The technical storage or access that is used exclusively for anonymous statistical purposes. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. The negative effects of local QRM on an, How does antenna radiation occur? 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. Change). This will yield the minimal capacitance of the variable capacitor. So the differences I see in the data sheets hysteresis curves are not the correct explanation. Most of the time 5 to 20W will be adequate for activation anyway. It is important that resonance may be achieved at each tap of the inductance. 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. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. 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 orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. The bottomline, your putting the relationships of 1) Toroid windings and to measure their inductance together with 2) the required capacitance calculation is exactly what I needed to move forward with my specific design plans. A week or two later I started to notice an occasional knocking sound inside the house. Wow, Gary! From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . The EFHW transformer box from outside. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. I decided to play with this to see what I could accomplish. 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. The highest voltages as well as radiation are also at the end of the antenna wire. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. 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. 2 0 obj This antenna is working for 80,40,20,10 and 6m bands. 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. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. That is an end-fed, but very different then the half wave construction. This is based on random lengths of the antenna, which is transformed with the un-un into a medium-ohmic impedance range with reactive components. The basic question before us is how does an antenna work? The SWR results are as follows: Which begs the question what happens when you attach the antenna? The low end of the secondary, which will be the tap, is bent back over to the center of the winding and covered with a small piece of Kapton tape, and then the primary is wound over the tape (and the secondary tap wire). Looking at several builds and discussions, such as commercial antennas (e.g. Could it be something to do with the new vertical aerial I had recently installed? 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. Below about 7 MHz, transmission losses increase as the core temperature increases. The photos above show a method that works fairly well. Can a diode be used to rectify signals smaller than its threshold voltage? For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. Look at the compensation coil slide. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. Some say you do not need a counterpoise, but that is false. 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. The point is to get the characteristic time constant for the cooling, which is the reciprocal of the exponent coefficient that Excel shows for the fitting equation. The End-Fed Half Wave Antenna a bit Differently, The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Ismerje meg a hozzszls adatainak feldolgozst, 40 M R/7E azaz a kirlyi ejternysk rdillomsa, jra megy az SSTV tjtsz 144,500 MHz-en. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). 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. Does your station desperately need a good RF ground to behave properly? This transformer has more surface area than a FT82-43 based one, so it has higher capacity to dissipate heat, and it is more efficient, so it will have higher power capacity than the FT82-43 based one. I wish you lots of productive experimentations and successful portable operations. = 1/30.e6 = 33 nS. It is worth experimenting with its length also. Change), You are commenting using your Facebook account. 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. Be cautious, such voltages may cause a quite painful skin scorch. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. 100W on a Wire antenna! Measurements were made on the unmounted transformer with just a ~2 inch length of lead from the secondary to the 2450 load and sampling resistor (jig connections as shown in the photo above). The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. 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. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. The antenna is effective and the materials and construction are of a very high quality. Is FT8 popularity growing at the cost of SSB Phone and CW? 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. My design objectives were: 1. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. 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. However, a key restriction is its 25W power rating, due to the small matching transformer. 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??). 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave Ham Radio DX 27.1K subscribers 19K views 7 months ago #HamRadio #AmateurRadio #EFHW Here are my experiments and modifications with an EFHW. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. In an ideal setting, the center of the antenna will have the lowest voltage, consequently impedance, which is why it is possible to feed it by 50 or 75 coaxial cable. See the second completed tuner depicted below. Elnzst krnk, de elsikkadt az zenete. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. Low SSN Why do most Hams find HF Radio so difficult? 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. Then record the change in temperature recorded at the core from the probe, and the elapsed time so I could corrected for not reaching perfect equilibrium. 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. 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). I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. 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). Compensation. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. This suggests an inductive reactance. I chose to use FT8 transmissions for this test since they generate 100% duty cycle during the transmission period with an average duty cycle of 12.6 sec / 30 sec = 42% overall when including the listening periods. Lowest frequency = 7.000 MHz. Some of my research showed that a small compensation coil can be added about 2 meters from the transformer to pull down the SWR on the higher bands. It is not necessary to calculate the above; the results are sown in the following table. 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. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. i liked it a lot, you give good ideas, many thanks. clear. The band compensating inductor placed on the wire is another story.
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