This gave me an effective coil diameter of 40.5mm. In the case of the EFHW 49:1 transformer, the major shortcomings of the most popular current designs are excessive leakage inductance and poor heat transfer from the ferrite material to the environment. : I see you were able to post your comment now, so I just copied my email answer here for others to see. And now I am planning to build one for 160/80m. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. All Rights Reserved. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. I drilled a couple of holes at each end of the former, a small one for the wire to pass through and a larger one for a bolt and wingnut for wire attachment as I wanted the end result to be portable across different antenna projects. This suggests an inductive reactance. I wish you lots of productive experimentations and successful portable operations. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. I was pleasantly surprised that the dips were so perfect across all of the bands and the SWR was low enough to not really need a tuner. It is likely that next time the tuning may be set according to the already found positions, and it will not be far off, requiring only slight adjustment. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. Trapped five band EFHW SOTA antenna. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. No wire counterpoise is used to reproduce the SOTA setup. And of course, a counterpoise with various lengths. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). I checked the wall brackets and mast, but all the fixings were nice and tight. As is often the case, packaging was determined by what boxes I had laying around. Frank VK1VK. Each geodesic great circle path displayed on the map originates from your location that is derived Read More, The Great Circle Map GCM We present an automatically rendered Great Circle Map GCM based on your location derived from your Internet IP address. It is quite difficult to satisfy both requirements of achieving proper impedance ratio and resonance of the tank circuit at each tap of the inductance. . The toroid with its many taps may be soldered directly on a multi-position switch. Of course, if both ends are raised higher, it will produce a more efficiently radiating antenna, but the portable and temporary installation is always compromised by conditions given by a location and its restrictions. Thank you Gary. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. It is much easier to wait ~2, know that you are going to see about 86% of the temperature change you would see if you waited until time infinity, and just make a simple correction. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. In an ideal setting, the center of the antenna will have the lowest voltage, consequently impedance, which is why it is possible to feed it by 50 or 75 coaxial cable. Why does antenna radiation occur? = .00 00 00 00 0 258 . Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. Look at the compensation coil slide. The point is to get the characteristic time constant for the cooling, which is the reciprocal of the exponent coefficient that Excel shows for the fitting equation. It is best to make the impedance matching adjustable, using switched transformation ratio. I installed a QRP SWR meter into the tuner that makes tuning very handy. To further improve the flux linkage, I wound the primary on top of the secondary. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. Zin=46.52+j6.72. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. end fed half wave antenna - awsh.org There are many resources online that explain the details better than I can, so Id suggest doing your own research if youd like to build one for yourself. . What are the advantages and disadvantages of the end-fed half wave antenna? The Counterpoise is a short, typically one twentieth (0.05 *. ) The computation method is also touched on. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. One point of my small-core, compact winding design was to be able to cool the core. The final turns ratio turned out to be 3:29. ON7EQ EFHW Antenna - qsl.net This graphical depiction makes it easier to visualize the current and impedance correlation between bands. It should be no surprise that 80pF is close to optimal. Selecting the variable capacitor that can be varied from this minimum to maximum capacity, will allow tuning to resonance for 40, 30, and 20m bands at each of the switch position of the tuner. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. I have been searching the internet for a very long time (AA5TB, VK3YE, SOTA Reflector, among MANY others), and your posting finally made clear for me the many questions I have had. It may be one or even five kilo-ohms. Highest frequency = 14.350 MHz. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. I tossed the line as far up as I could in a tree. It uses a coil as a compensation unit, and no counterpoise. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. I placed the box in a cool oven and let it get up to about 200 F, soak for a while, and then I took it out, hung it in still air and measured the temperature as time passed and the box cooled. I found it very useful to label the tuner with switch and capacitance positions. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. = 1/30.e6 = 33 nS. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. How to tune a multi-band EFHW antenna using a loading coil How-To: Make a Multiband EFHWA for Amateur Ham Radio Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. It is recommended to use at least 2W non-inductive resistors for this purpose. It is important to consider the voltages on this tank circuit. The above data from K1RF shows that the SWR for 20 meters (my dark red markings - SWR scales differ in each graph) is about the same with or without a capacitor in the transformer primary. The latest news about Efhw Compensation Coil Experiment. How to get started on ISS Cross band Repeater? Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. Your article was well written and very informative, thanks. How far could it possibly reach? PDF MANUAL: ENDFEDZ ALLBAND-KW 80-10 EFHW 1KW ICAS ANTENNA - DX Engineering My goal was to describe the parameters of an antenna that can be easily build, yet show enough theory for someone to design his or her own antenna and antenna tuner. Lets do a quick calculation to see how much an issue is this output capacitance. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. Typically the IC-751A would read about 60W on its power bridge, the Siliconix would show >50W on the 50W scale and 45W on the 500W scale, so there is ~20% uncertainty. Hence, we need to move along and start to include the antenna with our testing. How big and where to place it is likely best determined empirically. This will yield the maximum capacity of the variable capacitor. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. It depends on the selection of the inductance and the capacitor values. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. I wanted to test the hypothesis that an inductance near the box would compensate for the output capacitance and further improve match on those bands. After acquiring a MTR3b for SOTA activations I decided I needed a different antenna than the End Fed Random Wire (EFRW) or the speaker cable 20 meter dipole I use with my KX2. EFHW Antenna Frequency Compensation Lead - YouTube Some hams swear by them, yet some completely demean it. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. These dimensions were derived from modelling the antenna in EZNEC. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. Then record the change in temperature recorded at the core from the probe, and the elapsed time so I could corrected for not reaching perfect equilibrium. Hello, a wonderful approach for the problems.. The overlaid VSWR plots are shown below. Hence after about 3pF of output capacitance, the source will have a hard time charging up that capacitance before it is time to start discharging it. I dont have an amplifier, so only need to be able to handle 100W. Saturation of a warm core happens near 0.2 T (2000 g) and if you dont want to deal with significantly reduced permeability, then better to limit to 0.1T. This is typically a weak spot. It performed well on both the 2m and 70cm bands. See the table above. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. clear. When the transformer was mounted in its box and the output connected to an antenna connector feedthrough, the observed capacitance increased dramatically to about 6.0 pF. Jim, do you mind if I add your email and my answer as a comment to the article? With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. But I would caution its usage for higher power than 10-15W. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. In theory, the examination is supposed to be used to help clarify your medical condition and . The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. Two layers of 1mil Kapton tape are placed over the winding. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. Isn't it? The SWR figures were as follows: FT240-43 132ft/100pF capacitor Because of the division of power between the 3220 resistor and VNA input, there is effectively an attenuator of -10*log(50/(50+3220))=18.16dB, so |S21| has a component due to this division. EFHW Antenna Frequency Compensation Lead 5,144 views Jan 20, 2019 188 Dislike Share Save Steve Ellington 9.92K subscribers 8 inches of wire attached to the antenna post can lower the frequency. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. I would mention first its ease of installation. This provides proper insulation from the relatively high voltages on the seconder winding. I ran WSPR at 10mW for about 2 hours and got the results below. Ismerje meg a hozzszls adatainak feldolgozst . Lowest measured inductivity = 2.0 H. The usual problems of having the multiple band resonances all line up appear here with the end-fed design, similar to the same issue with off-center-fed designs. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. However, it has its idiosyncrasies. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. The bottomline, your putting the relationships of 1) Toroid windings and to measure their inductance together with 2) the required capacitance calculation is exactly what I needed to move forward with my specific design plans.