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. This is typically a weak spot. Ismerje meg a hozzszls adatainak feldolgozst . Jim, do you mind if I add your email and my answer as a comment to the article? I placed the box in a cool oven and let it get up to about 200 F, soak for a while, and then I took it out, hung it in still air and measured the temperature as time passed and the box cooled. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. 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. So the differences I see in the data sheets hysteresis curves are not the correct explanation. I then added two 220pf capacitors in series between the center conductor and ground. The cooling curve I measured is shown below. Transmitting on 15 meters was impossible because of RF into the radio. Looking at several builds and discussions, such as commercial antennas (e.g. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. It is all about getting the heat out. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. There is much more that can be written about this antenna and its matching, but that was not my aim. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. Research salary, company info, career paths, and top skills for Software Engineer - EDI I will go back and have the article corrected. : I see you were able to post your comment now, so I just copied my email answer here for others to see. Basically, the loading coil is operating as a trap. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. We do not know what the actual impedance will be at the end of the antenna radiator. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. I assume you know the GNARC source for EFHW antennas. Is FT8 popularity growing at the cost of SSB Phone and CW? Make sure the first wire is wrapped evenly around the whole toroid. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. Why had I not noticed this before? For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. Wow, Gary! 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. There are two aspects, however that we need to consider: Lets begin with the transformer. They will be adjusted for resonance at or close to the CW portion of the bands. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. Highest frequency = 14.350 MHz. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. i liked it a lot, you give good ideas, many thanks. The basic question before us is how does an antenna work? There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. Of course, you will need to find your tuning positions and apply your own position scale. 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 above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. 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. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. Thanks in advance, good health for you in these times, Z8Vq9_@x C\Agv#. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. Impressive article and so well done that I may give it a try. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Apply for the Job in Software Engineer - EDI at St. Louis, MO. I would mention first its ease of installation. Also find news related to Efhw Compensation Coil Experiment which is trending today. I settled on a compact secondary using #28 wire. 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. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. For the transformer, a T130-2 toroid will be sufficient, on which we wind the seconder with multiple taps, as shown in the below table. Can you give me an idea for your 100 W version, you built for 80/60/40 m. Change), You are commenting using your Twitter account. One end is about 5 meters high on an extended fishing pole. I needed to add an additional coil (approx 12.5 uH) about . I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. I decided to push for best efficiency with a 5-turn primary. 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 designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). 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. Your article was well written and very informative, thanks. P.S. It is best to make the impedance matching adjustable, using switched transformation ratio. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). We also need to know what are the frequencies or bands for which we plant to use this antenna. The antennas are set up as a sloper as in my SOTA outings. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. It is quite difficult to satisfy both requirements of achieving proper impedance ratio and resonance of the tank circuit at each tap of the inductance. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. I tossed the line as far up as I could in a tree. Show more. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. However, a key restriction is its 25W power rating, due to the small matching transformer. 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 purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. 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. Consequently, lets pick the lowest frequency 7,000MHz that we need to be able to tune the inductance to, for each of the taps on the inductance. 1. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. From that we can find Mismatch Loss. 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. Although it is simple to build and is a multiband antenna, it has several attributes that . So far so good. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. This is perhaps one of the most hotly debated rookie topics in. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Thank you for an interesting and informative read. 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. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. Even at 15W the voltage at the ends may reach 100-200V. Change), You are commenting using your Facebook account. This will yield the minimal capacitance of the variable capacitor. Hello, a wonderful approach for the problems.. 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. 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. Be aware counterpoise or ground radials are required for all hf antennas for better performance. (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . I found it very useful to label the tuner with switch and capacitance positions. Could it be something to do with the new vertical aerial I had recently installed? 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). Understanding Antennas The Good, the Bad, and the Ugly. Very interesting design. Does your station desperately need a good RF ground to behave properly? The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. (Tvir s tvbeszl gpek s kszlkek) Ksznm. The final turns ratio turned out to be 3:29. We also know, that both ends of the half wave antenna will have the highest voltage, thus impedance, which may reach up to several kilo-ohms. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. 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. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. Be sure to take a look for additional analysis and conclusions. 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. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. 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. Start by wrapping the wire around the toroid. = 258 * 10^-12. The results are shown below. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. It turns out that we can easily measure the effective parallel secondary capacitance by looking at the primary self resonance when the secondary is open. 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. All Rights Reserved. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. Thirty turns #28 are wound on the two FT114-43 cores. That is an end-fed, but very different then the half wave construction. How far could it possibly reach? 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. (LogOut/ And of course, a counterpoise with various lengths. 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. It is important to consider the voltages on this tank circuit. Look at the compensation coil slide. The SWR was measured for each of the three antennas across the CW portion of the bands. Do I count the six loops around the pvc in the measurement? 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. . I used the 14g enameled wire and wound it on the FT240-43. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. Regards VE9HAM. I was curious why this capacitor was added to the transformer. A week or two later I started to notice an occasional knocking sound inside the house. Lets do a quick calculation to see how much an issue is this output capacitance. 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. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. Radio Transceiver S-Meter Pitfalls to avoid, Atmospheric impact on VHF Radio Propagation, Terrestrial VHF Radio Signal Coverage LOS, Terrestrial VHF Radio Signal Coverage BLOS, HF Surface Wave Propagation (Ground Wave). The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. 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 lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. So, I embarked on testing it for myself. VK1OD.net (offline). Radio amateurs using this antenna might remain oblivious to the presence of many active DX traffic originating from the direction of the shadow regions in the nulls. There is lot of controversy around the EFHW antennas. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. 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. Lets call this element the LoadAttenuator. See the table above. 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. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. That will be the missing resistor in the resistor bridge of the below circuit. Some website features may not function optimally without cookies. 100W on a Wire Antenna - Is it good enough for DX? It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. Some hams swear by them, yet some completely demean it. To explore parameter space a little, I modeled a couple of lengths for the counterpoise and see how the wire is resonant across the band when fed with various impedances at the driven point. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Below is the schematic of the final build. The highest voltages as well as radiation are also at the end of the antenna wire. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. 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. Krem, rja le, mi a krdse. And not all hf antenna installation are same, with most requiring bit of tinkering. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG.