In theory, the examination is supposed to be used to help clarify your medical condition and . Small efficient matching transformer for an EFHW - owenduffy.net I then added two 220pf capacitors in series between the center conductor and ground. These, in turn, are instrumental Read More, Learn CW Morse Code Lesson Set 2 This is Lesson Set -2 in our multi-part series of CW Morse Code hands-on tutorials where we will introduce numerals and a few important punctuation marks as Read More. Engineering the EFHW 49:1 Transformer and Antenna 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??). How to get started on ISS Cross band Repeater? It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. High self-resonant frequency. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. A Smith chart view of EFHW transformer compensation From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Wow, Gary! You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. 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. 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. Update: Full size 132ft EFHW For one month I replaced the 66ft wire and loading coil and replaced it with a full 132ft of wire, connected to the FT240-43 balun. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. When I'm measuring the half way point on my EFHW, looking for 67', how do I factor in the compensation coil on the MyAntennas wire? The negative effects of local QRM on an, How does antenna radiation occur? Two layers of 1mil Kapton tape are placed over the winding. See the second completed tuner depicted below. 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. 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. High Q, hence low loss. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. This suggests an inductive reactance. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. 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. 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 swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. 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. 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. The VSWR plots below show results from the same transformer tested on the bench with minimal output capacitance, with a primary compensation capacitor, either 100pF or 27pF included, with the transformer installed in its aluminum box including antenna connector feedthrough, and with the transformer with an 18 clip-lead on the antenna output. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB - qsl.net used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. It is worth experimenting with its length also. 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. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. I particularly want to know how counterpoise affects the common mode currents on the coax. = 1/30.e6 = 33 nS. 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. I then used a piece of heat shrink on the outside to hold everything in place. AC Coil Replacement Cost 2023 - Forbes Home This is not an optimal value, benefit may be obtained by exploring small changes to that value. Independent Medical Evaluation - IME | Cynthia Hennessey When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. Just the bare 80m wire is shown in red. 2015. 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. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. Is FT8 popularity growing at the cost of SSB Phone and CW? I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. Let me review the salient observations from the previous work. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. 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. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? Looking at several builds and discussions, such as commercial antennas (e.g. From that we can find Mismatch Loss. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. 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. The 40-10m EFHW camping antenna is late but done. More info in - reddit My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. 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. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. Understanding Antennas The Good, the Bad, and the Ugly. 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. Intro EFHW Compensation Coil Experiment Steve Ellington 10.3K subscribers Subscribe 29K views 4 years ago The little coil helps place the EFHW resonance points where we want them. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. 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. The highest frequency could be14.350MHz. Thank you Gary. If we wish to limit the ferrite temperature to 130 C, then assuming ambient temperature of 30 C, we can tolerate a 100 C temperature rise. All Rights Reserved. Csatlakozz csapatunkhoz! 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. The Counterpoise is a short, typically one twentieth (0.05 *. ) 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. I used four parallel #28 wires (not twisted) for the primary. = 258 * 10^-12. The final turns ratio turned out to be 3:29. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. Note: If we change the primary number of turns, the impedance ratios will considerable change also. 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. Ismerje meg a hozzszls adatainak feldolgozst . Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. The resistance (real) component of the impedance is right where we want it near 50 ohms. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. Finally the tank circuits specification is complete, which is sown below. We will return to that shortly, but first let us look at the VSWR associated with such added capacitance when driving the 2450 load resistor. Does your station desperately need a good RF ground to behave properly? Is it any good? (Tvir s tvbeszl gpek s kszlkek) Ksznm. 73 The parasitic reactances near the feed-point also vary between installations. This is typically a weak spot. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. A ktelez mezket * karakterrel jelltk. The band compensating inductor placed on the wire is another story. 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'. It does not need any special components; in fact, most of us may have them in our shack drawers already. First, note that the transformer has low transmission loss up to nearly 50MHz. 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. By using traps, the antenna works on all three bands with no operator interaction. : I see you were able to post your comment now, so I just copied my email answer here for others to see. 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. There is lot of controversy around the EFHW antennas. Graphed with a log scale, it makes a nice straight line. 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. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. 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. It is much easier to wait ~2, know that you are going to see about 86% of the temperature change you would see if you waited until time infinity, and just make a simple correction. 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. 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. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. What are the advantages and disadvantages of the end-fed half wave antenna? I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. blue: 250pF, to much compensation. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. 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. PDF VK4YE Compact End-Fed 5 Band HF Antenna - SARC It depends on the selection of the inductance and the capacitor values. 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave - YouTube I look at the end-fed as just an extreme example of an off-center-fed antenna. 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. 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. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. With such a switch, it is impossible to forget to switch back to operational mode. 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. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. To be safe, better not get much above 120 C. 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. 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. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. One possible explanation is that the core losses drop with temperature. 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.
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