I decided to push for best efficiency with a 5-turn primary. I first mounted the SO239 connector to 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. 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. To this end, I weighed the main components of the box and looked up the specific heat capacities to get an approximate overall heat capacity for the entire box. point to the loading coil is 20.2m and this sets the 40m resonance at 7.1MHz, which in turn dictates the responses of the harmonically related bands 14MHz, 21MHz and 28MHz. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. So, how to construct an end-fed half wave antenna? It is much easier to wait ~2, know that you are going to see about 86% of the temperature change you would see if you waited until time infinity, and just make a simple correction. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. There is lot of controversy around the EFHW antennas. And now I am planning to build one for 160/80m. Looking at several builds and discussions, such as commercial antennas (e.g. It is not necessary to calculate the above; the results are sown in the following table. 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 SWR was low, but not unity, so the peak voltage was lower than the 50 ohm match value when measured with the high-Z scope probe. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. Be cautious, such voltages may cause a quite painful skin scorch. We will return to that shortly, but first let us look at the VSWR associated with such added capacitance when driving the 2450 load resistor. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. You cant really see the antenna wire, but the red line shows the antenna path. Hence, there is no optimum single-fit solution. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. SWR for 80-10 meter EFHW with no capacitor, SWR for 80-10 meter EFHW with 100 pfd capacitor, The above data from K1RF shows that the SWR for 20 meters (my dark red markings -, I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned, 40 meter and 20 meter (full wave) SWR with no cap. Lowest frequency = 7.000 MHz. 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. Z8Vq9_@x C\Agv#. The coil is just 12 turns of wire wrapped around a 0.7 inch diameter tube, located about 6 feet past the antenna's feedpoint. 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. And of course, a counterpoise with various lengths. Could it be something to do with the new vertical aerial I had recently installed? Therefore, installation is quite easy, and its tuner circuit is rather simple as well. First, note that the transformer has low transmission loss up to nearly 50MHz. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. clear. 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. Some website features may not function optimally without cookies. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. These dimensions were derived from modelling the antenna in EZNEC. 73 Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. Isn't it? 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. At this point, I'm leaning towards the EFHW, but any of these antennas seem . Nevertheless, the EFHW antenna had in the Read More, SSN, SFI, Solar Data for HF Radio Propagation Here are some of the important Solar activity parametric data that are responsible for influencing the behavior of the Ionosphere on earth. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. Replacing your AC evaporator or condenser coil might, on average, cost around $1,200, with the typical cost range between $800 and $2,400 depending on the brand, your region and other factors . 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. Transmitting on 15 meters was impossible because of RF into the radio. The usual problems of having the multiple band resonances all line up appear here with the end-fed design, similar to the same issue with off-center-fed designs. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. 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. 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. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. 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. Of course, if both ends are raised higher, it will produce a more efficiently radiating antenna, but the portable and temporary installation is always compromised by conditions given by a location and its restrictions. Low SSN Why do most Hams find HF Radio so difficult? Thank you for your comment and feedback on the article about the EFHW antenna. The worse SWR was 1:1.7 at the top end of 20 meters. 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? One end is about 5 meters high on an extended fishing pole. Zin=46.52+j6.72. I got the, http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html, End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil. The SWR for the 20 meter EFHW antenna was < 1.2:1 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. 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. Cmzett: Weince joseph How can we help? I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. Then I covered the coil in kapton tape to hold it together. 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. It depends on the selection of the inductance and the capacitor values. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. How badly can high Local Ambient QRM affect HF Radio? 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. Will there be the same performance for single band EFHWs? I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. This can then, fed with coaxial cable, in many cases be . One possible explanation is that the core losses drop with temperature. One point of my small-core, compact winding design was to be able to cool the core. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). High Q, hence low loss. 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. 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. This antenna is working for 80,40,20,10 and 6m bands. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. With no counterpoise wire it will be the coaxs shield providing it. 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. Understanding Antennas The Good, the Bad, and the Ugly. In his article, I will try to bust some of the myths associated with Inverted. The results are shown below. It does not need any special components; in fact, most of us may have them in our shack drawers already. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. But Ill find the error of my ways.and there are various on-line calculators to help me ensure I get the decimals and (H, mH, uH, pH, etc.) Many people use an inductor placed at the near end to make things level out on the higher bands. So the differences I see in the data sheets hysteresis curves are not the correct explanation. The original coil is designed for low power portable applications. 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. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. It tests out well on the antenna analyzer for 3.5 to 29.7 MHz. 2015. The final turns ratio turned out to be 3:29. The antenna is up. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. Check your inbox or spam folder to confirm your subscription. The antennas are set up as a sloper as in my SOTA outings. The difference here is that the target bands are low frequency. Why does antenna radiation occur? Workers' Comp. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. We also need to know what are the frequencies or bands for which we plant to use this antenna. 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. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. This antenna is only 15m long using 2 loading coils. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. What are the advantages and disadvantages of the end-fed half wave antenna? stream The overlaid VSWR plots are shown below. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. There's seemingly conflicting information out there, such as on QRZ the consensus seems to be to either use no choke on the coax, or choke it some ways away from the feedpoint - WA7ARK recommends .07 wavelength, which is about 9' on 40M. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. How does this SWR meter works? This is indeed a classic antenna that is not only, Introduction to Omnidirectional Antennas In the literal sense, an Omnidirectional antenna is an antenna that radiates uniformly in all directions. 2006. I use shock cord to connect the insulator at the end of the wire to my fence. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. i liked it a lot, you give good ideas, many thanks. coil inductance calculator at 66pacific.com. I am building an EFHW antenna for my new. Intro EFHW Compensation Coil Experiment Steve Ellington 10.3K subscribers Subscribe 29K views 4 years ago The little coil helps place the EFHW resonance points where we want them. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. This is typically a weak spot. That will be the missing resistor in the resistor bridge of the below circuit. |k"^N>F.AnJkJsq'PV}o0I. The parasitic reactances near the feed-point also vary between installations. Above is a sweep of the roughly compensated transformer. During portable operations, I noticed that I forgot the toggle switch in the tuning position, just to discover that no one calls me back to my relentless CQ-ing. This provides proper insulation from the relatively high voltages on the seconder winding.
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