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I may try to bring down the 20, 15 and 10m bands at some point, either with a small coil 2m from the feed point or with a short section of wire as a compensation lead added at the feed point as shown in the video below from Steve Ellington. 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. If we wish to limit the ferrite temperature to 130 C, then assuming ambient temperature of 30 C, we can tolerate a 100 C temperature rise. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. The total lenght is about 15mtr only and using 2 coils and a little stub (s) on the 80m coil or/and the 40m coil. 1. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. For . The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. A 100pF silvered mica was connected in shunt with the transformer . Thank you Gary. This will yield the maximum capacity of the variable capacitor. It is clear that the capacitance from just mounting the transformer in its box generates a significant reflection at 30MHz for the 10 meter band. Thank you for your comment and feedback on the article about the EFHW antenna. Below about 7 MHz, transmission losses increase as the core temperature increases. Regards VE9HAM. 2 0 obj The antennas are set up as a sloper as in my SOTA outings. No wire counterpoise is used to reproduce the SOTA setup. Ismerje meg a hozzszls adatainak feldolgozst . Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. Which begs the question what happens when you attach the antenna? 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. 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. Is FT8 popularity growing at the cost of SSB Phone and CW? xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. Evaluating it at a we get: which gives the power dissipation simply in terms of the heat capacity, cooling time constant and the temperature difference from ambient. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. 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. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. Copyright 2014-2023. Connected to the packaged transformer, I ran some SWR sweeps with just the bare wire and various configurations of small coils to act as band-tuning compensation. Check your inbox or spam folder to confirm your subscription. Impressive article and so well done that I may give it a try. During portable operations, I noticed that I forgot the toggle switch in the tuning position, just to discover that no one calls me back to my relentless CQ-ing. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. y73s de Michael DL9SKY, Visszajelzs: The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Az e-mail cmet nem tesszk kzz. I added some Christmas colored zip ties to hold everything in place. If you stare at the above frequency sweeps you will discover a few things. Even at 15W the voltage at the ends may reach 100-200V. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. 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. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. 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. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. The wire as I strung it up seemed to resist having a good SWR for the 20m band. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. Wow, Gary! In theory, the examination is supposed to be used to help clarify your medical condition and . VSWR<1.8 over all of HF. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. (LogOut/ Lowest frequency = 7.000 MHz. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. 3) Total losses are approximately independent of core volume. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. For the last step, I put together a RF choke to use between the radio and the feedline. The overall lenght is only 15m. 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. Finally the tank circuits specification is complete, which is sown below. I first mounted the SO239 connector to the box. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. 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. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, For several years the EF-10/20/40 MKII EndFedz has been my main station antenna for HF. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. 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. How badly can high Local Ambient QRM affect HF Radio? 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. It is worth experimenting with its length also. High self-resonant frequency. Best regards and thanks again for your comment. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. Taking the time derivative of the above equation you get the power dissipation. 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? For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. To this end, I weighed the main components of the box and looked up the specific heat capacities to get an approximate overall heat capacity for the entire box. The technical storage or access that is used exclusively for statistical purposes. Start by wrapping the wire around the toroid. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. So the differences I see in the data sheets hysteresis curves are not the correct explanation. As you stated early in your posting, I also have found 99.99% of all posting on the internet tell you WHAT they did.not HOW they determined the specific design criteria. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. Graphed with a log scale, it makes a nice straight line. 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. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. The SWR was measured for each of the three antennas across the CW portion of the bands. . It uses a coil as a compensation unit, and no counterpoise. ROB@COMCOIL.COM Let us touch on some necessary theory to begin with. I used the 14g enameled wire and wound it on the FT240-43. The results are shown below. This is not an optimal value, benefit may be obtained by exploring small changes to that value. I then added two 220pf capacitors in series between the center conductor and ground. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Im a hundred watt guy, so do not have a lot of experience with high voltage RF, but I know that ~5kV peak-to-peak RF voltage that you would expect at the 2450 output at kilowatt power levels could begin to cause you some trouble. = .000001 / 3868.88 In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you. 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. More designs can be found by Googling "80m loaded dipole.". I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. Effects of Local Ambient QRM on HF Radio Local ambient QRM (Noise) from various electrical appliances and other sources in the neighborhood often adversely affect HF radio communication. %PDF-1.4 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. P.S. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. I decided to push for best efficiency with a 5-turn primary. I look at the end-fed as just an extreme example of an off-center-fed antenna. 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. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. No capacitor was installed. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. With no counterpoise wire it will be the coaxs shield providing it. Very interesting design. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. I particularly want to know how counterpoise affects the common mode currents on the coax. 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. The 2 coils are 35uh and 90uh. 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. 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. It is better to build one for 160 and 80m, perhaps add 17m to the design described in this article, and for higher bands it is easier to use a linked dipole. : I see you were able to post your comment now, so I just copied my email answer here for others to see. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . Jos van den Helm's (PA1ZP) article published in Radcom: 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. This can then, fed with coaxial cable, in many cases be . Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. I settled on a compact secondary using #28 wire. 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. I am planning to use this latest one at the Field Day next year. 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. Firstly, bandwidth on 80m is restricted to about 80 kHz at . I will go back and have the article corrected. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? = 1/30.e6 = 33 nS. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. We do not know what the actual impedance will be at the end of the antenna radiator. Most of the time 5 to 20W will be adequate for activation anyway. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. These four data points are plotted on the Transmission Losses chart shown below as the yellow squares, all but the 80 meter point coming in a bit lower than expected losses based on the VNA measurements. I use shock cord to connect the insulator at the end of the wire to my fence. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 100W on a Wire antenna! In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. What are its disadvantages? If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. The radiation pattern of this antenna on most bands produces multiple lobes. Zin=46.52+j6.72. Lets do a quick calculation to see how much an issue is this output capacitance. Thirty turns #28 are wound on the two FT114-43 cores. A tutorial on estimating the impedance of a toroidal ferrite cored inductor for radio frequencies, Pulse test of a Hantek 6204BD 4 channel 200MHz USB DSO and supplied probe. At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. Also find news related to Efhw Compensation Coil Experiment which is trending today. Replacing your AC evaporator or condenser coil might, on average, cost around $1,200, with the typical cost range between $800 and $2,400 depending on the brand, your region and other factors . For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. Not the ideal antenna, but convenient! The real power limit will be core heating. Looking at several builds and discussions, such as commercial antennas (e.g. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. However, it has its idiosyncrasies. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. The Counterpoise is a short, typically one twentieth (0.05 *. ) i liked it a lot, you give good ideas, many thanks. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. Do I count the six loops around the pvc in the measurement? All Rights Reserved. |k"^N>F.AnJkJsq'PV}o0I. So far so good. 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. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. In this case, it looks important. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. I ran WSPR at 10mW for about 2 hours and got the results below. I used four parallel #28 wires (not twisted) for the primary. As is often the case, packaging was determined by what boxes I had laying around. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. The biggest uncertainty in these measurements was the actual power level used. The coil is just 12 turns of wire wrapped around a 0.7 inch diameter tube, located about 6 feet past the antenna's feedpoint. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. The photos above show a method that works fairly well. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. 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. Make sure the first wire is wrapped evenly around the whole toroid. With tension on the antenna wire, you can just roll the coil up/down the wire to try different positions as you are optimizing for a particular band. 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. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. I made one quite similar to it but 3T Primary with #16 speaker wire (2 parallel wires) and 15T Secondary close wound just using about one-third of the circumference of the 2 inch toroid. 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. Now I just need to build or acquire a decent radio to utilize this new antenna. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. Refurbishing aluminium antenna parts affected by weather / corrosion. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. A ktelez mezket * karakterrel jelltk. See the second completed tuner depicted below. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. 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. 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. In an urban area we are much more restricted, especially if we need to be stealth about it. It requires a set distance to hang both ends of the antenna, and that is not always given. To be safe, better not get much above 120 C. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. 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. Ive been thinking about getting an antenna up for 80m, and Ive come across a number of options that interest me and would suit the space I have available realistically no matter what I go for it will be a very compromised antenna, but still much better than none. Krem, rja le, mi a krdse. The antenna is effective and the materials and construction are of a very high quality. I assume you know the GNARC source for EFHW antennas. So I built myself an improved replacement matching transformer. He was afraid that being, Inverted V Antenna - A popular Dipole variant, The Center-fed Half-Wave Dipole Inverted V Antenna An Inverted V antenna is a very popular variant of the standard horizontal dipole. Im very pleased with that indeed. 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. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. 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. The parasitic reactances near the feed-point also vary between installations. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. Note that building loss into antenna system components is a legitimate and common method of taming VSWR excursions, eg TTFD, CHA250, many EFHW transformers, but in some applications, users may prioritise radiated power over VSWR.