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Reviews Categories | Antennas: HF Verticals and Wire | MFJ-1792 80/40 top-loaded vertical Help


Reviews Summary for MFJ-1792 80/40 top-loaded vertical
MFJ-1792 80/40 top-loaded vertical Reviews: 14 Average rating: 4.8/5 MSRP: $169.95
Description: 40/80 Meters vertical antenna
Product is in production.
More info: http://www.mfjenterprises.com/products.php?prodid=MFJ-1792
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SM7JKD Rating: 5/5 Jan 20, 2004 07:11 Send this review to a friend
Good Value, works well too  Time owned: 3 to 6 months
Purchased the above about 4 months ago.At first had it elevated on a 2m Al pole 50mm od, with 4 elevated 1/4 wave radials.Result was so so. Reduced the 2m pole to one foot, so now ground mounted.Bolted a rectangular frame with holes to the base, and started to add 1/4 wave radials on the ground.As I am only interested in SSB DX, my Res Fre is 3.777 Mhz.As I added the radials, the VSWR increased as expected,so I knew that I was heading in the right direction. I now have 55 radials, which seems to be enough.I must also thank Fern,VE2ZV, for all his help and advice and e mails! VSWR with 100 Watts is after some adjustments, 1.4:1 and I run one KW into it without any problems.I work North and South America most mornings as long as reasonable prop is there, with 5,6 to 5,9 plus 10 db reports. It is now most mornings, better than my 4 switchable 1/4 Wave slopers,against the 20m tower, and my dipole with apex at the same height.My Summer project is to buy another, space at 1/8 wave, direction 295 deg (NW) and phase the two with a Comtec Box.I choose 1/8 spacing due to my back yard is only 20m (EW) wide and 100m long (NS).The result will be fun to experience.I know these antennas work, as I talk to BOB,W9ARV,and Stan,W4AG often in the mornings, and they both use them for their 4 Squares,with good results.So good enough for them, good enough for me. They also gave me much useful advice,for which I'm thankful. For a 33 Ft top loaded vertical,you won't in my opinion, get much better for under 200 US Dollars.It took 3 hours to build,I have one set of 3 guys at the higher standard position, and it dances firmly in the wind at the top,without any problems.It also works well on 40m, with 1,3:1 VSWR on the whole band, but this is just a bonus, as I'm only interested in 80M.
Have fun with the hobby,...de David, SM7JKD.
 
WA3TTS Rating: 5/5 Feb 1, 2003 20:23 Send this review to a friend
WA3TTS PART2  Time owned: more than 12 months

Even with the two 1/8 wave radials on 160m, performance of this antenna is quite good across its 40KHz 3:1 VSWR bandwidth. Many contacts have been made at 2W QRP in casual 160m CW contest operating, and 100W has made it to the west coast. I seem to need the KW for EUs
but part of this equation is my QTH 7/8s up a hillside favoring the western direction.

I added 1/4 wave monopoles on 10 and 17 meters with an aluminum support plate about 12 inches long and 2 inches high by 3/16s thick, mounted about 12 inches above the feed point
on the vertical mast. Adding these monopoles changed the 160m resonance down about 30 KHz, so the new tap points were about one turn less inductance--which is good. Adding a 30
meter monopole might add even more capacitive effect on 160 meters. My only regret is not
ordering some extra 20 meter monopole parts from MFJ at the start to make a 30 meter add-on
when the antenna went up the first time.

I have the antenna guyed with 3/16s dacron line at guy points per the antenna instructions.
After several severe storms, some with 70MPH gusts, the antenna still stands straight. The
Dacon lines did stretch for about 6 months after the storm events, but after the initial stretch
out period they have remained tight.

Final Analysis: This is a simple and very durable antenna that will take all the power you feed
it. As a ground plane it is very effective and is much less work than planting a radial farm. With
simple modifications it can be an all band HF antenna at a cost much lower than the R7000
(which does not cover 160m) See "Elevated Vertical Antenna Systems", August 1988 QST by KB8I if you question the performance potential of simple two-radial elevated ground planes.

Mike, WA3TTS
76745.1565@compuserve.com
 
WA3TTS Rating: 5/5 Feb 1, 2003 20:19 Send this review to a friend
Simple, Effective, handles QRO, easy to modifiy  Time owned: more than 12 months

I decided to purchase an MFJ-1793 Vertical as a replacement for my
Crushcraft A5 vertical after having the dielectric in the A5's 40 and
20 meter traps failed under legal limit power levels from an AL-82
amplifier purchased a few months earlier. After 14 months of operation
there have been no problems with dielectric failures of the top loading
coil on the MFJ-1793.

This antenna is operated as a ground plane, supported on a 15 foot
mast directly behind my garage. It requires two people to raise and
lower the antenna, one on the roof for walk-up/walk-down and a second
person to man the guy wire pulling on the ground. Calm or light wind
conditions highly recommended for antenna raising/lowering.

With only two 66 foot radials running north and south at 15 feet, the
antenna resonated on the bottom of the 80m CW band. On 40 meters
it resonated around 6.6 MHz. Shortening the antenna at the base by loosening
the lower stainless clamp and shortening the vertical element 6 inches raised
resonance on 80m to 3.550 and 6.7 MHz on 40 meters. Adding a pair of 33 foot
opposing radials for 40M put the antenna with nearly flat VSWR across 40 meters.
Just keep the 80 & 40 meter radials apart by 10 or 15 degrees to minimize capacitive
coupling. Does it work? My first QSO on 40 meters was with YB1A on long path,
cracking the pile up in the first few calls.

For its modest $200 price tag, this antenna is easy to modify for other bands. For
160m, I added a 30 uh coil and 5KV 250 pf capacitor that is switched in and out with
a vacuum relay at the feed point. After finding resonance on 1.8MHz, I used pennies
with holes drilled in them to set the high current tap points and soldered them to the coil
where needed. Brass hardware and lugs make the connections. RF heating will quickly
smoke an alligator clip spring at QRO, so use good high current tap practices.
Even with the two 1/8 wave radials on 160m, performance of this antenna is quite good across its 40KHz 3:1 VSWR bandwidth. Many contacts h
 
EX_NS4T Rating: 4/5 Mar 13, 2001 08:48 Send this review to a friend
Good Performer  Time owned: 3 to 6 months
Review is actually for the MFJ 1793. That's the 1792 with a 1/4 wave 20 meter radiator added.

In my opinion, an untrapped vertical performs pretty much like any other untrapped vertical, and the MFJ performs satisfactorily. The radial system and soil conductivity play the major roles in these installations.

Other verticals I've used are homebrew (no trap 1/4 wave), Hygain multiband verticals, Cushcraft R-5 and the 5BTV.

My installation: Ground mounted with 48 thirty-three foot radials over average-poor clay soil.

SWR: covers entire 20 and 40 meter bands <1.7 :1. About 175 Khz <2:1 on 80 meters. Extends out to about 250 Khz with an 80 foot run of RG-8. The better the radial system I used, the better the SWR band. 80 meter tuning easily accomplished by trimming top capacitance loading wires - but must tilt down antenna to get to the wires. Not too difficult for average physically fit person. 20 meter tuning by adjusting two lock nuts at base of antenna. Quick and easy. 40 meter needs no tuning. Very flat across band.

Construction: Fairly lightweight but sturdy. Put up and took down 3 times in 4 months (Trying different locations/ground systems). Only failure was cheaply made small lug connecting feedpoint to vertical radiator. Also had a slight dimensional irregularity between one section of aluminum tubing and another causing very tight fit during assembly. Able to work it into place though. Took my time and was sidetracked by other jobs but I think total assembly time was 2-3 hours. If I hadn't decided to first try it mounted on top of a 3 stall aluminum covered carport with Pecan tree's all around it, I'm sure it would have been a more pleasurable experience!

Requires guying. MFJ recommends at two places. I used one set of guys and antenna swayed in high winds. Rock steady with two sets.

Overall: I was going to make a homebrew 80/40 top loaded vertical but when I looked at cost of getting the materials compared to cost of the MFJ, and then threw in my laziness factor (not really wanting to tinker a lot with the physical construction details) the MFJ was a very good value and good performer. I'm a "small cap gun" in contests but it has greatly boosted my performance on 80/40 meters over inverted-vee at 50 foot apex. During recent ARRL SSB contest, took advice of couple books and ran an additional two 240 foot radials out toward Europe and added another 13 multipliers during the next hour. As I said in the beginning, it's more the radial system than the antenna for these type of verticals.

I would buy this antenna again and would recommend it to my friends. It takes an almost perfect product to get a 5 out of 5 from me, so I gave it a 4.

Kevan Nason
NS4T
 
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