USING MFJ MOBILE HF VERTICALS
(Updated with feedback October 2012 - See bottom of article)
By "Yukon John", KL7JR
space? Need a very portable compact antenna that works DX?
I am very pleased
with the performance of the MFJ 40 meter mobile verticals (MFJ 1640T) I
used as a horizontal one-element V beam on July 17, 2010 from the Yukon as
VY1RST. The numbers were on
previous tests indoors from my apartment: SWR 1.4, R 65 and X 12 and
outdoors in the Yukon mounted on a picnic table: SWR 1.1, R 60 and X 0 for a height of about 8
Let's try the same idea with a pair of MFJ 20 meter mobile verticals (MFJ 1620T) and see if they are as flexible as the 40m models as used above. I mounted the 20m V beam on a ¾ inch EMT mast about 8 feet long inside the box of my truck. After a few minutes of pruning, test results were: SWR 2.3, frequency 14.200 MHz, "R" 45 and "X" 30. I ended up with a 6 1/2 inch long stinger (that's the entire supplied stinger inserted all the way in to the antenna and 6 ½ inches protruding. I'm sure once I get the antenna higher the SWR and X will come down to the levels I experienced with the 40m verticals but that won't happen from the RV park I'm staying at. I experimented with whip lengths of 6 inches to 8 inches and all had high "X" levels of 30-40. While I had everything set up, I wondered how long the antenna would be when used as a vertical. On 14.270 MHz the SWR was 1.2, with "R" at 50 and "X" at 10 for an overall antenna length of 33 inches making this a very compact antenna for 20 meters.
From another location the next day, I got the V beam up about 15 feet high in an area free of other objects to see the SWR and X down to lower levels. I fired up my TS-570 only to find S9 QRN and no audible signals. I am confident the 20 meter V beam will work DX as it's 40 meter cousin!
Shown in photo above, here's what I used for my antenna mounts. It doesn't get much easier than that. Hurricane "T" connectors ($4 at Lowes) bent and drilled out to accept 3/8 inch threaded connectors for horizontal or vertical dipole (left) or horizontal V Beam (right) mounting (black coil and wire is for another project). Detailed step-by-step homebrew info is available here for the dipole mount. V Beam mount is the same but one end of "T" bent 90 degrees.
In conclusion, it
appears the V beams need to be installed at least 15 feet high above
ground, somewhat far enough away from other objects and having a great big
body of water nearby doesn't hurt any! The bottom line, MFJ HF Mobile
HamTenna Whips, available for 6 through 75 meters, are economically priced
($19.95 each, 2010 price) heavy duty compact mobile antennas that perform
well, especially outside their intended design! If you work me in 2011
from the Dominican Republic (HI8/KL7JR), Hawaii (NH7DX) or the US Virgin
Islands (WP2JR), I'll be using these antennas!
October 27, 2010 Maui, Hawaii, "N7I" Special Events for US Islands program. Ops KH7/KL7JR and KH7/WL7MY
I experimented further using MFJ 20M short verticals as horizontal and vertical dipoles and as a V Beam. V Beam won hands down!
Maybe it's just because of poor propagation? Using 6 1/4 inch long stingers on the whips, [(MFJ 20 meter mobile verticals (MFJ 1620T)], I worked several stations in Washington, Arizona and Oregon on 20 meters and on 17M I snagged a pair of JA's and a Seattle station under extreme QSB and QRM.
Antenna was mounted on a broom handle lashed to the balcony of our 4th floor condo overlooking the ocean. Several different weather patterns and high winds were experienced the first 3 days of operating. Antenna with short whips loaded all bands 10-40M!
73, de Yukon John KL7JR
Update from Tim 2E0MKT October, 2012
The antennas that I used were from our local radio dealer Moonraker. They are not of MFJ quality but they are relatively inexpensive, about $32 each.
The metal fixings came from a builders merchants and are used to join wooden roof beams, they were about $16 in total.
Finally, the poles that I used were two tubular metal washing line posts joined together. They have swaged ends which makes them very portable.
I have not yet tried the antenna as a vertical dipole because of the proximity of the metal tube. I will change the poles to wooden or glass fibre and let you know how I get on.
Your design for a mini V beam antenna was brought to my attention by a fellow member who thought it would be an excellent project for someone starting out in amateur radio.
Over the past few months I have been using the antenna, mainly for PSK31, connected to a Yaesu FT817, LDG Z817 Autotuner and a Tigertronics SignaLink USB Interface using 4 watts
I am amazed at how far I can get using the antenna. I have used various configurations including your horizontal V beam, but currently it is just a straightforward dipole.
I tried to ascertain whether there was any directional bias to the antenna using your horizontal V beam configuration but I’ll have to say that it was not conclusive.
However, this may be down to the location of the UK in that most of the contacts are likely to be in Europe which is essentially due east from the UK with not a lot stations to the North and South.
Having said that I was delighted to get some contacts in the USA and Canada i.e. New Jersey, West Virginia, Vermont, Indiana and Quebec – all on 4 watts!
I have included a couple of images of the antenna and the mounting below, which is at a height of 16ft above ground level.
So, thank you very much John, your antenna has given me much inspiration to continue with amateur radio.
Regards Tim 2E0MKT