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MFJ-1792/1793 Instruction Manual

Vertical Antenna

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Summary of Contents for MFJ-1792

Page 1: ...ts Introduction 1 Description 1 Bandwidth SWR and Power Handling 2 Choosing a Location for the Antenna 3 Grounding 3 Maintenance 4 Tools and Time Required for Assembly 4 MFJ 1792 Parts List 5 Assembly and Installation Procedure 6 Raising the Antenna 11 Tuning the Antenna 12 Technical Assistance 13 ...

Page 2: ...ter wave or a shorter vertical antenna shorter than a quarter wave can go over 50 if special care is taken in constructing of the ground system and the loading method To attain an efficiency comparable with a 1 2 wave antenna in grounded antennas having heighths of 1 4 wavelength or less great care must be taken to reduce ground resistance and the resistance of any required loading inductors MFJ 1...

Page 3: ...D POWER HANDLING The 40 meter band has a very wide bandwidth approximately 800 KHz The entire band is covered at less than 1 5 1 SWR The 80 meter band is top loaded with a high Q loading coil The SWR on this band is very low less than 1 4 1 0 The bandwidth is approximately 80 KHz at 2 1 SWR measurements The lowest SWR is ensured on this band because the antenna is matched using a L network at the ...

Page 4: ...d plane hanging down until it reaches the ground then spreads out If the antenna is ground mounted it MUST be surrounded with a protective non metallic fencing This will increase the safety and lessen the likelihood of damage to the antenna GROUNDING Unlike some other verticals this antenna requires an RF ground system However it is a good idea to have some sort of earth connection to avoid lightn...

Page 5: ...ommonly sold as coax seal a pliable black sealing compound When installing any coax sealer NEVER completely cover the barrel of the coax connector The sealer should ONLY be placed near the junction of the threaded part of the chassis connector and the knurled area of the male connector This will leave the bottom of the male connector s outer sleeve open and permit the connector to breathe so it do...

Page 6: ...ing One 1 3 8 x 6 6061 T6 Aluminum tubing Two 1 1 4 x 6 6061 T6 Aluminum tubing One 1 1 8 x 6 6061 T6 Aluminum tubing One 1 1 8 x 55 6061 T6 Aluminum tubing Two 1 3 8 x 1 6061 T6 Aluminum Couplers One 1 1 4 x 1 6061 T6 Aluminum Coupler Three 3 8 solid rods one 55 threaded and two untreaded 6 for 20 meter element One fiberglass 80 meter loading coil assembly with 7 x 27 spokes One Angle Bracket to ...

Page 7: ...ly contacts any utility lines Never install an antenna near power lines 1 Be especially careful while moving or installing this antenna This antenna is bulky enough to cause a loss of balance if handled by an inexperienced person or if a capacitance spoke accidentally becomes snagged on a gutter a tree limb or any other object 2 Mount the antenna in a location completely out of reach or protect it...

Page 8: ...r the stub nuts Two 7 16 open end wrenches or wrench and one nut driver for U bolts and coupling bolts Large wire cutter for trimming capacitance spokes Safety glasses 4 Insert End B of Tube 2 into End B of Tube 1 Line up the holes Bolt tubes together with a 1 4 20 x 1 3 4 bolt 1 4 20 nut and split washer Place and secure a hose clamp over the slit See Figure 1 5 Insert End B of Tube 3 into End A ...

Page 9: ...h a 1 4 20 x 1 3 4 bolt 1 4 20 nut and split washer Place and secure a hose clamp over the slit See Figure 2 12 Insert End B of Tube 6 into End A of Coupler 3 Line up holes Bolt tube and coupler together with a 1 4 20 x 1 3 4 bolt 1 4 20 nut and split washer Slide and secure a hose clamp over the slit See Figure 2 NOTE Steps 13 16 22 and 23 are for 1793 assembly only 13 Assemble insulators to L br...

Page 10: ...r and a split washer NOTE Use the 1 4 spacer between the fiberglass rod and mount wall as shown in Figure 7 19 Insert 2 U bolts in the base mount designated holes Thread 1 4 20 nuts and split washers over them See figure iside front cover 20 Insert End B of Coupler 1 into End A of Tube 1 Insert the solid fiberglass rod into Coupler 1 Line up holes Bolt tube coupler and rod together with a 1 4 20 x...

Page 11: ...mate the length of the wire Add a few extra feet to your calculation to be on the safe side See Figure 8 NOTE It is possible to use a single set of guy lines to secure this antenna This set of guy lines can be placed on top of either the hose clamp or the 1 4 20 x 1 3 4 bolt of Tube 4 end B 25 Thread six 6 32 x 1 4 screws in the capacitor hat ring on the loading coil assembly Do not tighten them y...

Page 12: ...nd position Use the third set as a pulling wire to help raise the antenna into position 29 Insert the 10 32 x 1 3 4 screw into the hole provided on end A of Tube 6 Thread a 10 32 nut over the screw and tighten This will help to secure the loading coil 30 Slide a hose clamp over the top of the antenna Insert the base of the 80 meter loading coil into end A of Tube 6 1 1 8 tube Place the solder lug ...

Page 13: ...the lowest SWR occurs for the 80 40 and 20 meter bands The MFJ 1792 is tuned for lowest SWR either at the lower frequency of each band or slightly below NOTE Make sure to disconnect the connection to the matching network before lowering the antenna to tune the 80 or 40 meter bands Failure to do so will damage the matching network feed wire 40 Meter Band The MFJ 1792 generally does not require tuni...

Page 14: ...e trimmed 8 to adjust the antenna to resonance 20 Meter Band The 20 meter band is tuned by lengthening or shortening the threaded portion of the stubs This adjustment is very coarse If frequency is too low with the stub element extension at minimum the unthreaded end of the stub can be trimmed TECHNICAL ASSISTANCE If you have any problem with this unit first check the appropriate section of this m...

Page 15: ...MFJ 1792 1793 Instruction Manual Vertical Antenna 14 ...

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