efhw compensation coil

Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. Not the ideal antenna, but convenient! These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. I dont have an amplifier, so only need to be able to handle 100W. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. This is not an optimal value, benefit may be obtained by exploring small changes to that value. 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'. A week or two later I started to notice an occasional knocking sound inside the house. No wire counterpoise is used to reproduce the SOTA setup. I strung up a nominal 80m half-wave antenna wire into the trees, snaking it through the open screen door to the work bench where I was doing the tests. 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. The cooling rate is more difficult to calculate because it involves how heat moves through the structure, but it is easy to measure. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. It is important that resonance may be achieved at each tap of the inductance. I checked the wall brackets and mast, but all the fixings were nice and tight. 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. Most of the time 5 to 20W will be adequate for activation anyway. The difference here is that the target bands are low frequency. This will yield the minimal capacitance of the variable capacitor. Your posting put it all together for meTHANK YOU!!!! One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. Can a diode be used to rectify signals smaller than its threshold voltage? 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. We use cookies to optimize our website and our service. The equation should have a 10^6 and not 10^-6 in the nominator. Cmzett: Szvetnik Klmn Cmzett: Szvetnik Klmn dvzlm! One way or another there is always a counterpoise involved if the antenna is tuned correctly. 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). Can you give me an idea for your 100 W version, you built for 80/60/40 m. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. View the job description, responsibilities and qualifications for this position. See the table above. Let us touch on some necessary theory to begin with. 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. This antenna is working for 80,40,20,10 and 6m bands. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. After some internet research, I settled on making the former from a paint roller. 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. : I see you were able to post your comment now, so I just copied my email answer here for others to see. Well, in ham radio, everything works. I was curious why this capacitor was added to the transformer. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. 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. For the last step, I put together a RF choke to use between the radio and the feedline. Refurbishing aluminium antenna parts affected by weather / corrosion. Let me review the salient observations from the previous work. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? <> It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. In an urban area we are much more restricted, especially if we need to be stealth about it. 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. I am building an EFHW antenna for my new. 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. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. 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. = 1/30.e6 = 33 nS. Further if your antenna requires a biggeer counterpoise on some bands, you can increase the size of the radiating element or improve your Tuner by using fine tuning capacitor or altering the coils slightly by varying the coil windings (compressed/spread out) slightly. 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. Show more. 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. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. However, a key restriction is its 25W power rating, due to the small matching transformer. 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.) Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. 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. By using traps, the antenna works on all three bands with no operator interaction. 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. 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. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. Be aware counterpoise or ground radials are required for all hf antennas for better 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. Thank you Gary. The toroid with its many taps may be soldered directly on a multi-position switch. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. 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. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. This article will not address that antenna type. The antenna is effective and the materials and construction are of a very high quality. It does not need any special components; in fact, most of us may have them in our shack drawers already. 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 then used a piece of heat shrink on the outside to hold everything in place. Of course, you will need to find your tuning positions and apply your own position scale. Do I count the six loops around the pvc in the measurement? Compensation. Transmitting on 15 meters was impossible because of RF into the radio. 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. 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 worth experimenting with its length also. An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. A radio station is as good or as bad as the antenna it has. If you stare at the above frequency sweeps you will discover a few things. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. Graphed with a log scale, it makes a nice straight line. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. There are two aspects, however that we need to consider: Lets begin with the transformer. To be safe, better not get much above 120 C. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. Regards VE9HAM. Jos van den Helm's (PA1ZP) article published in Radcom: 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. Wrap the first wire around the toroid 27 times (I used a black wire for this). 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. 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. I installed a QRP SWR meter into the tuner that makes tuning very handy. 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. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. And not all hf antenna installation are same, with most requiring bit of tinkering. Basically, the loading coil is operating as a trap. 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. 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. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. Some hams swear by them, yet some completely demean it. 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. 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. With no counterpoise wire it will be the coaxs shield providing it. It depends on the selection of the inductance and the capacitor values. 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 We also need to know what are the frequencies or bands for which we plant to use this antenna. Why had I not noticed this before? 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. I may try to bring down the 20, 15 and 10m bands at some point, either with a small coil 2m from the feed point or with a short section of wire as a compensation lead added at the feed point as shown in the video below from Steve Ellington. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. 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. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? Above, 3t on the primary delivers Gcore<0.002S. I then added two 220pf capacitors in series between the center conductor and ground. The radiation pattern of this antenna on most bands produces multiple lobes. And of course, a counterpoise with various lengths. Typical EFHW Antenna Characteristics & Performance, Influence on Performance due to Deployment Environment, Construction Variables and Transmission Line Interface, Optimum Counterpoise length and Coupling Transformer, Influence of EFHW wire orientation on performance, Good Antenna for any Radio Station is vital The importance of antennas for radio communications can never be over-emphasized. used with a load such that the input impedance Zin is approximately 50+j0, Gin=0.02S; Duffy, O. 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. 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. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. Will there be the same performance for single band EFHWs? 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? Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. The wire as I strung it up seemed to resist having a good SWR for the 20m band. (LogOut/ Instead, this shifts everything down and makes it very easy to tune 10m. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. 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??). 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. It should be no surprise that 80pF is close to optimal. Cmzett: Weince joseph How can we help? It will present its parameters, so anybody with basic home-brew skills will be able to build it. Does your station desperately need a good RF ground to behave properly? I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. The point is to get the characteristic time constant for the cooling, which is the reciprocal of the exponent coefficient that Excel shows for the fitting equation. The results are presented below. Firstly, bandwidth on 80m is restricted to about 80 kHz at . Klubunknl folyamatos a tagfelvtel. The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. I look at the end-fed as just an extreme example of an off-center-fed antenna. I particularly want to know how counterpoise affects the common mode currents on the coax. But I would caution its usage for higher power than 10-15W. Thirty turns #28 are wound on the two FT114-43 cores. 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. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. 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). For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. What kind of balun is this? blue: 250pF, to much compensation. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. 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 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. 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. Your article was well written and very informative, thanks. 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. 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. 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 is not necessary to calculate the above; the results are sown in the following table. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. 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. Subscribe to our newsletter and receive regular updates on new posts and articles. I assume you know the GNARC source for EFHW antennas. Just the bare 80m wire is shown in red. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. The worse SWR was 1:1.7 at the top end of 20 meters. 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. 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. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. Csatlakozz csapatunkhoz! Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Highest frequency = 14.350 MHz. I was pleasantly surprised that the dips were so perfect across all of the bands and the SWR was low enough to not really need a tuner. . Could it be something to do with the new vertical aerial I had recently installed? The 1:64 transformer is wound on 3 stacked FT240-52 toroids, this provides same. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. 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. y73s de Michael DL9SKY, Visszajelzs: The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Az e-mail cmet nem tesszk kzz. 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 End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. (LogOut/ 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. The highest frequency could be14.350MHz. One possible explanation is that the core losses drop with temperature. The antennas are set up as a sloper as in my SOTA outings. The next important parameter is the parallel resonant circuits resonant frequency. Be sure to take a look for additional analysis and conclusions. The Counterpoise is a short, typically one twentieth (0.05 *. ) 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. I came up with a very simple way to build these coils on the antenna wire that proved quick and easy to change and test, involving small piece of PVC pipe and a piece of Velcro shown below. I use shock cord to connect the insulator at the end of the wire to my fence. Very interesting design. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. The SWR figures were as follows: FT240-43 132ft/100pF capacitor Frank VK1VK. 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. It is not necessary to calculate the above; the results are sown in the following table. One end is about 5 meters high on an extended fishing pole. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. 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 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. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. 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. 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 transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. 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. For a quarter wave that is about 8 nS. 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 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. Could it be something to do with the new vertical aerial I had recently installed? I found it very useful to label the tuner with switch and capacitance positions. 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. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. I added some Christmas colored zip ties to hold everything in place. Lets do a quick calculation to see how much an issue is this output capacitance. 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. If not a lightning strike, I will write an article about the experience as well. 2006. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. Current Balun 1. So, how to construct an end-fed half wave antenna? 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. The overlaid VSWR plots are shown below. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. 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. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. Thank you for an interesting and informative read. clear. We do not know what the actual impedance will be at the end of the antenna radiator. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. That will be the missing resistor in the resistor bridge of the below circuit.

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