Could it be something to do with the new vertical aerial I had recently installed? There is lot of controversy around the EFHW antennas. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. % End Fed Half Wave Antenna Coupler (EFHW) - M0UKD My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. The antenna is effective and the materials and construction are of a very high quality. I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned -- The experiments have been performed, check it out! From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. Consequently, this is how the capacitance values are determined. It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. 2006. At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. As I reexamined my formula, you pointed it out correctly, there is an error in it. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Thank you for your comment and feedback on the article about the EFHW antenna. 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. 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. How to tune a multi-band EFHW antenna using a loading coil Pocket-tenna core is finally done! Wire and compensation coil being Finally the tank circuits specification is complete, which is sown below. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? One point of my small-core, compact winding design was to be able to cool the core. Therefore the Great Circle Map generated below should be Read More, Multiband End-Fed Half-Wave EFHW Antenna The End Fed Half Wave antenna or the popularly known EFHW antenna has been around almost ever since the inception of HF radio. My concern with the KN5L design is mostly about voltage breakdown through the enamel insulation where the secondary crosses the primary ground. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. 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. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). 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 SWR figures were as follows: FT240-43 132ft/100pF capacitor It uses a coil as a compensation unit, and no counterpoise. For a quarter wave that is about 8 nS. |k"^N>F.AnJkJsq'PV}o0I. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. You can see the coil in the picture below (red arrow). EFHW 80m extension - MI0KXX A short 80m antenna for my lot - KB6NU's Ham Radio Blog %PDF-1.4 Many people use an inductor placed at the near end to make things level out on the higher bands. 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. In my research on End Fed Half Wave (EFHW) antennas I found that nearly all have a capacitor in the primary (rig) side of the transformer. Lets do a quick calculation to see how much an issue is this output capacitance. The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. We have been in the middle of Storm Arwen and Strom Barra here, so I had the pole down for a few days. A ktelez mezket * karakterrel jelltk. And of course, a counterpoise with various lengths. Check your inbox or spam folder to confirm your subscription. How does this SWR meter works? Of course, if both ends are raised higher, it will produce a more efficiently radiating antenna, but the portable and temporary installation is always compromised by conditions given by a location and its restrictions. Below about 7 MHz, transmission losses increase as the core temperature increases. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. <> 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. This can then, fed with coaxial cable, in many cases be . I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. MyAntennas.com Group | When I'm measuring the half way point on my EFHW I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! The antenna is up. This will yield the maximum capacity of the variable capacitor. Proudly created withWix.com. 2 0 obj ROB@COMCOIL.COM End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer 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. Above 7MHz, there is very little temperature dependence at all. blue: 250pF, to much compensation. 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. The goal of the temperature characterization is to determine how much temperature difference (core to ambient) there will be for a given level of power dissipation. It not a loading coil. We do not know what the actual impedance will be at the end of the antenna radiator. Be sure to take a look for additional analysis and conclusions. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? The comparison is done on 4 bands - 10m, 20m, 40, and 80m. Contact Commercial Coils It is not necessary to calculate the above; the results are sown in the following table. The impedance per unit length of a lumped transmission line is where L and C are values per unit length. Your article was well written and very informative, thanks. 73! I mentioned in the reference article that the metric A/l captures the geometry, the larger it is, the fewer turns for same inductance / impedance. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. 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. 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 technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. 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. I am planning to use this latest one at the Field Day next year. Two layers of 1mil Kapton tape are placed over the winding. As you stated early in your posting, I also have found 99.99% of all posting on the internet tell you WHAT they did.not HOW they determined the specific design criteria. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. It may be one or even five kilo-ohms. 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. When you are discussing a distributed capacitance, it is difficult to know exactly what you are measuring. Copyright 2014-2023. 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. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. Hello, a wonderful approach for the problems.. 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 . In my research on End Fed Half Wave (EFHW) antennas I found that nearly all have a capacitor in the primary (rig) side of the transformer. 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 . This is perhaps one of the most hotly debated rookie topics in. Lowest frequency = 7.000 MHz. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. I found it very useful to label the tuner with switch and capacitance positions. The biggest uncertainty in these measurements was the actual power level used. I dont have an amplifier, so only need to be able to handle 100W. 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. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. 100W on a Wire Antenna - Is it good enough for DX? If not a lightning strike, I will write an article about the experience as well. However, it has its idiosyncrasies. Z8Vq9_@x C\Agv#. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. The SWR was measured for each of the three antennas across the CW portion of the bands.
efhw compensation coil