The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! Having recently built a MTR2 3-band CW transceiver, I was keen to make band switching on a mountain top as simple as possible. 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. Nagyon j ez a cikk. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. But systems that work better increase the prospects of contacts. 5 Band EFHW Antenna 80m-10m | 49:1 End Fed Half Wave Ham Radio DX 27.1K subscribers 19K views 7 months ago #HamRadio #AmateurRadio #EFHW Here are my experiments and modifications with an EFHW. We also need to know what are the frequencies or bands for which we plant to use this antenna. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). I am planning to use this latest one at the Field Day next year. If you want to minimize leakage inductance, the way to do that is to keep the two windings very close to one another. 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. After acquiring a MTR3b for SOTA activations I decided I needed a different antenna than the End Fed Random Wire (EFRW) or the speaker cable 20 meter dipole I use with my KX2. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. End-Fed antennas are useful in many ways, includes easier mounting of cable at one end (freeing the antenna from unnecessary weight of cable) & antenna maintenance in future. 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. One end is about 5 meters high on an extended fishing pole. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. Your posting put it all together for meTHANK YOU!!!! I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. 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 clear that the capacitance from just mounting the transformer in its box generates a significant reflection at 30MHz for the 10 meter band. I may try to bring down the 20, 15 and 10m bands at some point, either with a small coil 2m from the feed point or with a short section of wire as a compensation lead added at the feed point as shown in the video below from Steve Ellington. It may be one or even five kilo-ohms. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. The band compensating inductor placed on the wire is another story. 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. I look at the end-fed as just an extreme example of an off-center-fed antenna. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Even at 15W the voltage at the ends may reach 100-200V. The overlaid VSWR plots are shown below. Even at only 100W, the RF voltage on the high Z output of the transformer can easily be >1300 Vpp, so this is not an idle concern. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. It is all about getting the heat out. One of the many confusing terms used in Workers' Compensation, "IME" stands for Independent Medical Evaluation or Independent Medical Examination. In fact, this was the second one I had built, as I had also made one for a 30m/15m end fed antenna. I checked the wall brackets and mast, but all the fixings were nice and tight. 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. Steps to improve the heat transfer over the present design could make this small transformer work at even higher power levels. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. A week or two later I started to notice an occasional knocking sound inside the house. 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. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). We use cookies to optimize our website and our service. 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. Toll Free 800-532-2645 636-532-1523 Fax: 636-532-8259. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. How does this SWR meter works? The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. It performed well on both the 2m and 70cm bands. 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. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. It is recommended to use at least 2W non-inductive resistors for this purpose. Finally the tank circuits specification is complete, which is sown below. If not a lightning strike, I will write an article about the experience as well. Note the material 43 hysteresis curves shown below for 25 C and 100 C has a smaller open area (and hence lower losses) at the higher temperature. 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. Above 7MHz, there is very little temperature dependence at all. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. The final turns ratio turned out to be 3:29. This gave me an effective coil diameter of 40.5mm. The usual problems of having the multiple band resonances all line up appear here with the end-fed design, similar to the same issue with off-center-fed designs. That will be the missing resistor in the resistor bridge of the below circuit. 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. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. Basically, the loading coil is operating as a trap. Wire antennas with an Un-Un-transformer 1: 9 have become more and more popular. 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. Im very pleased with that indeed. 2006. I wish I had a simple answer, but really this is where some experimentation can pay off. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? The wire as I strung it up seemed to resist having a good SWR for the 20m band. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. Note: If we change the primary number of turns, the impedance ratios will considerable change also. |k"^N>F.AnJkJsq'PV}o0I. It is common to use "compensation" coils of a few turns of the antenna wire to improve the alignment of the bands. Change), You are commenting using your Facebook account. I am building an EFHW antenna for my new MTR3b, but do I need to include the capacitor for 20, 30 and 40 meters? Change), You are commenting using your Twitter account. A 100pF silvered mica was connected in shunt with the transformer primary. 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 . The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. Then record the change in temperature recorded at the core from the probe, and the elapsed time so I could corrected for not reaching perfect equilibrium. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). Csatlakozz csapatunkhoz! What kind of balun is this? In the problematic upper bands, the resonant wire significantly improved the in-band SWR compared to the resistively terminate box (purple). We do not know what the actual impedance will be at the end of the antenna radiator. 2. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. At this point, I'm leaning towards the EFHW, but any of these antennas seem . I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. This antenna is only 15m long using 2 loading coils. I set up an EFHW for field day using a similar transformer with 25 ft. of coax from the box, everything floating, to my battery powered radio. This antenna is working for 80,40,20,10 and 6m bands. 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. In an urban area we are much more restricted, especially if we need to be stealth about it. (LogOut/ Im very happy with the result. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. It not a loading coil. The SWR results are as follows: 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. 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. Thanks again Jim. 100W on a Wire Antenna - How far would it reach? The technical storage or access that is used exclusively for statistical purposes. 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. With no counterpoise wire it will be the coaxs shield providing it. The disadvantage of this switch is that one needs one hand to hold it, another to key down, and yet another to tune the capacitor. This is based on random lengths of the antenna, which is transformed with the un-un into a medium-ohmic impedance range with reactive components. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. Next, I started winding the transformer. 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. Why had I not noticed this before? End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer. One end may even be close to the ground, not yielding the best radiation efficiency, but much activation proved it still operational. I was pleasantly surprised that the dips were so perfect across all of the bands and the SWR was low enough to not really need a tuner. 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. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. As is often the case, packaging was determined by what boxes I had laying around. It is worth experimenting with its length also. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? Lowest frequency = 7.000 MHz. Nevertheless, the EFHW antenna had in the past, been rather sparingly used by amateur radio operators due to various reasons. Refurbishing aluminium antenna parts affected by weather / corrosion. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. I settled on a compact secondary using #28 wire. Basu Bhattacharya (VU2NSB). Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. i liked it a lot, you give good ideas, many thanks. The EFHW transformer box from outside. The above illustration displays a typical set of Azimuth and Elevation sections of the radiation patterns that one might expect from a horizontally configured EFHW Wire Antenna deployed at an average height of 40 ft. above ground level (AGL). Thank you Gary. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit.
