This reveals we only need to compensate for the reactive component. It may be one or even five kilo-ohms. I decided to play with this to see what I could accomplish.
EFHW Compensation Coil Experiment - YouTube Next, I started winding the transformer.
The End-Fed Half Wave Antenna a bit Differently The SWR results are as follows: Some website features may not function optimally without cookies. Hence, there is no optimum single-fit solution. If you really wanted to push this design, you could include thermal grease or thermal pads in the stack-up to improve the heat transfer, but I chose to keep it clean and see how it would do without any special effort. Each geodesic great circle path displayed on the map originates from your location that is derived Read More, The Great Circle Map GCM We present an automatically rendered Great Circle Map GCM based on your location derived from your Internet IP address. For the last step, I put together a RF choke to use between the radio and the feedline. No wire counterpoise is used to reproduce the SOTA setup. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. After acquiring a MTR3b for SOTA activations I decided I needed a different antenna than the End Fed Random Wire (EFRW) or the speaker cable 20 meter dipole I use with my KX2. 5) It is very hard to avoid stray capacitance on the output. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. The cooling curve I measured is shown below. Regards VE9HAM. Im very happy with the result. 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. 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 original coil is designed for low power portable applications. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. Zin=46.52+j6.72. 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 results are as follows: Considering the compromised installation (ends about 2.5-3m above ground, inverted V with peak at 8m) I am pretty happy with this so far. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned -- The experiments have been performed, check it out!
end fed half wave antenna - awsh.org Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. Hello, a wonderful approach for the problems.. That will be the missing resistor in the resistor bridge of the below circuit. How badly can high Local Ambient QRM affect HF Radio? Lowest measured inductivity = 2.0 H. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. This can then, fed with coaxial cable, in many cases be . 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. It is not necessary to calculate the above; the results are sown in the following table. 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. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. Some say you do not need a counterpoise, but that is false. Thanks for your comments. 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. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. 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. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. I mounted the transformer on a tree for testing. Some hams swear by them, yet some completely demean it. 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. 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. 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. Since I wont be connecting a counterpoise, the antenna will use the coax shield as the counterpoise, so the RF choke will keep any unwanted RF from feeding back through the coax. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . Nevertheless, I will also describe, how it is designed, if one decides to embark on building it for different bands. Apply for the Job in Software Engineer - EDI at St. Louis, MO. Let's find out! We do not know what the actual impedance will be at the end of the antenna radiator. And now I am planning to build one for 160/80m. We would like to try to fly a kite with a halfway antenna wire and see what miracle we achieve. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd.
The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. 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. I fashioned an antenna connector with washers made from some acrylic rod I had on hand. I wanted to test the hypothesis that an inductance near the box would compensate for the output capacitance and further improve match on those bands. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. 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. Interpretation of S-Meter Noise Floor in HF Radio Receivers. It is worth experimenting with its length also. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? 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. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. It performed well on both the 2m and 70cm bands. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. 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. The impedance matching circuit is essentially a simple parallel resonant LC circuit. I am building an EFHW antenna for my new. . This article will describe a 40/30/20m band end-fed half wave antenna, focusing on its matching unit. 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??). They will be adjusted for resonance at or close to the CW portion of the bands. From this article one may build a 40, 30, 20m end fed half wave antenna, with no special parts needed, or no special skills required. 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? The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. 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.
The Truth, ,and Nothing But The Truth (as I've experienced it) Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. 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. So the differences I see in the data sheets hysteresis curves are not the correct explanation. Graphed with a log scale, it makes a nice straight line. Adding an additional 2 meters to the counterpoise did very little to affect the resonant frequencies, much less than adding that length to the main wire would accomplish. 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. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. 1.
End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil This will yield the maximum capacity of the variable capacitor.
PDF shortened multi-band End-Fed Half Wave (EFHW) antenna for 80-10m Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. Lets call this element the LoadAttenuator. 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. The EFHW transformer box from outside. VSWR<1.8 over all of HF. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Thanks again Jim. The wire as I strung it up seemed to resist having a good SWR for the 20m band. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. Even at 15W the voltage at the ends may reach 100-200V. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. Show more. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. It should be no surprise that 80pF is close to optimal. 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. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. Well, in ham radio, everything works. I've always had issues with 10m loading up properly so I'll also be adding a compensation coil 78 inches from the feed point on the wire. 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 is not necessary to calculate the above; the results are sown in the following table. Jim, do you mind if I add your email and my answer as a comment to the article? With such a switch, it is impossible to forget to switch back to operational mode. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. = 258 * 10^-12. 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'.
The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. 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. 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. However, a key restriction is its 25W power rating, due to the small matching transformer. The computation method is also touched on. Change), You are commenting using your Twitter account. The above illustration displays a typical set of Azimuth and Elevation sections of the radiation patterns that one might expect from a horizontally configured EFHW Wire Antenna deployed at an average height of 40 ft. above ground level (AGL). So, I embarked on testing it for myself. The bottomline, your putting the relationships of 1) Toroid windings and to measure their inductance together with 2) the required capacitance calculation is exactly what I needed to move forward with my specific design plans. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. In practice, exactly how you wind the primary turns can drastically affect the high frequency behavior of the transformer when measured into a 2450 load.
Pocket-tenna core is finally done! Wire and compensation coil being Look at the compensation coil slide. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! Does your station desperately need a good RF ground to behave properly? So far so good. To be safe, better not get much above 120 C. The biggest uncertainty in these measurements was the actual power level used. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. After some internet research, I settled on making the former from a paint roller. The SWR was measured for each of the three antennas across the CW portion of the bands. It is important to consider the voltages on this tank circuit. I found it very useful to label the tuner with switch and capacitance positions. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. Csatlakozz csapatunkhoz! 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. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. How big and where to place it is likely best determined empirically. 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. Dutch radio amateurs in particular have been active in this area: John, PD7MAA's blog - http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html Jos van den Helm's (PA1ZP) article published in Radcom: "A 3- or 5-Band End Fed Antenna", February 2016, Radcom, published by the RSGB in the UK. There are many good descriptions on the net about this type of antenna. The SWR figures were as follows: FT240-43 132ft/100pF capacitor . Your article was well written and very informative, thanks. = .00 00 00 00 0 258 Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. Lets do a quick calculation to see how much an issue is this output capacitance. A 100pF silvered mica was connected in shunt with the transformer .
EFHW 80m extension - MI0KXX Change), You are commenting using your Facebook account. I will go back and have the article corrected. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. To explore parameter space a little, I modeled a couple of lengths for the counterpoise and see how the wire is resonant across the band when fed with various impedances at the driven point. Functioning as an, HF Wire Antennas - A Primer When we speak about wire antennas, the first and foremost thought that comes to mind is the 1/2 Dipole antenna.
Independent Medical Evaluation - IME | Cynthia Hennessey AC Coil Replacement Cost 2023 - Forbes Home To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. Change). I assume you know the GNARC source for EFHW antennas. 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. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, Once I had upgraded the matching transformer for my EF-10/20/40 MKII "EndFedz" (see Part 1) my thoughts turned to the loading coil. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. 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. One possible explanation is that the core losses drop with temperature. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. The highest frequency could be14.350MHz. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). This gave me an effective coil diameter of 40.5mm. However, a key restriction is its 25W power rating, due to the small matching transformer. 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. The technical storage or access that is used exclusively for statistical purposes. However, it has its idiosyncrasies. 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 patterns fro the horizontal wire is compared with those of an inverted-V configuration. 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. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below.
PDF MANUAL: ENDFEDZ ALLBAND-KW 80-10 EFHW 1KW ICAS ANTENNA - Vibroplex I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. I used the coil inductance calculator at 66pacific.com and after a few tries came up with 83 turns over a length of about 83mm as shown below. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. The tests here were using a dummy load on the transformer, and that did allow confirmation of the design and expected loss at 3.6MHz. (LogOut/ 100W on a Wire Antenna - Is it good enough for DX? 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.
MyAntennas.com Group | When I'm measuring the half way point on my EFHW The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. Just the bare 80m wire is shown in red. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. I needed to add an additional coil (approx 12.5 uH) about . Below is the schematic of the final build. I have been searching the internet for a very long time (AA5TB, VK3YE, SOTA Reflector, among MANY others), and your posting finally made clear for me the many questions I have had. With most operations you only transmit for 50% of the time, and since a small transformer with four or more primary turns can achieve >90% efficiency, that implies that I really only need to dissipate ~5W. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? But I would caution its usage for higher power than 10-15W. 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. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. ROB@COMCOIL.COM A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. The overlaid VSWR plots are shown below. 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. 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. I will publish my findings, but I cannot not promise to complete it until early fall. Research salary, company info, career paths, and top skills for Software Engineer - EDI On the transformer, I added a few wingnuts to tighten down the antenna wire. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. Note that building loss into antenna system components is a legitimate and common method of taming VSWR excursions, eg TTFD, CHA250, many EFHW transformers, but in some applications, users may prioritise radiated power over VSWR. Compensation. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. Finally the tank circuits specification is complete, which is sown below. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters.
Contact Commercial Coils 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. Be cautious, such voltages may cause a quite painful skin scorch. That is an end-fed, but very different then the half wave construction. The difference here is that the target bands are low frequency. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. It does not need any special components; in fact, most of us may have them in our shack drawers already. 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.