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MFJ ANTENNA-TALK #1
"Hang & Play" Basic Collinear Arrays
These days many Hams are seeking ways to improve their reception and up their signal strength, and are resorting to wire antennas from the past fed with ladder-line, used in conjunction with tuners and/or baluns to accomplish matching to 50-Ohm coaxial line. G5RV's and various flat-top configurations fed at the center, or off-center as in the Windom antenna, are very popular as well.
These are generally used as multi-band antennas, but usually require tuning of some sort on each band as previously mentioned. Routing the ladder-line into the operating environment sometimes results in RF voltage nodes appearing in the operating area (shack), and may cause interference/adverse affects to telephones, computers, and other electronic/ electrical devices used in the home.
What if we used an antenna that in the first place is quiet when compared to inverted "Vee's" (and verticals, especially)? A reduction of two to three "S" units of noise may make the difference in that DX contact you can now hear above the noise! And, the modest gain this antenna exhibits (1.6 - 1.8db) might also make the difference in whether that station also hears you. For example, only 1.5 db of gain increases your effective radiated power by half-again as much; from 100 watts to 150 watts. Increased receive capture area is another factor in the good performance of this antenna; twice the capture area of a doublet, or inverted vee-type "droopy doublet."
The MFJ version of the classic Collinear Array consisting of two ½ wave radiators in phase certainly fits the bill in all these circumstances. And, as a bonus, you can virtually "hang & play" this antenna as we construct them. No tuning, trimming, etc. required.
Once connected, you'll find the antenna presents a low SWR across the entire band. However, it is a "one-band antenna" depending which band you chose. Figure 1 is a generic illustration of the antenna with its shorted stub and coaxial connection.
Dimension "L" represents a ½ wave, and "F" represents a ¼ wave, which, in this case is a ¼ wave stub, used for matching and phase-shifting. The antenna is a "broadside array," and is bidirectional perpendicular to the run of the wire. A pair of these antennas at right angles (NE/SW; NW/SE for example) can provide world-wide coverage. And, when used with a suitable antenna switching system (Ameritron RCS-10), switching is convenient and fast, with only a single-line feed into the shack. Or, you can run both coaxial lines into the shack, and effect switching with a wall-mounted unit (MFJ-1700C).
If height is a constraint, this antenna functions better than average at even a bit less than a ¼ wavelength above ground/structure. However, it really performs best if "hung" at a ½ wave; up to ¾ wave. Higher than that provides diminishing return.
Especially important is keeping the symmetry of the antenna in reference to its ½ wave radiators. They must not sag more than a foot or so, with pulled-tight being the best installation. The feedline/stub can be "bent" at the bottom, or pulled away at an angle, and some twisting is OK. Practically, it is best to let the stub/feeder hang straight down and tie it off with rope to avoid lashing about in windy conditions.
To summarize, these antennas are intended for single-band use (your favorite):
They require two tie-off points spaced far enough to accomdate their width/length, and a height at least close to ¼ wavelength. When using two antennas, try to locate the antennas in an "L" or "T" ("X") configuration (at right angles) as illustrated in Figure 2.
(Looking Down From Above)
We hope you will benefit from their ease of installation, efficiency, and quality construction.
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