Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. With the cooling curve and a good estimate for the heat capacity of the box, now it is just a matter of running some power through the transformer and measuring the the temperature rise from ambient to be able to determine the power that turns to heat in the transformer. The basic question before us is how does an antenna work? It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. I used the 14g enameled wire and wound it on the FT240-43. 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. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. 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. . CG K/ J/ S/ B to 4-20mA 0-1800 Celsius Thermocouple Converter TC Input 4-20mA Output Head-mounted Temperature Transducer first impressions, Some wisdom that shapes articles on this site, Designing high performance VHF/UHF receive systems, A new impedance calculator for RF inductors on ferrite cores, Calculate ferrite cored inductor (from Al), Calculate VSWR and Return Loss from Zload (or Yload) and Zo, https://owenduffy.net/files/EstimateZFerriteToroidInductor.pdf. 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. Further if your antenna requires a biggeer counterpoise on some bands, you can increase the size of the radiating element or improve your Tuner by using fine tuning capacitor or altering the coils slightly by varying the coil windings (compressed/spread out) slightly. I dont have an amplifier, so only need to be able to handle 100W. I wish I had a simple answer, but really this is where some experimentation can pay off. Above is a sweep of the roughly compensated transformer. 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 SWR figures were as follows: FT240-43 132ft/100pF capacitor 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. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. I found that sometimes the multimeter that was measuring the temperature would give unreliable information when RF was present, so the off periods provided regular intervals for measuring the temperature. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. 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. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. IIRC they call it a "compensator". 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. Thanks for your comments. PART - 1 : The EFHW antenna as a radiating and receiving element is a decent multi-band antenna with good efficiency on all bands, provided it is driven at its feed-point using a well configured and well-matched driving source. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. Hence, we need to move along and start to include the antenna with our testing. nanoVNA-H can firmware be updated if it has a broken USB socket? Is FT8 popularity growing at the cost of SSB Phone and CW? The resistance (real) component of the impedance is right where we want it near 50 ohms. Csatlakozz csapatunkhoz! Impressive article and so well done that I may give it a try. Wrap the first wire around the toroid 27 times (I used a black wire for this). Your article was well written and very informative, thanks. Could it be something to do with the new vertical aerial I had recently installed? The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Why had I not noticed this before? I will go back and have the article corrected. And now I am planning to build one for 160/80m. You can see the coil in the picture below (red arrow). 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. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. The low end of the secondary, which will be the tap, is bent back over to the center of the winding and covered with a small piece of Kapton tape, and then the primary is wound over the tape (and the secondary tap wire). Im very happy with the result. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. A ktelez mezket * karakterrel jelltk. If you stare at the above frequency sweeps you will discover a few things. 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 in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. 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. Regards VE9HAM. For . To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. blue: 250pF, to much compensation. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. Thanks! After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Why does antenna radiation occur? The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. Nagyon j ez a cikk. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. Some website features may not function optimally without cookies. 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. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. It is worth experimenting with its length also. Let us touch on some necessary theory to begin with. 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. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. 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. % The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a [email protected] email-cmen, vagy egy klubnapon jelentkezni nlunk! Im very pleased with that indeed. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. coil inductance calculator at 66pacific.com. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. To explore parameter space a little, I modeled a couple of lengths for the counterpoise and see how the wire is resonant across the band when fed with various impedances at the driven point. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. 2015. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. I added some Christmas colored zip ties to hold everything in place. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? Proudly created withWix.com. The previous table already contains these measurements. Your posting put it all together for meTHANK YOU!!!! This is typically a weak spot. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. 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. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. The results are presented below. Research salary, company info, career paths, and top skills for Software Engineer - EDI To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 100W on a Wire Antenna - Is it good enough for DX? In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). It is quite possible that designing more than three or four bands into a tuner will lead to a failure. 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. 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. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. The impedance matching circuit is essentially a simple parallel resonant LC circuit. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. On the transformer, I added a few wingnuts to tighten down the antenna wire. 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. [email protected] It requires a set distance to hang both ends of the antenna, and that is not always given. 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. 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. The EFHW transformer box from outside. So the differences I see in the data sheets hysteresis curves are not the correct explanation. If you really want to get the heat out, add some fins to the aluminum box. The highest frequency could be14.350MHz. Most of the time 5 to 20W will be adequate for activation anyway. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. |k"^N>F.AnJkJsq'PV}o0I. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. 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. Some hams swear by them, yet some completely demean it. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. This will yield the maximum capacity of the variable capacitor. Jim, do you mind if I add your email and my answer as a comment to the article? Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. Ive been wanting to get back into radio stuff for a while now, but the only antenna that I have up now is a 40 meter dipole. 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. The smallest number I measured was 1.6 pF, derived from the self-resonance at 41 MHz with the leakage inductance (measured at 198 nH) when the secondary was shorted. Based on a 2014 survey, the most popular antennas for SOTA (Summit On The Air) activation are the following (see sotabeams.co.uk/blog/5-most-popular-hf-portable-antennas for details): Let us not confuse the End-Fed Half Wave antenna with the Random Length End Fed wire. 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. We need to measure the inductances of the toroid with the tapped coil. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. First, note that the transformer has low transmission loss up to nearly 50MHz. We use cookies to optimize our website and our service. I will publish my findings, but I cannot not promise to complete it until early fall. The transformer fits sideways in the box with a few millimeters to spare. The real power limit will be core heating. The technical storage or access that is used exclusively for anonymous statistical purposes. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. 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. = .00 00 00 00 0 258 The impedance per unit length of a lumped transmission line is where L and C are values per unit length. Next, I started winding the transformer. It not a loading coil. 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. Zin=46.52+j6.72. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. application of Kirchhoff's current Law on a typical EFHW antenna configuration. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. 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'. The final turns ratio turned out to be 3:29. 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. Understanding Antennas The Good, the Bad, and the Ugly. But systems that work better increase the prospects of contacts. Klubunknl folyamatos a tagfelvtel. Basically, the loading coil is operating as a trap. This will also be handling 100W. 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. Lowest measured inductivity = 2.0 H. The results are shown below. This antenna is working for 80,40,20,10 and 6m bands. clear. Of course, you will need to find your tuning positions and apply your own position scale. I look at the end-fed as just an extreme example of an off-center-fed antenna. How far could it possibly reach? 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! 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. 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. I then used a piece of heat shrink on the outside to hold everything in place. 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 suspect that a small coil near the transformer is generally a good idea, whether it is my transformer design or others, since it is very difficult to get the antenna wire out of the box without incurring some excess capacitance. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. %PDF-1.4 When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. Best regards and thanks again for your comment. However, it has its idiosyncrasies. 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. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. This antenna is only 15m long using 2 loading coils. How badly can high Local Ambient QRM affect HF Radio? 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. If you really wanted to push this design, you could include thermal grease or thermal pads in the stack-up to improve the heat transfer, but I chose to keep it clean and see how it would do without any special effort. I was curious why this capacitor was added to the transformer. Now I just need to build or acquire a decent radio to utilize this new antenna. From that we can find Mismatch Loss. 100W on a Wire Antenna - How far would it reach? I would mention first its ease of installation. This can then, fed with coaxial cable, in many cases be . 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? Increasing the drive impedance tends to move the resonances to slightly higher frequencies. Update: Full size 132ft EFHW For one month I replaced the 66ft wire and loading coil and replaced it with a full 132ft of wire, connected to the FT240-43 balun. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. Even at 15W the voltage at the ends may reach 100-200V. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. I particularly want to know how counterpoise affects the common mode currents on the coax. This happens to place the coil near the peak of a current maximum for the 20m band, which coincidentally appears to have significantly improved the match on that band. There are many good descriptions on the net about this type of antenna. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. Then I covered the coil in kapton tape to hold it together. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. The antennas are set up as a sloper as in my SOTA outings. On one end, I added a ring terminal to connect it to the transformer and on the other end, I connected an electric fence insulator. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. It uses a coil as a compensation unit, and no counterpoise. Above 7MHz, there is very little temperature dependence at all. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. 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. The antenna is up. If not a lightning strike, I will write an article about the experience as well. 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. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. Firstly, bandwidth on 80m is restricted to about 80 kHz at . This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. 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. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Let's find out! There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. Interpretation of S-Meter Noise Floor in HF Radio Receivers. The wire as I strung it up seemed to resist having a good SWR for the 20m band. 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. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. This suggests an inductive reactance. Copyright 2014-2023. 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. 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. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. And of course, a counterpoise with various lengths.
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