Product Review MFJ 1775 Rotating Mini Dipole

MFJ--1775-Rotating mini dipole-Review MFJ--1775-Rotating mini dipole-Review

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Product Review: MFJ-1775 6-Band Rotatable Mini -Dipole

Phil Salas – AD5X

Introduction

When I received the 2006 MFJ catalog, their new MFJ -1775 compact dipole caught my

attention . This antenna was appealing to me because I live on a small city lot, where my

entire backyard is completely taken up with a swimming pool. So I only have room for a

Butternut vertical in the corner of my yard, up against a cedar fence and surrounded by

large shrubs. Obviously not the best antenna situation, though it has been g ood enough to

provide me plenty of fun over the years. However, I have wanted something that could

possibly give me improved performance, especially on the higher HF bands. Enter the

MFJ -1775

MFJ -1775 Description

The MFJ -1775 is a mini 14 -foot 40/20/15/ 10/6/2-meter rotatable dipole designed to fit on

the smallest roof , making it perfect for town houses, apartments and condos. It can even

be mounted inside an attic. It is light, inconspicuous and low profile , and is not much

bigger than a TV antenna, ma king it easily turned by a lightweight TV rotator. Efficient

end -loading coils and capacitance hats permit full 1500 watt legal limit power on the HF

bands . F ull -length half -wave dipoles for 6- and 2-meters are incorporated into the

antenna , but power handling is reduced on these bands due to the design of the balun .

RF Specifications

Power

Band CW SSB 2:1 SWR BW

40m 1500 1500 40 KHZ

20m 1500 1500 60 KHZ

15m 1500 1500 400 KHZ

10m 1500 1500 1.2 MHZ

6m 300 750 600 KHZ

2m 200 300 4.0 MHZ

Mechanical Specifications

Mast Size: 1- to 1-1/2” diameter

Overall Length: 14 feet

Turning Radius: 7 feet

Weight: 15 pounds

Wind Load: 2 square feet

The MFJ -1775 Experience

After making the decision to acquire this antenna , within a short time a 6” x 6” by 5-1/2

foot box arrived. I guess I was expecting a larger package – after all, this is an HF

antenna! However, the longest piece supplied is just 5 -feet in length, so everything fits

easily into the small box . Photo “AllParts” shows all the components of the disassembled

antenna spread out on the floor of my “shack”.

MFJ-1775 Unpacked – All parts are shown

I assembled the entire antenna inside my home, except for the final job of attaching the

end loading coils. I moved the antenna outside for the final assembly, which is made

easy by using saw-horses for support. It took me just under two hours for the complete

assembly . Photo “Assembled” shows the completed antenna. Note how difficult it is to

see the capacitance hat spokes! MFJ warns you to use eye protection when working

around this antenna, as the spokes could cause injury.

Fully assembled MFJ -1775

Next comes antenna tuning. This entails trimming the capacitance spokes with a pair of

heavy wire cutters while monitoring SWR with an antenna analyzer. First, you must

mount the antenna temporarily at a height of about 6-8 feet so that you have access to the

spokes for trimming. I had a 1.5-inch diameter tube, and a 1.375-inch diameter tube that

I telescoped together so that I could lower the antenna to about 5-feet for trimming, and

then extend it to about 10-feet for checking the tuning. The tubes were attached to fence

posts with hose clamps. Photos “TrimHeight” and “MeasuringHeight” show my trim/test

set-up. The MFJ-1775 Assembly/Test manual gives approximate spoke trimming lengths

versus frequency change, and recommend s that you “sneak up” on the desired resonance

points, as it is hard to add spoke length if you trim too far!. I was careful to do this, and

wound up trimming about ¼” at a time from the spokes. This tuning effort took me

approximately three hours. Six- and 2-meter tuning takes just a few minutes, as adjusting

those dipoles is very easy. There are some spurious 2-meter resonances that could be

confusing, but the MFJ manual does a good job of explaining how to tune around these

resonances.

Trimming Height Measuring Height

Once the antenna was tuned, it was time for me to put it up. I’d originally planned on

mounting the antenna on a mast on my chimney . However, this position is currently

occupied by my Cushcraft ASL670 50-450 MHz log periodic, and I didn’t want to

remove this antenna as I also use that antenna for HDTV reception! Plus, this could

possibly give me the ability to make some comparisons between the ASL670 and the

MFJ-1775, depending on conditions and activity on 6 - and 2-meters.

Since I live within a few miles of Texas Towers, I drove there and purchased a Rohn H50

50-foot push-up mast, which is supported by attaching it to the eave of my house at about

the 9-foot level. As the MFJ-1775 is so light, it was very easy for me to install it on the

Rohn H50 using a 7-foot step ladder. This was literally a one-man job. Since I was only

supporting the H50 at 9-feet, I only pushed up the mast to a height of 30-feet. The photos

below show the MFJ-1775 in its final position. Note how unobtrusive the antenna is!

Front sidewalk view of the MFJ-1775 Street view of the MFJ-1775

Performance

As everyone knows, HF band conditions are pretty awful now, and will continue to be so

for the next several years. However, there is good activity on 40- and 20-meters. And

since I’m retired, I can also monitor 15- and 10-meters during the day and I have been

lucky enough to find a little activity on these bands as well. So, how does the antenna

perform? I was pleasantly surprised.

My antenna conditions are as follows: The MFJ-1775 is located at a height of 30-feet as

shown in the photos. This antenna was compared against my ground -mounted Butternut

vertical. The Butternut is mounted in the corner of my yard, surrounded by a cedar fence

on two sides and a 15-foot shrub immediately in front of it. The Butternut has ten short

random length radials fanning out towards one side of the swimming pool, one radial tied

into the swimm ing pool electrical ground, one radial tied into the steel landscape edging

near one end of the pool, one radial extending along my neighbor ’s fence that “T’s” off

my fence, two radials extending along my fence and grounded every 6-feet to the steel

fence posts, and one radial that sneaks through my fence and ties into the CATV

amplifier ground in the alley! Definitely not the best antenna location and ground plane

overall, but the best that I can do at my particular location.

I used my FT-1000MP MKV S-meter for the antenna comparison. I have two back-to-

back 4-position MFJ-1704 coax switches so I can rapidly switch any of four different rigs

into any of four different antennas. The results shown below are in S-units, though I’m

not claiming that these S-units will translate exactly between different radios. The results

shown below are based on two weeks of active operating.

Band MFJ-1775 compared to Butternut

40M +1 to -2 S-units better/worse than Butternut

20M +1 to -1 S-unit better/worse than Butternut

15M +1 to +2 S-units better than Butternut

10M +1 to +3 S-units better than Butternut

So, generally the MFJ-1775 is a little worse than the Butternut on 40-meters, and about

the same as the Butternut on 20-meters, though occasionally it does outperform the

Butternut on these two bands. The MFJ-1775 virtually always outperforms the Butternut

on 15- and 10-meters. Additionally, the MFJ-1775 has a 2-3 S-unit LOWER noise floor

on 40-meters compared to the Butternut. This has permitted me to work weaker stations

that I could not have worked when using my Butternut. Not bad for a shortened, loaded

dipole at 30-feet!

And how about 6- and 2-meters? Well, there has been no 2-meter activity since I’ve put

up the antenna. However, I have had one good 6-meter opening between the Dallas area

and the east coast. Because of high winds, I had the MFJ-1775 at only 20-feet, the same

height as my chimney -mounted Cushcraft ASL670 log periodic. The results? The MFJ -

1775 typically outperformed the log periodic by about one S-unit as measured on my IC-

706MKIIG and also reported by stations I worked. I suspect this had to do with a

difference in take-off angles between the two antennas and the distances involved.

However, I was still surprised, and further investigation is warranted! Over time, I

should be able to accumulate some more data to help explain this.

Conclusion

If you are unable to put in an effective antenna system due to property restrictions, you

may want to consider the MFJ-1775. Of course there is a bandwidth trade-off due to the

reduced size of this antenna on the 40- and 20-meter bands. However, the MFJ-1775 is a

surprising performer. And besides getting coverage of the popular 40-, 20-, 15-, and 10-

meter bands, you get 6- and 2-meters thrown in to boot!