The purpose of the transformer is to step down the high impedance of a resonant EFHW, not as a resonant circuit or tank itself. (LogOut/ With no counterpoise wire it will be the coaxs shield providing it. 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. A tutorial on estimating the impedance of a toroidal ferrite cored inductor for radio frequencies, Pulse test of a Hantek 6204BD 4 channel 200MHz USB DSO and supplied probe. Even at 15W the voltage at the ends may reach 100-200V. The model results show the need for a not entirely insignificant counterpoise. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. 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. The solution was to make a small coil of the coax feed line, thrown on the ground, before connecting it to the radio. SWR for 80-10 meter EFHW with no capacitor, SWR for 80-10 meter EFHW with 100 pfd capacitor, The above data from K1RF shows that the SWR for 20 meters (my dark red markings -, I hope to do more experiments with single and multi band EFHW antennas above 20 meters - stay tuned, 40 meter and 20 meter (full wave) SWR with no cap. Once that's done, the instructions say "adjust the coil as necessary" to bring the other bands into resonance. The biggest uncertainty in these measurements was the actual power level used. This will also be handling 100W. Trapped five band EFHW SOTA antenna. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. MyAntennas), G0KYA, K1RF, K1TA, K6ARK, N4LQ, W8JI AND WA7ARK; they all have a primary capacitor of 100 pfd to 220 pfd. I would mention first its ease of installation. 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. A ktelez mezket * karakterrel jelltk. Above, the magenta curve is measurement of a real transformer from 1-11MHz with nominal resistance load and three compensation options: cyan: 0pF, too little compensation; magenta: 80pF, optimal compensation; and. 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. This gave me an effective coil diameter of 40.5mm. i liked it a lot, you give good ideas, many thanks. I checked the wall brackets and mast, but all the fixings were nice and tight. This happens to place the coil near the peak of a current maximum for the 20m band, which coincidentally appears to have significantly improved the match on that band. The transformer was attached to the 30 meter EFHW antenna and turns were removed for best match to 50 ohms. The blue trace above shows the results of adding a 6-turn 2 coil about 6.5 ft. from the box. IIRC they call it a "compensator". High self-resonant frequency. There is lot of controversy around the EFHW antennas. The technical storage or access is strictly necessary for the legitimate purpose of enabling the use of a specific service explicitly requested by the subscriber or user, or for the sole purpose of carrying out the transmission of a communication over an electronic communications network. 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%. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. This is typically a weak spot. Lowest measured inductivity = 2.0 H. I designed and built a few EFHW tuners already (calculating them from scratch, I only optimized the formula for the article). 100W on a Wire Antenna How far would it reach? The other end, attached to the transformer and antenna analyzer, is about 1 meter above the ground. Very interesting design. Functioning as an, HF Wire Antennas - A Primer When we speak about wire antennas, the first and foremost thought that comes to mind is the 1/2 Dipole antenna. 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. I assume you know the GNARC source for EFHW antennas. P.S. Below is the schematic of the final build. 'Capacitor flattens SWR at higher frequencies' - WA7ARK. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. 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. One possible explanation is that the core losses drop with temperature. I settled on a compact secondary using #28 wire. The bridge than will measure zero voltage across the bridge, and the LED will turn off. A/l for the chosen core is 3.5 times that of a FT82-43 yet it is only 1.6 times the mass. On the transformer, I added a few wingnuts to tighten down the antenna wire. I found it very useful to label the tuner with switch and capacitance positions. Your article was well written and very informative, thanks. To calculate the impedance ratio, use the following equation: A completed tuner is shown here, which depicts the inductance assembly. Tuning the antenna to its resonance will result in 50 seen at the output of the SWR circuit. View the job description, responsibilities and qualifications for this position. 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. In this case, it looks important. From this article one may build a 40, 30, 20m end fed half wave antenna, with no special parts needed, or no special skills required. The technical storage or access that is used exclusively for anonymous statistical purposes. So, how to construct an end-fed half wave antenna? 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. Thank you Gary. First, note that the transformer has low transmission loss up to nearly 50MHz. Let's find out! Why does antenna radiation occur? I added some Christmas colored zip ties to hold everything in place. Highest frequency = 14.350 MHz. You can start with the links below. 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 . RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. Accordingly, calculate the capacity for the resonance at the highest frequency to be covered with the highest inductivity taken in consideration. A design by VK3JEG is only 66-ft. long, about the size of a 40m dipole. Best results are with 2450 drive impedance and the 3.3m counterpoise, so it is not surprising that 49:1 transformers are the common choice. 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. It is not necessary to calculate the above; the results are sown in the following table. Subscribe to our newsletter and receive regular updates on new posts and articles. = 1/30.e6 = 33 nS. The results are presented below. The change in heat content in the box as it cools can be written: where and are the ambient temperature and heat content respectively. Your posting put it all together for meTHANK YOU!!!! Regards VE9HAM. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. It is important that resonance may be achieved at each tap of the inductance. Note: More extensive experiments including operation at HF frequencies higher than 20 meters, harmonic versus fundamental operation and transformer efficiency is posted in this blog. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. Research salary, company info, career paths, and top skills for Software Engineer - EDI This antenna is working for 80,40,20,10 and 6m bands. The real power limit will be core heating. I strung up a nominal 80m half-wave antenna wire into the trees, snaking it through the open screen door to the work bench where I was doing the tests. Most of the time 5 to 20W will be adequate for activation anyway. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. Above 7MHz, there is very little temperature dependence at all. The point is to get the characteristic time constant for the cooling, which is the reciprocal of the exponent coefficient that Excel shows for the fitting equation. 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. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. Just the bare 80m wire is shown in red. 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. Disclaimer | Privacy Policy | Cookie Policy | Terms of Use. From our measurements of the box cooling curve, this would correspond to the box dissipating about 14W in still air. Ha elolvasod alapszablyunkat s a benne lertakat elfogadod, akkor nincs ms teendd, mint a ha5kdr@ha5kdr.hu email-cmen, vagy egy klubnapon jelentkezni nlunk! End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? With the cooling curve and a good estimate for the heat capacity of the box, now it is just a matter of running some power through the transformer and measuring the the temperature rise from ambient to be able to determine the power that turns to heat in the transformer. The SWR results are as follows: Considering the compromised installation (ends about 2.5-3m above ground, inverted V with peak at 8m) I am pretty happy with this so far. 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). 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. 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. 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. Firstly, bandwidth on 80m is restricted to about 80 kHz at . I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. The computation method is also touched on. I place a 2 inch coil of the antenna wire with 3 turns (green) or 6 turns (brown) close to the box. Proudly created withWix.com. 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. I started with a small piece of PVC pipe and drilled a few holes in it to run the wire through. 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. However, to minimize capacitance, you want to spread turns and keep windings apart, so what is the right approach? (The antenna wire could also be tuned for the lower end of 80 meters without the coil but the . 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 6-turn loading coil lowers the resonant frequency into the CW portion of the 80 meter and higher bands. 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. I am already seeing interesting things with it, but not enough measurements to make any conclusions yet. A method for estimating the impedance of a ferrite cored toroidal inductor at RF. A week or two later I started to notice an occasional knocking sound inside the house. The coil uses 26 AWG (27 SWG) enamelled copper wire close wound on a machined plastic former. It is basically an end fed half wave dipole on 20m/40m and an end fed full wave dipole on 10m. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. So I built myself an improved replacement matching transformer. Consequently, lets pick the lowest frequency 7,000MHz that we need to be able to tune the inductance to, for each of the taps on the inductance. 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. Zin=46.52+j6.72. If you really want to get the heat out, add some fins to the aluminum box. 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 checked the inductance again to make sure this hadnt been overly affected, and it remained unchanged at 109.8H, good enough! of the wavelength. It performed well on both the 2m and 70cm bands. I dont have an amplifier, so only need to be able to handle 100W. In an ideal setting, the center of the antenna will have the lowest voltage, consequently impedance, which is why it is possible to feed it by 50 or 75 coaxial cable. So the differences I see in the data sheets hysteresis curves are not the correct explanation. The band compensating inductor placed on the wire is another story. Another completed tuner, which is more compact then the pervious one shown, also it is lighter, more suitable for portable operations. It is quite difficult to satisfy both requirements of achieving proper impedance ratio and resonance of the tank circuit at each tap of the inductance. 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.
Fireworks Safe Zone San Antonio, Articles E
Fireworks Safe Zone San Antonio, Articles E