In an urban area we are much more restricted, especially if we need to be stealth about it. This is why we need the impedance transformer from the 50 coaxial feed-line to the several kilo-ohm antenna connections. = 1/30.e6 = 33 nS. Csatlakozz csapatunkhoz! Don't sweat the digits to the right of the decimal point too much, the SWR readings changed as the feed height and droop of the antenna changed. 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 SWR for 30 meters, 1.05:1, was the lowest of all three antennas since the transformer was tuned for impedance match at 30 meters. From the condition, it looked like it had been installed outdoors for a few years, so I got it at a good price. I would mention first its ease of installation. The procedure was to run for around 30 minutes starting from the box cool at ambient temperature. Because we are considering this tuner for SOTA activations or casual portable operation, we do not need to design it for more then 100W. (Tvir s tvbeszl gpek s kszlkek) Ksznm. 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. 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. Above is a sweep of the uncompensated prototype with a 3220+50 load. From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. Looking at several builds and discussions, such as commercial antennas (e.g. 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. In the open-box image above you can see the thermal probe I used to measure the ferrite core temperature for a thermal characterizations. Elnzst krnk, de elsikkadt az zenete. Finally the tank circuits specification is complete, which is sown below. Well, in ham radio, everything works. 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. The final turns ratio turned out to be 3:29. Throw one end of the antenna wire, extended with a rope, as high as you can on a three, and walk away with the other end and attach it to the tuner. Winding the wire manually was a bit tedious but once done I temporarily held the wire with cable ties and checked the inductance. The antennas are set up as a sloper as in my SOTA outings. Some say you do not need a counterpoise, but that is false. Instead, this shifts everything down and makes it very easy to tune 10m. 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. For calculating the length of a half wave in metres, I use 141 (MHz) for wire elements. This animated illustration shows the harmonically related current conditions that exist on the EFHW antenna wire on various HF bands. I've been using a 1:8 ratio transformer successfully in other EFHW antennas, so I planned the same for this one. It does not need any special components; in fact, most of us may have them in our shack drawers already. I used the coil inductance calculator at 66pacific.com and after a few tries came up with 83 turns over a length of about 83mm as shown below. My favorite SOTA antenna is the End-Fed Half Wave Antenna. It is quite possible that designing more than three or four bands into a tuner will lead to a failure. So far so good. End Fed Half Wave Antenna Coupler Schematic - 7-30MHz. During portable operations, I noticed that I forgot the toggle switch in the tuning position, just to discover that no one calls me back to my relentless CQ-ing. 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. A radio station is as good or as bad as the antenna it has. It is better to build one for 160 and 80m, perhaps add 17m to the design described in this article, and for higher bands it is easier to use a linked dipole. 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This will also be handling 100W. Now I just need to build or acquire a decent radio to utilize this new antenna. 101: The Independent Medical Evaluation - "IME" By: Cynthia M. Hennessey Attorney. Graphed with a log scale, it makes a nice straight line. 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. Change), You are commenting using your Twitter account. After some internet research, I settled on making the former from a paint roller. Basu Bhattacharya (VU2NSB). 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. I built one that you see in the article, another one that is much smaller and lighter for SOTA outings. 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. There is much more that can be written about this antenna and its matching, but that was not my aim. clear. On the transformer, I added a few wingnuts to tighten down the antenna wire. It is common to use compensation coils of a few turns of the antenna wire to improve the alignment of the bands. This could be achieved by increasing the spacing of the windings, hence reducing the interwinding capacitance. This could be achieved by: Using thicker wire; increasing the diameter/length ratio; using a low loss former. Impressive article and so well done that I may give it a try. Or transmitting about 50% of the time, the peak power you would want to run with would be about 300W. However, a key restriction is its 25W power rating, due to the small matching transformer. 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. It is likely that next time the tuning may be set according to the already found positions, and it will not be far off, requiring only slight adjustment. The equation should have a 10^6 and not 10^-6 in the nominator. This will allow good matching of the half-wave radiating antenna wire to the 50 coaxial cable at virtually any location. High self-resonant frequency. P.S. The above illustration displays a typical set of Azimuth and Elevation sections of the radiation patterns that one might expect from a horizontally configured EFHW Wire Antenna deployed at an average height of 40 ft. above ground level (AGL). Essentially, the matching is done with a tank circuit, which represents the highest impedance when it is tuned to resonance. Increasing the drive impedance tends to move the resonances to slightly higher frequencies. Being conservative, assume we are just 90% efficient, then the average power level we could support would be about 140W. 3) Total losses are approximately independent of core volume. I needed to add an additional coil (approx 12.5 uH) about . Why had I not noticed this before? Best regards and thanks again for your comment. 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'. But before we do, let us look at the insertion and transmission loss that the VNA is reporting. This is perhaps one of the most hotly debated rookie topics in. Consider the RC time for a source with 2500 impedance into a 1pF capacitor. Some hams swear by them, yet some completely demean it. And since I am interested in building EFHW antennas for a single band or a few bands, how will that impact my design? This condition is rarely met in typical amateur radio EFHW antenna deployments leading to compromised overall antenna system performance. 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. It will have six turns around a 1.25" diameter PVC fitting that will bump the 10m resonance down about MHz. Therefore, installation is quite easy, and its tuner circuit is rather simple as well. 1. I use shock cord to connect the insulator at the end of the wire to my fence. Very interesting design. 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. Start by wrapping the wire around the toroid. That will be the missing resistor in the resistor bridge of the below circuit. In this case C~5pF and Z~2450 suggests that the inductance needed should be about 30 H. 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. Some website features may not function optimally without cookies. From that we can find Mismatch Loss. Frank VK1VK. The original coil is designed for low power portable applications. Calculate the capacity for the resonance at the lowest frequency to be covered with the lowest inductivity taken in consideration. I assume you know the GNARC source for EFHW antennas. Basically, the loading coil is operating as a trap. A few comments have been made about why the capacitor is needed: 'Improves higher frequency UNUN performance' and 'Compensates for UNUN primary leakage' - K1RF 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%. 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. 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. The following is the most up-to-date information related to EFHW Compensation Coil Experiment. The equation in the article is corrected now. The original coil is designed for low power portable applications. However, in reality, the term Omnidirectional needs to be taken in the context of the communication. A krdsem az, hogy a knyv elrhet esetleg pdf-ben is? (LogOut/ EFHW coil and 80m extension in place (coil visible at tip of red arrow) With the coil and its wire attached I fired up my AA-35 Zoom analyzer from RigExpert and had a look. If the antenna is not tuned properly, and it represents other than 50, the diode will rectify the current flowing across the bridge and the LED will light up. As it turns out K1RF had similar questions about the capacitor and published data showing that the capacitor does improve SWR performance at frequencies higher than 20 meters. Fill in your details below or click an icon to log in: You are commenting using your WordPress.com account. A typical schematic representation of an EFHW antenna with a short counterpoise and driven with a impedance transformer Unun. Is it any good? Apply for the Job in Software Engineer - EDI at St. Louis, MO. An example is shown in this figure of a 49:1 transformer with a 100 pfd capacitor in the primary side of the transformer. Change), You are commenting using your Facebook account. These, in turn, are instrumental Read More, Learn CW Morse Code Lesson Set 2 This is Lesson Set -2 in our multi-part series of CW Morse Code hands-on tutorials where we will introduce numerals and a few important punctuation marks as Read More. Real end fed antennas operated harmonically do not present a constant impedance, not even in harmonically related bands. Yes, indeed EFHW antennas are very useful for SOTA or other field operation. A week or two later I started to notice an occasional knocking sound inside the house. Zin=46.52+j6.72. Note that the primary winding on the toroid is using the inner lead of an RG-58 coaxial cable. The SWR results are as follows: The final turns ratio turned out to be 3:29. An End Fed Half Wave (EFHW) antenna for operation on 20, 30 and 40 meters was built for SOTA operation. I installed an eyebolt on one end as a pull-point, and a BNC connector on the other. Regards VE9HAM. It not a loading coil. I settled on a compact secondary using #28 wire. Firstly, lets estimate at 3.6MHz minimum number of turns to ensure that magnetising conductance is less than about 0.002S (for better than 90% core efficiency). And of course, a counterpoise with various lengths. After cleaning it up and testing it, I installed it on the side of my house on top of a straight pole. Change). 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. 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 antenna is effective and the materials and construction are of a very high quality. I recommend a good reading on this subject by Steve Yates, AA5TB at: www.aa5tb.com/efha.html. IIRC they call it a "compensator". You cant really see the antenna wire, but the red line shows the antenna path. End Fed Half Wave Antennas: Is a Primary Capacitor Really Needed? One point of my small-core, compact winding design was to be able to cool the core. There are many good descriptions on the net about this type of antenna. This is indeed a classic antenna that is not only, Introduction to Omnidirectional Antennas In the literal sense, an Omnidirectional antenna is an antenna that radiates uniformly in all directions. Nothing drastic but likely the SWR on the summit will vary as conditions and the setup change. Hence, we need to move along and start to include the antenna with our testing. The difference here is that the target bands are low frequency. Thanks again Jim. inductance as one FT240-43 and is able to withstand 1kW 50/50% duty cycle with help of a cooling fan. In this case =1058 seconds, about 18 minutes, is the characteristic thermal equilibration time in still air. Two layers of 1mil Kapton tape are placed over the winding. On top of the first wire, wrap a second one around the toroid three times (I used a red wire for this). The SWR figures were as follows: FT240-43 132ft/100pF capacitor This antenna is only 15m long using 2 loading coils. Note: Crosswalk CAA administers the LIHEAP in Franklin, Jefferson, and Williamson Counties. I was a little long on 80m not surprisingly, so folded back about 40cm of wire leaving about 2.1m beyond the coil. If you stare at the above frequency sweeps you will discover a few things. 1) More primary turns and primary inductance improve the transformer efficiency and low end performance. I am planning to use this latest one at the Field Day next year. These dimensions were derived from modelling the antenna in EZNEC. Hence, even operating at 1000W on the 160m band, the cores would not saturate with the 5-turn primary. Krem, rja le, mi a krdse. (30 votes, Rating: 5.00) - Please vote the article with your valuable star rating. Home Antenna Wire Antennas Multiband End-fed Half-wave EFHW Antenna. That does not seem inconsistent with the expectation calculated above of about 10% core loss at 3.6MHz. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 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. This graphical depiction makes it easier to visualize the current and impedance correlation between bands. http://www.hamuniverse.com/randomwireantennalengths.html, https://km1ndy.com/diy-491-unun-impedence-transformer-for-end-fed-half-wave-efhw-antenna/. I then used a piece of heat shrink on the outside to hold everything in place. I then added two 220pf capacitors in series between the center conductor and ground. Ez az oldal az Akismet szolgltatst hasznlja a spam cskkentsre. The EFHW's SWR will be affected by height above ground, type of ground, feed line interaction, and any nearby conductive surfaces. 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. Refurbishing aluminium antenna parts affected by weather / corrosion. 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. Im very pleased with that indeed. I swept the antenna with a nano vna from 2 to 30MHz and there were nice dips at each band. Hi Ajai, RC = 2500 x 1.0e-12 = 2.5 nS Now consider the period of a 30 MHz wave. 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. If not a lightning strike, I will write an article about the experience as well. This is based on random lengths of the antenna, which is transformed with the un-un into a medium-ohmic impedance range with reactive components. No capacitor was installed. Next, I started winding the transformer. As the length of the antenna is around 2/3 of the span of a half-wave dipole on 80m, there are two compromises. Because of the turns ratio N, the secondary capacitance will appear N2 larger at the primary and will resonate with the primary magnetizing inductance. I was curious why this capacitor was added to the transformer. 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.) From experience, I found that with this tuner my SWR was better by simply disconnecting the counterpoise at lower bands. 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. Current Balun 1. Do I count the six loops around the pvc in the measurement? xZ Wxi@@=\A,Y1I0E~?)JdWfe.z/|iqLI?>BPo>Pf*w~]WZu.VZZZM5zjO=?`yC^l_-H{q|m|U]21xgS6~ltFGZH}(6FE4n0D9Klx`T/;! % The high frequency performance was extraordinarily sensitive to anything that could add capacitance to the output lead.
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