From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. The orientation of these lobes varies with the frequency band of operation thus resulting in directional inconsistencies between bands. There are many good descriptions on the net about this type of antenna. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). One way or another there is always a counterpoise involved if the antenna is tuned correctly. Above is a thermograph of the transformer at 20W input at 3.6MHz. = .000001 / 3868.88 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 . Then we find Bmax = 0.076 T. The Type 43 data sheets show us what we have to look out for. You can achieve this inductance with half a dozen turns of the antenna wire tied in a small coil. I needed to add an additional coil (approx 12.5 uH) about . This antenna is working for 80,40,20,10 and 6m bands. I have been searching the internet for a very long time (AA5TB, VK3YE, SOTA Reflector, among MANY others), and your posting finally made clear for me the many questions I have had. Assuming, most of us use the 40/30/20m band for HF SOTA activation, so the following table shows the SOTA frequencies, and the calculated half wave radiator wire of the antenna. = 1/30.e6 = 33 nS. It matches the impedance fairly well to the half-wave antennas high impedance at one of its ends. Jos van den Helm's (PA1ZP) article published in Radcom: Fig.1 - Withdraw the radiating element carefully to avoid damaging the matching components A few years ago I bought a secondhand Diamond X50 dual band (144/430) antenna at a radio car boot sale. Nagyon j ez a cikk. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. 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. The Truth, ,and Nothing But The Truth (as I've experienced it) I settled on a compact secondary using #28 wire. End Fed Half Wave (EFHW) Antenna Upgrade Part 1 - The Matching Transformer coil inductance calculator at 66pacific.com. <> A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. Graphed with a log scale, it makes a nice straight line. EFHW Antenna Frequency Compensation Lead - YouTube Ive been wanting to put together a decent multi-band antenna for a long time and finally settled on an end fed half wave antenna. We also need to know what are the frequencies or bands for which we plant to use this antenna. Proudly created withWix.com. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. Selecting the variable capacitor that can be varied from this minimum to maximum capacity, will allow tuning to resonance for 40, 30, and 20m bands at each of the switch position of the tuner. The model results show the need for a not entirely insignificant counterpoise. The effect of the capacitor is very apparent for 17 meters and above, flattening and lowering the SWR curve through 10 meters. The SWR was measured for each of the three antennas across the CW portion of the bands. EFHW Compensation Coil Experiment - YouTube You cant really see the antenna wire, but the red line shows the antenna path. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. Software Engineer - EDI - salary.com Krem, rja le, mi a krdse. Above is a sweep of the uncompensated prototype with a 3220+50 load. The SWR was low, but not unity, so the peak voltage was lower than the 50 ohm match value when measured with the high-Z scope probe. Make sure the first wire is wrapped evenly around the whole toroid. The combination of the transformer with the end-fed dipole results in a positive reactance. So I built myself an improved replacement matching transformer. HA5CBM Mikls, Finally the tank circuits specification is complete, which is sown below. There are two aspects, however that we need to consider: Lets begin with the transformer. The worse SWR was 1:1.7 at the top end of 20 meters. I used the 14g enameled wire and wound it on the FT240-43. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. To compensate for the antenna connector capacitance, the solution might be to add the appropriate inductance on the wire right near the box. It turns out that we can easily measure the effective parallel secondary capacitance by looking at the primary self resonance when the secondary is open. 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. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. . 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??). The transformer is wound as an autotransformer, 3+21 turns, ie 1:8 turns ratio. Lets call this element the LoadAttenuator. Scaling the small core to higher power levels would mean that the flux level in the ferrite core would increase. How badly can high Local Ambient QRM affect HF Radio? stream A Brief Synopsis of the Antenna Features & characteristics, EFHW Antenna Geometry versus Center-Fed Dipole. The real power limit will be core heating. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. For the transformer, a T130-2 toroid will be sufficient, on which we wind the seconder with multiple taps, as shown in the below table. I wish you lots of productive experimentations and successful portable operations. Why had I not noticed this before? The latest news about Efhw Compensation Coil Experiment. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. Do I count the six loops around the pvc in the measurement? = 258 * 10^-12. End Fed Half Wave Antenna Coupler (EFHW) - M0UKD 100W on a Wire antenna! When I'm measuring the half way point on my EFHW, looking for 67', how do I factor in the compensation coil on the MyAntennas wire? Above, 3t on the primary delivers Gcore<0.002S. Other observations along the way: 4) Tight windings or backwinding over the primary can significantly reduce leakage inductance. Trapped five band EFHW SOTA antenna | VK3IL Blog Frank VK1VK. Trapped 20/30/40 Meter EFHW Antenna - AI6XG Geeksite That will be the missing resistor in the resistor bridge of the below circuit. Of course, you will need to find your tuning positions and apply your own position scale. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? It was difficult to work out where it was coming from but I found that it was more noticeable when it was windy outside. In comparison to the EFHW antenna, a simple dipole offers a far better prospect. Now I just need to build or acquire a decent radio to utilize this new antenna. AC Coil Replacement Cost 2023 - Forbes Home For the antenna wire itself, I used 119 feet of 22g stranded hookup wire. With no counterpoise wire it will be the coaxs shield providing it. Select components with good insolating materials and properly chosen, relatively high voltage rated parts. A week or two later I started to notice an occasional knocking sound inside the house. There could be any number of reasons for that, where I put the bends in the wire, the location of tree branches, etc. I have also had SSB QSOs in Europe, USA and Canada on 20m so havent seen any degradation in performance on that band. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. Ambient temperature is 20, and the core temperature increased by 5 over 120s @ 20W continuous input. nanoVNA-H can firmware be updated if it has a broken USB socket? 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. 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. Although the original loading coil is very well engineered, I thought I could make a more efficient version given that I did not need to make it 'trail friendly'. The final turns ratio turned out to be 3:29. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. With such a switch, it is impossible to forget to switch back to operational mode. 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. Hi Ajai, 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. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. If you stare at the above frequency sweeps you will discover a few things. With tension on the antenna wire, you can just roll the coil up/down the wire to try different positions as you are optimizing for a particular band. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! I dont have an amplifier, so only need to be able to handle 100W. I decided to play with this to see what I could accomplish. I then used a piece of heat shrink on the outside to hold everything in place. This totally un-rigorous calculation just gives a quick idea of how much you have to be careful. How far could it possibly reach? (LogOut/ Inverted V Antenna A popular Dipole variant, EMI-RFI and Noise related HF Radio Station performance loss. This can then, fed with coaxial cable, in many cases be . Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. It performed well on both the 2m and 70cm bands. Compensation. Do your own experiments with your own set up, 2019 - 2022 by Dan Koellen AI6XG. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. 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. Jim, do you mind if I add your email and my answer as a comment to the article? is the initial disequilibrium temperature, is the equilibration time constant, and is the heat capacity. 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.) My End-Fed Half-Wave (EFHW) AmateurRadio.com You can find more info here: https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. If not a lightning strike, I will write an article about the experience as well. The End-Fed Half Wave Antenna a bit Differently I also will ask, why didnt it work for you. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. . Thank you Gary. I use shock cord to connect the insulator at the end of the wire to my fence. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces.
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