efhw compensation coil efhw compensation coil

I mounted the transformer on a tree for testing. 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. 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. 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. It is all about getting the heat out. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. Hi Ajai, If you stare at the above frequency sweeps you will discover a few things. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. Is FT8 popularity growing at the cost of SSB Phone and CW? 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. I look at the end-fed as just an extreme example of an off-center-fed antenna. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. 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. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. For the last step, I put together a RF choke to use between the radio and the feedline. The tests here were using a dummy load on the transformer, and that did allow confirmation of the design and expected loss at 3.6MHz. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. You can see the coil in the picture below (red arrow). It is best to make the impedance matching adjustable, using switched transformation ratio. In this case, it looks important. 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. 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. The equation in the article is corrected now. 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. of the wavelength. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. Regards VE9HAM. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. 1. The disadvantage of this switch is that one needs one hand to hold it, another to key down, and yet another to tune the capacitor. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. The SWR results are as follows: An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. A 100pF silvered mica was connected in shunt with the transformer primary. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. Understanding Antennas The Good, the Bad, and the Ugly. 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. 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. 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. 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. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. The SWR figures were as follows: FT240-43 132ft/100pF capacitor Thanks! 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. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. . But systems that work better increase the prospects of contacts. Lets call this element the LoadAttenuator. The model results show the need for a not entirely insignificant counterpoise. This suggests an inductive reactance. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. How big and where to place it is likely best determined empirically. I installed a QRP SWR meter into the tuner that makes tuning very handy. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. I've always had issues with 10m loading up properly so I'll also be adding a compensation coil 78 inches from the feed point on the wire. 100W on a Wire Antenna How far would it reach? For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. And now I am planning to build one for 160/80m. 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. 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. 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. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. Wow, Gary! The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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. 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 . I tossed the line as far up as I could in a tree. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. The Counterpoise is a short, typically one twentieth (0.05 *. ) For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. The technical storage or access that is used exclusively for statistical purposes. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. Highest frequency = 14.350 MHz. 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 will also be handling 100W. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. Although it is simple to build and is a multiband antenna, it has several attributes that . This is perhaps one of the most hotly debated rookie topics in. This reveals we only need to compensate for the reactive component. The band compensating inductor placed on the wire is another story. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? I am currently working on measurements of an EFHW antenna. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. And not all hf antenna installation are same, with most requiring bit of tinkering. These four data points are plotted on the Transmission Losses chart shown below as the yellow squares, all but the 80 meter point coming in a bit lower than expected losses based on the VNA measurements. It is recommended to use at least 2W non-inductive resistors for this purpose. To further improve the flux linkage, I wound the primary on top of the secondary. I use shock cord to connect the insulator at the end of the wire to my fence. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. 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. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. Im very pleased with that indeed. Most of the time 5 to 20W will be adequate for activation anyway. At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. Also find news related to Efhw Compensation Coil Experiment which is trending today. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? Thank you Gary. Workers' Comp. 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. If not a lightning strike, I will write an article about the experience as well. 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 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. 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. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. All Rights Reserved. You cant really see the antenna wire, but the red line shows the antenna path. 2006. To be safe, better not get much above 120 C. Show more. The SWR results are as follows: Considering the compromised installation (ends about 2.5-3m above ground, inverted V with peak at 8m) I am pretty happy with this so far. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. 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. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. The overlaid VSWR plots are shown below. What are its disadvantages? So far so good. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. See the table above. 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. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. 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. These dimensions were derived from modelling the antenna in EZNEC. Being a more efficient design that some, it might result is a wider VSWR excursion that those others as transformer loss can serve to mask the variations in the radiator itself. Change), You are commenting using your Twitter account. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. For my build, I started with a waterproof enclosure from the hardware store, a panel mount SO239 connector, an FT240-43 toroid, two 220pf 15KV capacitors, and 14g enameled copper wire, and some hardware to connect it all up. The wire as I strung it up seemed to resist having a good SWR for the 20m band. This gave me an effective coil diameter of 40.5mm. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. I then added two 220pf capacitors in series between the center conductor and ground. 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. Subscribe to our newsletter and receive regular updates on new posts and articles. (Tvir s tvbeszl gpek s kszlkek) Ksznm. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. This provides proper insulation from the relatively high voltages on the seconder winding. My favorite SOTA antenna is the End-Fed Half Wave Antenna. I can give a link if you need. 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. The results are presented below. 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. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). 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. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. 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. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. nanoVNA-H can firmware be updated if it has a broken USB socket? We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. The above illustration displays a typical set of Azimuth and Elevation sections of the radiation patterns that one might expect from a horizontally configured EFHW Wire Antenna deployed at an average height of 40 ft. above ground level (AGL). Thank you for your comment and feedback on the article about the EFHW antenna. Cmzett: Weince joseph How can we help? In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. This can then, fed with coaxial cable, in many cases be . How far could it possibly reach? 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. 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. Ismerje meg a hozzszls adatainak feldolgozst . Therefore, installation is quite easy, and its tuner circuit is rather simple as well. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. 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. As I reexamined my formula, you pointed it out correctly, there is an error in it. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. 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. Above is a sweep of the uncompensated prototype with a 3220+50 load. VK1OD.net (offline). The 2 coils are 35uh and 90uh. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. The equation should have a 10^6 and not 10^-6 in the nominator. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. I decided to push for best efficiency with a 5-turn primary. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. 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. In an urban area we are much more restricted, especially if we need to be stealth about it. 5) It is very hard to avoid stray capacitance on the output. 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. blue: 250pF, to much compensation. Compensation. The technical storage or access that is used exclusively for anonymous statistical purposes. 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. 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 antenna is effective and the materials and construction are of a very high quality. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. 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. 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.