I used four parallel #28 wires (not twisted) for the primary. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. Contact Commercial Coils The combination of the transformer with the end-fed dipole results in a positive reactance. Current Balun 1. By using traps, the antenna works on all three bands with no operator interaction. You can see the coil in the picture below (red arrow). 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave - YouTube An EFHW antenna has a very high impedance at the end point and you need a matching transformer to feed power to it. I am planning to use this latest one at the Field Day next year. This will yield the minimal capacitance of the variable capacitor. The End-Fed Half Wave Antenna a bit Differently Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). Effects of Local Ambient QRM on HF Radio Local ambient QRM (Noise) from various electrical appliances and other sources in the neighborhood often adversely affect HF radio communication. Why does a wire carrying RF current radiates to produce EM waves which travel through, Beware of Skip Zone while working HF radio A good radio amateur friend of mine from Poland sounded quite anxious when he told me that his new antenna was behaving peculiarly. uBITX HF Transceiver Build - My Adventures in Engineering To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. The technical storage or access that is used exclusively for statistical purposes. 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. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 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. The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. Thanks again Jim. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. Most of the time 5 to 20W will be adequate for activation anyway. How-To: Make a Multiband EFHWA for Amateur Ham Radio P.S. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. Zin=46.52+j6.72. Klubunknl folyamatos a tagfelvtel. Subscribe to our newsletter and receive regular updates on new posts and articles. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. Pocket-tenna core is finally done! Wire and compensation coil being 2. The equation should have a 10^6 and not 10^-6 in the nominator. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. Also find news related to Efhw Compensation Coil Experiment which is trending today. Once completed and tape-wrapped, I applied a layer of liquid electrical tape over the surface and the interior wire connections, ready to go outdoors. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. No capacitor was installed. Basically, the loading coil is operating as a trap. I used the 14g enameled wire and wound it on the FT240-43. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. 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. Being a more efficient design that some, it might result is a wider VSWR excursion that those others as transformer loss can serve to mask the variations in the radiator itself. View the job description, responsibilities and qualifications for this position. Un-Uns for Endfed-Antennas (EFHW) by DK7ZB - qsl.net It is important to consider the voltages on this tank circuit. 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. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. What are the advantages and disadvantages of the end-fed half wave antenna? 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. stream The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead. The finished tran, End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. Above is a thermograph of the transformer at 20W input at 3.6MHz. 100W on a Wire Antenna - Is it good enough for DX? How to get started on ISS Cross band Repeater? Be aware counterpoise or ground radials are required for all hf antennas for better performance. It is recommended to use at least 2W non-inductive resistors for this purpose. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. 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. 2 0 obj After some internet research, I settled on making the former from a paint roller. So, how to construct an end-fed half wave antenna? Basu (VU2NSB), Antenna Bearings Geodesic Map We present automatically rendered Antenna Bearings with Geodesic Paths projected on a Rectangular Map. nanoVNA-H can firmware be updated if it has a broken USB socket? I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? To be safe, better not get much above 120 C. 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. ENDFED/EFHW Antenna & Choke - F5NPV - V85NPV Connected to the packaged transformer, I ran some SWR sweeps with just the bare wire and various configurations of small coils to act as band-tuning compensation. This suggests an inductive reactance. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. 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. 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. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. It should be no surprise that 80pF is close to optimal. I checked the wall brackets and mast, but all the fixings were nice and tight. 40M EFHW & 3D printing - Member Projects & Builds - Parker Radio One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. Lets do a quick calculation to see how much an issue is this output capacitance. I installed a QRP SWR meter into the tuner that makes tuning very handy. Impressive article and so well done that I may give it a try. 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. I use shock cord to connect the insulator at the end of the wire to my fence. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. We also know, that both ends of the half wave antenna will have the highest voltage, thus impedance, which may reach up to several kilo-ohms. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. I wish you lots of productive experimentations and successful portable operations. Above, the magenta curve is measurement of a real transformer from 1-11MHz with nominal resistance load and three compensation options: cyan: 0pF, too little compensation; magenta: 80pF, optimal compensation; and. 73 Of course, you will need to find your tuning positions and apply your own position scale. Some website features may not function optimally without cookies. Then I covered the coil in kapton tape to hold it together. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. Research salary, company info, career paths, and top skills for Software Engineer - EDI 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. I found it very useful to label the tuner with switch and capacitance positions. And now I am planning to build one for 160/80m. 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. 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. Wow, Gary! And of course, a counterpoise with various lengths. Your posting put it all together for meTHANK YOU!!!! Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. Is it any good? 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. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. It not a loading coil. Refurbishing aluminium antenna parts affected by weather / corrosion. 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. Do I count the six loops around the pvc in the measurement? = .00 00 00 00 0 258 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. It is hard to wait an infinitely long time for the box to equilibrate to a given power level. A short 80m antenna for my lot - KB6NU's Ham Radio Blog 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. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. 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. The Truth, ,and Nothing But The Truth (as I've experienced it) 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.) (Tvir s tvbeszl gpek s kszlkek) Ksznm. Multiband End-fed Half-wave EFHW Antenna - VU2NSB.com Why had I not noticed this before? It uses a coil as a compensation unit, and no counterpoise. I ran WSPR at 10mW for about 2 hours and got the results below. I decided to push for best efficiency with a 5-turn primary. 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. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. 5) It is very hard to avoid stray capacitance on the output. 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 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. At this point, I'm leaning towards the EFHW, but any of these antennas seem . 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. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. This antenna is working for 80,40,20,10 and 6m bands. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. Now I just need to build or acquire a decent radio to utilize this new antenna. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. Which begs the question what happens when you attach the antenna? Thermal gasketing between the cores and the aluminum heat sinks could help a lot, as would a single piece of aluminum rather than the stack up of thin sections I used. There is lot of controversy around the EFHW antennas. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. Does your station desperately need a good RF ground to behave properly? 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. of the wavelength. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. The above factors often also lead to unacceptably high CMC on the coaxial cable transmission line thus rendering a rather poor antenna system. 3) Total losses are approximately independent of core volume. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. We also need to know what are the frequencies or bands for which we plant to use this antenna. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. Independent Medical Evaluation - IME | Cynthia Hennessey