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MFJ 1798 Manual
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MFJ 1798 Manual

Vertical antenna
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NOTE: This Drawing Is Not
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Summary of Contents for MFJ 1798

  • Page 1 NOTE: This Drawing Is Not To Scale!
  • Page 2 MFJ-1798 has a counterpoise elevation of one half wavelength on 10 meters. DESCRIPTION The MFJ-1798 is a multi-band vertical that operates on every amateur band between 80 and two meters. The inverted radiating element is constructed from heavy duty 6061-T6 aluminum tubing.

  • Page 3: Choosing A Location For The Antenna

    MFJ-1798 Vertical Antenna Instructions A small adjustable "T" section near the bottom allows adjustment of the resonant frequency of the full size radiating element on 20 meters. A three section loading coil with capacitance hats for 30, 40, and 80 meters is mounted next to the 20 meter "T"...

  • Page 4: Mounting Location

    The MFJ-1798 will perform quite well in ground mounted installations. The lower end of the antenna should be at least 5 ft above ground level. If the antenna is ground mounted, it MUST be surrounded with a protective non-metallic fencing.

  • Page 5: Maintenance

    MFJ-1798 Vertical Antenna Instructions smooth, wide, heavy conductors. This includes connecting the power line grounding rod to the feedlines ground. Never use woven flexible braiding for ground connections unless absolutely necessary. Braiding has very high resistance to both RF and lightning. Copper flashing, wide copper foil, or large gauge solid copper wires are the proper materials for use in RF and lightning grounding applications.
  • Page 6 MFJ-1798 Vertical Antenna Instructions The required tools are: 1/4" standard screwdriver 3/8" open end wrench 5/16" nut driver 7/16" nut driver 7/16" open end wrench Large wire cutters #1 Philips screwdriver #2 Philips screwdriver Eye protection Temporary mast (5-8'). Step ladder or saw horses.
  • Page 7 MFJ-1798 Vertical Antenna Instructions [ ] One balun and feedline assembly with small coil and capacitor network Group B (Hardware Bag #1) [ ] One bag of hardware containing the following parts groups: (1) Five #4 self tapping screws (4) Twenty-nine 6-32 nuts Five 4-40 x 3/8"...
  • Page 8 [ ] Quality low-loss 50-Ohm coax with PL-259 connectors to reach from antenna to transmitter. [ ] A SWR meter or Analyzer (MFJ-207, MFJ-249 or equivalent). [ ] Enough 1/8 to 3/16" nylon rope to reach the ground from the antenna's final location.
  • Page 9 MFJ-1798 Vertical Antenna Instructions After the antenna is assembled, you must double check the hardware for proper tightening and assembly. The resonant frequency and SWR can be tested with the antenna only a few feet above ground on a temporary support before raising it to the final tower or rooftop position.
  • Page 10 MFJ-1798 Vertical Antenna Instructions NOTE - A small adjustable crescent wrench can substitute for the 3/8" and 7/16" open end wrenches. IMPORTANT: Do not use a high torque electric screwdriver to mount the capacitance spokes or any of the #4 through #10 hardware.
  • Page 11 MFJ-1798 Vertical Antenna Instructions In the following steps you will refer to figure 2. Locate the following parts: One 72" long 1-3/8" tubing (A) One 72" long 1-1/4" tubing (A) One 50" long 1-1/8" tubing (A) Three 1/4-20 bolts (B1) Three 1/4-20 nuts (B3) Three 1/4"...
  • Page 12 MFJ-1798 Vertical Antenna Instructions 9- Find the end of the 1-3/8" tubing that has a 1/4" hole located around four inches from the end. Insert the solid fiberglass base insulator on the base mount into this end of the tubing. Use a 1/4" bolt to secure the tubing. Place a hose clamp over the outer end of the slit area of the tubing.
  • Page 13 MFJ-1798 Vertical Antenna Instructions Figure Refer to figure 4 for the next assembly steps. Locate the following parts: Six 6-32 x 5/8" screws (B3) Six 6-32 nuts (B4) Three small "L" brackets (C1) Five flat rectangular fiberglass stub insulators (C2) 14- With four fiberglass stub insulators and two aluminum "L"...
  • Page 14 MFJ-1798 Vertical Antenna Instructions NOTE: Make sure all brackets are assembled the in the same manner (fit on top of each other the same way). This is to help you to mount them on the same side of the antenna and keep them lined up.
  • Page 15 MFJ-1798 Vertical Antenna Instructions 21- Pass the threaded end of the rods through the holes of the first X-bracket. Thread one 10-32 nut down 2" on the threaded portion of each rod. 22- Pass the threaded rod ends through the four stub mounting holes at the outside middle of the counterpoise support plate.
  • Page 16 MFJ-1798 Vertical Antenna Instructions One 19" rod threaded one end Six black cable ties 24- Thread a #10 nut 1" in from the outer end of the 19" element. Mount the 19" element in the "2 meter element" hole of the counterpoise support plate (see page 11, figure 3). Insert the threaded end of this element into the top of the hole so it sticks out ABOVE the top of the antenna (away from the base mount and the other stubs).
  • Page 17 MFJ-1798 Vertical Antenna Instructions screws into the PEM nuts, from the outside end, of three drilled flange counterpoise clamps (Figure 6). 30- Install the four other screws by passing them through the solder lungs of the counterpoise clamp wires, then threading them into the counterpoise clamps with no flange (Figure 6).
  • Page 18 MFJ-1798 Vertical Antenna Instructions 36- Connect the black wire (from the coax center conductor) to the 2 meter Figure element by removing the #10 mounting nut and replacing it over the black wire's solder lug (see Figure 5). 37- Attach the matching network to the square support bracket (coaxial cable towards center of antenna) by inserting the 6-32 x 3"...
  • Page 19 MFJ-1798 Vertical Antenna Instructions 38- Mount the three remaining 1/4" x 6' long tubes in position using the remaining clamps. Be sure that the clamps with the drilled flange are in the innermost slots and have their flanged ends pointed outwards. Be sure the tubes are between 1/4 and 1/2 inch from the 1-1/8"...
  • Page 20 MFJ-1798 Vertical Antenna Instructions Four short capacitance hat spokes (A) Sixteen 6-32 x 1/4" screws (B2) One 30" fiberglass loading coil assembly (A) Four hose clamps (D) Warning: Only tighten the screw that fastens the loading coil terminal lugs to the capacitance hat if the ring is loose.
  • Page 21 Tighten the 6-32 x 5/8" screw to lock the rods in place (see Figure 10 on the following page). 47- The antenna assembly is now complete, it can be tested using a transceiver on low power or with an SWR analyzer such as MFJ-249 or MFJ-259. It should be tuned before mounting it in any elevated location.
  • Page 22 MFJ-1798 Vertical Antenna Instructions Figure FREQUENCY AND SWR ADJUSTMENT This antenna covers wide frequency ranges on higher bands, and narrower segments on lower frequency bands. The 40 meter band has the narrowest range of operation (approximately 40 KHz). The 80 meter band has a bandwidth of approximately 60 KHz and is the most sensitive to adjustments.
  • Page 23 MFJ-1798 Vertical Antenna Instructions If you suspect the resonant frequency is lower than your equipment can detect, for example below 3.5 MHz, take one 80 meter spoke entirely off the antenna. Make another attempt to measure the resonant frequency. If you still can not find the resonant frequency, check another band.
  • Page 24 TUNING THE ANTENNA ON LOW FREQUENCIES Measure and record the frequency of lowest SWR occurs on each band. The MFJ-1798 is tuned for lowest SWR either at or below the lowest frequency of each HF band.
  • Page 25 MFJ-1798 Vertical Antenna Instructions in frequency if (or when) the antenna is relocated. Moving the antenna higher, or farther from other objects, will usually cause an slight increase in the resonant frequency. Caution: Always tune the lowest three frequency bands in order, starting with 80 meters.
  • Page 26 MFJ-1798 Vertical Antenna Instructions 1- Measure the resonant frequency of the antenna. Determine the frequency shift required by subtracting the initial frequency from the desired frequency. Use the result to determine the proper amount to cut a spoke. 2- If the calculated amount of element shortening exceeds 10", cut one inch from the inside end of all six spokes for each 10"...
  • Page 27 MFJ-1798 Vertical Antenna Instructions TUNING 17 THROUGH 2 METERS Frequency adjustments on 17 through 2 meters are accomplished by shortening or lengthening the various stub elements. Since the counterpoise is electrically large on these bands, and the elements are full size, the bandwidths are fairly broad. This makes tuning fairly non-critical.
  • Page 28 Technical Assistance If you have any questions that the manual does not answer, please contact MFJ Enterprises. You may call MFJ toll-free at 1-800-647-TECH (8324), FAX 1-601-323-6551, or TELEX 53 4590 MFJ STKV. Outside the continental USA please call 601-323-5869. Please have the model number, date of purchase, this manual and all additional information you can supply close by the telephone.

  • Page 29: Full 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.
  • Page 30 MFJ-1798 Vertical Antenna Instructions 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. All MFJ products to be serviced in-warranty or out-of-warranty should be addressed to MFJ Enterprises, Inc., 921A Louisville Road, Starkville, Mississippi 39759, USA and must be...