This can then, fed with coaxial cable, in many cases be . (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . If you stare at the above frequency sweeps you will discover a few things. The resistance (real) component of the impedance is right where we want it near 50 ohms. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. It is worth experimenting with its length also. 100W on a Wire Antenna How far would it reach? A week or two later I started to notice an occasional knocking sound inside the house. Most informative and appreciated. The computation method is also touched on. = .00 00 00 00 0 258 The technical storage or access that is used exclusively for statistical purposes. Two layers of 1mil Kapton tape are placed over the winding. It not a loading coil. One possible explanation is that the core losses drop with temperature. For my build, I started with a waterproof enclosure from the hardware store, a panel mount SO239 connector, an FT240-43 toroid, two 220pf 15KV capacitors, and 14g enameled copper wire, and some hardware to connect it all up. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. The difference here is that the target bands are low frequency. Measurements were made on the unmounted transformer with just a ~2 inch length of lead from the secondary to the 2450 load and sampling resistor (jig connections as shown in the photo above). Of course, you will need to find your tuning positions and apply your own position scale. I dont have an amplifier, so only need to be able to handle 100W. Also find news related to Efhw Compensation Coil Experiment which is trending today. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. The final turns ratio turned out to be 3:29. Look at the compensation coil slide. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? This is based on random lengths of the antenna, which is transformed with the un-un into a medium-ohmic impedance range with reactive components. blue: 250pF, to much compensation. It is best to make the impedance matching adjustable, using switched transformation ratio. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. Thank you for your comment and feedback on the article about the EFHW antenna. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. The band compensating inductor placed on the wire is another story. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Klubunknl folyamatos a tagfelvtel. document.getElementById( "ak_js_1" ).setAttribute( "value", ( new Date() ).getTime() ); Enter your email address to subscribe to this blog and receive notifications of new posts by email. The transformer fits sideways in the box with a few millimeters to spare. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. The coil came out at 89mm in length rather than the theoretical 83mm not surprisingly, but the inductance was bang on at just over 109H. Does your station desperately need a good RF ground to behave properly? For . The SWR results are as follows: When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. EFHW coil and 80m extension in place (coil visible at tip of red arrow) With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. My End-Fed Half-Wave (EFHW) AmateurRadio.com The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Yes, there is a coil a few feet from the box but it is NOT TRAP, it is no secret as well, actually, everything in this antenna was published and patented by few people a long ago. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. Efhw Compensation Coil Experiment - Local Search Denver Post ENDFED/EFHW Antenna & Choke - F5NPV - V85NPV On the transformer, I added a few wingnuts to tighten down the antenna wire. The VSWR plots below show results from the same transformer tested on the bench with minimal output capacitance, with a primary compensation capacitor, either 100pF or 27pF included, with the transformer installed in its aluminum box including antenna connector feedthrough, and with the transformer with an 18 clip-lead on the antenna output. At FT82-43 matching transformer for an EFHW I wrote about the likely losses at 3.6MHz of a common design using a FT82-43 ferrite core with a 3t primary. Make sure the first wire is wrapped evenly around the whole toroid. I added some Christmas colored zip ties to hold everything in place. It is recommended to use at least 2W non-inductive resistors for this purpose. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. In practice, exactly how you wind the primary turns can drastically affect the high frequency behavior of the transformer when measured into a 2450 load. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. I have been using a 40m End-Fed Half Wave (EFHW) antenna very successfully for the last few months and I wanted to extend the design to multi-band whilst avoiding the need to take a . . However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? 40M EFHW & 3D printing - Member Projects & Builds - Parker Radio End-Fed antennas are useful in many ways, includes easier mounting of cable at one end (freeing the antenna from unnecessary weight of cable) & antenna maintenance in future. I have been offered input VSWR curves for such a configuration, and they are impressive but VSWR curves do not address the question of loss / efficiency. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. I ran WSPR at 10mW for about 2 hours and got the results below. 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. These dimensions were derived from modelling the antenna in EZNEC. 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. Software Engineer - EDI - salary.com : I see you were able to post your comment now, so I just copied my email answer here for others to see. For a quarter wave that is about 8 nS. Assuming, most of us use the 40/30/20m band for HF SOTA activation, so the following table shows the SOTA frequencies, and the calculated half wave radiator wire of the antenna. I've always had issues with 10m loading up properly so I'll also be adding a compensation coil 78 inches from the feed point on the wire. That will be the missing resistor in the resistor bridge of the below circuit. Taking the time derivative of the above equation you get the power dissipation. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. 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. % From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. As I reexamined my formula, you pointed it out correctly, there is an error in it. Below about 7 MHz, transmission losses increase as the core temperature increases. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. I got the, http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html, End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil. Dutch radio amateurs in particular have been active in this area: John, PD7MAA's blog - http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html Jos van den Helm's (PA1ZP) article published in Radcom: "A 3- or 5-Band End Fed Antenna", February 2016, Radcom, published by the RSGB in the UK. A week or two later I started to notice an occasional knocking sound inside the house. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. Don't sweat the digits to the right of the decimal point too much, the SWR readings changed as the feed height and droop of the antenna changed. However, it has its idiosyncrasies. The SWR for the 20 meter EFHW antenna was < 1.2:1, The SWR for the 40 meter EFHW was ~1.4:1 for 40 meters and 1.2:1 for 20 meters (full wavelength), For my 20, 30 and 40 meter EFHW antennas I will not use a capacitor in the primary. The 2 coils are 35uh and 90uh. The next important parameter is the parallel resonant circuits resonant frequency. Below is the schematic of the final build. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. Best regards and thanks again for your comment. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? clear. It is important to consider the voltages on this tank circuit. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned -- The experiments have been performed, check it out! Then I covered the coil in kapton tape to hold it together. Highest frequency = 14.350 MHz. A half-wave at the lowest band of interest will also work well on all harmonically-related bands which has become particularly attractive to those wanting a quick portable wire antenna. Multiband End-fed Half-wave EFHW Antenna - VU2NSB.com From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . It is hard to wait an infinitely long time for the box to equilibrate to a given power level. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. Most of the time 5 to 20W will be adequate for activation anyway. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. The maximum B field in the core is proportional to the imposed voltage, as: where A is the cross sectional area of the core, f is the frequency and N is the number of turns. . What are the advantages and disadvantages of the end-fed half wave antenna? Im very happy with the result. 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. End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil Your article was well written and very informative, thanks. I used the 14g enameled wire and wound it on the FT240-43. How does this SWR meter works? This illustration provides a graphical view of approximate comparative difference in expected Common-Mode-Current (CMC) that could flow on the transmission line to undermine the overall performance of the antenna system. With the entire winding length short, the flux from the primary need not travel all the way around the core to link all of the secondary turns. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. You cant really see the antenna wire, but the red line shows the antenna path. All Rights Reserved. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. Transmitting on 15 meters was impossible because of RF into the radio. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. Some website features may not function optimally without cookies. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. 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 wish I had a simple answer, but really this is where some experimentation can pay off. The biggest uncertainty in these measurements was the actual power level used. It is worth experimenting with its length also. Basically, the loading coil is operating as a trap. Trapped 20/30/40 Meter EFHW Antenna - AI6XG Geeksite End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. 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. Above, the magenta curve is measurement of a real transformer from 1-11MHz with nominal resistance load and three compensation options: cyan: 0pF, too little compensation; magenta: 80pF, optimal compensation; and. Change), You are commenting using your Facebook account. Why does a wire carrying RF current radiates to produce EM waves which travel through, Beware of Skip Zone while working HF radio A good radio amateur friend of mine from Poland sounded quite anxious when he told me that his new antenna was behaving peculiarly. This is typically a weak spot. They will be adjusted for resonance at or close to the CW portion of the bands. In my research on End Fed Half Wave (EFHW) antennas I found that nearly all have a capacitor in the primary (rig) side of the transformer. 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave Ham Radio DX 27.1K subscribers 19K views 7 months ago #HamRadio #AmateurRadio #EFHW Here are my experiments and modifications with an EFHW. Lets call this element the LoadAttenuator. Impressive article and so well done that I may give it a try. We use cookies to optimize our website and our service. Adding an additional 2 meters to the counterpoise did very little to affect the resonant frequencies, much less than adding that length to the main wire would accomplish. Thanks in advance, good health for you in these times, In my research on End Fed Half Wave (EFHW) antennas I found that nearly all have a capacitor in the primary (rig) side of the transformer. 2 0 obj Therefore the Great Circle Map generated below should be Read More, Multiband End-Fed Half-Wave EFHW Antenna The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. I am currently working on measurements of an EFHW antenna. Thanks again Jim. 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. If you really want to get the heat out, add some fins to the aluminum box. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. Firstly, bandwidth on 80m is restricted to about 80 kHz at . Although it is simple to build and is a multiband antenna, it has several attributes that . The Truth, ,and Nothing But The Truth (as I've experienced it) In theory, the examination is supposed to be used to help clarify your medical condition and . I then used a piece of heat shrink on the outside to hold everything in place. Note: More extensive experiments including operation at HF frequencies higher than 20 meters, harmonic versus fundamental operation and transformer efficiency is posted in this blog. Fig.1 - Withdraw the radiating element carefully to avoid damaging the matching components A few years ago I bought a secondhand Diamond X50 dual band (144/430) antenna at a radio car boot sale. of the wavelength. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. 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. One end is about 5 meters high on an extended fishing pole. Lowest measured inductivity = 2.0 H. Why does antenna radiation occur? And of course, a counterpoise with various lengths. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Copyright 2014-2023. Consequently, this is how the capacitance values are determined. (LogOut/
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