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. % It is hard to wait an infinitely long time for the box to equilibrate to a given power level. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. 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. The equation should have a 10^6 and not 10^-6 in the nominator. To be safe, better not get much above 120 C. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. Since I wont be connecting a counterpoise, the antenna will use the coax shield as the counterpoise, so the RF choke will keep any unwanted RF from feeding back through the coax. PART - 1 : The EFHW antenna as a radiating and receiving element is a decent multi-band antenna with good efficiency on all bands, provided it is driven at its feed-point using a well configured and well-matched driving source. Hence, we need to move along and start to include the antenna with our testing. The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. 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%. 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At 5W input the connector at the end of the antenna wire may be up to 160V, and at 15W it may be 270V. The biggest uncertainty in these measurements was the actual power level used. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. How to get started on ISS Cross band Repeater? Gut feeling says that should be possible with just a couple of FT114-43 cores, similar to the design by John Oppenheimer, KN5L. PART - 2 : Most EFHW antenna configurations resort to the use of broadband impedance transformers at the feed-point to attain acceptable SWR on all operational bands. |k"^N>F.AnJkJsq'PV}o0I. 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. coil inductance calculator at 66pacific.com. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. The radiation pattern of this antenna on most bands produces multiple lobes. I wish you lots of productive experimentations and successful portable operations. Well, in ham radio, everything works. Taking the time derivative of the above equation you get the power dissipation. Which begs the question what happens when you attach the antenna? The 6-turn loading coil lowers the resonant frequency into the CW portion of the 40 meter and higher bands. The antennas are set up as a sloper as in my SOTA outings. 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'. 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. Hello, a wonderful approach for the problems.. Some say you do not need a counterpoise, but that is false. Wrap the first wire around the toroid 27 times (I used a black wire for this). For . The bottomline, your putting the relationships of 1) Toroid windings and to measure their inductance together with 2) the required capacitance calculation is exactly what I needed to move forward with my specific design plans. stream It requires a set distance to hang both ends of the antenna, and that is not always given. The wire as I strung it up seemed to resist having a good SWR for the 20m band. clear. What are its disadvantages? The following is the most up-to-date information related to EFHW Compensation Coil Experiment. There is no substitute for playing with the analyzer, trimming the wire, adjusting the compensation coils, etc., and going through the process for a few iterations to get the multiband antenna to work well for you as you have it installed. Isn't it? Some hams swear by them, yet some completely demean it. Your article was well written and very informative, thanks. = 258 * 10^-12. The bridge than will measure zero voltage across the bridge, and the LED will turn off. 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. (LogOut/ An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. I dont have an amplifier, so only need to be able to handle 100W. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. The highest voltages as well as radiation are also at the end of the antenna wire. Be cautious, such voltages may cause a quite painful skin scorch. I decided to push for best efficiency with a 5-turn primary. Thanks! The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. The photos above show a method that works fairly well. The highest frequency could be14.350MHz. Two layers of 1mil Kapton tape are placed over the winding. The conjugate impedance matching arrangement of this nature is far from perfect resulting in considerable reactive currents on some of the bands. This antenna is only 15m long using 2 loading coils. Intro EFHW Compensation Coil Experiment Steve Ellington 10.3K subscribers Subscribe 29K views 4 years ago The little coil helps place the EFHW resonance points where we want them. However, a key restriction is its 25W power rating, due to the small matching transformer. Interpretation of S-Meter Noise Floor in HF Radio Receivers. %PDF-1.4 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. 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. IIRC they call it a "compensator". And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? of the wavelength. So I built myself an improved replacement matching transformer. I used four parallel #28 wires (not twisted) for the primary. 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. With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. I checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! My goal was to describe the parameters of an antenna that can be easily build, yet show enough theory for someone to design his or her own antenna and antenna tuner. 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. Note that the resonances do not necessarily line up harmonically, there is commonly some enharmonic effect. Hence, there is no optimum single-fit solution. Workers' Comp. 100W on a Wire antenna! 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??). For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. This gave the RF some place else to go, trapped by the coil and capacitively shunted to ground, rather than on to the transceiver. 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 recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. Firstly, bandwidth on 80m is restricted to about 80 kHz at . The final turns ratio turned out to be 3:29. 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. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. 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. No capacitor was installed. The following describes such a transformer using a Fair-rite 2643625002 core (16.257.2914.3mm #43). The resistance (real) component of the impedance is right where we want it near 50 ohms. The original coil is designed for low power portable applications. 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. This transformer has more surface area than a FT82-43 based one, so it has higher capacity to dissipate heat, and it is more efficient, so it will have higher power capacity than the FT82-43 based one. 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. 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. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. 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? 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. This illustration provides a graphical view of approximate comparative difference in expected Common-Mode-Current (CMC) that could flow on the transmission line to undermine the overall performance of the antenna system. Let us touch on some necessary theory to begin with. It may be one or even five kilo-ohms. How big and where to place it is likely best determined empirically. 2 0 obj The technical storage or access is necessary for the legitimate purpose of storing preferences that are not requested by the subscriber or user.