Diagram of MFJ 1798 PDF format.

After deciding, I talked with MFJ about doing a review on their antenna, The following is an excerpt from my letter to them.

MFJ agreed to the terms, and I was to pick the antenna at Dayton.

As I was leaving Mr. Jue made the comment, " If you have any problems give us a call and we will help in any way we can". This was very refreshing coming the president of the company.

Theory of Design    from MFJ 1798 Instruction manual

"The MFJ-1798 is an 80 through 2 meter ground independent vertical antenna.  This antenna has several unique features including an inverted radiating element, a fully elevated counterpoise, lumped constant end loading, and linear Stub decoupling.   These unique features eliminate the traditional problems encountered in ground independent mulit-band vertical designs.

Established antenna theory dictates that maximum radiation occurs in the high current portion of the antenna.  While conventional antennas generally place the highest current at the bottom or center of the radiating element, the MFJ-1798's unique design places the highest current and the maximum radiation point at the very top of the radiating element.  This feature produces the lowest wave angle possible for a given antenna height, and elevates the radiating section away from the lossy earth.

It is a well-documented fact that bending or folding a radiating element at a high current point reduces antenna system efficiency.  The MFJ-1798 eliminates all bending or folding of the important high current areas by using linear decoupling stubs on frequencies above 14 MHz.  These linear decoupling stubs provide low loss operation without compromising bandwidth.  Efficient lumped constant end loading produces the highest efficiency possible on frequencies below 14 MHz.

Counterpoises must be an appreciable fraction of a wavelength above ground if losses are to be minimized.  The MFJ-1798 design places the counterpoise at the top of the radiating element.  This provides maximum separation between the counterpoise and the lossy earth.  For example, a ground mounted MFJ-1798 has a counterpoise elevation of one half wavelength on 10 meters."

Back at home on Sunday May 15, 1999, we started assembling the antenna, Charles Randy Adams -- NT8N (me) and Albert Huffman -- KB4SAF. Beginning about 11:30 a.m. and finishing 8 hours later at 7:45 p.m. This is a very long time for assembling an antenna, but the manual needs some clarification to make assembly faster. Overall, the assembly of the antenna went well, everything fit and there where no missing parts. All parts where packed nicely. Parts lists are included in each bag of materials for easy identification. Markings on each bag would have made finding groups of parts faster. Such as group A, B etc.

On page 12 of the manual number 12, the text refers to the "edge lip facing up". What the manual is trying to say is the aluminum side of the top plate faces down, and the brackets are attached to the bottom or aluminum side of the top plate.

The most difficult section to understand was page 13 number 15. The section on how to: assemble and install the "I" bracket. This does not seem such a task reading the manual, but if not assembled correctly the linear decoupling stubs will not be straight.

If you will assemble the "I" beam as shown in the picture above, making sure your right is the bottom of the antenna. This will assure alignment of the decoupling stubs. Pay close attention to the direction and placement of the angle bracket. See picture below.

In the step on page 14 number, 19 you will need a small round file; the couplers are not de-burred, and will not fit on the rods without filing them down.

Pay close attention to the alignment of band stubs with respect to main radiator. The 17 meter stub ( the longest stub) is located on the same side as the balun coil. A bit off center from the coil. You can see this diagram on page 14 section 22.

On page 17 section 37 the manual does not make clear, without close inspection, as to what side the counterpoise tubes attach too. They sit on top of the plate and the brackets inserted from the bottom. See the pictures below.

Tuning of the 12,17,15,10 and 2 meter, bands are accomplished via shorting or lengthening respective stub. This is done by the hold down nuts as shown in the above picture

The antenna can be assembled and tuned on the ground. Although, MFJ says in to use a five foot pole when tuning, I installed it on a 3-foot pole and tuned the antenna with no problems. The spokes you see in the picture below are the means of tuning the antenna on the 30,40 and 80 meter bands.

The antenna is initially resonate at:

All frequencies are at the low end of the band.

Tuning of the bands above 30 meters are easily done by means of the stubs. 30-meters and below are accomplished by trimming spokes on the loading coils. These bands must be tuned in succession, starting with the 80-meter band. See page 22 of the manual for complete details

If you would like a MFJ1798 manual before purchase, you can get one from MFJ's web site.

The final installation is on a 30-foot tower with no ground radials. I found this antenna to be very good performer and works well on all bands with less than 2:1 SWR. I can work the entire band from 2 meter - 20 meters, 65 kHz on 80 meters and 100 kHz on 40 meters with no trouble.

Update 5-19-2000

I installed the antenna on 6-25-99 and have now used it for almost a year.   Some problems accrued over the winter months with the antenna.  Sometime in December my SWR went up over 10.  Upon examination of the MFJ-1798 I found that the So-239 connector at the bottom of the antenna was not making contact.  Again in January my SWR went up, this time it was varying with weather conditions.  I found that the top section of the antenna was icing and causing the problem.  Then again at the last of January, first of February when ice was accumulated at the top the wind managed to bend the main section, not a very strong wind just about 20 mph.  The MFj-1798 is a very good performer for a vertical.  It just needs beefed up a bit.

So, I have finally decided to go with a proven performer and manufacture.  The A3S w/40 meter add on kit by Cushcraft.  Installation of the antenna is scheduled  for June 3, 2000.  I will be posting pictures of the antenna assembly and raising here.