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Ive spent some time on digital modes over the last week and and my signal reports seem very similar to the pre-80m-extension period, which is good, and I am getting out well past 1000 miles on 20, 40m and 80m digital. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. 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. Make sure the first wire is wrapped evenly around the whole toroid. The negative effects of local QRM on an, How does antenna radiation occur? A 100pF silvered mica was connected in shunt with the transformer . My design objectives were: 1. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. It is likely that next time the tuning may be set according to the already found positions, and it will not be far off, requiring only slight adjustment. Two layers of 1mil Kapton tape are placed over the winding. Some hams swear by them, yet some completely demean it. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. 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. It depends on the selection of the inductance and the capacitor values. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. I would mention first its ease of installation. 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. 100W on a Wire antenna! 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 following is the most up-to-date information related to EFHW Compensation Coil Experiment. coil inductance calculator at 66pacific.com. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! PDF VK4YE Compact End-Fed 5 Band HF Antenna - SARC I am building an EFHW antenna for my new. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. Im very happy with the result. The basic question before us is how does an antenna work? It is recommended to use at least 2W non-inductive resistors for this purpose. In this case, it looks important. 2. I decided to play with this to see what I could accomplish. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. 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. Below about 7 MHz, transmission losses increase as the core temperature increases. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. It does not need any special components; in fact, most of us may have them in our shack drawers already. Assuming, most of us use the 40/30/20m band for HF SOTA activation, so the following table shows the SOTA frequencies, and the calculated half wave radiator wire of the antenna. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. On one end, I added a ring terminal to connect it to the transformer and on the other end, I connected an electric fence insulator. Selecting the variable capacitor that can be varied from this minimum to maximum capacity, will allow tuning to resonance for 40, 30, and 20m bands at each of the switch position of the tuner. 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. 73! Regards VE9HAM. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. Generally a loading coil has far more inductance and shortens the length of the antenna significantly. Multiband End-fed Half-wave EFHW Antenna - VU2NSB.com In theory, the examination is supposed to be used to help clarify your medical condition and . 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. 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. Hence, there is no optimum single-fit solution. Your posting put it all together for meTHANK YOU!!!! Well, in ham radio, everything works. Most informative and appreciated. I checked the wall brackets and mast, but all the fixings were nice and tight. 2006. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. This will yield the minimal capacitance of the variable capacitor. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. Csatlakozz csapatunkhoz! Trapped five band EFHW SOTA antenna | VK3IL Blog A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF I used a section of 40mm external diameter PVC waste pipe and 1mm diameter enameled magnet wire to make the coil. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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. It turns out that we can easily measure the effective parallel secondary capacitance by looking at the primary self resonance when the secondary is open. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. This reveals we only need to compensate for the reactive component. How-To: Make a Multiband EFHWA for Amateur Ham Radio 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! stream Best regards and thanks again for your comment. This gave me an effective coil diameter of 40.5mm. The worse SWR was 1:1.7 at the top end of 20 meters. y73s de Michael DL9SKY, Visszajelzs: The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Az e-mail cmet nem tesszk kzz. Basu Bhattacharya (VU2NSB). A week or two later I started to notice an occasional knocking sound inside the house. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. To further improve the flux linkage, I wound the primary on top of the secondary. When the transformer was mounted in its box and the output connected to an antenna connector feedthrough, the observed capacitance increased dramatically to about 6.0 pF. 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). |k"^N>F.AnJkJsq'PV}o0I. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! 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. 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. Zin=46.52+j6.72. Even at only 100W, the RF voltage on the high Z output of the transformer can easily be >1300 Vpp, so this is not an idle concern. This antenna is working for 80,40,20,10 and 6m bands. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. With no counterpoise wire it will be the coaxs shield providing it. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. I am planning to use this latest one at the Field Day next year. It is worth experimenting with its length also. Thanks again Jim. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. Also find news related to Efhw Compensation Coil Experiment which is trending today. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. Transmitting on 15 meters was impossible because of RF into the radio. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. I was curious why this capacitor was added to the transformer. However, a key restriction is its 25W power rating, due to the small matching transformer. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. If you stare at the above frequency sweeps you will discover a few things. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. With such a switch, it is impossible to forget to switch back to operational mode. I tossed the line as far up as I could in a tree. 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. End Fed Half Wave Antenna Coupler (EFHW) - M0UKD The results are presented below. Simulating the end-fed half-wave (EFHW) dipole antenna Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. How big and where to place it is likely best determined empirically. 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. 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. It uses a coil as a compensation unit, and no counterpoise. Interpretation of S-Meter Noise Floor in HF Radio Receivers. This can then, fed with coaxial cable, in many cases be . A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. 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. Above, 3t on the primary delivers Gcore<0.002S. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. 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. Be aware counterpoise or ground radials are required for all hf antennas for better performance. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. ENDFED/EFHW Antenna & Choke - F5NPV - V85NPV To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. 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.