The overall lenght is only 15m. It uses a coil as a compensation unit, and no counterpoise. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. Compensation. I mentioned in the reference article that the metric A/l captures the geometry, the larger it is, the fewer turns for same inductance / impedance. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. 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. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. Im very happy with the result. There are two aspects, however that we need to consider: Lets begin with the transformer. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. Lets do a quick calculation to see how much an issue is this output capacitance. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. I needed to add an additional coil (approx 12.5 uH) about . I dont have an amplifier, so only need to be able to handle 100W. Can a diode be used to rectify signals smaller than its threshold voltage? Why had I not noticed this before? But systems that work better increase the prospects of contacts. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. I wish you lots of productive experimentations and successful portable operations. 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. Although the original loading coil is very well engineered, I thought I could make a more efficient version given that I did not need to make it 'trail friendly'. Thank you Gary. 73 I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. So, how to construct an end-fed half wave antenna? of the wavelength. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. 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. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. point to the loading coil is 20.2m and this sets the 40m resonance at 7.1MHz, which in turn dictates the responses of the harmonically related bands 14MHz, 21MHz and 28MHz. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, Once I had upgraded the matching transformer for my EF-10/20/40 MKII "EndFedz" (see Part 1) my thoughts turned to the loading coil. 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. PART - 2 : Most EFHW antenna configurations resort to the use of broadband impedance transformers at the feed-point to attain acceptable SWR on all operational bands. The negative effects of local QRM on an, How does antenna radiation occur? This gave me an effective coil diameter of 40.5mm. Basically, the loading coil is operating as a trap. The SWR for 30 meters, 1.05:1, was the lowest of all three antennas since the transformer was tuned for impedance match at 30 meters. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. Taking the time derivative of the above equation you get the power dissipation. SWR for 80-10 meter EFHW with no capacitor, SWR for 80-10 meter EFHW with 100 pfd capacitor, The above data from K1RF shows that the SWR for 20 meters (my dark red markings -, I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned, 40 meter and 20 meter (full wave) SWR with no cap. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. Start by wrapping the wire around the toroid. 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. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. 100W on a Wire antenna! 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. This antenna is only 15m long using 2 loading coils. This is indeed a classic antenna that is not only, Introduction to Omnidirectional Antennas In the literal sense, an Omnidirectional antenna is an antenna that radiates uniformly in all directions. Thank you for your comment and feedback on the article about the EFHW antenna. Cmzett: Weince joseph How can we help? At this point, I'm leaning towards the EFHW, but any of these antennas seem . A graphical presentation of the mathematical analysis of EFHW antenna SWR variations on account of variations in counterpoise length as well as the Unun impedance transformer at the feed-point. How big and where to place it is likely best determined empirically. The parasitic reactances near the feed-point also vary between installations. It should be no surprise that 80pF is close to optimal. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. (LogOut/ I can give a link if you need. I am currently working on measurements of an EFHW antenna. However, from the measurements we made on the self resonance frequency, we know that most of this capacitance is right at the output of the transformer and not internal to the windings. Trapped five band EFHW SOTA antenna. 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. Impressive article and so well done that I may give it a try. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Your article was well written and very informative, thanks. It is worth experimenting with its length also. The biggest uncertainty in these measurements was the actual power level used. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! The commonly used primary compensation capacitor does not work very well for this winding method which keeps the leakage inductance as low as it does. |k"^N>F.AnJkJsq'PV}o0I. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. . Ive been wanting to put together a decent multi-band antenna for a long time and finally settled on an end fed half wave antenna. I used the 14g enameled wire and wound it on the FT240-43. You can start with the links below. The 2 coils are 35uh and 90uh. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Krem, rja le, mi a krdse. I have an EFHW and the SWR is acceptable on all the bands with the exception of the WARC bands which is to be expected since the harmonic relationship is different. Nagyon j ez a cikk. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. I tossed the line as far up as I could in a tree. The SWR for the 20 meter EFHW antenna was < 1.2:1 Therefore, installation is quite easy, and its tuner circuit is rather simple as well. It is all about getting the heat out. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. Best results are with 2450 drive impedance and the 3.3m counterpoise, so it is not surprising that 49:1 transformers are the common choice. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. I particularly want to know how counterpoise affects the common mode currents on the coax. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. For the transformer, a T130-2 toroid will be sufficient, on which we wind the seconder with multiple taps, as shown in the below table. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. Klubunknl folyamatos a tagfelvtel. Does your station desperately need a good RF ground to behave properly? The final turns ratio turned out to be 3:29. Above, 3t on the primary delivers Gcore<0.002S. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. 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. I wish I had a simple answer, but really this is where some experimentation can pay off. Just the bare 80m wire is shown in red. With no counterpoise wire it will be the coaxs shield providing it. I ran WSPR at 10mW for about 2 hours and got the results below. There is much more that can be written about this antenna and its matching, but that was not my aim. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. Could it be something to do with the new vertical aerial I had recently installed? It is important to consider the voltages on this tank circuit. My favorite SOTA antenna is the End-Fed Half Wave Antenna. The final turns ratio turned out to be 3:29. It is not necessary to calculate the above; the results are sown in the following table. It is very hard to know what will be the best solution for a given antenna installation if you want to hit all of the bands exactly. Radio Transceiver S-Meter Pitfalls to avoid, Atmospheric impact on VHF Radio Propagation, Terrestrial VHF Radio Signal Coverage LOS, Terrestrial VHF Radio Signal Coverage BLOS, HF Surface Wave Propagation (Ground Wave). However, the insertion loss of the packaged transformer would be intolerable on the 10 meter band if it appeared the same way with an antenna wire connected. I would mention first its ease of installation. Above is a sweep of the roughly compensated transformer. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. However, a key restriction is its 25W power rating, due to the small matching transformer. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. Even at 15W the voltage at the ends may reach 100-200V. 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. Of course, you will need to find your tuning positions and apply your own position scale. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. 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. Throw one end of the antenna wire, extended with a rope, as high as you can on a three, and walk away with the other end and attach it to the tuner. We will return to that shortly, but first let us look at the VSWR associated with such added capacitance when driving the 2450 load resistor. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. 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. When I'm measuring the half way point on my EFHW, looking for 67', how do I factor in the compensation coil on the MyAntennas wire? A week or two later I started to notice an occasional knocking sound inside the house. 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. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. blue: 250pF, to much compensation. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Lets call this element the LoadAttenuator. Why had I not noticed this before? Do I count the six loops around the pvc in the measurement? So the differences I see in the data sheets hysteresis curves are not the correct explanation. Most of the time 5 to 20W will be adequate for activation anyway. The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. Tap and primary high-side are soldered together near the middle of the secondary winding; the ground side of the autotransformer is located over the low-end of the secondary turns. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. 0 7t8An. }pKumm" t7Vb55nx S;/E}*+RS'|(q&wA;n";&.'KDff9H0^SF7 O0~{h9*QX\Mwk> u)Y h&kvDc%=(]F_$?6!:\EsM4"+>R%;93|"Jn\j+1 z}?>xBaR3 c +U+WLX`\Ld.Q2.VDHh']o.)k;a6*~s" Be sure to take a look for additional analysis and conclusions. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. The wire as I strung it up seemed to resist having a good SWR for the 20m band. The results are shown below. Can I get away with no capacitor in my design? Select components with good insolating materials and properly chosen, relatively high voltage rated parts. The photos above show a method that works fairly well. I strung up a nominal 80m half-wave antenna wire into the trees, snaking it through the open screen door to the work bench where I was doing the tests. The EFHW transformer box from outside. A 100pF silvered mica was connected in shunt with the transformer primary. Above is a thermograph of the transformer at 20W input at 3.6MHz. 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. 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. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . . All Rights Reserved. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. Thanks again Jim. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. Consequently, this is how the capacitance values are determined. As I reexamined my formula, you pointed it out correctly, there is an error in it. What are its disadvantages? It is best to make the impedance matching adjustable, using switched transformation ratio. The SWR was measured for each of the three antennas across the CW portion of the bands. 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. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. Basu Bhattacharya (VU2NSB). For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. I look at the end-fed as just an extreme example of an off-center-fed antenna. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! 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. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). The radiation pattern of this antenna on most bands produces multiple lobes. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Best regards and thanks again for your comment. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. I also will ask, why didnt it work for you. VK1OD.net (offline). The basic question before us is how does an antenna work? 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. After some internet research, I settled on making the former from a paint roller. A ktelez mezket * karakterrel jelltk. This will yield the minimal capacitance of the variable capacitor. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible.
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