Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. 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. I also will ask, why didnt it work for you. 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. There's seemingly conflicting information out there, such as on QRZ the consensus seems to be to either use no choke on the coax, or choke it some ways away from the feedpoint - WA7ARK recommends .07 wavelength, which is about 9' on 40M. 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. I have seen and read quite a few reports of making this antenna, and some got away no problem with the 110uH when they came to set up and adjust the antenna, others needed to tweak their coil turns. In the case of the EFHW 49:1 transformer, the major shortcomings of the most popular current designs are excessive leakage inductance and poor heat transfer from the ferrite material to the environment. No wire counterpoise is used to reproduce the SOTA setup. 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. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. coil inductance calculator at 66pacific.com. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. Im very pleased with that indeed. xZ
Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. = 1/30.e6 = 33 nS. 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. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. I assume you know the GNARC source for EFHW antennas. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). Typically the IC-751A would read about 60W on its power bridge, the Siliconix would show >50W on the 50W scale and 45W on the 500W scale, so there is ~20% uncertainty. These dimensions were derived from modelling the antenna in EZNEC. 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. Isn't it? 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. 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. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. stream Above is a sweep of the roughly compensated transformer. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). Of course, you will need to find your tuning positions and apply your own position scale. 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. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. Ismerje meg a hozzszls adatainak feldolgozst . It is important that resonance may be achieved at each tap of the inductance. 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 results are presented below. In his article, I will try to bust some of the myths associated with Inverted. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. It is worth experimenting with its length also. Change), You are commenting using your Facebook account. The aluminum box is the logical heatsink, so I cut a few scraps of aluminum to make a thermal connection to the bottom of the box and to the lid, adjusting with aluminum shims so that when the box lid is screw down, the entire thermal assembly, with the cores in the middle, is under a little compression. The original coil is designed for low power portable applications. The antenna is up. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. of the wavelength. 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. Refurbishing aluminium antenna parts affected by weather / corrosion. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. 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. It is worth experimenting with its length also. 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. 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. 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. 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. What kind of balun is this? Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. Make sure the first wire is wrapped evenly around the whole toroid. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. I am currently working on measurements of an EFHW antenna. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. 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. This will also be handling 100W. 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. . Measurements were made on the unmounted transformer with just a ~2 inch length of lead from the secondary to the 2450 load and sampling resistor (jig connections as shown in the photo above). In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. application of Kirchhoff's current Law on a typical EFHW antenna configuration. 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. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. What are its disadvantages? The combination of the transformer with the end-fed dipole results in a positive reactance. Proudly created withWix.com. There are many good descriptions on the net about this type of antenna. See the second completed tuner depicted below. 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. Well, in ham radio, everything works. Just the bare 80m wire is shown in red. With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. I drilled a couple of holes at each end of the former, a small one for the wire to pass through and a larger one for a bolt and wingnut for wire attachment as I wanted the end result to be portable across different antenna projects. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. Below is the schematic of the final build. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. 100W on a Wire Antenna - Is it good enough for DX? 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 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. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. I installed a QRP SWR meter into the tuner that makes tuning very handy. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. My favorite SOTA antenna is 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 $2,400 depending on the brand, your region and other factors . We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. A tutorial on estimating the impedance of a toroidal ferrite cored inductor for radio frequencies, Pulse test of a Hantek 6204BD 4 channel 200MHz USB DSO and supplied probe. 0 7t8An. }pKumm" t7Vb55nx S;/E}*+RS'|(q&wA;n";&.'KDff9H0^SF7 O0~{h9*QX\Mwk> u)Y
h&kvDc%=(]F_$?6!:\EsM4"+>R%;93|"Jn\j+1 z}?>xBaR3 c +U+WLX`\Ld.Q2.VDHh']o.)k;a6*~s" It is quite possible that designing more than three or four bands into a tuner will lead to a failure. A week or two later I started to notice an occasional knocking sound inside the house. The transformer fits sideways in the box with a few millimeters to spare. The model results show the need for a not entirely insignificant counterpoise. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Typical EFHW Antenna Characteristics & Performance, Influence on Performance due to Deployment Environment, Construction Variables and Transmission Line Interface, Optimum Counterpoise length and Coupling Transformer, Influence of EFHW wire orientation on performance, Good Antenna for any Radio Station is vital The importance of antennas for radio communications can never be over-emphasized. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. 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. The SWR for the 20 meter EFHW antenna was < 1.2:1 This article will not address that antenna type. These, in turn, are instrumental Read More, Learn CW Morse Code Lesson Set 2 This is Lesson Set -2 in our multi-part series of CW Morse Code hands-on tutorials where we will introduce numerals and a few important punctuation marks as Read More. I found it very useful to label the tuner with switch and capacitance positions. The EFHW transformer box from outside. Wrap the first wire around the toroid 27 times (I used a black wire for this). However, a key restriction is its 25W power rating, due to the small matching transformer. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. I use shock cord to connect the insulator at the end of the wire to my fence. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. As is often the case, packaging was determined by what boxes I had laying around. The latest news about Efhw Compensation Coil Experiment. This antenna is working for 80,40,20,10 and 6m bands. Thank you Gary. For our transformer at 100W (==> 71 Vrms into 50 ) , the core cross section for the two FT114s is 0.74 cm2 , consider the lowest frequency as 3.5 MHz and our 5-turn primary, then plugging in the numbers we find Bmax = 0.012 T. Lets consider a much more challenging extreme: 1000W and the 160m band. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. . A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. 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. 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. The technical storage or access that is used exclusively for anonymous statistical purposes. 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. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. I decided to play with this to see what I could accomplish. 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. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. 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. 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. Look at the compensation coil slide. Nagyon j ez a cikk. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. How to get started on ISS Cross band Repeater? 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. I will publish my findings, but I cannot not promise to complete it until early fall. Below about 7 MHz, transmission losses increase as the core temperature increases. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. 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. 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. 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'. = .000001 / 3868.88 The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. 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. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. So the differences I see in the data sheets hysteresis curves are not the correct explanation. As I reexamined my formula, you pointed it out correctly, there is an error in it. I checked the wall brackets and mast, but all the fixings were nice and tight. The wire as I strung it up seemed to resist having a good SWR for the 20m band. I particularly want to know how counterpoise affects the common mode currents on the coax. The equation should have a 10^6 and not 10^-6 in the nominator. Why had I not noticed this before? Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. Could it be something to do with the new vertical aerial I had recently installed? I have been using a 40m End-Fed Half Wave (EFHW) antenna very successfully for the last few months and I wanted to extend the design to multi-band whilst avoiding the need to take a . The cooling curve I measured is shown below. Firstly, bandwidth on 80m is restricted to about 80 kHz at . It is recommended to use at least 2W non-inductive resistors for this purpose. 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. Can I get away with no capacitor in my design? End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? 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. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. 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. This can then, fed with coaxial cable, in many cases be . All Rights Reserved. 2015. You can start with the links below. Note: If we change the primary number of turns, the impedance ratios will considerable change also. From this article one may build a 40, 30, 20m end fed half wave antenna, with no special parts needed, or no special skills required. 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. |k"^N>F.AnJkJsq'PV}o0I. Copyright 2014-2023. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. The band compensating inductor placed on the wire is another story. It is best to make the impedance matching adjustable, using switched transformation ratio. As you look to use this transformer at higher power levels, I can imagine that the bottleneck might be voltage breakdown or corona in the windings. 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. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. Transmitting on 15 meters was impossible because of RF into the radio. 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. Note that there is some uncertainty in the measurements, but we can be confident that the loss is no where near the figure estimated for the FT82-43 design. To be safe, better not get much above 120 C. 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. Functioning as an, HF Wire Antennas - A Primer When we speak about wire antennas, the first and foremost thought that comes to mind is the 1/2 Dipole antenna. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. High Q, hence low loss. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. 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. 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. 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. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? I needed to add an additional coil (approx 12.5 uH) about . A method for estimating the impedance of a ferrite cored toroidal inductor at RF. Do I count the six loops around the pvc in the measurement? (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . Which begs the question what happens when you attach the antenna? 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. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. See the table above. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. The toroid with its many taps may be soldered directly on a multi-position switch. We also need to know what are the frequencies or bands for which we plant to use this antenna. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. But systems that work better increase the prospects of contacts. 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 see you were able to post your comment now, so I just copied my email answer here for others to see. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. How badly can high Local Ambient QRM affect HF Radio? Lowest measured inductivity = 2.0 H. Thanks! Some hams swear by them, yet some completely demean it. 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. The antenna is effective and the materials and construction are of a very high quality. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. Thank you for your comment and feedback on the article about the EFHW antenna. I wish you lots of productive experimentations and successful portable operations. 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. Change). 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. 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. Finally the tank circuits specification is complete, which is sown below. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Most of the time 5 to 20W will be adequate for activation anyway. 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. 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. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. At this point, I'm leaning towards the EFHW, but any of these antennas seem . Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. 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.
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