LAZY END-CONNECTED OFF-CENTER-FED DIPOLE
Most of you are probably thinking, what is an ECOCFD?
First, without the "Lazy":
The 'End-Connected' 'Off-Center-Fed Dipole' is a hybrid between and 'Off-Center-Fed Dipole' and an 'End-Fed Half-Wave Dipole'. Like the EFHW, the coax exits one end of the antenna, but unlike the EFHW, the feedpoint is not located at the end.
Like the OCFD, the ECOCFD's feedpoint is somewhere between the center and the end of the antenna at a point where the feedpoint impedance is approximately 200 Ohms. It is fed with a 4:1 Ruthroff UNUN. The long leg of the antenna is standard antenna wire, but the short leg uses the outer surface of the coaxial shield (for part of the coaxial feedline). Radiation is terminated at the end of the radiating section of the coax by a 1:1 Guanella [choke] balun.
As we know, the EFHW is voltage-fed at the point for the tendency to develop common mode current is the highest. It also requires a high-ratio transformer balun (i.e., 49:1 or 64:1). These high ratio baluns have more loss than good 4:1 transformer baluns.
The two advantages of the ECOCFD over the EFHW are:
- Its 4:1 balun is simpler to build and more efficient than either of the high-ratio baluns, and
- It does not have common mode current on the TX side of the Guanella balun.
The antenna shown above is the same size as a full-size 40m dipole and has low SWR on 40/20/15/10m.
MORE INFO: ECOCFD Antenna
Now Let's Make it LAZY
To save space, we run part of the antenna vertically up a non-metallic pole (i.e., fiberglass pole) and we run the rest of the wire diagonally back towards the ground.
Although the drawing shows two diagonal wire, we only use one wire. The green wire (45 deg.) shows the minimum angle we should use. The blue wire (60 deg.) will be a better performer if you can hang it this high. Of course you may hang it any angle in between, or even higher than 60 degrees.
The Guanella balun should be at least 1 meter (or 3 ft.) above ground.
The far end of the antenna has high voltage on it and should be kept high enough above ground to be out of reach of humans and animals.
Like the Inv-L, this antenna is fairly omni-directional.
The performance of the Lazy Inv-V-ECOCFD is surprisingly close to that of a full size dipole erected at the height of the apex (highest point of this antenna) . . . which is 'not bad' for a multi-band antenna taking only half the space of a dipole for the lowest band of this antenna.
SWR CHARACTERISTICS (across the HF Bands):
As seen on the right, the SWR on 40/20/15/10m is very low.
Not so on the WARC bands.
17 & 12m may be used with an antenna tuner. The SWR on 30m is very high. Even if your tuner can find a match on this band, performance will be degraded.
Note: Measurements made at the Guanella Choke-Balun.
SWR CHARACTERISTICS (by Bands)
(Note: Measurements made at the Guanella Choke-Balun.)
click on image to expand:
Before someone asks:
- No, we cannot move the resonance on 10m higher without affecting the curves of the other bands.
- Yes, I can lower the resonance on 40m by increasing the capacitance by 50 to 100 pF.
Here is a Photo of the Installation:
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