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. 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. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. It is not necessary to calculate the above; the results are sown in the following table. Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Ismerje meg a hozzszls adatainak feldolgozst . Many people use an inductor placed at the near end to make things level out on the higher bands. What are its disadvantages? I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. Understanding Antennas The Good, the Bad, and the Ugly. Thank you for an interesting and informative read. It is all about getting the heat out. 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. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. Be sure to take a look for additional analysis and conclusions. Check your inbox or spam folder to confirm your subscription. Why had I not noticed this before? The wire as I strung it up seemed to resist having a good SWR for the 20m band. With such a switch, it is impossible to forget to switch back to operational mode. 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. 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??). Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! However, from the measurements we made on the self resonance frequency, we know that most of this capacitance is right at the output of the transformer and not internal to the windings. 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. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. I look at the end-fed as just an extreme example of an off-center-fed antenna. 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. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. More designs can be found by Googling "80m loaded dipole.". You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. 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. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. The basic question before us is how does an antenna work? Wow, Gary! (LogOut/ Even at 15W the voltage at the ends may reach 100-200V. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. Nagyon j ez a cikk. Wrap the first wire around the toroid 27 times (I used a black wire for this). Change), You are commenting using your Facebook account. The antenna is effective and the materials and construction are of a very high quality. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. Let us touch on some necessary theory to begin with. coil inductance calculator at 66pacific.com. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. 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. 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. 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. With no counterpoise wire it will be the coaxs shield providing it. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. I was curious why this capacitor was added to the transformer. Lowest measured inductivity = 2.0 H. It does not need any special components; in fact, most of us may have them in our shack drawers already. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. 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. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. 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. Refurbishing aluminium antenna parts affected by weather / corrosion. (LogOut/ Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. The SWR figures were as follows: FT240-43 132ft/100pF capacitor I will publish my findings, but I cannot not promise to complete it until early fall. Effects of Local Ambient QRM on HF Radio Local ambient QRM (Noise) from various electrical appliances and other sources in the neighborhood often adversely affect HF radio communication. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. VK1OD.net (offline). An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. 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 needed to add an additional coil (approx 12.5 uH) about . That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. Now I just need to build or acquire a decent radio to utilize this new antenna. I installed a QRP SWR meter into the tuner that makes tuning very handy. I am building an EFHW antenna for my new. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. Note: If we change the primary number of turns, the impedance ratios will considerable change also. Trapped five band EFHW SOTA antenna. That is an end-fed, but very different then the half wave construction. Above, 3t on the primary delivers Gcore<0.002S. Above, the magenta curve is measurement of a real transformer from 1-11MHz with nominal resistance load and three compensation options: cyan: 0pF, too little compensation; magenta: 80pF, optimal compensation; and. My question is what is 'higher frequency' specifically? This suggests an inductive reactance. 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. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. Zin=46.52+j6.72. 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. A week or two later I started to notice an occasional knocking sound inside the house. 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. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. I dont have an amplifier, so only need to be able to handle 100W. 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. With the entire winding length short, the flux from the primary need not travel all the way around the core to link all of the secondary turns. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. 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 . Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. = .00 00 00 00 0 258 Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. 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. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. ROB@COMCOIL.COM 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 coil came out at 89mm in length rather than the theoretical 83mm not surprisingly, but the inductance was bang on at just over 109H. 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. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. I tossed the line as far up as I could in a tree. It may be one or even five kilo-ohms. 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. 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. Finally the tank circuits specification is complete, which is sown below. The SWR results are as follows: Your posting put it all together for meTHANK YOU!!!! 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. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. Compensation. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. 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. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. 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. 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. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. Apply for the Job in Software Engineer - EDI at St. Louis, MO. 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. 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. 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. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. I also built one that is heavy-duty handling easily up to 100W for 80/60/40m bands. I decided to play with this to see what I could accomplish. 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.
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