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MFJ MFJ-941EK, Instruction Manual

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MFJ MFJ-941EK Instruction Manual Download Page 12

MFJ-941EK Tuner Kit

 

 

 

Instruction Manual

 

- 11 - 

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. 
These form a triangle -- two at the rear and one in front. Spacers are mounted as 
shown below in Diagram 4: 

KEP Nut

PC Board

Spacer

Screw

Chassis

 

 

Diagram 4: PC Board Mounting 

 
[  ] Install spacers with 1/2" screws and spacer. Don't fully tighten.  
[  ] Align and install the circuit board on top of the spacers. 
[  ] Tighten the threaded spacers in place.  
[  ] Secure the circuit board on top of spacers using KEP nuts.   
 

 
 
Rear Panel Components:  

 

Coax connectors are mounted from the inside of the chassis as shown below in 
Diagram 5: 
 
 

 

 

Diagram 5: Coax Mounting

 

 

Summary of Contents for MFJ-941EK

Page 1: ...AUTION 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 Model MFJ 941EK VERSION 1A ...

Page 2: ...itional handbooks or other official publications The copy of this manual provided to the customer will not be updated to reflect current data Customers using this manual should report errors or 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: ... use muffin tins egg cartons or small paper cups to organize your parts To reduce eyestrain choose an area with strong overhead lighting and add a high intensity desk lamp for close up work Construction requires the tools listed below Soldering iron with a narrow chisel tip Soldering iron holder with a moistened cleaning sponge Your choice of leaded or lead free solder with rosin or no clean flux ...

Page 4: ... keys to strong solder MFJ 941EK Parts Inventory Use the bill of material BOM on the next page to account for all the pieces in your kit checking each part off as you go 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 compo...

Page 5: ...glass Washer 714 06125 1 6 32 x 1 4 Nylon Spacer 718 1218 0250 8 6 x 3 8 Screw Sheet Metal Black 656S 0375B A 2 6 x 3 8 Sheet Metal Screw 656S 0375A 2 10 32 x 3 32 Set Screw Hex 660 0187 SA 1 10 32 x 3 4 Machine Screw PH 660 0750 1 10 32 Hex Nut KEP 705 1032K 1 10 32 Wing Nut 705 1032S W 1 10 Solder Lug 720E 0621L 1 10 Split Lock Washer 711 1037S SL 2 10 Flat Washer 710 1050 1 1 4 ID Heyco Shaft B...

Page 6: ...citor 1kV 33 200 0033 2 1 220pF Disc Ceramic Capacitor 1kV 221 200 0220 2 5 01uF Disc Ceramic Capacitor 50 V 103 200 2100 1 3 10 pF Trim Cap Horizontal Mtg 280 2010 1 680 uH Choke blue gray brown 401 5680 1 Directional Coupler Xfmr 37 OD Toroid 10 01003 2 Schottky Diode CDSH270 or 1N270 302 0270 1 Switch DPDT Push On Push Off 504 0022 1 Switch 4PDT Push On Push Off 504 0023 1 2 1 mm PCB Power Jack...

Page 7: ...6 0201 2 12 313 pF Air Variable Capacitor 282 2006 1 3 8 OD Plastic Pushbutton Red 760 2140 1 3 8 OD Plastic Pushbutton Black 760 2122 4 1 4 ID x 1 OD Knob Black 760 0035 1 Switch 8PDT 2 Section Rotary 500 0028 1 1 2 1 mm DC Power Cable with Coax Plug 620 8321 Finally these separate bag items are bagged seperately X Qty Description MFJ Part Number 1 941E Inductor and Switch Assembly 10 13003 1 MFJ...

Page 8: ...d take a minute to survey the component side legend for various part locations When you re ready to begin construction find the five resistors listed below 2 100 ohm brown black brown 1 150 ohm brown green brown 1 3 3K orange orange red 1 47K yellow violet orange Install a 150 ohm 1 2 Watt resistor at R1 and solder Install a 3 3K resistor at R2 and solder Install a 100 ohm resistor at R3 and solde...

Page 9: ...ntify the banded end Refer to Diagram 1 Cathode End Diagram 1 Diode Orientation Install a diode at D1 with the banded end cathode toward the D1 legend Install the second diode at D2 with banded end toward the D2 legend Find the following items 1 Switch DPDT push on push off 6 pins 1 Switch 4PDT push on push off 12 pins 1 2 1 mm PCB power jack Install the DPDT switch at SW1 Confirm all pins are ful...

Page 10: ...een SW1 and SW2 and solder Install a white wire at RMTR opposite side of SW2 and solder Find the following items to construct SWR transformer T2 1 37 OD toroid with bifilar winding 1 4 Teflon shoulder bushing 1 Small brass eyelet 1 5 1 4 length of 16 buss wire Refer to Diagram 2 below Buss Wire Brass eyelet Bend Wire Over Solder to Pad T2 Shoulder Bushing BussWire Top View Install Toroid Side View...

Page 11: ...ix 6 additional 5 1 4 lengths of 16 buss wire Install a buss wire at D L and solder rear of SW4 Install a buss wire at WIRE and solder Install a buss wire at COAX2 and solder Install a buss wire at COAX1 and solder Install a buss wire at C2 and solder right front of SW4 The sixth buss wire is connected between the pc board and a tab on SW4 Refer to Diagram 3 below D L Wire SW4 Connect and Solder D...

Page 12: ...sis These form a triangle two at the rear and one in front Spacers are mounted as shown below in Diagram 4 KEP Nut PC Board Spacer Screw Chassis Diagram 4 PC Board Mounting Install spacers with 1 2 screws and spacer Don t fully tighten Align and install the circuit board on top of the spacers Tighten the threaded spacers in place Secure the circuit board on top of spacers using KEP nuts Rear Panel...

Page 13: ...1 buss wire to COAX 1 connector trim install and solder Route COAX2 buss wire to COAX 2 connector trim install and solder Route T2 buss wire to TRANSMITTER connector trim install and solder Route D L buss wire to DUMMY LOAD connector trim install and solder Find the following Ground Post items 1 10 32 x 3 4 Machine Screw PHH 1 10 32 Hex Nut KEP 1 10 32 Wing Nut 1 10 Solder Lug 2 10 Flat Washer 1 1...

Page 14: ... Nut Diagram 7 Groundpost Mounting Install a terminal post at WIRE on the back panel next to GND and secure Install two terminal posts at BALANCED LINE and secure On the pc board locate the buss lead labeled WIRE Trim and install it on the WIRE terminal post Solder Find the following components to install the 300 W 4 1 Balun 1 300 W 4 1 Balun on 1 Toroid Form 1 6 32 x 1 Machine Screw SS PH 1 6 32 ...

Page 15: ...balun over the spacer orienting leads toward the back panel Install the second 1 1 4 fiberglass washer to sandwich the balun in place Install a 6 flat washer and KEP nut Tighten but don t crush balun windings Locate B W twisted lead on balun Install on the ground post lug and solder Trim and install the white lead on either BALANCED LINE post and solder Trim and install the black lead on the other...

Page 16: ... assembly that protrudes from the back of the meter Orienting the bracket as shown gently lower the meter onto it Move into mounting position aligning meter face with the panel opening With bracket aligned on mounting holes install using two 6 3 8 SM screws Refer to Diagram 9 wiring pictorial install the 01 capacitors and hookup wire leads as shown Install a 01 uF capacitor across the and terminal...

Page 17: ...e inductor to the chassis Also note that the frame of the wafer switch will be isolated from chassis ground using fiber washers The shoulder washer centers the switch in the panel opening Shoulder Washer Flat Fiber Washer Flat Metal Washer Control Nut Inductor Switch Mounting Lugs Diagram 10 Inductor Mounting Install the fiber shoulder washer on the Inductor switch as shown above in Diagram 10 Ins...

Page 18: ...ber 1 3 8 ID x 5 8 OD Flat Washer Teflon 2 3 8 ID x 3 4 OD Flat Washer Teflon Flat 3 4 Insulating Washer Flat 5 8 Metal Washer Control Nut Flat 5 8 Insulating Washer Flat 3 4 Insulating Washer Stator Rotor Diagram 11 Capacitor Mounting Install a 3 4 fiber flat washer on one of the variable capacitors Insert the shaft at TRANSMITTER with the stator to the right side as shown in Diagram 11 From the ...

Page 19: ...r the left lead end to the switch tab adjacent to C1 at SW4 The pad at legend C1 and the exposed tab on SW4 are common to each other Connecting the buss wire directly to the switch tab is simpler than lifting the board to solder it in at C1 To complete tuner wiring find the remaining 16 buss wire Trim and install a buss wire onto the rotor tab of the Antenna capacitor Install the opposite end as a...

Page 20: ...d into the coupler Temporarily secure front set screw using an Allen wrench Install the 1 knob aligning its set screw with the flatted side of the shaft Tighten the knob in place with a 5 64 Allen wrench Rotate the switch fully counter clockwise to its stop Loosen front shaft coupler screw rotate knob to Dummy Load on the left side Re tighten the coupler set screw Rotate knob and confirm pointer a...

Page 21: ...tch Position 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 Install the black plastic pushbutton at 300W 30W range switch The tuner s cover will be installed later after testing and calibration ...

Page 22: ...tor to stator shorts With straightedge confirm inductor is at 1 8 or more below top of panels Inspect inductor No taps turns or switch wires should be shorted together Confirm meter needles both rest on zero Confirm all knob pointers are aligned correctly and turn smoothly Check pushbuttons to confirm push on push off action without sticking Meter Lamp To test the meter lamp use the 2 1 mm male po...

Page 23: ...ss 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 Avoid using low cost references with unknown specifications Also y...

Page 24: ...uner components Important Warning Do not actuate the Antenna Selector or Inductor switch with RF applied Damage to your tuner and radio may result Forward Power Setup and Bridge Null To begin calibration tune your radio to 14 200 MHz and select a mode that will deliver the radio s full rated CW output Use short 50 Ohm coaxial patch cables 3 feet or less for interconnections the shorter the better ...

Page 25: ...or 5 W 50 on the 0 60W scale If your radio will turn down to a lower power level use a 2W or 3W reference instead of 5W T Network Check This procedure checks the RF path through the T network to confirm the three main tuner components are connected properly and functional Connect your transceiver back to Transmitter Connect your dummy load and reference meter back to Coax 1 Return the range switch...

Page 26: ...ck 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 1 Antenna Switching Recheck buss wire solder connections at the various destinations Also check the swiching action of SW4 and confirm that the shaft coupler is tight...

Page 27: ...tory assistance TECHNICAL ASSISTANCE If you have any problem with this unit first check the appropriate section of this manual If the manual does not reference your problem or reading the manual does not solve your problem you may call 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 ha...

Page 28: ... option if you use a radio with a tunable PA Dummy Load Option Standard operating procedure for a radio with a tunable PA is to tune up into a 50 Ohm load before connecting it to the tuner If you re running a rig with a tube PA we recommend installing a 50 Ohm load such as the MFJ 260C permanently at Ext Dummy Load Then use this setup procedure Set the Antenna Selector to Bypass Dummy Load Tune yo...

Page 29: ...ut of the tuner s RF path Selects between two coax lines a single wire feed and a dummy load If your transceiver has a tunable PA you ll want to use the Dummy Load port in conjunction with an external 50 Ohm load However for solid state radios with fixed 50 Ohm output you may elect to use Dummy Load for a third coaxial fed antenna the RF path is the same as for Coax 1 and Coax 2 To accommodate lad...

Page 30: ...setting capacitors fully meshed 0 for 160 and 75 meters 3 4 meshed 2 5 for 60 20 meters and 1 2 meshed 5 0 for 20 10 meters before starting to tune Once the capacitors are pre set find a staring point for the Inductor control by listening in receive mode and finding the switch position that yields the strongest background noise After the Inductor switch is set for highest background noise apply a ...

Page 31: ...e 4 1 Balun The 4 1 balun transforms loads connected at the Balanced Line terminal posts from Zin to Zout 4 and converts the signal path from balanced to unbalanced Thus a 200 Ohm load will be transformed to 50 Ohms SWR 1 1 and a 400 Ohm load will become 100 Ohms SWR 2 1 BALANCED LINE WIRE GND Install Jumper By switching in the T network it s possible to correct most but not all mismatches you mig...

Page 32: ...hat is close to an odd multiple of an electrical quarter wave Never center feed a full wave doublet with a balanced line that is close to an even multiple of an electrical half wave If the tuner won t match a multi band antenna on a particular band change your feedline length by 1 8 wavelength as calculated for the affected band Never attempt to load a G5RV on a band below its half wave design Bet...

Page 33: ...01 R3 100 R4 100 C3 33 pF REF FWD R5 50K R6 50K R7 50K R8 50K 47K R9 SW2a SW2b SW4 L A SW3a SW3b Coax 2 Coax 1 Ext Dummy Load Bal Line Ground Wire 4 1 Balun Inductor Transmitter Antenna 12 313 pF Transmitter Antenna Selector 60W Cal 6W Cal 60W Cal 30W Cal 300W 01 01 SW1a Meter Lamp 01 Power 6W 300W 30W Directional Coupler B C D E F G H I J K L1 D1 D2 C1 C2 Null ...

Page 34: ...MFJ 941EK Tuner Kit Instruction Manual 33 NOTES ...

Page 35: ...be provided to cover postage and handling 4 This warranty is NOT void for owners who attempt to repair defective units Technical consultation is available by calling 601 323 5869 5 This warranty does not apply to kits sold by or manufactured by MFJ Enterprises Inc 6 Wired and tested PC board products are covered by this warranty provided only the wired and tested PC board product is returned Wired...

Page 36: ...MFJ 941EK Manual Version 1A Printed In U S A 300 Industrial Park Road Starkville MS 39759 ...

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