We need to measure the inductances of the toroid with the tapped coil. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. 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. Best results are with 2450 drive impedance and the 3.3m counterpoise, so it is not surprising that 49:1 transformers are the common choice. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. 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. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? ENDFED/EFHW Antenna & Choke - F5NPV - V85NPV EFHW-8010-Is this the ultimate 'magic' antenna? - MyAntennas.com High self-resonant frequency. Next, I started winding the transformer. I particularly want to know how counterpoise affects the common mode currents on the coax. One end is about 5 meters high on an extended fishing pole. 100W on a Wire Antenna How far would it reach? I needed to add an additional coil (approx 12.5 uH) about . If not a lightning strike, I will write an article about the experience as well. As you stated early in your posting, I also have found 99.99% of all posting on the internet tell you WHAT they did.not HOW they determined the specific design criteria. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. The Truth, ,and Nothing But The Truth (as I've experienced it) Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Trapped five band EFHW SOTA antenna. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. 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. No wire counterpoise is used to reproduce the SOTA setup. I will publish my findings, but I cannot not promise to complete it until early fall. As is often the case, packaging was determined by what boxes I had laying around. These dimensions were derived from modelling the antenna in EZNEC. The results are shown below. In an urban area we are much more restricted, especially if we need to be stealth about it. It is important to consider the voltages on this tank circuit. How-To: Make a Multiband EFHWA for Amateur Ham Radio It not a loading coil. Hence, we need to move along and start to include the antenna with our testing. 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. coil inductance calculator at 66pacific.com. Some say you do not need a counterpoise, but that is false. 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. 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. It performed well on both the 2m and 70cm bands. They will be adjusted for resonance at or close to the CW portion of the bands. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. stream Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. I settled on a compact secondary using #28 wire. It will present its parameters, so anybody with basic home-brew skills will be able to build it. Impressive article and so well done that I may give it a try. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. At this point, I'm leaning towards the EFHW, but any of these antennas seem . The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. ON7EQ EFHW Antenna - qsl.net This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. 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. The transformer fits sideways in the box with a few millimeters to spare. There is much more that can be written about this antenna and its matching, but that was not my aim. I also will ask, why didnt it work for you. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. PDF MANUAL: ENDFEDZ 40-10-KW EFHW 1KW ICAS ANTENNA - Vibroplex I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. Your article was well written and very informative, thanks. This article will not address that antenna type. 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. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). I was curious why this capacitor was added to the transformer. Krem, rja le, mi a krdse. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. 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 suspect that a small coil near the transformer is generally a good idea, whether it is my transformer design or others, since it is very difficult to get the antenna wire out of the box without incurring some excess capacitance. This reveals we only need to compensate for the reactive component. It is not necessary to calculate the above; the results are sown in the following table. Typically the IC-751A would read about 60W on its power bridge, the Siliconix would show >50W on the 50W scale and 45W on the 500W scale, so there is ~20% uncertainty. For fun, I attached an 18 clip lead to the secondary output and observed 7.2 pF due to the dangling clip lead. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. The band compensating inductor placed on the wire is another story. It should be no surprise that 80pF is close to optimal. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. Lets call this element the LoadAttenuator. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. . 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. And of course, a counterpoise with various lengths. The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. PDF VK4YE Compact End-Fed 5 Band HF Antenna - SARC Graphed with a log scale, it makes a nice straight line. Klubunknl folyamatos a tagfelvtel. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. i liked it a lot, you give good ideas, many thanks. I tossed the line as far up as I could in a tree. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Trapped five band EFHW SOTA antenna | VK3IL Blog A week or two later I started to notice an occasional knocking sound inside the house. That is an end-fed, but very different then the half wave construction. The technical storage or access that is used exclusively for anonymous statistical purposes. Will there be the same performance for single band EFHWs? Pocket-tenna core is finally done! Wire and compensation coil being Increasing the drive impedance tends to move the resonances to slightly higher frequencies. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. The commonly used primary compensation capacitor does not work very well for this winding method which keeps the leakage inductance as low as it does. 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 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. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. A radio station is as good or as bad as the antenna it has. Change). 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. Thanks in advance, good health for you in these times, A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. The previous table already contains these measurements. The antennas are set up as a sloper as in my SOTA outings. 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. 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 the material 43 hysteresis curves shown below for 25 C and 100 C has a smaller open area (and hence lower losses) at the higher temperature. Thanks for your comments. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. 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. But I would caution its usage for higher power than 10-15W. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. Why had I not noticed this before? This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. You can see the coil in the picture below (red arrow). VSWR<1.8 over all of HF. EFHW coil and 80m extension in place (coil visible at tip of red arrow) With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio.
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