efhw compensation coil

blue: 250pF, to much compensation. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Ive been wanting to get back into radio stuff for a while now, but the only antenna that I have up now is a 40 meter dipole. Thanks for your comments. Zin=46.52+j6.72. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. It is worth experimenting with its length also. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. 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. And of course, a counterpoise with various lengths. 1. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. Most informative and appreciated. Apply for the Job in Software Engineer - EDI at St. Louis, MO. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. 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. Im very happy with the result. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. 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. A half-wave at the lowest band of interest will also work well on all harmonically-related bands which has become particularly attractive to those wanting a quick portable wire antenna. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. Based on a 2014 survey, the most popular antennas for SOTA (Summit On The Air) activation are the following (see sotabeams.co.uk/blog/5-most-popular-hf-portable-antennas for details): Let us not confuse the End-Fed Half Wave antenna with the Random Length End Fed wire. 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. 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. One point of my small-core, compact winding design was to be able to cool the core. The overlaid VSWR plots are shown below. A short 80m antenna for my lot - KB6NU's Ham Radio Blog |k"^N>F.AnJkJsq'PV}o0I. 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. What seemed to work best was to concentrate the turns on the tap-side of the secondary winding, using several (#28) wires in parallel for the primary turns such that they covered about half of the underlying secondary winding. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). The antenna is effective and the materials and construction are of a very high quality. 100W on a Wire Antenna - Is it good enough for DX? I particularly want to know how counterpoise affects the common mode currents on the coax. Software Engineer - EDI - salary.com Im not interested in trialing coil-loaded dipoles at the minute (from my limited reading bandwidth can be a real issue) so the options I like include: The G0KYA/PD7MAA/IK0IXI EFHW extension to cover 80m calls for a 110uH coil placed at the end of the EFHW, with a further 2-2.5m of wire beyond this. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. By using traps, the antenna works on all three bands with no operator interaction. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. Contact Commercial Coils But I would caution its usage for higher power than 10-15W. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. The SWR for the 20 meter EFHW antenna was < 1.2:1, The SWR for the 40 meter EFHW was ~1.4:1 for 40 meters and 1.2:1 for 20 meters (full wavelength), For my 20, 30 and 40 meter EFHW antennas I will not use a capacitor in the primary. Your posting put it all together for meTHANK YOU!!!! 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. Trapped 20/30/40 Meter EFHW Antenna - AI6XG Geeksite A ktelez mezket * karakterrel jelltk. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. 2. Z8Vq9_@x C\Agv#. The cooling curve I measured is shown below. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. 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. To further improve the flux linkage, I wound the primary on top of the secondary. I wish I had a simple answer, but really this is where some experimentation can pay off. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. Above 7MHz, there is very little temperature dependence at all. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. of the wavelength. With no counterpoise wire it will be the coaxs shield providing it. Since the tuners location is best if it is handy for the operator, one end of the end-fed antenna is also close to the operator. The SWR for the 20 meter EFHW antenna was < 1.2:1 See the table above. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. Just the bare 80m wire is shown in red. The toroid with its many taps may be soldered directly on a multi-position switch. 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. At this point, I'm leaning towards the EFHW, but any of these antennas seem . 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. Then I covered the coil in kapton tape to hold it together. 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). The results are shown below. The results are presented below. Start by wrapping the wire around the toroid. 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). A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. 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. Ismerje meg a hozzszls adatainak feldolgozst . At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. 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. Will there be the same performance for single band EFHWs? 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. These dimensions were derived from modelling the antenna in EZNEC. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Loss (to mean PowerIn/PowerOut) can be calculated in dB as -|S21|-LoadAttenuator-MismatchLoss=18.64-18.16-0.03=0.450dB, or an efficiency of 10^(-0.45/10)=90.2%. 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. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? 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. If you stare at the above frequency sweeps you will discover a few things. The impedance matching circuit is essentially a simple parallel resonant LC circuit. I will go back and have the article corrected. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. 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. Low SSN Why do most Hams find HF Radio so difficult? This can then, fed with coaxial cable, in many cases be . I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. I wish you lots of productive experimentations and successful portable operations. Look at the compensation coil slide. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. 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. Be sure to take a look for additional analysis and conclusions. I used the 14g enameled wire and wound it on the FT240-43. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. Thanks! Below is the schematic of the final build. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. Hi Ajai, Above is a sweep of the roughly compensated transformer. The EFHW transformer box from outside. Wrap the first wire around the toroid 27 times (I used a black wire for this). The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. PDF MANUAL: ENDFEDZ ALLBAND-KW 80-10 EFHW 1KW ICAS ANTENNA - Vibroplex I am planning to use this latest one at the Field Day next year. VSWR<1.8 over all of HF. IIRC they call it a "compensator". A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. This article will not address that antenna type. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. Lets call this element the LoadAttenuator. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. In an urban area we are much more restricted, especially if we need to be stealth about it. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. It uses a coil as a compensation unit, and no counterpoise. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. What are the advantages and disadvantages of the end-fed half wave antenna? Why had I not noticed this before? Radio amateurs using this antenna might remain oblivious to the presence of many active DX traffic originating from the direction of the shadow regions in the nulls. nanoVNA-H can firmware be updated if it has a broken USB socket? It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. The antennas are set up as a sloper as in my SOTA outings. 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 . Current Balun 1. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF 100W on a Wire Antenna - How far would it reach? This provides proper insulation from the relatively high voltages on the seconder winding. %PDF-1.4 = 1/30.e6 = 33 nS. 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. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. 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 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. More designs can be found by Googling "80m loaded dipole.". 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. Thank you for an interesting and informative read. I checked the wall brackets and mast, but all the fixings were nice and tight. The biggest uncertainty in these measurements was the actual power level used. Simulating the end-fed half-wave (EFHW) dipole antenna I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). No wire counterpoise is used to reproduce the SOTA setup. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. The comparison is done on 4 bands - 10m, 20m, 40, and 80m. The SWR figures were as follows: FT240-43 132ft/100pF capacitor Klubunknl folyamatos a tagfelvtel. I mounted the transformer on a tree for testing. Some hams swear by them, yet some completely demean it. It not a loading coil. 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'. Which begs the question what happens when you attach the antenna? The SWR results are as follows: 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. So, how to construct an end-fed half wave antenna? For the transformer, a T130-2 toroid will be sufficient, on which we wind the seconder with multiple taps, as shown in the below table. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. A graphical presentation of the mathematical analysis of EFHW antenna SWR variations on account of variations in counterpoise length as well as the Unun impedance transformer at the feed-point. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Trapped five band EFHW SOTA antenna. 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 antenna wire could also be tuned for the lower end of 40 meters without the coil but the . 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 antenna is up. 40M EFHW & 3D printing - Member Projects & Builds - Parker Radio Do I count the six loops around the pvc in the measurement? stream The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). . At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. The second smallest number I measured was 2.7pF, derived from the self resonance at 2.72 MHz with the magnetizing inductance (measured at 25.8 H) with the secondary open and the output wire folded to a small 1/2 length. 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 transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. The highest voltages as well as radiation are also at the end of the antenna wire. PDF MANUAL: ENDFEDZ ALLBAND-KW 80-10 EFHW 1KW ICAS ANTENNA - DX Engineering The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. Change), You are commenting using your Twitter account. There is lot of controversy around the EFHW antennas. It is important that resonance may be achieved at each tap of the inductance. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. This is perhaps one of the most hotly debated rookie topics in. Above, 3t on the primary delivers Gcore<0.002S. What are its disadvantages? Proudly created withWix.com. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. Therefore the Great Circle Map generated below should be Read More, Multiband End-Fed Half-Wave EFHW Antenna The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. I installed a QRP SWR meter into the tuner that makes tuning very handy. However, it has its idiosyncrasies. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. The disadvantage of this switch is that one needs one hand to hold it, another to key down, and yet another to tune the capacitor. Hence, we need to move along and start to include the antenna with our testing. The band compensating inductor placed on the wire is another story. Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. I then added two 220pf capacitors in series between the center conductor and ground. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. The worse SWR was 1:1.7 at the top end of 20 meters. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. EFHW-8010-Is this the ultimate 'magic' antenna? - MyAntennas.com But systems that work better increase the prospects of contacts. The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. 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.

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