These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. One point of my small-core, compact winding design was to be able to cool the core. 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. Why had I not noticed this before? We use cookies to optimize our website and our service. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. 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. 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. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. Now I just need to build or acquire a decent radio to utilize this new antenna. It will present its parameters, so anybody with basic home-brew skills will be able to build it. View the job description, responsibilities and qualifications for this position. This reveals we only need to compensate for the reactive component. As it turns out K1RF had similar questions about the capacitor and published data showing that the capacitor does improve SWR performance at frequencies higher than 20 meters. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. The wire as I strung it up seemed to resist having a good SWR for the 20m band. 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. This will also be handling 100W. On the transformer, I added a few wingnuts to tighten down the antenna wire. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. Compensation. With tension on the antenna wire, you can just roll the coil up/down the wire to try different positions as you are optimizing for a particular band. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). 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. 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. The End-Fed Half Wave Antenna a bit Differently I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. 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. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? 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. It does not need any special components; in fact, most of us may have them in our shack drawers already. To further improve the flux linkage, I wound the primary on top of the secondary. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. I can give a link if you need. 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. Of course, you will need to find your tuning positions and apply your own position scale. Refurbishing aluminium antenna parts affected by weather / corrosion. 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. Ismerje meg a hozzszls adatainak feldolgozst . 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. Next, I started winding the transformer. % Engineering the EFHW 49:1 Transformer and Antenna 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. Trapped 20/30/40 Meter EFHW Antenna - AI6XG Geeksite After some internet research, I settled on making the former from a paint roller. Feeling brave, I decided to tape my coil up and solder connectors on and hope I would be one of the lucky ones who wouldnt need much coil adjustment (will I be right??). I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. application of Kirchhoff's current Law on a typical EFHW antenna configuration. 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. Most informative and appreciated. Look at the compensation coil slide. 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 procedure was to run for around 30 minutes starting from the box cool at ambient temperature. 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 resistance (real) component of the impedance is right where we want it near 50 ohms. For the last step, I put together a RF choke to use between the radio and the feedline. EFHW 80m extension - MI0KXX I used four parallel #28 wires (not twisted) for the primary. : I see you were able to post your comment now, so I just copied my email answer here for others to see. 73 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. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. The highest frequency could be14.350MHz. 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. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. My design objectives were: 1. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Regards VE9HAM. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. It should be no surprise that 80pF is close to optimal. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. 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. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. Not the ideal antenna, but convenient! This will yield the minimal capacitance of the variable capacitor. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. 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. 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. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. Energy Assistance (LIHEAP) | Crosswalk Community Action Agency A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. 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. Thanks! I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. The original coil is designed for low power portable applications. Taking the time derivative of the above equation you get the power dissipation. This is perhaps one of the most hotly debated rookie topics in. If you stare at the above frequency sweeps you will discover a few things. = 1/30.e6 = 33 nS. How to get started on ISS Cross band Repeater? Don't sweat the digits to the right of the decimal point too much, the SWR readings changed as the feed height and droop of the antenna changed. Why had I not noticed this before? I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. <> End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. 2 0 obj Check your inbox or spam folder to confirm your subscription. PDF MANUAL: ENDFEDZ ALLBAND-KW 80-10 EFHW 1KW ICAS ANTENNA - DX Engineering The commonly used primary compensation capacitor does not work very well for this winding method which keeps the leakage inductance as low as it does. I wish I had a simple answer, but really this is where some experimentation can pay off. 100W on a Wire antenna! One way or another there is always a counterpoise involved if the antenna is tuned correctly. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. 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. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. If not a lightning strike, I will write an article about the experience as well. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. The results are shown below. Pocket-tenna core is finally done! Wire and compensation coil being An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. 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. It is all about getting the heat out. The overall lenght is only 15m. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. 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. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. Workers' Comp. I decided to play with this to see what I could accomplish. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. 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. (LogOut/ Graphed with a log scale, it makes a nice straight line. 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. Let's find out! It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Could it be something to do with the new vertical aerial I had recently installed? Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. Highest frequency = 14.350 MHz. 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. The computation method is also touched on. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. A ktelez mezket * karakterrel jelltk. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. As I reexamined my formula, you pointed it out correctly, there is an error in it. Thirty turns #28 are wound on the two FT114-43 cores. 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 latest news about Efhw Compensation Coil Experiment. Frank VK1VK. stream All Rights Reserved. How does this SWR meter works? I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF It is important to consider the voltages on this tank circuit. I also will ask, why didnt it work for you. There is much more that can be written about this antenna and its matching, but that was not my aim. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. I used the 14g enameled wire and wound it on the FT240-43. The transformer fits sideways in the box with a few millimeters to spare. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. It may be one or even five kilo-ohms. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. The basic question before us is how does an antenna work? Looking at several builds and discussions, such as commercial antennas (e.g. is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, For several years the EF-10/20/40 MKII EndFedz has been my main station antenna for HF. Some website features may not function optimally without cookies. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. VSWR<1.8 over all of HF. Below about 7 MHz, transmission losses increase as the core temperature increases. End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil Wrap the first wire around the toroid 27 times (I used a black wire for this). 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 . end fed half wave antenna - awsh.org The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 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. And now I am planning to build one for 160/80m. Simulating the end-fed half-wave (EFHW) dipole antenna 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! It is worth experimenting with its length also. These dimensions were derived from modelling the antenna in EZNEC. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. In this case, it looks important. 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. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. 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. Note: More extensive experiments including operation at HF frequencies higher than 20 meters, harmonic versus fundamental operation and transformer efficiency is posted in this blog. Well, in ham radio, everything works. For . Lowest frequency = 7.000 MHz. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. The SWR results are as follows: You can see the coil in the picture below (red arrow). No wire counterpoise is used to reproduce the SOTA setup. 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. High Q, hence low loss. Thermal gasketing between the cores and the aluminum heat sinks could help a lot, as would a single piece of aluminum rather than the stack up of thin sections I used. 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. IIRC they call it a "compensator". We need to measure the inductances of the toroid with the tapped coil. . The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. You cant really see the antenna wire, but the red line shows the antenna path. A radio station is as good or as bad as the antenna it has. Finally the tank circuits specification is complete, which is sown below. 3) Total losses are approximately independent of core volume. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. I mounted the transformer on a tree for testing. 5) It is very hard to avoid stray capacitance on the output. Thanks in advance, good health for you in these times, 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. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. Experiments with 160m antennas | VK3IL Blog . Some say you do not need a counterpoise, but that is false. This is not an optimal value, benefit may be obtained by exploring small changes to that value. The real power limit will be core heating. Let us touch on some necessary theory to begin with. I have an EFHW and the SWR is acceptable on all the bands with the exception of the WARC bands which is to be expected since the harmonic relationship is different. 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/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. The parasitic reactances near the feed-point also vary between installations. The results are presented below. 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. I added some Christmas colored zip ties to hold everything in place. 100W on a Wire Antenna - Is it good enough for DX? I will publish my findings, but I cannot not promise to complete it until early fall. However, a key restriction is its 25W power rating, due to the small matching transformer. How to tune a multi-band EFHW antenna using a loading coil