The wire as I strung it up seemed to resist having a good SWR for the 20m band. Looking at several builds and discussions, such as commercial antennas (e.g. 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. I did struggle with the C in pF calculation..I seem to be getting hung up on the correct decimal placement..for example, for the 40-meter Capacitor requirement, I get .000000000258: C pF = .000001 / [ ( 2 * 3.14 * 7 MHz) ^2 ] * 2 uH Let's find out! RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. blue: 250pF, to much compensation. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Radio Transceiver S-Meter Pitfalls to avoid, Atmospheric impact on VHF Radio Propagation, Terrestrial VHF Radio Signal Coverage LOS, Terrestrial VHF Radio Signal Coverage BLOS, HF Surface Wave Propagation (Ground Wave). % Firstly, bandwidth on 80m is restricted to about 80 kHz at . One way or another there is always a counterpoise involved if the antenna is tuned correctly. For Jackson County, please call Western Egyptian Economic Opportunity Council, in Steeleville, at (618) 965-9031. 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. If you really want to get the heat out, add some fins to the aluminum box. 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. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. There's seemingly conflicting information out there, such as on QRZ the consensus seems to be to either use no choke on the coax, or choke it some ways away from the feedpoint - WA7ARK recommends .07 wavelength, which is about 9' on 40M. 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. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. This is not an optimal value, benefit may be obtained by exploring small changes to that value. 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. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). Im a hundred watt guy, so do not have a lot of experience with high voltage RF, but I know that ~5kV peak-to-peak RF voltage that you would expect at the 2450 output at kilowatt power levels could begin to cause you some trouble. Even at 15W the voltage at the ends may reach 100-200V. One cable is the coax feedline, the second is the supply to the cooling fan and control of relays. Although it is simple to build and is a multiband antenna, it has several attributes that . Some of my research showed that a small compensation coil can be added about 2 meters from the transformer to pull down the SWR on the higher bands. And of course, a counterpoise with various lengths. Thanks again Jim. Check your inbox or spam folder to confirm your subscription. 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 checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! 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. 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. 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. There are two aspects, however that we need to consider: Lets begin with the transformer. My design objectives were: 1. The next important parameter is the parallel resonant circuits resonant frequency. The resistance (real) component of the impedance is right where we want it near 50 ohms. The VSWR plots below show results from the same transformer tested on the bench with minimal output capacitance, with a primary compensation capacitor, either 100pF or 27pF included, with the transformer installed in its aluminum box including antenna connector feedthrough, and with the transformer with an 18 clip-lead on the antenna output. The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. 2. 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. 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. 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. Thank you for an interesting and informative read. Typically the IC-751A would read about 60W on its power bridge, the Siliconix would show >50W on the 50W scale and 45W on the 500W scale, so there is ~20% uncertainty. The biggest uncertainty in these measurements was the actual power level used. 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 $2,400 depending on the brand, your region and other factors . Ive been wanting to put together a decent multi-band antenna for a long time and finally settled on an end fed half wave antenna. I drilled a couple of holes at each end of the former, a small one for the wire to pass through and a larger one for a bolt and wingnut for wire attachment as I wanted the end result to be portable across different antenna projects. We need to measure the inductances of the toroid with the tapped coil. With such a switch, it is impossible to forget to switch back to operational mode. = 1/30.e6 = 33 nS. The highest frequency could be14.350MHz. Dutch radio amateurs in particular have been active in this area: John, PD7MAA's blog - http://pa-11019.blogspot.com/2012/04/149-transformer-for-endfed-antennas-35.html Jos van den Helm's (PA1ZP) article published in Radcom: "A 3- or 5-Band End Fed Antenna", February 2016, Radcom, published by the RSGB in the UK. There is no BIG secret about the EFHW-8010 antenna, it is just a wideband low loss transformer and a piece of wire. First, note that the transformer has low transmission loss up to nearly 50MHz. Does your station desperately need a good RF ground to behave properly? The 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. 0 7t8An. }pKumm" t7Vb55nx S;/E}*+RS'|(q&wA;n";&.'KDff9H0^SF7 O0~{h9*QX\Mwk> u)Y h&kvDc%=(]F_$?6!:\EsM4"+>R%;93|"Jn\j+1 z}?>xBaR3 c +U+WLX`\Ld.Q2.VDHh']o.)k;a6*~s" 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. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF With no counterpoise wire it will be the coaxs shield providing it. If you need to change it, is necessary to recalculate the secondary turns, and the resonance frequency needs to be adjusted also. Research salary, company info, career paths, and top skills for Software Engineer - EDI It is important that resonance may be achieved at each tap of the inductance. 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). On the ends of each winding I slip the end under the last turn and pull tight to lock the winding in place. It is not necessary to calculate the above; the results are sown in the following table. This can then, fed with coaxial cable, in many cases be . The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. After doing some research on the internet I eventually came across something about rattling radiating elements in Diamond vertical ant, For several years the EF-10/20/40 MKII EndFedz has been my main station antenna for HF. The impedance matching circuit is essentially a simple parallel resonant LC circuit. I look at the end-fed as just an extreme example of an off-center-fed antenna. My limited experience with these antennas also suggest that one must be cognizant of the RF current pushed onto the feed-line coax. The transformer fits sideways in the box with a few millimeters to spare. It is worth experimenting with its length also. Radio amateurs using this antenna might remain oblivious to the presence of many active DX traffic originating from the direction of the shadow regions in the nulls. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. Thanks! Payment: If you are eligible, Crosswalk CAA will make the appropriate payment to your energy provider (s) on your behalf. Ive been thinking about getting an antenna up for 80m, and Ive come across a number of options that interest me and would suit the space I have available realistically no matter what I go for it will be a very compromised antenna, but still much better than none. The negative effects of local QRM on an, How does antenna radiation occur? How big and where to place it is likely best determined empirically. 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. Wrap the first wire around the toroid 27 times (I used a black wire for this). Another design by KB0ZZ is a little longer, but resonates on both 40m and 80m. 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%. Instead, this shifts everything down and makes it very easy to tune 10m. In case you need to perform calculations, use the formula: Where the frequency f is in MHz and the inductance L is in H. 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 SWR for the 20 meter EFHW antenna was < 1.2:1, The SWR for the 40 meter EFHW was ~1.4:1 for 40 meters and 1.2:1 for 20 meters (full wavelength), For my 20, 30 and 40 meter EFHW antennas I will not use a capacitor in the primary. The Counterpoise is a short, typically one twentieth (0.05 *. ) Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. I think the idea is to begin by tuning 40m operation, adjusting the wire length as needed. It will present its parameters, so anybody with basic home-brew skills will be able to build it. However, let me write about it from a slightly different perspective that was not very obvious from the articles I read. Klubunknl folyamatos a tagfelvtel. In that case, expected efficiency (meaning PowerOut/PowerIn) of the transformer was less than 65% at 3.6MHz. Consequently, this is how the capacitance values are determined. Being end fed, it needs a transformer to transform the higher impedance of the wire to the 50ish ohms the radio is expecting. (LogOut/ How far could it possibly reach? Thirty turns #28 are wound on the two FT114-43 cores. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. The SWR was measured for each of the three antennas across the CW portion of the bands. 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'. It depends on the selection of the inductance and the capacitor values. However, it has its idiosyncrasies. The previous table already contains these measurements. The toroid with its many taps may be soldered directly on a multi-position switch. On the transformer, I added a few wingnuts to tighten down the antenna wire. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. At this point, I'm leaning towards the EFHW, but any of these antennas seem . 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. The patterns fro the horizontal wire is compared with those of an inverted-V configuration. 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 . A graphical presentation of the mathematical analysis of EFHW antenna SWR variations on account of variations in counterpoise length as well as the Unun impedance transformer at the feed-point. 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. The in-band SWR improved significantly with this localized inductance to compensate for the boxs capacitance. I settled on a compact secondary using #28 wire. Hence, there is no optimum single-fit solution. So, I embarked on testing it for myself. 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. Wideband RF components ultimately succumb to the non-ideal behavior of materials and assembly methods. By using traps, the antenna works on all three bands with no operator interaction. For the last step, I put together a RF choke to use between the radio and the feedline. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. 2015. I am testing it with the tuned tank circuit and a coax to the tuner with and without a common mode rejection choke. This is perhaps one of the most hotly debated rookie topics in. (LogOut/ Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance.
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