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However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. 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 that resonance may be achieved at each tap of the inductance. 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. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. It is not necessary to calculate the above; the results are sown in the following table. I got the, http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html, End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil. I can give a link if you need. This will yield the maximum capacity of the variable capacitor. The basic question before us is how does an antenna work? I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. Basically, the loading coil is operating as a trap. 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. The technical storage or access that is used exclusively for statistical purposes. It performed well on both the 2m and 70cm bands. The original coil is designed for low power portable applications. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. 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! And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? 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. Finally the tank circuits specification is complete, which is sown below. Yes, there is a coil a few feet from the box but it is NOT TRAP, it is no secret as well, actually, everything in this antenna was published and patented by few people a long ago. That will be the missing resistor in the resistor bridge of the below circuit. What kind of balun is this? The impedance per unit length of a lumped transmission line is where L and C are values per unit length. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. Because of the division of power between the 3220 resistor and VNA input, there is effectively an attenuator of -10*log(50/(50+3220))=18.16dB, so |S21| has a component due to this division. I wanted to test the hypothesis that an inductance near the box would compensate for the output capacitance and further improve match on those bands. Lets do a quick calculation to see how much an issue is this output capacitance. That is an end-fed, but very different then the half wave construction. Graphed with a log scale, it makes a nice straight line. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. I tossed the line as far up as I could in a tree. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. 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. I am building an EFHW antenna for my new. Zin=46.52+j6.72. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. Below is the schematic of the final build. 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. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. You cant really see the antenna wire, but the red line shows the antenna path. 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. And of course, a counterpoise with various lengths. The technical storage or access that is used exclusively for anonymous statistical purposes. In theory, the examination is supposed to be used to help clarify your medical condition and . 100W on a Wire Antenna - How far would it reach? ROB@COMCOIL.COM HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. 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. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. As is often the case, packaging was determined by what boxes I had laying around. 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. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. Tap and primary high-side are soldered together near the middle of the secondary winding; the ground side of the autotransformer is located over the low-end of the secondary turns. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. The overall lenght is only 15m. 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. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. Best regards and thanks again for your comment. How badly can high Local Ambient QRM affect HF Radio? The negative effects of local QRM on an, How does antenna radiation occur? My favorite SOTA antenna is the End-Fed Half Wave Antenna. Ismerje meg a hozzszls adatainak feldolgozst . An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. The cooling curve I measured is shown below. Proudly created withWix.com. 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. Lets call this element the LoadAttenuator. 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. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. This is typically a weak spot. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. This can then, fed with coaxial cable, in many cases be . 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. (Tvir s tvbeszl gpek s kszlkek) Ksznm. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. However, a key restriction is its 25W power rating, due to the small matching transformer. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. It is important to consider the voltages on this tank circuit. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. High self-resonant frequency. This is not an optimal value, benefit may be obtained by exploring small changes to that value. So, how to construct an end-fed half wave antenna? It uses a coil as a compensation unit, and no counterpoise. The impedance matching circuit is essentially a simple parallel resonant LC circuit. Now I just need to build or acquire a decent radio to utilize this new antenna. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. The difference here is that the target bands are low frequency. Note: If we change the primary number of turns, the impedance ratios will considerable change also. . This reveals we only need to compensate for the reactive component. The band compensating inductor placed on the wire is another story. High Q, hence low loss. The highest voltages as well as radiation are also at the end of the antenna wire. Can I get away with no capacitor in my design? The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. 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'. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. Although it is simple to build and is a multiband antenna, it has several attributes that . I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). Above 7MHz, there is very little temperature dependence at all. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. End-Fed antennas are useful in many ways, includes easier mounting of cable at one end (freeing the antenna from unnecessary weight of cable) & antenna maintenance in future. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. 3) Total losses are approximately independent of core volume. Im a hundred watt guy, so do not have a lot of experience with high voltage RF, but I know that ~5kV peak-to-peak RF voltage that you would expect at the 2450 output at kilowatt power levels could begin to cause you some trouble. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. There are many resources online that explain the details better than I can, so Id suggest doing your own research if youd like to build one for yourself. 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. I use shock cord to connect the insulator at the end of the wire to my fence. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. I made one quite similar to it but 3T Primary with #16 speaker wire (2 parallel wires) and 15T Secondary close wound just using about one-third of the circumference of the 2 inch toroid. No wire counterpoise is used to reproduce the SOTA setup. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. 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. 73 = .000001 / 3868.88 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. I dont have an amplifier, so only need to be able to handle 100W. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. 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. 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. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. 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. It should be no surprise that 80pF is close to optimal. . 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. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. Im very pleased with that indeed. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes. 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. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? This will yield the minimal capacitance of the variable capacitor. It not a loading coil. 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 . There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. The SWR results are as follows: i liked it a lot, you give good ideas, many thanks. The bridge than will measure zero voltage across the bridge, and the LED will turn off. One point of my small-core, compact winding design was to be able to cool the core. 100W on a Wire Antenna How far would it reach? (LogOut/ Make sure the first wire is wrapped evenly around the whole toroid. Very interesting design. Instead, this shifts everything down and makes it very easy to tune 10m. A week or two later I started to notice an occasional knocking sound inside the house. 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). From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. The photos above show a method that works fairly well. Change), You are commenting using your Facebook account. 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 solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. But systems that work better increase the prospects of contacts. To further improve the flux linkage, I wound the primary on top of the secondary. 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. In this case, it looks important. 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. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. P.S. Also find news related to Efhw Compensation Coil Experiment which is trending today. 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. Be sure to take a look for additional analysis and conclusions. As I reexamined my formula, you pointed it out correctly, there is an error in it. 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. 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. Why had I not noticed this before? 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'. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Subscribe to our newsletter and receive regular updates on new posts and articles. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? Looking at several builds and discussions, such as commercial antennas (e.g. 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. Transmitting on 15 meters was impossible because of RF into the radio. With the cooling curve and a good estimate for the heat capacity of the box, now it is just a matter of running some power through the transformer and measuring the the temperature rise from ambient to be able to determine the power that turns to heat in the transformer. 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. 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.