efhw compensation coil
albia, iowa arrestsI found it very useful to label the tuner with switch and capacitance positions. Then I covered the coil in kapton tape to hold it together. 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. It should be no surprise that 80pF is close to optimal. It depends on the selection of the inductance and the capacitor values. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. 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. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. Also find news related to Efhw Compensation Coil Experiment which is trending today. 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" 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. 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. The final turns ratio turned out to be 3:29. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. We also need to know what are the frequencies or bands for which we plant to use this antenna. How to get started on ISS Cross band Repeater? 2015. Instead, this shifts everything down and makes it very easy to tune 10m. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. How badly can high Local Ambient QRM affect HF Radio? Below is the schematic of the final build. (LogOut/ Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. Above 7MHz, there is very little temperature dependence at all. Since the tuners location is best if it is handy for the operator, one end of the end-fed antenna is also close to the operator. IIRC they call it a "compensator". MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. 1. Nevertheless, the EFHW antenna had in the Read More, SSN, SFI, Solar Data for HF Radio Propagation Here are some of the important Solar activity parametric data that are responsible for influencing the behavior of the Ionosphere on earth. Change), You are commenting using your Twitter account. stream The negative effects of local QRM on an, How does antenna radiation occur? I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. 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. Firstly, bandwidth on 80m is restricted to about 80 kHz at . 73! 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. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. One end is about 5 meters high on an extended fishing pole. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. 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. The 2 coils are 35uh and 90uh. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. Let us touch on some necessary theory to begin with. 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. One possible explanation is that the core losses drop with temperature. PART - 2 : Most EFHW antenna configurations resort to the use of broadband impedance transformers at the feed-point to attain acceptable SWR on all operational bands. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. Let's find out! 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. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF This was a little bit of a compromise as the last 20ft of the antenna had to run down a fence to fit it into the garden. 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. In this case, it looks important. Zin=46.52+j6.72. 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. 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. Some hams swear by them, yet some completely demean it. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. I first mounted the SO239 connector to the box. 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. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? Be aware counterpoise or ground radials are required for all hf antennas for better performance. The highest frequency could be14.350MHz. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. Impressive article and so well done that I may give it a try. The original coil is designed for low power portable applications. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. On the transformer, I added a few wingnuts to tighten down the antenna wire. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. 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. Your article was well written and very informative, thanks. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. The EFHW transformer box from outside. For a quarter wave that is about 8 nS. The equation should have a 10^6 and not 10^-6 in the nominator. This provides proper insulation from the relatively high voltages on the seconder winding. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. So I built myself an improved replacement matching transformer. coil inductance calculator at 66pacific.com. I wish I had a simple answer, but really this is where some experimentation can pay off. 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 SWR for 30 meters, 1.05:1, was the lowest of all three antennas since the transformer was tuned for impedance match at 30 meters. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. 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. 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. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. Thanks for your comments. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. I then added two 220pf capacitors in series between the center conductor and ground. 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. This antenna is working for 80,40,20,10 and 6m bands. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. 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. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. The computation method is also touched on. With most operations you only transmit for 50% of the time, and since a small transformer with four or more primary turns can achieve >90% efficiency, that implies that I really only need to dissipate ~5W. 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. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. Copyright 2014-2023. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. Krem, rja le, mi a krdse. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. 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. 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. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. Check your inbox or spam folder to confirm your subscription. The SWR for the 20 meter EFHW antenna was < 1.2:1 That is an end-fed, but very different then the half wave construction. In an urban area we are much more restricted, especially if we need to be stealth about it. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Look at the compensation coil slide. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. (LogOut/ We need to measure the inductances of the toroid with the tapped coil. 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. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. You can see the coil in the picture below (red arrow). 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 then used a piece of heat shrink on the outside to hold everything in place. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. 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 . VK1OD.net (offline). Lowest measured inductivity = 2.0 H. It is important to consider the voltages on this tank circuit. 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. The antenna is effective and the materials and construction are of a very high quality. Not the ideal antenna, but convenient! End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. 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. It does not need any special components; in fact, most of us may have them in our shack drawers already. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. The bridge than will measure zero voltage across the bridge, and the LED will turn off. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). 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 building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? Yes, indeed EFHW antennas are very useful for SOTA or other field operation. Does your station desperately need a good RF ground to behave properly? Show more. Cmzett: Weince joseph How can we help? Isn't it? I checked the wall brackets and mast, but all the fixings were nice and tight. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. 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! Select components with good insolating materials and properly chosen, relatively high voltage rated parts. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. Refurbishing aluminium antenna parts affected by weather / corrosion. There is lot of controversy around the EFHW antennas. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. 73 As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. Selecting the variable capacitor that can be varied from this minimum to maximum capacity, will allow tuning to resonance for 40, 30, and 20m bands at each of the switch position of the tuner. Since I wont be connecting a counterpoise, the antenna will use the coax shield as the counterpoise, so the RF choke will keep any unwanted RF from feeding back through the coax. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. 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. : I see you were able to post your comment now, so I just copied my email answer here for others to see. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. It is not necessary to calculate the above; the results are sown in the following table. 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. Trapped five band EFHW SOTA antenna. The highest voltages as well as radiation are also at the end of the antenna wire. 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. The basic question before us is how does an antenna work? How does this SWR meter works? 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. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. 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. Lets do a quick calculation to see how much an issue is this output capacitance. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. 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. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. In practice, exactly how you wind the primary turns can drastically affect the high frequency behavior of the transformer when measured into a 2450 load. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. Can you give me an idea for your 100 W version, you built for 80/60/40 m. 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. However, it has its idiosyncrasies. Although it is simple to build and is a multiband antenna, it has several attributes that . You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. I am building an EFHW antenna for my new. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. If you really want to get the heat out, add some fins to the aluminum box. 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. 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. Could it be something to do with the new vertical aerial I had recently installed? 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 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. Im very pleased with that indeed. Most informative and appreciated. A ktelez mezket * karakterrel jelltk. 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. 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). I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . 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. You can start with the links below. Just the bare 80m wire is shown in red. Start by wrapping the wire around the toroid. Klubunknl folyamatos a tagfelvtel. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance.