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. The SWR for the 20 meter EFHW antenna was < 1.2:1 Firstly, bandwidth on 80m is restricted to about 80 kHz at . I first mounted the SO239 connector to the box. The results are shown below. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. 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 technical storage or access that is used exclusively for anonymous statistical purposes. In theory, the examination is supposed to be used to help clarify your medical condition and . After some internet research, I settled on making the former from a paint roller. If you really want to get the heat out, add some fins to the aluminum box. One way or another there is always a counterpoise involved if the antenna is tuned correctly. 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. (LogOut/ 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 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). Lets call this element the LoadAttenuator. 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. 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. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. With a very short counterpoise it is difficult to resonate the fundamental with any drive impedance. This gave me an effective coil diameter of 40.5mm. 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??). The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. In his article, I will try to bust some of the myths associated with Inverted. Is FT8 popularity growing at the cost of SSB Phone and CW? Ive been thinking about getting an antenna up for 80m, and Ive come across a number of options that interest me and would suit the space I have available realistically no matter what I go for it will be a very compromised antenna, but still much better than none. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. On the transformer, I added a few wingnuts to tighten down the antenna wire. Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. Above is a sweep of the roughly compensated transformer. Looking at several builds and discussions, such as commercial antennas (e.g. Once completed and tape-wrapped, I applied a layer of liquid electrical tape over the surface and the interior wire connections, ready to go outdoors. The technical storage or access that is used exclusively for statistical purposes. Not the ideal antenna, but convenient! Could it be something to do with the new vertical aerial I had recently installed? The following is the most up-to-date information related to EFHW Compensation Coil Experiment. 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. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. Krem, rja le, mi a krdse. I will publish my findings, but I cannot not promise to complete it until early fall. He was afraid that being, Inverted V Antenna - A popular Dipole variant, The Center-fed Half-Wave Dipole Inverted V Antenna An Inverted V antenna is a very popular variant of the standard horizontal dipole. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. With the cooling curve and a good estimate for the heat capacity of the box, now it is just a matter of running some power through the transformer and measuring the the temperature rise from ambient to be able to determine the power that turns to heat in the transformer. The band compensating inductor placed on the wire is another story. Note: If we change the primary number of turns, the impedance ratios will considerable change also. I can give a link if you need. 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. No wire counterpoise is used to reproduce the SOTA setup. ROB@COMCOIL.COM 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. of the wavelength. I assume you know the GNARC source for EFHW antennas. Wow, Gary! Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. In the case of the EFHW 49:1 transformer, the major shortcomings of the most popular current designs are excessive leakage inductance and poor heat transfer from the ferrite material to the environment. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. 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. . The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. Does your station desperately need a good RF ground to behave properly? I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. Connected to the packaged transformer, I ran some SWR sweeps with just the bare wire and various configurations of small coils to act as band-tuning compensation. In an urban area we are much more restricted, especially if we need to be stealth about it. 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. This provides proper insulation from the relatively high voltages on the seconder winding. The antenna is effective and the materials and construction are of a very high quality. 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. Nagyon j ez a cikk. This will yield the minimal capacitance of the variable capacitor. 100W on a Wire antenna! The equation in the article is corrected now. Elnzst krnk, de elsikkadt az zenete. I have seen and read quite a few reports of making this antenna, and some got away no problem with the 110uH when they came to set up and adjust the antenna, others needed to tweak their coil turns. EFHW Antenna Frequency Compensation Lead 5,144 views Jan 20, 2019 188 Dislike Share Save Steve Ellington 9.92K subscribers 8 inches of wire attached to the antenna post can lower the frequency. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. My favorite SOTA antenna is the End-Fed Half Wave Antenna. High self-resonant frequency. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. We do not know what the actual impedance will be at the end of the antenna radiator. 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. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. Lets do a quick calculation to see how much an issue is this output capacitance. Cmzett: Weince joseph How can we help? Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. 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. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. The resistance (real) component of the impedance is right where we want it near 50 ohms. Note: More extensive experiments including operation at HF frequencies higher than 20 meters, harmonic versus fundamental operation and transformer efficiency is posted in this blog. 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. It is best to make the impedance matching adjustable, using switched transformation ratio. I was curious why this capacitor was added to the transformer. This will also be handling 100W. 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. Let's find out! Hence after about 3pF of output capacitance, the source will have a hard time charging up that capacitance before it is time to start discharging it. Current Balun 1. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. P.S. Most informative and appreciated. How big and where to place it is likely best determined empirically. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. nanoVNA-H can firmware be updated if it has a broken USB socket? Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. It is important to consider the voltages on this tank circuit. 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. 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. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. There is no substitute for playing with the analyzer, trimming the wire, adjusting the compensation coils, etc., and going through the process for a few iterations to get the multiband antenna to work well for you as you have it installed. The Counterpoise is a short, typically one twentieth (0.05 *. ) To be safe, better not get much above 120 C. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'.