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. Let me review the salient observations from the previous work. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Radio Transceiver S-Meter Pitfalls to avoid, Atmospheric impact on VHF Radio Propagation, Terrestrial VHF Radio Signal Coverage LOS, Terrestrial VHF Radio Signal Coverage BLOS, HF Surface Wave Propagation (Ground Wave). The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. 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. Copyright 2014-2023. ON7EQ EFHW Antenna - qsl.net 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). The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. IIRC they call it a "compensator". http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. This antenna is working for 80,40,20,10 and 6m bands. Cmzett: Weince joseph How can we help? I settled on a compact secondary using #28 wire. 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 . It requires a set distance to hang both ends of the antenna, and that is not always given. . Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. 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. Nagyon j ez a cikk. This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. The cooling curve I measured is shown below. 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'. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. Update: Full size 132ft EFHW For one month I replaced the 66ft wire and loading coil and replaced it with a full 132ft of wire, connected to the FT240-43 balun. A week or two later I started to notice an occasional knocking sound inside the house. Compensation. Im very happy with the result. The smallest number I measured was 1.6 pF, derived from the self-resonance at 41 MHz with the leakage inductance (measured at 198 nH) when the secondary was shorted. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. But I would caution its usage for higher power than 10-15W. 2015. Best regards and thanks again for your comment. A week or two later I started to notice an occasional knocking sound inside the house. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. 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. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. = .000001 / 3868.88 Looking at several builds and discussions, such as commercial antennas (e.g. 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.) MyAntennas.com Group | When I'm measuring the half way point on my EFHW That is an end-fed, but very different then the half wave construction. 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. % Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. The real power limit will be core heating. That will be the missing resistor in the resistor bridge of the below circuit. 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. In this case, it looks important. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. I assume you know the GNARC source for EFHW antennas. Refurbishing aluminium antenna parts affected by weather / corrosion. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. 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. There are many good descriptions on the net about this type of antenna. end fed half wave antenna - awsh.org 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 such a switch, it is impossible to forget to switch back to operational mode. Start by wrapping the wire around the toroid. Does your station desperately need a good RF ground to behave properly? CG K/ J/ S/ B to 4-20mA 0-1800 Celsius Thermocouple Converter TC Input 4-20mA Output Head-mounted Temperature Transducer first impressions, Some wisdom that shapes articles on this site, Designing high performance VHF/UHF receive systems, A new impedance calculator for RF inductors on ferrite cores, Calculate ferrite cored inductor (from Al), Calculate VSWR and Return Loss from Zload (or Yload) and Zo, https://owenduffy.net/files/EstimateZFerriteToroidInductor.pdf. So the differences I see in the data sheets hysteresis curves are not the correct explanation. The End-Fed Half Wave Antenna a bit Differently Simulating the end-fed half-wave (EFHW) dipole antenna You can see the coil in the picture below (red arrow). 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. I added some Christmas colored zip ties to hold everything in place. So, how to construct an end-fed half wave antenna? I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. Above is a thermograph of the transformer at 20W input at 3.6MHz. Which begs the question what happens when you attach the antenna? Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. However, the insertion loss of the packaged transformer would be intolerable on the 10 meter band if it appeared the same way with an antenna wire connected. This reveals we only need to compensate for the reactive component. Z8Vq9_@x C\Agv#. The antenna is effective and the materials and construction are of a very high quality. 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. (LogOut/ 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 will go back and have the article corrected. Will there be the same performance for single band EFHWs? The 40-10m EFHW camping antenna is late but done. More info in - reddit The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. 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. 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 calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. 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. Be cautious, such voltages may cause a quite painful skin scorch. . 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave - YouTube 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. 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. 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. Most of the time 5 to 20W will be adequate for activation anyway. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Fig.1 - Withdraw the radiating element carefully to avoid damaging the matching components A few years ago I bought a secondhand Diamond X50 dual band (144/430) antenna at a radio car boot sale. On the transformer, I added a few wingnuts to tighten down the antenna wire. We need to measure the inductances of the toroid with the tapped coil. A ktelez mezket * karakterrel jelltk. Apply for the Job in Software Engineer - EDI at St. Louis, MO. To further improve the flux linkage, I wound the primary on top of the secondary. High self-resonant frequency. My goal was to describe the parameters of an antenna that can be easily build, yet show enough theory for someone to design his or her own antenna and antenna tuner. 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. 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. I mounted the transformer on a tree for testing. A short 80m antenna for my lot - KB6NU's Ham Radio Blog blue: 250pF, to much compensation. 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. Can I get away with no capacitor in my design? The equation in the article is corrected now. 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. One end is about 5 meters high on an extended fishing pole. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. 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. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. From that we can find Mismatch Loss. Krem, rja le, mi a krdse. With no counterpoise wire it will be the coaxs shield providing it. Effects of Local Ambient QRM on HF Radio Local ambient QRM (Noise) from various electrical appliances and other sources in the neighborhood often adversely affect HF radio communication. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. 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This graphical depiction makes it easier to visualize the current and impedance correlation between bands. Do I count the six loops around the pvc in the measurement? 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. 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. 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). 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. The overlaid VSWR plots are shown below. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. 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 . I used four parallel #28 wires (not twisted) for the primary. Be sure to take a look for additional analysis and conclusions. 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. I made one quite similar to it but 3T Primary with #16 speaker wire (2 parallel wires) and 15T Secondary close wound just using about one-third of the circumference of the 2 inch toroid. 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. These four data points are plotted on the Transmission Losses chart shown below as the yellow squares, all but the 80 meter point coming in a bit lower than expected losses based on the VNA measurements. I then added two 220pf capacitors in series between the center conductor and ground. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. View the job description, responsibilities and qualifications for this position. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. In his article, I will try to bust some of the myths associated with Inverted. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. . PDF MANUAL: ENDFEDZ ALLBAND-KW 80-10 EFHW 1KW ICAS ANTENNA - Vibroplex EFHW Compensation Coil Experiment - YouTube 40M EFHW & 3D printing - Member Projects & Builds - Parker Radio Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. Taking the time derivative of the above equation you get the power dissipation. 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. 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. At this point, I'm leaning towards the EFHW, but any of these antennas seem . Below is the schematic of the final build. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. I was curious why this capacitor was added to the transformer. I use my MFJ-939Y AMU regularly anyway, and it has zero trouble with this setup.