MFJ-1715S. N3GO has a much more detailed description of the J-Pole antenna here. It is designed as a highly portable wire antenna, easily set up as an inverted V, horizontal, sloper, or in the case of higher frequencies, a vertical radiator. I want to improve an existing end fed wire in an attic used only for shortwave listening. The antenna should not cross any … With an “end fed halfwave” where you use a voltage transformer it is most convenient for the earth / counterpoise side of the transformer secondary usage. Figure 16 - Return via Stray Capacitance to Environment and Feedline. If the current is minimized on the "counterpoise", then potential common mode problems are minimized too. 10:1 for Za = 5000 ohms. The device can be tied down on the connection end with the hole provided. End Fed Halfwave. I suspect that the difference in data is due to the fact that the predicted data was for a free space antenna and the measured data was for a real antenna at a low height in a relatively cluttered environment. 17). The range of frequency in which short dipole operates is around 3KHz to 30MHz. Antenna. Discussion in 'Antennas, Feedlines, Towers & Rotors' started by HA6AN, Oct 15, 2019. The exact impedance of an end fed half wave length antenna has been debated but if you design a coupler to match close to the impedance range in figure 3 a good match can be obtained. 6) you will see that a ratio of 8:1 provides the most stable SWR versus "counterpoise" length. We continue our antenna offerings with this single band, 80m-10m end fed half wave wire antenna. During Field Day activities I can usually rack up 500 contacts using only 4 or 5 Watts. This shows the general idea anyway. Read more . Remember, the impedance is relatively high at this point so a very short "counterpoise" is all that is required. However, due to the very high impedances involved currents levels are very low when the antenna is of the proper length and when the LC circuit is adjusted properly decreasing common mode currents. For permanent home use you may also want to try a conventional L-network consisting of an inductor in series and a capacitor to ground on the antenna side. With an efficiency of 98.6% I don't see any reason to lay down an elaborate radial system for a 1/2 wave length vertical from an efficiency point of view. The end fed 1/2 wave antenna, much like the 43 foot vertical, has become a cult phenomena. 18). MMANA Tut 4. Give it a try! : will be set at 1000 for a good continuous plot, the Start Freq. As far as completing the half wavelength antenna is concerned there is no difference between vertical and horizontal orientation! The length is 43 ft fed into a vintage tube receiver using 75 ohm TV coax. As the "counterpoise" itself approaches a half wavelength, the impedance approaches 5000 ohms. Lesson 6.1 Antenna Basics. Since myself and others have been very successful at doing the seemingly "impossible", I will attempt to describe what I think is going on. Given that the impedance is high designing a choke balun with enough impedance to be effective may be difficult anyway. In some cases simply the stray capacitance of the LC circuit to the environment and feed system will provide enough counterpoise as shown here (fig. The Total Pts. Za = antenna's resistive impedance Characteristics. There are some distinct advantages to using QRP. I just hope that it helps others successfully use this type of antenna since it does have some unique advantages. 9:1 or 49:1 for end-fed long/random wire. MMANA Tut 5. M MANA is an antenna analyzing tool based on the moment method introduced in MININEC ... End Fed Matching. However, if this setup is being used in the field with very short or no coax (direct attachment to rig) then any common mode currents that do exist will be negligible. Also, keep in mind that I usually use this antenna at low power levels (<20W). The coupler was tuned to resonance on the bench first using a resistive load. The high impedance, half wave wire is matched to your 50 ohm feed point by an integral impedance matching toroid transformer, and rated is at 10 watts. An Off-Center-Fed (OCF) dipole with total span of 84+17=101 ft, with the feed point at 1/6th of the total span (101 / 6 ≈ 17 ft = 17%) from one end ( = 83 / 17 OCF). In the above diagram you can see that the half wave portion of the antenna presents very high impedance to the 0.05 wavelength section added and free space presents very high impedance to the other end of the 0.05 wavelength "counterpoise". There have been many heated arguments between folks who really only differed in whether they sided with the practical aspects of using this antenna or the sterile theoretical description of the antenna (fig. 21). On this page I will try and describe what I know about End Fed Half Wave Length Antennas. Loaded Vertical. In reality, most couplers will be able to tune out the reactance to achieve a much lower SWR but you should try to operate at the point where the antenna's load is resistive, especially if the feed line and coupler are the "counterpoise" as in figure 15. RSS. The most common method of feeding energy to this type of antenna is at the center where the current is maximum and the voltage is minimum. Whether or not you consider ground loss several wave Impedance/SWR. The SWR is further broadened and lowered across 80m-10m with a high voltage capacitor on the primary of the transformer using band specific radiator lengths. Figure 7 - Measured SWR vs "Counterpoise" Length vs Turns Ratio Data for an End Fed Half Wave Antenna. Amateur Gear eBay Auctions Ending Soon Amateur Radio Equipment … However, in the real world it is possible to connect the return side of the LC circuit to the ground side of the feed line as shown below (fig. If this is done then the current into any length of "counterpoise" is minimal except when those lengths approach a half wave length. No transmitting. Note that a perfect match occurs when the vertical is about 0.47 wave lengths tall. Thru Hole Digital Dial / Frequency Counter Product Page, QRPGuys Multi-DC 10/12/15m CW Transceiver, QRPGuys Portable Tri-Band Vertical Antenna 40/30/20m, QRPGuys No Tune End Fed Half Wave Antenna 80-10m, QRPGuys Multi-Band End Fed Antenna 40/30/20m, QRPGuys 80m-10m Mini No Tune End Fed Half Wave Antenna, QRPGuys 10/20/30dB 50Ω Switched Attenuator, 12W Dummy Load / Power Meter Product Page, QRPGuys TCXO Frequency Standard/Reference, Multi-DC transceiver pcb fabricated chassis, SO8 to DIP8 Adapter Mounting Instructions, DJ3KK SPRAT CW Announced Frequency Counter, KD1JV Dual Lever (Iambic) Combo CW Trainer. Below (fig. Any deviation from the resonant antenna length will require a similar increase in "counterpoise" requirement. However, in order to maintain a balance an equal amount of length is required to be added to the antenna itself. This is assuming direct transformation of the antenna's complex impedance to 50 ohms. The far end hangs down. MMANA Tut 3. End-Fed Antenna projects and plans category is a curation of 63 web resources on , QRO End Fed Half Wave Antenna Coupler, N2CX on End-Fed Halfwave Antennas, Endfed wire antenna tuner by KC8AON. Helical Modeling. These are the points where the antenna is resonant, at 0.25 wave lengths, 0.47 wave lengths, and again at 0.74 wave lengths. Halfwave Vertical. 10). Red color indicates the stronger radiation on the 3D views. However, I am skeptical about how much of these ground (or surface) wave currents, if any, return back to the feed point and contribute to the feed point losses. [1] HF Antennas for All Locations, L.A. Moxon, RSGB, 1990, Horizontal is 90°. Typically, a parallel tuned circuit is used at the end of the antenna with the feed line link coupled or tapped to the coil in the circuit. The J-pole antenna is an end-fed omnidirectional half-wave antenna that is matched to the feedline by a quarter wave parallel transmission line stub of Lecher system form. The black dots represent exact harmonics of the 3.57 MHz fundamental resonance. If you take this a few steps further you can see how the antenna evolves into a classical J-Pole antenna that is often used at VHF with good success (fig. This standing wave consists of both current and voltage that are 90 degrees out of phase. Frequency range. I then removed the 1m long counterpoise and I was no longer able to obtain a match at any setting (fig. The end result is a distribution of current that is at a maximum at the center and a distribution of voltage that is at a maximum at the ends (fig.1). Below is the ideal setup for an end-fed half wavelength antenna that I have determined through experiments and antenna modeling (fig. Your feed line is essentially the counterpoise, so a separate one is not needed. With higher antennas I almost always achieve a 1:1 SWR without retuning the coupler. If the coupler and end fed half wave antenna are properly adjusted then you should have no problems using a very short "counterpoise" or depending on stray capacitance for the return. December 19, 2014 No comments. At this point the antenna worked well. Another possible problem scenario could be when the antenna is fed through a 1/4 wavelength of coax to a grounded rig. Taking this to the extreme is to feed the half wavelength antenna at its end. 5). The main potential path for imbalance will be through capacitance to the surrounding environment, just as is the case with any dipole. Don't try to run 1.5kW through a tiny coupler using polyvaricons! I use this type of antenna extensively in the field with my little single band QRP rigs. At first thought this would seem to be impossible yet many people have done it very successfully. Amateur Radio Gear Swapshop For Sale & Want ads. The graph below (fig. Here are some other examples of the end fed half wave antenna. This is not to say that the antenna cannot be used at other frequencies. Let's say you just use a ground rod for a return. Electronic devices and circuit theory (robert boylestad)(1) Download. Any improvement that you make to this lossy ground will improve this situation. Figure 6 - SWR vs "Counterpoise" Length vs Turns Ratio for an End Fed Half Wave Free Space Antenna. With no physical connection to the feed line common mode currents along the outside of the feed line will be at a minimum. Even though there should be no limitation as to what frequency this antenna can be used on my discussion here is mainly related to HF since this is where this type of antenna is most practical. Up is 0°. MFJ-1717 High Gain Dualband Flexible Duck HT Antenna - BNC . Once again the "counterpoise" requirements are the same as above. In this case many people say that a large radial system consisting of up to 120 radials are required just as is required for a 1/4 wavelength vertical (see below). It should be noted that increasing the counterpoise beyond 1m made no noticeable improvement. It is designed as a highly portable wire antenna, easily set up as an inverted V, horizontal, sloper, or in the case of higher frequencies, a vertical radiator. Notice that there is nothing magical about the often recommended 1/4 wavelength "counterpoise" with this antenna! 2). One common orientation is vertical. So how is this possible? Figure 3 - Impedance versus "Counterpoise" Length for an End Fed Half Wave Free Space Antenna, Figure 4 - Two Half Wave Length Conductors End-To-End for Determining Resonance in Modeling. The following data are for the far field radiation patterns and 3D color views of a sloping End Fed Half Wave antenna with the feed point near ground and curving upward to 40 feet at the far end. Figure 11 - Improper Feed - No counterpoise at all, no worky. Down at earth it can be used in any configuration that an ordinary center fed dipole can be used. For a height of 0.25 wave lengths the resistive impedance is about 35 ohms and a height of 0.5 wave lengths it is about 2450 ohms. I use an end-fed half-wave as my mobile antenna, and it has served me well over the years. MFJ-1717S High Gain … Here are my thoughts (right or wrong) about ground losses with end fed half wave vertical antennas. This gives us an efficiency of 98.6% for the 1/2 wave length vertical. Consequently, the impedance at this point is low and on the order of 72 ohms. I have successfully used 100W without any problems with this coupler. Testing My Mini 64:1 Half-Wave End-Fed Antenna Transformer. The 1/4 wavelength radial recommendation often given is based on the assumption that a high impedance at the open end of the "counterpoise" will present a very low impedance at the return side of the coupler. Even though no apparent "counterpoise" is connected the feedline and/or rig is actually used as the "counterpoise". So far this discussion has had the antenna floating in space for the most part. Can we end-feed a halfwave antenna, or end-feed any antenna, without a ground or counterpoise? then, However, at about a 1/4 wave length from the base of a 1/2 wave length vertical the ground currents once again increase. It should be noted that in these cases adding the often recommended 1/4 wavelength radial will not necessarily alleviate the problem either. Keep in mind that even in the real measurement above the SWR could have been brought down to 1:1 in most circumstances by simply adjusting the coupler's tuned circuit and/or turns ratio but the idea is to show the result when the coupler is fixed tuned at the bench first. MMANA Modeling. 5) there doesn't seem to be much of an issue. MMANA Images. For this reason a bunch of (>1/2 wave length) radials should make an improvement on ground wave field strengths or on very low elevation sky wave paths by lowering the pseudo-Brewster angle. Mobile … Electronic devices and circuit theory (robert boylestad)(1) No radials are required. The wire runs from the balcony or window to a tree or support away from the building. If you design a coupler to feed an impedance of 2450 ohms (7:1 turns ratio), then the expected SWR for a vertical monopole operated against ground is shown below (fig. 8:1 for Za = 3200 ohms Obviously the above two configurations appear to have the potential for the dreaded common mode currents if some sort of choke balun is not used. I am always learning so you may see this page change from time to time as I learn more and correct errors. Turns Ratio = √(Za/50) Recently Chinese manufacturers have begun producing a low cost wide band (100 kHz - 30 MHz) magnetic loop HF antenna known as the MLA-30. A single ground rod will often suffice for a ground system to complete the circuit since very little current has to flow through this ground system. If you adjust your coupler into a resistive load on the bench first and then adjust the antenna for a proper match then you should have a resistive match that will minimize current through the coupler and through the "counterpoise". I believe this accounts for some of the failures that have been described in ham reports that were supposedly corrected when a 1/4 wavelength radial was added. It is designed to use without a tuner and give an SWR of ≤1.2 for any portion of the band after optimizing the driven element. 8) is what I understand Moxon [1] tries to describe. 1,181 3,813. Figure 5 - Ideal End Fed Half Wave Length Antenna. MLA-30 Active HF Loop Antenna. MFJ-1716. 20) gives an example of the feed point impedance of a vertical monopole versus its height in terms of wave length. The direction of radiation is the Blue trace on the polar graphs. 80-10 end-fed half-wave antenna 10 meters on the analyzer looked a little weird (typically, 10 meters appears almost flat), pos-sibly because of the compensation coil, which is in place primarily for 80 meters.
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