The antennas are set up as a sloper as in my SOTA outings. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. Consequently, this is how the capacitance values are determined. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. The EFHW transformer box from outside. In his article, I will try to bust some of the myths associated with Inverted. I am building an EFHW antenna for my new. I chose to use FT8 transmissions for this test since they generate 100% duty cycle during the transmission period with an average duty cycle of 12.6 sec / 30 sec = 42% overall when including the listening periods. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. . This can then, fed with coaxial cable, in many cases be . 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" Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. After some internet research, I settled on making the former from a paint roller. This reveals we only need to compensate for the reactive component. Can you give me an idea for your 100 W version, you built for 80/60/40 m. Now I just need to build or acquire a decent radio to utilize this new antenna. coil inductance calculator at 66pacific.com. The original coil is designed for low power portable applications. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. There is no substitute for playing with the analyzer, trimming the wire, adjusting the compensation coils, etc., and going through the process for a few iterations to get the multiband antenna to work well for you as you have it installed. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. Feeling brave, I decided to tape my coil up and solder connectors on and hope I would be one of the lucky ones who wouldnt need much coil adjustment (will I be right??). Wrap the first wire around the toroid 27 times (I used a black wire for this). What are the advantages and disadvantages of the end-fed half wave antenna? 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 . <> By using traps, the antenna works on all three bands with no operator interaction. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. |k"^N>F.AnJkJsq'PV}o0I. I set up an EFHW for field day using a similar transformer with 25 ft. of coax from the box, everything floating, to my battery powered radio. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. The latest news about Efhw Compensation Coil Experiment. 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. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. 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 matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. Could it be something to do with the new vertical aerial I had recently installed? Research salary, company info, career paths, and top skills for Software Engineer - EDI Do I count the six loops around the pvc in the measurement? The cooling curve I measured is shown below. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. It is not necessary to calculate the above; the results are sown in the following table. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. Jim, do you mind if I add your email and my answer as a comment to the article? Frank VK1VK. Thermal gasketing between the cores and the aluminum heat sinks could help a lot, as would a single piece of aluminum rather than the stack up of thin sections I used. This will yield the maximum capacity of the variable capacitor. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. Very interesting design. 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. In theory, the examination is supposed to be used to help clarify your medical condition and . The photos above show a method that works fairly well. Klubunknl folyamatos a tagfelvtel. 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. And not all hf antenna installation are same, with most requiring bit of tinkering. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. 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. 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. It is not necessary to calculate the above; the results are sown in the following table. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. It will present its parameters, so anybody with basic home-brew skills will be able to build it. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. The second smallest number I measured was 2.7pF, derived from the self resonance at 2.72 MHz with the magnetizing inductance (measured at 25.8 H) with the secondary open and the output wire folded to a small 1/2 length. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Firstly, lets estimate at 3.6MHz minimum number of turns to ensure that magnetising conductance is less than about 0.002S (for better than 90% core efficiency). = 1/30.e6 = 33 nS. Zin=46.52+j6.72. A radio station is as good or as bad as the antenna it has. 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. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. All Rights Reserved. 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. 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. With such a switch, it is impossible to forget to switch back to operational mode. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. 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. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. . Is it any good? If you stare at the above frequency sweeps you will discover a few things. 100W on a Wire antenna! I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. In this case, it looks important. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. If the antenna is not tuned properly, and it represents other than 50, the diode will rectify the current flowing across the bridge and the LED will light up. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. I will go back and have the article corrected. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . Just the bare 80m wire is shown in red. = 258 * 10^-12. The SWR was low, but not unity, so the peak voltage was lower than the 50 ohm match value when measured with the high-Z scope probe. How to get started on ISS Cross band Repeater? Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! 2015. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. 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. Ive spent some time on digital modes over the last week and and my signal reports seem very similar to the pre-80m-extension period, which is good, and I am getting out well past 1000 miles on 20, 40m and 80m digital. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. But Ill find the error of my ways.and there are various on-line calculators to help me ensure I get the decimals and (H, mH, uH, pH, etc.) Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. (LogOut/ However, a key restriction is its 25W power rating, due to the small matching transformer. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. I did struggle with the C in pF calculation..I seem to be getting hung up on the correct decimal placement..for example, for the 40-meter Capacitor requirement, I get .000000000258: C pF = .000001 / [ ( 2 * 3.14 * 7 MHz) ^2 ] * 2 uH I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. The original coil is designed for low power portable applications. It uses a coil as a compensation unit, and no counterpoise. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. 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. Once completed and tape-wrapped, I applied a layer of liquid electrical tape over the surface and the interior wire connections, ready to go outdoors. 3) Total losses are approximately independent of core volume. The highest frequency could be14.350MHz. It is best to make the impedance matching adjustable, using switched transformation ratio. The final turns ratio turned out to be 3:29. The model results show the need for a not entirely insignificant counterpoise. There is much more that can be written about this antenna and its matching, but that was not my aim. The transformer fits sideways in the box with a few millimeters to spare. This antenna is only 15m long using 2 loading coils. I came up with a very simple way to build these coils on the antenna wire that proved quick and easy to change and test, involving small piece of PVC pipe and a piece of Velcro shown below. I am planning to use this latest one at the Field Day next year. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. And of course, a counterpoise with various lengths. The next important parameter is the parallel resonant circuits resonant frequency. Some say you do not need a counterpoise, but that is false. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? I then added two 220pf capacitors in series between the center conductor and ground. Thanks in advance, good health for you in these times, A week or two later I started to notice an occasional knocking sound inside the house. After doing the ferrite transformer scaling experiments last time, and learning a bit more about what matters in these transformers, it was time to make a stab at designing one. 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. Change), You are commenting using your Facebook account. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . What are its disadvantages? 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. 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. Taking the time derivative of the above equation you get the power dissipation. 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. Wow, Gary! This is not an optimal value, benefit may be obtained by exploring small changes to that value. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. Best regards and thanks again for your comment. Why had I not noticed this before? (LogOut/ Thank you for an interesting and informative read. Is FT8 popularity growing at the cost of SSB Phone and CW? On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. So, I embarked on testing it for myself. Compensation. I mounted the transformer on a tree for testing. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. This is perhaps one of the most hotly debated rookie topics in. Lowest measured inductivity = 2.0 H. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. It requires a set distance to hang both ends of the antenna, and that is not always given. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. I use shock cord to connect the insulator at the end of the wire to my fence. 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? Why does antenna radiation occur? You can start with the links below. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Can I get away with no capacitor in my design? used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. 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. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. It is important that resonance may be achieved at each tap of the inductance. My favorite SOTA antenna is the End-Fed Half Wave Antenna. Next, I started winding the transformer. In an urban area we are much more restricted, especially if we need to be stealth about it. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. It turns out that we can easily measure the effective parallel secondary capacitance by looking at the primary self resonance when the secondary is open. To be safe, better not get much above 120 C. Does your station desperately need a good RF ground to behave properly? For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. The SWR results are as follows: This transformer has more surface area than a FT82-43 based one, so it has higher capacity to dissipate heat, and it is more efficient, so it will have higher power capacity than the FT82-43 based one. Lets do a quick calculation to see how much an issue is this output capacitance. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. : I see you were able to post your comment now, so I just copied my email answer here for others to see. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. How far could it possibly reach? The basic question before us is how does an antenna work? 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. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. I found it very useful to label the tuner with switch and capacitance positions. Be sure to take a look for additional analysis and conclusions. Two layers of 1mil Kapton tape are placed over the winding. 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. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. My question is what is 'higher frequency' specifically? 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. 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. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. Above 7MHz, there is very little temperature dependence at all. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. I first mounted the SO239 connector to the box. It is important to consider the voltages on this tank circuit. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. How does this SWR meter works? Even at only 100W, the RF voltage on the high Z output of the transformer can easily be >1300 Vpp, so this is not an idle concern. It should be no surprise that 80pF is close to optimal. A 100pF silvered mica was connected in shunt with the transformer primary. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). 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 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. It is worth experimenting with its length also. On the transformer, I added a few wingnuts to tighten down the antenna wire. Apply for the Job in Software Engineer - EDI at St. Louis, MO. = .000001 / 3868.88 As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. The final turns ratio turned out to be 3:29. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. VK1OD.net (offline). However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! P.S. 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. The SWR for the 20 meter EFHW antenna was < 1.2:1 Cmzett: Weince joseph How can we help? We also know, that both ends of the half wave antenna will have the highest voltage, thus impedance, which may reach up to several kilo-ohms. The band compensating inductor placed on the wire is another story. The results are presented below. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. Change). Let us touch on some necessary theory to begin with. The goal of the temperature characterization is to determine how much temperature difference (core to ambient) there will be for a given level of power dissipation. 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. Some of my research showed that a small compensation coil can be added about 2 meters from the transformer to pull down the SWR on the higher bands. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. To further improve the flux linkage, I wound the primary on top of the secondary. That is an end-fed, but very different then the half wave construction. 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. blue: 250pF, to much compensation. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. Impressive article and so well done that I may give it a try. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Thank you Gary. This antenna is working for 80,40,20,10 and 6m bands. I also will ask, why didnt it work for you. I am currently working on measurements of an EFHW antenna. 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. I checked the wall brackets and mast, but all the fixings were nice and tight. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. (LogOut/ i liked it a lot, you give good ideas, many thanks. I used the 14g enameled wire and wound it on the FT240-43. The 2 coils are 35uh and 90uh. Instead, this shifts everything down and makes it very easy to tune 10m. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. I used four parallel #28 wires (not twisted) for the primary. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. % Note the material 43 hysteresis curves shown below for 25 C and 100 C has a smaller open area (and hence lower losses) at the higher temperature. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Subscribe to our newsletter and receive regular updates on new posts and articles. The End-Fed Half Wave Antenna a bit Differently, The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Ismerje meg a hozzszls adatainak feldolgozst, 40 M R/7E azaz a kirlyi ejternysk rdillomsa, jra megy az SSTV tjtsz 144,500 MHz-en. Understanding Antennas The Good, the Bad, and the Ugly. 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. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. 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.