Does your station desperately need a good RF ground to behave properly? Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. However, I think I made a good choice with a Hammond 1590A diecast aluminum box. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. The technical storage or access that is used exclusively for statistical purposes. The combination of the transformer with the end-fed dipole results in a positive reactance. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. 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.) 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. However, it has its idiosyncrasies. Above is a thermograph of the transformer at 20W input at 3.6MHz. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. I checked the wall brackets and mast, but all the fixings were nice and tight. To further improve the flux linkage, I wound the primary on top of the secondary. Apply for the Job in Software Engineer - EDI at St. Louis, MO. After some internet research, I settled on making the former from a paint roller. Thank you Gary. This antenna is working for 80,40,20,10 and 6m bands. But I would caution its usage for higher power than 10-15W. 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. Cmzett: Weince joseph How can we help? I use shock cord to connect the insulator at the end of the wire to my fence. Highest frequency = 14.350 MHz. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. It may be one or even five kilo-ohms. This antenna is only 15m long using 2 loading coils. 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. 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. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. There are many resources online that explain the details better than I can, so Id suggest doing your own research if youd like to build one for yourself. Don't sweat the digits to the right of the decimal point too much, the SWR readings changed as the feed height and droop of the antenna changed. Could it be something to do with the new vertical aerial I had recently installed? 5) It is very hard to avoid stray capacitance on the output. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. The basic question before us is how does an antenna work? 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. Above is a sweep of the uncompensated prototype with a 3220+50 load. I cut 2.5m of 16AWG wire, added a connector, and hooked this up to one end of the inductor. A 100pF silvered mica was connected in shunt with the transformer . Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. This illustration provides a graphical view of approximate comparative difference in expected Common-Mode-Current (CMC) that could flow on the transmission line to undermine the overall performance of the antenna system. It will present its parameters, so anybody with basic home-brew skills will be able to build it. I have been offered input VSWR curves for such a configuration, and they are impressive but VSWR curves do not address the question of loss / efficiency. There are many good descriptions on the net about this type of antenna. Let us touch on some necessary theory to begin with. I dont have an amplifier, so only need to be able to handle 100W. It is fun to build them and measure the lower and upper frequency limits and to see how close the calculation was. Lowest frequency = 7.000 MHz. 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. Nagyon j ez a cikk. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. The maximum B field in the core is proportional to the imposed voltage, as: where A is the cross sectional area of the core, f is the frequency and N is the number of turns. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. 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. 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. The results are presented below. 1. See the second completed tuner depicted below. Subscribe to our newsletter and receive regular updates on new posts and articles. 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. 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 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. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. stream The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 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. Show more. There is no substitute for playing with the analyzer, trimming the wire, adjusting the compensation coils, etc., and going through the process for a few iterations to get the multiband antenna to work well for you as you have it installed. Not the ideal antenna, but convenient! clear. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. 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 transformer fits sideways in the box with a few millimeters to spare. Below about 7 MHz, transmission losses increase as the core temperature increases. 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. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. Next, I started winding the transformer. The final turns ratio turned out to be 3:29. Many people use an inductor placed at the near end to make things level out on the higher bands. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. Workers' Comp. 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. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. 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. Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. 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. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. Refurbishing aluminium antenna parts affected by weather / corrosion. I particularly want to know how counterpoise affects the common mode currents on the coax. So the differences I see in the data sheets hysteresis curves are not the correct explanation. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. 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. The wire as I strung it up seemed to resist having a good SWR for the 20m band. 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. 100W on a Wire antenna! 100W on a Wire Antenna - How far would it reach? Which begs the question what happens when you attach the antenna? With no counterpoise wire it will be the coaxs shield providing it. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. 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 . <> A method for estimating the impedance of a ferrite cored toroidal inductor at RF. 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. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. This provides proper insulation from the relatively high voltages on the seconder winding. 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. 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. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. The SWR results are as follows: Hence, we need to move along and start to include the antenna with our testing. The highest frequency could be14.350MHz. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. I used the 14g enameled wire and wound it on the FT240-43. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. What kind of balun is this? 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. Measurements were made on the unmounted transformer with just a ~2 inch length of lead from the secondary to the 2450 load and sampling resistor (jig connections as shown in the photo above). My design objectives were: 1. 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. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. Yes, there is a coil a few feet from the box but it is NOT TRAP, it is no secret as well, actually, everything in this antenna was published and patented by few people a long ago. Be sure to take a look for additional analysis and conclusions. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. Well, in ham radio, everything works. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. 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 . One end is about 5 meters high on an extended fishing pole. Lets do a quick calculation to see how much an issue is this output capacitance. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. One possible explanation is that the core losses drop with temperature. Compensation. This suggests an inductive reactance. Best regards and thanks again for your comment. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. A lot of radio amateurs have made similar antennas to this with larger transformers for higher power handling. 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. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. 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. You can see the coil in the picture below (red arrow). Proudly created withWix.com. There is much more that can be written about this antenna and its matching, but that was not my aim. Do I count the six loops around the pvc in the measurement? I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough!