efhw compensation coil

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. 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. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. Why had I not noticed this before? This reveals we only need to compensate for the reactive component. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. 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. 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. The photos above show a method that works fairly well. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. 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. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. It is not necessary to calculate the above; the results are sown in the following table. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. From that we can find Mismatch Loss. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave Ham Radio DX 27.1K subscribers 19K views 7 months ago #HamRadio #AmateurRadio #EFHW Here are my experiments and modifications with an EFHW. And of course, a counterpoise with various lengths. The wire as I strung it up seemed to resist having a good SWR for the 20m band. This antenna is working for 80,40,20,10 and 6m bands. . Although it is simple to build and is a multiband antenna, it has several attributes that . Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. 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. Z8Vq9_@x C\Agv#. 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. 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. Some hams swear by them, yet some completely demean it. There is much more that can be written about this antenna and its matching, but that was not my aim. 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 used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. Tap and primary high-side are soldered together near the middle of the secondary winding; the ground side of the autotransformer is located over the low-end of the secondary turns. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). 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. The final turns ratio turned out to be 3:29. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. For the last step, I put together a RF choke to use between the radio and the feedline. blue: 250pF, to much compensation. 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. It requires a set distance to hang both ends of the antenna, and that is not always given. However, a key restriction is its 25W power rating, due to the small matching transformer. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. I mentioned in the reference article that the metric A/l captures the geometry, the larger it is, the fewer turns for same inductance / impedance. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. 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. It depends on the selection of the inductance and the capacitor values. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. Looking at several builds and discussions, such as commercial antennas (e.g. I decided to play with this to see what I could accomplish. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. Frank VK1VK. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. Workers' Comp. I wish you lots of productive experimentations and successful portable operations. Ive been wanting to put together a decent multi-band antenna for a long time and finally settled on an end fed half wave antenna. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! 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. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. They will be adjusted for resonance at or close to the CW portion of the bands. 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. I will publish my findings, but I cannot not promise to complete it until early fall. For a quarter wave that is about 8 nS. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. As I reexamined my formula, you pointed it out correctly, there is an error in it. I added some Christmas colored zip ties to hold everything in place. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. 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. To be safe, better not get much above 120 C. 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 antenna is only 15m long using 2 loading coils. The worse SWR was 1:1.7 at the top end of 20 meters. Which begs the question what happens when you attach the antenna? IIRC they call it a "compensator". Impressive article and so well done that I may give it a try. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. It is important that resonance may be achieved at each tap of the inductance. . 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. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. 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. 100W on a Wire Antenna How far would it reach? Thanks again Jim. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. 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. The biggest uncertainty in these measurements was the actual power level used. There are two aspects, however that we need to consider: Lets begin with the transformer. I did struggle with the C in pF calculation..I seem to be getting hung up on the correct decimal placement..for example, for the 40-meter Capacitor requirement, I get .000000000258: C pF = .000001 / [ ( 2 * 3.14 * 7 MHz) ^2 ] * 2 uH A tutorial on estimating the impedance of a toroidal ferrite cored inductor for radio frequencies, Pulse test of a Hantek 6204BD 4 channel 200MHz USB DSO and supplied probe. Lowest frequency = 7.000 MHz. 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. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. Since it is a EFHW and not a non-resonant end fed, the wire length for 40m is about 67 feet. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. And not all hf antenna installation are same, with most requiring bit of tinkering. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. In an urban area we are much more restricted, especially if we need to be stealth about it. At this point, I'm leaning towards the EFHW, but any of these antennas seem . I also will ask, why didnt it work for you. Looking at several builds and discussions, such as commercial antennas (e.g. A 100pF silvered mica was connected in shunt with the transformer . 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. 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. However, a key restriction is its 25W power rating, due to the small matching transformer. 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. = .00 00 00 00 0 258 The original coil is designed for low power portable applications. Research salary, company info, career paths, and top skills for Software Engineer - EDI In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). Best regards and thanks again for your comment. 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. Hence, we need to move along and start to include the antenna with our testing. Interpretation of S-Meter Noise Floor in HF Radio Receivers. Current Balun 1. 2006. 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. 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. 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. The technical storage or access is required to create user profiles to send advertising, or to track the user on a website or across several websites for similar marketing purposes. Note that there is some uncertainty in the measurements, but we can be confident that the loss is no where near the figure estimated for the FT82-43 design. I ran WSPR at 10mW for about 2 hours and got the results below. Is FT8 popularity growing at the cost of SSB Phone and CW? Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. To mitigate the voltage issue mentioned above, I used a couple layers of Kapton tape over the secondary winding. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). Above is a sweep of the roughly compensated transformer. 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. What are the advantages and disadvantages of the end-fed half wave antenna? I tossed the line as far up as I could in a tree. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. |k"^N>F.AnJkJsq'PV}o0I. You can start with the links below. 5) It is very hard to avoid stray capacitance on the output. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. Now I just need to build or acquire a decent radio to utilize this new antenna. Understanding Antennas The Good, the Bad, and the Ugly. 73 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. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. High self-resonant frequency. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. Ismerje meg a hozzszls adatainak feldolgozst . 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. 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. 100W on a Wire antenna! 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. Thanks for your comments. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. 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. The VSWR plots below show results from the same transformer tested on the bench with minimal output capacitance, with a primary compensation capacitor, either 100pF or 27pF included, with the transformer installed in its aluminum box including antenna connector feedthrough, and with the transformer with an 18 clip-lead on the antenna output. The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network. 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 will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. The model results show the need for a not entirely insignificant counterpoise. Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. I used the 14g enameled wire and wound it on the FT240-43. The band compensating inductor placed on the wire is another story. 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. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. It uses a coil as a compensation unit, and no counterpoise. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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. 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. So the differences I see in the data sheets hysteresis curves are not the correct explanation. Moreover, this antenna produces several inter-lobe nulls creating multiple band dependant shadow regions in its coverage. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. 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. Let's find out! The vector sum total of all currents flowing on various physical antenna wires plus other currents like CMC on the transmission line or parasitic induced currents on masts or nearby objects must always be equal to zero. I found it very useful to label the tuner with switch and capacitance positions. So, how to construct an end-fed half wave antenna? If you really want to get the heat out, add some fins to the aluminum box. The SWR figures were as follows: FT240-43 132ft/100pF capacitor The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? 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. 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. = .000001 / 3868.88 The total lenght is about 15mtr only and using 2 coils and a little stub (s) on the 80m coil or/and the 40m coil. It is important to consider the voltages on this tank circuit. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. 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. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. 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. Change). 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'. Your posting put it all together for meTHANK YOU!!!! Why had I not noticed this before? How big and where to place it is likely best determined empirically. Let us touch on some necessary theory to begin with. A week or two later I started to notice an occasional knocking sound inside the house. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. What kind of balun is this? 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. This is based on random lengths of the antenna, which is transformed with the un-un into a medium-ohmic impedance range with reactive components. This is perhaps one of the most hotly debated rookie topics in. Below is the schematic of the final build. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. 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. The antennas are set up as a sloper as in my SOTA outings. Best results are with 2450 drive impedance and the 3.3m counterpoise, so it is not surprising that 49:1 transformers are the common choice. The impedance matching circuit is essentially a simple parallel resonant LC circuit. VSWR<1.8 over all of HF. (LogOut/ The computation method is also touched on. (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . 2. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. . 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. 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. The SWR for 30 meters, 1.05:1, was the lowest of all three antennas since the transformer was tuned for impedance match at 30 meters.

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