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. Can you give me an idea for your 100 W version, you built for 80/60/40 m. My question is what is 'higher frequency' specifically? 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??). It is worth experimenting with its length also. 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. This reveals we only need to compensate for the reactive component. As is often the case, packaging was determined by what boxes I had laying around. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. 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. 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. A week or two later I started to notice an occasional knocking sound inside the house. It is quite difficult to satisfy both requirements of achieving proper impedance ratio and resonance of the tank circuit at each tap of the inductance. The wire as I strung it up seemed to resist having a good SWR for the 20m band. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. Zin=46.52+j6.72. Below about 7 MHz, transmission losses increase as the core temperature increases. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). 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. 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. For the last step, I put together a RF choke to use between the radio and the feedline. RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. 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. 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. My favorite SOTA antenna is the End-Fed Half Wave Antenna. Thanks for your comments. . 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. Instead, this shifts everything down and makes it very easy to tune 10m. There's seemingly conflicting information out there, such as on QRZ the consensus seems to be to either use no choke on the coax, or choke it some ways away from the feedpoint - WA7ARK recommends .07 wavelength, which is about 9' on 40M. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. As you look to use this transformer at higher power levels, I can imagine that the bottleneck might be voltage breakdown or corona in the windings. Could it be something to do with the new vertical aerial I had recently installed? A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. 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. Let's find out! I checked the wall brackets and mast, but all the fixings were nice and tight. Your posting put it all together for meTHANK YOU!!!! 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. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. The equation in the article is corrected now. I installed a QRP SWR meter into the tuner that makes tuning very handy. The radiation pattern of this antenna on most bands produces multiple lobes. The toroid with its many taps may be soldered directly on a multi-position switch. With the cooling curve and a good estimate for the heat capacity of the box, now it is just a matter of running some power through the transformer and measuring the the temperature rise from ambient to be able to determine the power that turns to heat in the transformer. View the job description, responsibilities and qualifications for this position. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. The transformer fits sideways in the box with a few millimeters to spare. I decided to play with this to see what I could accomplish. 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. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. 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 photos above show a method that works fairly well. The real power limit will be core heating. The results are shown below. Interpretation of S-Meter Noise Floor in HF Radio Receivers. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. Note: If we change the primary number of turns, the impedance ratios will considerable change also. One way or another there is always a counterpoise involved if the antenna is tuned correctly. Current Balun 1. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). = 1/30.e6 = 33 nS. A 100pF silvered mica was connected in shunt with the transformer primary. (LogOut/ 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. 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. I used four parallel #28 wires (not twisted) for the primary. The permeability rapidly goes away above the Curie temperature, about 160 C on the data sheet. This happens to place the coil near the peak of a current maximum for the 20m band, which coincidentally appears to have significantly improved the match on that band. I also will ask, why didnt it work for you. Let me review the salient observations from the previous work. <> From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. Csatlakozz csapatunkhoz! (The antenna wire could also be tuned for the lower end of 40 meters without the coil but the . Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. Evaluating it at a we get: which gives the power dissipation simply in terms of the heat capacity, cooling time constant and the temperature difference from ambient. Above my old grey-haired head to be certain BUT well written enough to guide the neophyte through it all. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. = 258 * 10^-12. Very interesting design. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. My design objectives were: 1. Not the ideal antenna, but convenient! The impedance matching circuit is essentially a simple parallel resonant LC circuit. The original coil is designed for low power portable applications. 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. These, in turn, are instrumental Read More, Learn CW Morse Code Lesson Set 2 This is Lesson Set -2 in our multi-part series of CW Morse Code hands-on tutorials where we will introduce numerals and a few important punctuation marks as Read More. With very little counterpoise, the antenna is being fed at a high impedance point so a rather large impedance step-up is employed. These inductances are required in determining the right capacitance values, of which two values are important: the minimal and the maximum capacitance values. The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. The results are presented below. Be sure to take a look for additional analysis and conclusions. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? 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. 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 radio station is as good or as bad as the antenna it has. 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. What are the advantages and disadvantages of the end-fed half wave antenna? Best regards and thanks again for your comment. Be aware counterpoise or ground radials are required for all hf antennas for better performance. ROB@COMCOIL.COM 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. 5) It is very hard to avoid stray capacitance on the output. 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. To be safe, better not get much above 120 C. Do I count the six loops around the pvc in the measurement? 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. It is important that resonance may be achieved at each tap of the inductance. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. It is not necessary to calculate the above; the results are sown in the following table. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. The basic question before us is how does an antenna work? It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m.

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