-941EK Operating Instructions General Installation Suggestions: As its "manufacturer", you are now quite familiar with the MFJ-941EK, its four basic station-accessory functions, and the location of all the controls, jacks, and switches. Acquiring this kind of inside-out knowledge is one of the true benefits...
  • Page 29 MFJ-941EK Tuner Kit Instruction Manual OPERATING INSTRUCTIONS To measure forward and reflected power: [ ] Select the desired forward power range (300W or 30W) and transmit a carrier. [ ] View the Forward scale to read incident power. [ ] View the Reflected scale to read reverse power.
  • Page 30 MFJ-941EK Tuner Kit Instruction Manual OPERATING INSTRUCTIONS less inductance at high frequencies. Rotating the knob clockwise -- from A toward L -- progressively decreases inductance and increases the tuner's operating frequency. [ ] The Transmitter and Antenna capacitors deliver maximum capacitance at "0"...
  • Page 31 MFJ-941EK Tuner Kit Instruction Manual OPERATING INSTRUCTIONS [ ] Logging regularly used tuner settings is useful for two reasons. First, it speeds your setup time considerably. Second, it will alert you right away if something has changed out at the antenna site.
  • Page 32 MFJ-941EK Tuner Kit Instruction Manual OPERATING INSTRUCTIONS Fixing Problem Antenna Systems: The feedpoint impedance for most antennas you'll encounter will swing rapidly toward some high or low extreme as you move away from resonance. By the same token, depending on electrical length, the transmission line may take those...
  • Page 33 MFJ-941EK Tuner Kit Instruction Manual SCHEMATIC MFJ-941EK Schematic Diagram: Transmitter Directional Coupler Null 33 pF 3-10 pF Coax 2 Antenna Selector 220 pF SW3a SW3b Coax 1 12-313 pF 3.3K 1/2W Dummy Load Transmitter Antenna CDSH CDSH Wire Cal-6W Cal-30W...
  • Page 34 MFJ-941EK Tuner Kit Instruction Manual NOTES - 33 -...

  • Page 35: Full 12 Month Warranty

    MFJ Enterprises, Inc. at the time of warranty service. MFJ Enterprises, Inc. shall have the discretion to deny warranty without dated proof-of-purchase.
  • Page 36 MFJ-941EK Manual 300 Industrial Park Road Version 1A Starkville, MS 39759 Printed In U.S.A.

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Versa-tuner ii

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