I ran WSPR at 10mW for about 2 hours and got the results below. Let us touch on some necessary theory to begin with. Finally the tank circuits specification is complete, which is sown below. I drilled a couple of holes at each end of the former, a small one for the wire to pass through and a larger one for a bolt and wingnut for wire attachment as I wanted the end result to be portable across different antenna projects. Above, 3t on the primary delivers Gcore<0.002S. 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. It requires a set distance to hang both ends of the antenna, and that is not always given. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. 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. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. The bridge than will measure zero voltage across the bridge, and the LED will turn off. The previous table already contains these measurements. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. 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. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. On the transformer, I added a few wingnuts to tighten down the antenna wire. 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. I went with a 49:1 unun to match the unbalanced antenna to the unbalanced feed line. Low SSN Why do most Hams find HF Radio so difficult? It is not necessary to calculate the above; the results are sown in the following table. Below is the schematic of the final build. 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. Since the tuners location is best if it is handy for the operator, one end of the end-fed antenna is also close to the operator. 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. For my build, I started with a waterproof enclosure from the hardware store, a panel mount SO239 connector, an FT240-43 toroid, two 220pf 15KV capacitors, and 14g enameled copper wire, and some hardware to connect it all up. 73! nanoVNA-H can firmware be updated if it has a broken USB socket? Highest frequency = 14.350 MHz. The negative effects of local QRM on an, How does antenna radiation occur? Well, in ham radio, everything works. So the differences I see in the data sheets hysteresis curves are not the correct explanation. Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. This will yield the minimal capacitance of the variable capacitor. There are two aspects, however that we need to consider: Lets begin with the transformer. I am currently working on measurements of an EFHW antenna. Graphed with a log scale, it makes a nice straight line. A short 80m antenna for my lot - KB6NU's Ham Radio Blog Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. It should be no surprise that 80pF is close to optimal. The technical storage or access that is used exclusively for anonymous statistical purposes. = .000001 / 3868.88 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. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. 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. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. 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. 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. Some hams swear by them, yet some completely demean it. 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. 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). I tried to operate from a hotel, and learned the hard way that this type of antenna is not suitable for such location. 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. 1. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. Research salary, company info, career paths, and top skills for Software Engineer - EDI In comparison to the EFHW antenna, a simple dipole offers a far better prospect. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. The 2 coils are 35uh and 90uh. 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 resistance (real) component of the impedance is right where we want it near 50 ohms. 40M EFHW & 3D printing - Member Projects & Builds - Parker Radio 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. Can you give me an idea for your 100 W version, you built for 80/60/40 m. The End-Fed Half Wave Antenna a bit Differently, The End-Fed Half Wave Antenna a bit Differently Coventry Amateur Radio Society, Ismerje meg a hozzszls adatainak feldolgozst, 40 M R/7E azaz a kirlyi ejternysk rdillomsa, jra megy az SSTV tjtsz 144,500 MHz-en. If you really want to get the heat out, add some fins to the aluminum box. 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. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. You can see the coil in the picture below (red arrow). Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. The SWR was measured for each of the three antennas across the CW portion of the bands. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. Most of the time 5 to 20W will be adequate for activation anyway. PDF VK4YE Compact End-Fed 5 Band HF Antenna - SARC Im very happy with the result. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. Thank you for your comment and feedback on the article about the EFHW antenna. This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. Consequently, this is how the capacitance values are determined. I used my IC-751As power meter and an in-line Siliconix power meter as well as a voltage probe on the feed cable. 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. For . An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. Thanks for your comments. I chose to use FT8 transmissions for this test since they generate 100% duty cycle during the transmission period with an average duty cycle of 12.6 sec / 30 sec = 42% overall when including the listening periods. The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. 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. Three EFHW single band antennas were prepared for 20, 30, and 40 meter bands. Do I count the six loops around the pvc in the measurement? In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. 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 . This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. Not the ideal antenna, but convenient! Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. It is best to make the impedance matching adjustable, using switched transformation ratio. High Q, hence low loss. However, a key restriction is its 25W power rating, due to the small matching transformer. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. stream An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. Is FT8 popularity growing at the cost of SSB Phone and CW? Newtons Law of Cooling tells us that heat flow is proportional to the temperature difference. Interpretation of S-Meter Noise Floor in HF Radio Receivers. If you stare at the above frequency sweeps you will discover a few things. 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. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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.

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