Description:
This is MFJ's 1792 80m, 40m 33' Vertical with an added 20m stub. Had mine a year and a half now, installed on 6/21/18 on a 36" 2"OD Galvanized pipe cemented in the ground properly. About 12" exposed. MFJ recommends two guy ropes but I found one set works fine. DXEngineering nylon guy ring with three Mastrant 2mm ropes 120º apart to nearby trees. Not any issues since. See my picture on this thread here, follow antenna down to first branch and go left and downward.
Tuning of the 80m cap hat is quite a hassle. It has to be laid down to cut your "spokes." Mine did come with eight as you can see, but tuning it ended up with six equally shortened ones. I kept them symmetrical. Easier to start pulling spokes to figure out your total length needed for your segment of the band, and then cutting the leftover spokes to equal lengths. During this tuning process which definitely needs at least two people to raise it without bending it, which I found out the hard way. Using the guy ropes to help you raise and lower is a plus. I now have a "spare" section courtesy of MFJ under warranty to replace the bent section during this process for when that section really needs replacement. Don't fix something that is working. So what for a slightly "curved" antenna. You can see that curved pic on my QRZ page.
I originally had four 33' radials THHN 14ga wire (HomeDepot 500' spool, with their online) Orbit Galvanized ¼" loop stakes (Internet #203720638 Model #65730L $1.50/10pk free delivery to your local store,) simply stainless hose clamped about 4" off the ground on the mast itself, and it "worked" OK on the three bands. I couldn't make a full "cross" of the radials as the AT is at the corner of the property. Two radials around a tree at extreme corner of property and don't cross themselves. I also slightly coupled (read: commandeered) the neighbors 70' fence by intertwining one radial through his links a bit. Acceptable for a while, ("F'now," a contraction of "for now,") and then the old "the more radials the better" kicked in again. Added four 66' radials in a 110º fan configuration to stay on the property (mostly that is, I had to overlap the neighbor a few feet behind his fence,) one radial needed to be 67' to make it to the stations 8' ground rod for the Generac. This was the most improvement found. Signal reports on all three bands increased noticeably on my 100w. DX Range also improved. Total of eight radials: four 40m and four 80m, a ¼ wave on each band. Worked All Continents on 40 and 80 quickly from here. Some time later, "the more radials the better" kicked in yet again, and I added a set of four 17.5' for 20m, and then later another 13'11" set for 17m, both in full "cross" configuration and not overlapping any other wires. Once the 17m radials were installed it "seemed" to give it some actual gain on 17m, as WAC was made in no time from there. A 40m antenna being naturally close to 5/8 wave on 17m. Sixteen radials now installed, close to, but not full-tuned, four for each of 80, 40, 20 and 17m. With this configuration and my MFJ-962C manual tuner, this antenna likes 60m & 30m also. WAC on 30m was achieved on this AT also. Still waiting for Asia to show up on 60m to complete that one with 100w on an old FT-747GX.
Conclusion on radials, minimum four 33' radials, works very well with four more of 66'. Adding more radials started diminishing returns on this AT at this location, except for 17m. Thinking that the 40m and 80m radials are doing a better job than the 20's actually do on 20m. Those are in a true cross, so still adding more symmetry to the radial field. For some reason this particular AT doesn't like 15m. I can tune it with the tuner, but no real satisfation, even on RX. The Anttron 305 (not an A-99, but same engineers,) much outperforms it. The 1793 likes 10m, being a that it has three "modes" of its design to work on, a near natural full wave on 40m, two full waves on 80m, and a direct half wave on 20m, but this is ground mounted so is not working with a tuner nearly as well as the 305 is naturally on a 10' mast on the roof tripod. The 1793 may like being roof mounted for 10m a lot better.
This antenna is a physical "natural" ¼ wave on 40m being 33' tall. No tuning really needed if you follow the manual. If needed, any autotuner will make quick work of any mismatches to your needed portion of the band.
The 20m stub is quite simple, but I suggest that when you originally install it, that you don't shorten the ferrules between the sections, don't push the sections deep into them, just enough to tighten the setscrews to them. Keep their length in the ferrules as long as possible as you can always re-shorten it at the bottom with the tuning section. Mine needed about ¼" more length overall to get "happier" into the digital portion without a tuner. Those gaps in the ferrules were in the key to the needed extra length. Tuning is at the base, so quite easy. Another op has reworked his 20m stub with a thicker radiator. That should fix most problems and add some BW. Might be able to drill the insulators and feedpoint out a bit and lathe the original, or get new wider ferrules.
In conclusion, for my $190 at R&L (at the time in 2018,) this antenna is excellent bang for buck. Knowing the history of MFJ products, you do need to plan ahead for your install counting for missing, and/or broken pieces and the physical layout of your radial field which IS required for this AT. I highly recommend this antenna for its cost-effectiveness. Yes, there are much better ATs out there, but again, this is a ¼ wave and it performs as well as a ¼ wave is expected to, and the bonus of being more than a wet noodle on the many other bands you can use it on is a freebie/plus.
73
KD2HCE |