There is lot of controversy around the EFHW antennas. Lowest measured inductivity = 2.0 H. 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. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. Ismerje meg a hozzszls adatainak feldolgozst . It is worth experimenting with its length also. Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. 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. My question is what is 'higher frequency' specifically? Which begs the question what happens when you attach the antenna? Below about 7 MHz, transmission losses increase as the core temperature increases. You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. 2015. At FT82-43 matching transformer for an EFHW I wrote about the likely losses at 3.6MHz of a common design using a FT82-43 ferrite core with a 3t primary. application of Kirchhoff's current Law on a typical EFHW antenna configuration. The coil came out at 89mm in length rather than the theoretical 83mm not surprisingly, but the inductance was bang on at just over 109H. coil inductance calculator at 66pacific.com. Wow, Gary! 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 . Wrap the first wire around the toroid 27 times (I used a black wire for this). This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. point to the loading coil is 20.2m and this sets the 40m resonance at 7.1MHz, which in turn dictates the responses of the harmonically related bands 14MHz, 21MHz and 28MHz. This will yield the maximum capacity of the variable capacitor. Performance of 49:1 Ferrite CoreTransformers, 24 Hour Animated PSK Reporter ReceptionReports. After doing the ferrite transformer scaling experiments last time, and learning a bit more about what matters in these transformers, it was time to make a stab at designing one. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. The technical storage or access that is used exclusively for anonymous statistical purposes. The five primary turns cover about 60% of the secondary winding, leaving the high-side of the secondary not covered. Jim, do you mind if I add your email and my answer as a comment to the article? I wish you lots of productive experimentations and successful portable operations. = .000001 / 3868.88 An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. A 100pF silvered mica was connected in shunt with the transformer . 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. Saturation of a warm core happens near 0.2 T (2000 g) and if you dont want to deal with significantly reduced permeability, then better to limit to 0.1T. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. For the last step, I put together a RF choke to use between the radio and the feedline. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. It performed well on both the 2m and 70cm bands. 2) Winding capacitance and leakage inductance, especially present as you increase the number of turns, limit the high frequency performance. It is not necessary to calculate the above; the results are sown in the following table. Update: Full size 132ft EFHW For one month I replaced the 66ft wire and loading coil and replaced it with a full 132ft of wire, connected to the FT240-43 balun. Nevertheless, this is a rather curious result that might have derating implications for the 160 and 80 meter bands. It will present its parameters, so anybody with basic home-brew skills will be able to build it. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. This was a little bit of a compromise as the last 20ft of the antenna had to run down a fence to fit it into the garden. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. The vector sum total of all currents flowing on various physical antenna wires plus other currents like CMC on the transmission line or parasitic induced currents on masts or nearby objects must always be equal to zero. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. 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. Because of the division of power between the 3220 resistor and VNA input, there is effectively an attenuator of -10*log(50/(50+3220))=18.16dB, so |S21| has a component due to this division. Research salary, company info, career paths, and top skills for Software Engineer - EDI This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. stream 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. How badly can high Local Ambient QRM affect HF Radio? Tackling both of these issues at once led to a much smaller, lighter, and less costly transformer with better loss characteristics than previous designs. The cooling curve I measured is shown below. 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. What are its disadvantages? Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. See the second completed tuner depicted below. <> Thirty turns #28 are wound on the two FT114-43 cores. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. The last few years have seen a resurgence of interest in the end fed half-wave wire EFHW antenna. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. The wire as I strung it up seemed to resist having a good SWR for the 20m band. The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user. 1. There are two aspects, however that we need to consider: Lets begin with the transformer. clear. Be sure to take a look for additional analysis and conclusions. Apply for the Job in Software Engineer - EDI at St. Louis, MO. 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 . Measurements were made on the unmounted transformer with just a ~2 inch length of lead from the secondary to the 2450 load and sampling resistor (jig connections as shown in the photo above). The Counterpoise is a short, typically one twentieth (0.05 *. ) That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. 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. A transformer was wound on a FT50-43 toroid with 3 bifilar turns followed by another 31 turns of #26 enameled magnetic wire. 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. Change), You are commenting using your Twitter account. Some hams swear by them, yet some completely demean it. The previous table already contains these measurements. I am currently working on measurements of an EFHW antenna. The low end of the secondary, which will be the tap, is bent back over to the center of the winding and covered with a small piece of Kapton tape, and then the primary is wound over the tape (and the secondary tap wire). The capacitor makes very little difference to the low frequency behavior, but it reduces the input VSWR significantly at the high end. By using traps, the antenna works on all three bands with no operator interaction. Therefore, I picked a momentary push button to switch the operational mode to tuning mode while tuning up. Do I count the six loops around the pvc in the measurement? This antenna is working for 80,40,20,10 and 6m bands. I decided to play with this to see what I could accomplish. The computation method is also touched on. I was curious why this capacitor was added to the transformer. |k"^N>F.AnJkJsq'PV}o0I. The difference here is that the target bands are low frequency. I got the, http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html, End Fed Half Wave (EFHW) Antenna Upgrade Part 2 - The Loading Coil. 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 have been offered input VSWR curves for such a configuration, and they are impressive but VSWR curves do not address the question of loss / efficiency. 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. So far so good. 100W on a Wire antenna! My design objectives were: 1. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. Your calculation is correct, the result I get is also .000000000258, which is clearly wrong (it is Farads instead of pF). They will be adjusted for resonance at or close to the CW portion of the bands. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. Some say you do not need a counterpoise, but that is false. Well, in ham radio, everything works. Klubunknl folyamatos a tagfelvtel. Workers' Comp. On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. The toroid with its many taps may be soldered directly on a multi-position switch. This suggests an inductive reactance. The final turns ratio turned out to be 3:29. Be cautious, such voltages may cause a quite painful skin scorch. A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. The technical storage or access that is used exclusively for statistical purposes. Let me review the salient observations from the previous work. 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. Thank you Gary. The Counterpoise is a short, typically one twentieth (0.05 * ) of the wavelength. Graphed with a log scale, it makes a nice straight line. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. I've always had issues with 10m loading up properly so I'll also be adding a compensation coil 78 inches from the feed point on the wire. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. How does this SWR meter works? The original coil is designed for low power portable applications. Basu Bhattacharya (VU2NSB). We use cookies to optimize our website and our service. I have an EFHW and the SWR is acceptable on all the bands with the exception of the WARC bands which is to be expected since the harmonic relationship is different. I then added two 220pf capacitors in series between the center conductor and ground. The slim coil is torpedo shaped to prevent it being snagged in trees when deployed in 'the great outdoors'. 73! A 100pF silvered mica was connected in shunt with the transformer primary. At equilibrium, the heat leaving the box due to cooling will exactly equal the heating power input. IIRC they call it a "compensator". Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. 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. 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. However, a key restriction is its 25W power rating, due to the small matching transformer. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. 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. I thought to test this hypothesis by measuring the losses as an oven-heated transformer box cools down. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. Commercial Coils, Inc. 213 Chesterfield Industrial Blvd Chesterfield, Missouri 63005. Without a subpoena, voluntary compliance on the part of your Internet Service Provider, or additional records from a third party, information stored or retrieved for this purpose alone cannot usually be used to identify you. I found it very useful to label the tuner with switch and capacitance positions. Z8Vq9_@x C\Agv#. An end fed half wave antenna, or efhw, is a variation of a half wave dipole, but it is fed from one end. 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. I tossed the line as far up as I could in a tree. One point of my small-core, compact winding design was to be able to cool the core. No capacitor was installed. Let's find out! The radiation pattern of this antenna on most bands produces multiple lobes. 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. You can start with the links below. The 2 coils are 35uh and 90uh. These dimensions were derived from modelling the antenna in EZNEC. 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. 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 found that sometimes the multimeter that was measuring the temperature would give unreliable information when RF was present, so the off periods provided regular intervals for measuring the temperature. Let's find out by checking the performance of a transformer with no capacitor for single band EFHWs for 20, 30 and 40 meters. However, a key restriction is its 25W power rating, due to the small matching transformer. I wanted to test the hypothesis that an inductance near the box would compensate for the output capacitance and further improve match on those bands. 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 was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. Be aware counterpoise or ground radials are required for all hf antennas for better performance. Above 7MHz, there is very little temperature dependence at all. 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. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. Loss (to mean PowerIn/PowerOut) can be calculated in dB as -|S21|-LoadAttenuator-MismatchLoss=18.64-18.16-0.03=0.450dB, or an efficiency of 10^(-0.45/10)=90.2%. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. If you really want to get the heat out, add some fins to the aluminum box. 2006. 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. 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.