E Technology, Inc. Part Number Description List Partial List, More than 400kb Please note that some of the lists are quite long Please select company by. Ferrite Core Inductor Software Developer' title='Ferrite Core Inductor Software Developer' />Six Band HF CenterLoaded OffCenterFed Dipole. Six Band HF CenterLoaded OffCenterFed Dipole. Serge Stroobandt, ON4. AAHome. Antenna Designs. Band HF CL OCFDON4. AAs six band CL OCFD The resistor R is only there to protect the capacitor C against static electricity surges. Having any questions about the CL OCFD antenna Wanting to discuss OCFDs and single wire fed Windom antennas Then post your question to the Amateur Radio Results and pictures are shared in the Windom Antenna Design goalsoutput tank of a PALike many fellow radio amateurs, I own a fairly standard shortwave radio station consisting of a 1. W HF transceiver driving a 1 k. W tube power amplifier. I never chose to spend any money on a k. W rated antenna tuner. Anyhow, I can tune out VSWRs as high as 31 with the adjustable pi network of the output filter tank inside my power amplifier. Thus I set out to design an HF antenna with a VSWR of 31, or less, over the full bandwidth of as many amateur radio HF bands as possible. At the same time, my preference went out to the low and the non WARC bands. This design exercise resulted in a new kind of antenna which I dubbed Center Loaded Off Center Fed Dipole Antenna, or CL OCFD for short. Performanceon target. In proof of its performance, an EZNEC calculated VSWR graph of the CL OCFD antenna is presented in Figure 2. This antenna works without a tuner over the entire bandwidth of the 8. If your final output stage is a transistor amplifier, you definitely will need an antenna tuner though. In such, this antenna is the first described single wire antenna to be offering these capabilities. Application Notes. To search our Application Notes, either browse the list below or type a Keyword or Part Number into our search box at the top right of this page. Theory and construction of a multiband antenna which works without a tuner over the entire bandwidth of the 80, 40, 30, 20, 15 and 10mband. VSWR of the six band CL OCFD as a function of frequency. Why off center fed When offsetting the feed position of a dipole antenna away from its center, at some point, similar feed impedances can be obtained for a number of frequency bands. This occurs at the fundamental 2 dipole resonant frequency as well as a number of harmonic resonant frequencies. This is possible because a standing wave is present along the dipole which causes the feed impedance to change. In the span of a quarter wavelength, it varies from a very high value at the antenna ends several k to the value of the radiation resistance at the corresponding frequency. At its fundamental resonant frequency, in free space and for an infinitesimal thin wire, the dipoles theoretical center feed impedance would be 7. However, the optimal multiband feed point will have a higher impedance than this theoretical center feed impedance. Hence, a good quality impedance transforming balun will be necessary to match the optimal balanced feed impedance to that of the unbalanced coaxial feed cable. Full 8. 0 m band coveragefull 8. Operating a center fed dipole over the entire 8. With 8. 2 relative bandwidth the 8. MHz is exceptionally broad. Cumbersome cage dipoles or load switching arrangements deliver only partially satisfactory results. However, any OCF dipole easily outperforms aforementioned obtrusive antenna arrangements. Here is why Placing the feed point away from the center, increases the resistive part of the feed impedance and feeder load more than the reactive imaginary part of the resonant antenna, which is nearly resonant. This effectively lowers the loaded Q factor of the antenna at the feed point. Offsetting the feed position of a dipole antenna, will result in a lower loaded Q factor and hence a broader working bandwidth at the fundamental frequency. QloadeddownarrowequivfracXinRinuparrowRfeederuparrowquadtextrmandquad QloadedfracfresBWquadRightarrowquadBWuparrow,fracfresQloadeddownarrowIn summary, offset feeding causes the antenna to be loaded differently. The effect is most pronounced at the fundamental frequency. This is a first reason why it pays off to build your OCF dipole with 8. An additional reason will be given in the section about center loading. Please note that a year after the publication of this article, Eugene G. Preston, K5. GP, described a dualband 1. CL OCFD exhibiting comparable broadband behaviour on 8. However, this 8. 0 m broadband performance is achieved in a slightly different manner. The antenna is actually a 3 band CL OCFD antenna 1. VSWR of the six band CL OCFD on 8. Literaturecontinuous renewal. Rather than reinventing the wheel, every antenna project should start with a quick literature study of similar published antenna designs. Doing so for the multiband Windom or off center fed dipole antenna see table below, leads to a stunning revelation. Over many years, antenna dimensions and feed locations have not changed much from the original single wire design, whereas balun feed impedances have decreased from 5. This, of course, is reason enough to become very suspicious about published multiband Windom designs. Literature and web survey of multiband OCFDs. W8. GZ1. 92. 95. 00 0. VS1. AA4. 19. 37. K4. ABT1. 94. 92. DJ2. KY5. 19. 71. FD44. 19. 71. 30. V8. 0 4. 0 2. 0 1. FD46. 19. 71. 30. NANANAtop 1. 2 mends 8  3 masymm. V8. 0 4. 0 2. 0 1. K8. SYH7. 0s. 30. I7. SWX7,8. 19. 88. JA7. KPI1. 99. 42. V8. 0 4. 0 2. 0 1. K3. MT1. 99. 74. 50 4. V8. 0 4. 0 2. 0 1. ON4. BAA2. 00. 23. ON4. BAA2. 00. 32. W8. JI2. 00. 63. 00 4. ON4. AA2. 00. 72. K5. GP2. 00. 82. 00 7. Table notes The open end of the antenna corresponds to 0 offset, the middle of the dipole to 5. VSWR 31 only within a narrow portion of the 8. Inconsistent data in brochure end insulator separation and heights do not correspond to angle between dipole legs at specified height. Antenna made of soft PVC insulated HO7 V K 4 wire. As a matter of fact, I first made this table in 2. I held the call ON4. BAA. It promptly triggered me to start using the power of computer modelling to study this poorly understood antenna. This resulted in two designs a 3. Both had feeding locations much closer to the antenna end than usual. Autocad Civil 3D Line Types Drawing. This improved the VWSR performance quite a bit. In 2. 00. 6, Tom Rauch, W8. JI, reproduced these findings with a slightly longer bare copper wire antenna. However, two problems remained Although the traditional OCF dipole had very broad band segments, the VSWR minima of either the 8. Also, designs that did better on 8. Apparently, OCF dipole designs had so far been a compromise between these three bands. The renowned FD4 antenna was not an exception Have a look at its VSWR specification on pages 1. Furthermore, none of these designs offered 3. This is a pity, because most hams would put up a wire antenna especially for the lower bands where beam antennas are more difficult to erect. The next section explains why traditional OCF dipoles have these inherent limitations. Rest assured, both problems are dealt with by the CL OCFD, also listed at the bottom of Table 1. Resonant lengths. It is often said that the HF amateur radio bands are harmonics of the 8. But is this really the case The statement can easily be tested by considering a horizontal wire at a practical height 1. Sm r  5. I use gauge 4 mm copper wire insulated by a 0. PVC. For the remainder of only this section, the length of the wire is such that it achieves 2 dipole resonance at the geometric center frequency fc of the Region I 8. MHz. At the geometric center frequency of every other band, we will now determine how much wire needs to be added or subtracted to achieve harmonic resonance. It should be very little if the bands were truly harmonic. Note that bare copper wire at higher heights and above better ground would yield longer resonant lengths, due to less capacitive coupling to the ground. Either way, this does not affect the validity of what follows. Let us now look at the even and odd harmonics in separate groups, starting with the even harmonics. Even harmonics. Table 2 clearly shows that the lower band edges are exactly harmonic all frequencies are integer multiples of 7. MHz. All even harmonic bands also have similar relative bandwidths i. The FM portion of the 1.