Coax Feedline Lengths To Avoid

I recommend semi-rigid coax it you have it. General purpose coaxial cable, best for long cable runs Comparison of three commonly used types of coaxial cable. • Avoid center feed a half-wave multi-band antenna with a high impedance feedline that is close to an odd multiple of a quarter-wave long. (305 m) of 3-1/8 inch (8 cm) rigid copper feedline with about 0. 26 to 27 meters - 85 to 88 ft. Incorrect feedline and antenna lengths can make an otherwise perfect antenna sy stem very difficult or impossible to tune. Open-wire parallel feedline has several advantages over coax for this type of antenna: it can operate at very high VSWR’s with almost zero loss, where coaxial cable becomes quite lossy (and RF in the shack!) at high SWR’s; open-wire parallel feedline is much cheaper than decent quality coax, and can be home-built as shown. 25in length of regular 18AWG covered stranded wire. (20 meters), the wire length exceeds sixty feet for 40 and 80 meters. The inner conductor is disposed in coaxial arrangement with the inner conductor and forms a dielectric supply lumen therebetween. Signal resistance increases with feedline length. At least once a week we receive a request a for high ratio balun (6:1, 9:1, 12:1) to manage the transition from high impedance ladder line / open wire feedline to coax. The length is just enough to serve as a U-bolt keeper bar. An-tenna action will also cause a voltage to be impressed along the length of the cable, which can appear as a common-mode component on the signal conductor(s). How much energy will we lose if we use this cable as a feedline? We can arrive at some answers by using a program like TLW. The graph below shows lengths to avoid for different collections of bands. 25in of RG-174 the coax end is reached. After the war, amateur radio operators began using the readily available surplus coaxial cable for their antenna feedline systems. Simply put, the coax is losing 8. • Try to use wire antennas and open/ladder line feedline. [The worst possible line lengths are shown in brackets]: 160 meter dipole: 35-60, 170-195 or 210-235 feet [Avoid 130, 260 ft] 80 meter dipole: 34-40, 90-102 or 160-172 feet [Avoid 66, 135, 190 ft]. 72 meters (rounded up to two decimal places) Once you have your length of wire for your desired band you will need to cut the wire in half again for (one for each side of the dipole). ARRL suggest such a length of coax for frequency coverage between 3. max size 160/80 loop • Total length of coax, may need to avoid varactors altogether Strong signal. To in theory get a 1. Use fingers only to tighten. While studying this question enroute to writing an article on "A Slightly Off-Center-Fed Diople" in QST for September 2019, I learned that connecting the feedline to the antenna at a current node will essentially prevent the antenna from taking power at that frequency. matching of an antenna feedline that has not been matched previously. Coax is so much easier in this regard- simply lay it across the ground, or perhaps bury it just slightly. The balun [NV2K] built is a bifilar 1:1 design, with two parallel. The loss of 1/2" Heliax at 150Mhz is 0. Coaxial cable loss is normally specified in dB loss per 100 feet of cable. The other configuration, is one I plan to write more about later. By Todd, KY4TS A common overlooked part of putting together a repeater system is the selection of proper feedline. The right picture shows a gap coupler of size G that has a width equal to that of the resonator and feedline center trace, W. The SMA connector is the coax connection. There is no significant difference between the two types RG-58 cable has less loss at a given frequency RG-8 cable has less loss at a given frequency RG-58 cable can handle higher power levels * T9B11 Which of the following types of feedline has the lowest loss at VHF and UHF? 50-ohm flexible coax Multi-conductor unbalanced cable Air-insulated. The G5RV antenna is similar with the exception that a length of open twin wire feed line or “ladder line” is used to create a broadband feedline balun before connecting to the coax. The inner conductor is disposed in coaxial arrangement with the inner conductor and forms a dielectric supply lumen therebetween. Basically the 75 ohm side of this transformer (BNC connector) is connected to the 50 ohm output of the radio and the 50 ohm side (F-Connector) of the transformer is connected to the 75 ohm feed line or load. Maximum efficiency and absolute minimum feedline radiation will occur when the antenna is tuned as in the steps above. If you use coax, check a coax loss calculator to understand impact of coax loss on your system. Results were less than a te= nth of a dB difference. The total length is given by 468/f where f is the frequency in MHz. 25in of RG-174 the coax end is reached. Keep feedline length inside a dwelling as short as possible to reduce chances of RF feedback. The antenna assembly includes a feedline having an inner conductor, an outer conductor and an inner insulator disposed therebetween and a radiating portion i. 706 m shorter than the coaxes # 1, 4 feeding the outer dipoles. frequency near 4. To avoid problems matching or feeding any dipole antenna with high impedance lines, keep the lines around the length in the green area of the chart below. Suppose that we connect a typical coaxial cable to the feedpoint and use 100' of the line to reach the shack. Leads to the element are short and direct. Page 2 BAND LENGTH A LENGTH B LENGTH C LENGTH D 6 Meter 9' 1" 7' 7. 287 MHz, or a dipole length of about 32. 12: Close-ups of the installation with the feedline spacers. One “high visibility” heaving line / halyard. - On 144MHz you can get away with just using equal PHYSICAL lengths of phasing lines (assuming you are using the same velocity factor of cable for all cables). the coax to the boom for strain relief. Its challenger is the famous Belden 9913 , more expensive but very well protected against RFI and well adapted to very high frequencies. Start practicing with this loop, it doesn't have to pass the feedline, so a little deformation is permitted. The balun [NV2K] built is a bifilar 1:1 design, with two parallel. unbalanced feedline certainly will. 34 to 35 meters - 111 to 115 ft. for 915 MHz and Table 2 for 9021903 MHz. 36 feet as a starting point. 845db / 100ftalmost half the loss of LMR-400. The Antenna Coax Feedline is a 20' length of RG59 Coaxial Cable. These losses are not significant in the short line length used in Fig. I was having a real bad time with the elevated radials of my 160m antenna=. 5 MHz, the traps are far from their resonance frequency and artificially increases the length of the antenna, which still resonates half wave. The coax is not just feedline: it’s an intimate part of the antenna! Furthermore, as we’ve seen, it’s connected back through your electrical wiring to your neighbor’s dimmer switch. On 15 meters, this length is almost exactly 1/4 wavelength. This can throw off the antenna's radiation pattern, affect tuning, etc. The antenna is oriented in a North-South plane and fed in a bottom corner (slant polarized) with a quarterwave of 75 ohm coax to match it to the 50 ohm feedline, through a homebrew choke balun. • Try to use wire antennas and open/ladder line feedline. 287 MHz, or a dipole length of about 32. Well, immediate suspension of my amateur radio license for starters, followed by confiscation of all my amateur radio equipment! Seriously, I can't remember exactly what it was that was said, something like avoid either 1/4 or 1/2 wavelength lengths of cable, at the operating frequencies you wish to use. It's just for coax only. The second drawback is that you need to be careful of how you route balanced lines. 698 71/90= 7. 26 to 27 meters - 85 to 88 ft. Connect a 50-ohm antenna feedline coax to the ANT 1 jack on the back of the AT-100Plus, and optionally connect a second antenna feedline to the ANT 2 jack. At least once a week we receive a request a for high ratio balun (6:1, 9:1, 12:1) to manage the transition from high impedance ladder line / open wire feedline to coax. Keep coiling the counterpoise back and checking the SWR until you find the length that gives the lowest SWR. The required physical lengths are shorter as determined by the velocity factor of the feedline. Improper termination of cable shields within equipment (the Pin 1 problem) injects. 1 MHz at +10 dBm. Current-type baluns™ are especially effective in reducing RF current on outer surface of a coaxial cable's shield. Coax is OK, as long as you understand impact of loss on the bands to be used on… • Try to make antenna length at least ½ wavelength of lowest frequency. picture on the first page, with the feedline sloping down at a 45 degree angle. The other configuration, is one I plan to write more about later. Then the antenna must have an electrical length of 66 feet, and suitable feedlines would have electrical lengths of 8, 14, 16, 24, 25, 41, 46, 77, feet. This can throw off the antenna's radiation pattern, affect tuning, etc. The feedline was terminated in a BNC plug, which you can see loosely coiled for storage at the left. Larry Horlick wrote: > > > I have a drawing from Sinclair that shows 4 stacked folded dipoles (it > does not indicate an > antenna model) using all 50 ohm cable. The only cure is a very good common mode choke at the feedpoint. See the article by K3BC on the Bibliography page for an example of a balanced feed arrangement. 2:1) then try moving the band switch up and down one position and repeating steps 2) - 5). People seem to spend a lot of time messing with the length of antenna or feedline trying to get an acceptable SWR on multiple bands. Coax is OK, as long as you understand impact of loss on the bands to be used on… • Try to make antenna length at least ½ wavelength of lowest frequency. When mounting an antenna on the roof or in the attic be sure to use quality feedline (coax). An apparatus has an improved antenna pattern for a cross dipole antenna. The two terms generally mean the same thing. Feedline radiation can be reduced by placing toroids on the feedline at the antenna. Having 30 feet of coax coiled up in a corner will reduce the effectiveness of the antenna dramatically. For 2 meters. So far the performance has been at least as good as the previous. While studying this question enroute to writing an article on "A Slightly Off-Center-Fed Diople" in QST for September 2019, I learned that connecting the feedline to the antenna at a current node will essentially prevent the antenna from taking power at that frequency. Suggested lengths for high impedance feedline on dipole type antennas Good lengths are green shaded area in the chart below. In the absence of common-mode currents, then the optimum feedline length is 0, because a longer feedline only increases your feedline losses. ) perform consistently well. * The longer the feed line, the higher the signal loss. A wavelength on this line is about two-thirds of its free-space length. "As far as I know, the only feedline materials available for hams are coax, twin-lead, and window line. the supplied coax jumper cable, or a similar 50 ohm coax cable rated 125 watts or higher. To build a good one that will handle high power. A feedline should be chosen based on the length of the cable run and the frequency of the signal. Transmission Lines - Whenever you choose a coax feedline, the frequency of operation is a very important consideration. Naturally, if these metal objects are short you can get closer than 30'. Avoid lengths where then antenna becomes one wavelength long an any frequency you intend to use. Example of the bending of the inner loop (the smaller one). Connect the coaxial line from the relay box to the “RELAY BOX” SO-239 connector. The length is just enough to serve as a U-bolt keeper bar. The solution isn NOT to use magic coax lengths, you need to fix your antenna so that it isn't inducing common-mode currents on your feedline. Except that when the coax is used to make the line long enough to reach from transmitter to antenna the performance is obviously worse. Herman, you may have common-mode current on your feedline (RF coming back to your radio on the coax braid). In free air space, the wavelength (in feet), is 492 / Freq (in Mhz). “Knead” (squeeze and press) the Coax Seal™ again to assure a perfect seal. This gives an estimated 1/2 wave electrical length of 57 feet at 8. This half wave makes it work and makes it frequency dependant. At high frequency, as gets larger, the values of R and G becomes less significant in comparison with L and C. T9B1 It is important to have a low SWR in an antenna system that uses coaxial cable feedline to provide efficient transfer of power and reduce losses. Having 30 feet of coax coiled up in a corner will reduce the effectiveness of the antenna dramatically. However, this conclusion would be warranted only for cases in which the coax end was either free or was isolated by some attenuation device to the degree that it acted like a free end. The plots were calculated using the "high accuracy" (NEC Sommerfeld) ground model with a. the supplied coax jumper cable, or a similar 50 ohm coax cable rated 125 watts or higher. Choose feed line that is designed for little signal loss when setting up for high frequency emissions (such as RG-213 coax). The only difference is that the shield of the coax is grounded, and the ladder line is not, so it acts in common-mode to bring in and radiate induced RF. Although it would be impractical to run the ~128ft feedline that would be prescribed for 80m, not to mention ~256ft for 160m, it would still be interesting to know whether other feedline lengths might provide lower SWR across the board. As mentioned earlier, feed line loss can be a significant issue. The 9:1 will make contacts but can also light up the coax with hot RF. Side Feed : If the designer desires the “Mast Any Length” of figure 1 to be much longer, perhaps becoming the guyed antenna support all the way to ground, a pipe-T may be placed near the bottom. One cut for 7 MHz should also work on 21 MHz. People seem to spend a lot of time messing with the length of antenna or feedline trying to get an acceptable SWR on multiple bands. Open-wire parallel feedline has several advantages over coax for this type of antenna: it can operate at very high VSWR’s with almost zero loss, where coaxial cable becomes quite lossy (and RF in the shack!) at high SWR’s; open-wire parallel feedline is much cheaper than decent quality coax, and can be home-built as shown. Inside the coax, the common-mode current is zero. Well, I wouldn’t say that it is absolutely critical, but if you want to avoid tuning difficul-ties on some bands, you shouldn’t stray too far from this length. The two terms generally mean the same thing. A short length of very low loss coaxial cable connects your transmatch to the RemoteBalun™. The higher the frequency of the signal passing through the coaxial cable, the higher the loss over a given length. Member: Joined: Oct Mon 05, 2015 10:04 pm Posts: 778 Location: Worcester Massachusetts Worcester Massachusetts. 4 feet) coaxial cable to connect it to the rpi. Introduction. Unless you model your own scenario in some detail, it is probably a good idea to strive for a dipole length of 35% of a wavelength or longer. To avoid problems matching or feeding any dipole antenna with high impedance open wire lines, keep the lines around these lengths. TYPICAL INSTALLATION: Between one balanced-line antenna tuner and several balanced-line antennas. ) With those two sets of antenna and feedline lengths I set up a series of test cases. To reduce or get rid of this unwanted RF, use a "balun" transformer or RF choke which would consist of several turns on a 8 in diameter form. Open-Wire Feedline Lloyd Butler - VK5BR. It is usually specified in dB/foot and is a linear relationship. The balun should be located near the tuner, keeping the coaxial cable between it and the tuner as short as possible. The antenna assembly includes a feedline having an inner conductor, an outer conductor and an inner insulator disposed therebetween and a radiating portion i. But, in this case we want the feedline to radiate! Extra Radiation. Go up to 10 meters and it will be even higher. [The worst possible line lengths are shown in brackets]: 160 meter dipole: 35-60, 170-195 or 210-235 feet [Avoid 130, 260 ft] 80 meter dipole: 34-40, 90-102 or 160-172 feet [Avoid 66, 135, 190 ft]. Feedline - The length of 63. Position the antenna to receive signals. While studying this question enroute to writing an article on "A Slightly Off-Center-Fed Diople" in QST for September 2019, I learned that connecting the feedline to the antenna at a current node will essentially prevent the antenna from taking power at that frequency. You should have insulators at the end and the center to prevent arcing at higher power and interaction with the objects at the end. This practice is often applied when, in fact, it might be more efficient, or even more convenient, to use balanced open wire lines. How much energy will we lose if we use this cable as a feedline? We can arrive at some answers by using a program like TLW. 26 to 27 meters - 85 to 88 ft. There is no significant difference between the two types RG-58 cable has less loss at a given frequency RG-8 cable has less loss at a given frequency RG-58 cable can handle higher power levels * T9B11 Which of the following types of feedline has the lowest loss at VHF and UHF? 50-ohm flexible coax Multi-conductor unbalanced cable Air-insulated. Always cut feedline to the minimum usable length. At one time, RG-58, RG-8X and RG-8U were military standards but now these terms are used rather loosely and refer primarily to the size of the cable. A short length of very low loss coaxial cable connects your transmatch to the RemoteBalun™. For VHF 2M, the center frequency is about 146MHz. A feedline impedance of 50Ω and a load impedance of 25Ω produces an SWR of 2:1. My favorite is an air core balun wound from coax. On to the tests! Comparing a small, unidirectional active antenna with directive beverages from 225 to 500 meters long is a bit like comparing a family sedan with a racing car - and half expecting the former to win. • All bands are connected together via the coax links and are all fed by a single feedline. Example of the bending of the inner loop (the smaller one). In order to deliver the most power to the antenna, the impedance of the antenna has to be the same as the line and the radio (matched). They can be made to work but usually not by a HF beginner. Dress the feedline so it is perpendicular to the dipole and perpendicular to. The way I understood it to tune dual Wilson antennas you take a single coax of equal length and check SWR (and make adjustments if necessary) on each antenna seperately, then hook the dual coax up and away you go. In free air space, the wavelength (in feet), is 492 / Freq (in Mhz). com I wish more people would go out into the wild with a 9:1 balun and recommended length(s) of wire and also a resonant end fed half wave (EFHW) using a 64:1 type transformer and correct wire lengths for either a 40-10m or 80-10m version. The two terms generally mean the same thing. The reason people use multiples of 1/4 wavelengths is to allow a method of measuring the line's ELECTRICAL length. It is NOT the 75 or 50 Ohm which makes the difference. If you connect a coax feedline straight up to a dipole antenna, the shield of the coax absolutely will radiate. The "Best" Random Wire Antenna Lengths - Blogger. (305 m) of 3-1/8 inch (8 cm) rigid copper feedline with about 0. The random wire antenna is probably one of the least expensive, easiest and cheapest HF antennas to use if you have a tuner and you want to get the "most" out of a length of "random" wire without having to pull out that calculator, doing the math, getting the center insulator built or bought, running the feedline, and all the rest that goes. With the traps and a coaxial feedline, the band is not accessible without significant power losses in the line. Attach the coaxial cable to the balun. The coil of coaxial cable underneath the box is a common-mode choke, which is a good addition to just about any HF antenna. Feedline - The length of 63. So: Due to the way coax is constructed, the inside of the coax will only support energy transfer in the differential, transmission-line mode. The coax used is RG-174. * Electrical length of a section of coaxial Cable (Select models) * Feedline loss of a length of Coaxial cable * Frequency Counter and signal generation * Graphing display (Select Models) * Memory for storing graphs (Select models) * Multi language display (Select models). 5Mhz and 30Mhz. If line loss is low it is perfectly acceptable to make SWR measurements at the transmitter end of the feedline. When mounting an antenna on the roof or in the attic be sure to use quality feedline (coax). This really is an article in itself, but I’ll just mention a few points here. 50 or 1 wave length of the center frequency of the antenna you are connecting to. I have tried different lengths and configurations. Understanding that the dipole and feedline will radiate, what are optimum feedline & dipole lengths to avoid TVI to the surrounding neighborhood?. coax lengths to reach them. It's expensive, but long-lasting and has very low loss compared to conventional coax. 5 MHz (for non-amateur use), coax fed, without the use of traps or a tuner. This may not seem much of a loss but look at the Power Compensatoragain and you will see that 100w from your transmitter would have to be increased to 108. Make sure it “whets” (sticks) to the case and to the wire. Herman, you may have common-mode current on your feedline (RF coming back to your radio on the coax braid). 64 for each leg). Connect the antenna connector of an antenna tuner to the antenna switch COM terminals with a short length of balanced line. My recommendation is to avoid this technique if at all possible. Ca= lculated the attenuation based on the loss and then used the SWR121 to te= st the same length of coax at the same freq. The coax used is RG-174. unbalanced feedline certainly will. Once you are satisfied with the overall length of the radiator, lace the end of the wire through the end insulator as shown in Fig. The coil of coaxial cable underneath the box is a common-mode choke, which is a good addition to just about any HF antenna. With openwire feedline we may also incur common mode current. Don't use anything but. This line should not be attached directly to the mast. 706 m Simply put: coaxes # 2, 3 can be 1. My favorite is an air core balun wound from coax. It is the signal lost during to and fro transmission between the radio and antenna. In the absence of common-mode currents, then the optimum feedline length is 0, because a longer feedline only increases your feedline losses. How much energy will we lose if we use this cable as a feedline? We can arrive at some answers by using a program like TLW. Now, if for some reason your SWR changes with differing lengths in your coaxial feedline, then you've got common mode RF flowing on the OUTSIDE of the coax (braid). 28 of a wavelength overall (0. My recommendation is to avoid this technique if at all possible. The antenna assembly includes a feedline having an inner conductor, an outer conductor and an inner insulator disposed therebetween and a radiating portion i. In case you wish to use a reflector, cover pieces of cardboard with tin foil and attach to the plank. To avoid problems matching or feeding any dipole antenna with high impedance lines, keep the lines around the length in the green area of the chart below. With the antenna removed, the feedline shows a 1/4 wave null at 4. Before deciding on the cable length, you would want to first think about the mounting location. I can have a 4:1 current balun at the house entry and then it would be about a 20' coax run to my tuner. Excess coax between your radio and antenna mount should never be wound into a circular coil of less than 12" in diameter. Whatever real gain an antenna might have, using high loss transmission lines (e. It's just for coax only. Keep the antenna under a few feet in length especially if strong stations are nearby. IF the antenna itself is resonant (which is the object of "tuning" an antenna) it will read the same at the end of the 20 feet or the short jumper. Reduce the gain control on the transmitter to a minimum, and place the transmitter in t tstandbyt. of 66%, so we do this. For instance, to work 40m be sure the antenna is at least 10m or 33' long. While studying this question enroute to writing an article on "A Slightly Off-Center-Fed Diople" in QST for September 2019, I learned that connecting the feedline to the antenna at a current node will essentially prevent the antenna from taking power at that frequency. , Dallas, TX 75247 (W5KF, VP). The braid of the coax will become part of the antenna. >102" whip and 102" coax x the volocity factor of the coax. 'VB-8 coaxial cable from Decibel Products Corp. Never center feed a full-wave antenna with any feedline close to a multiple of a halfwave long. This line should not be attached directly to the mast. EXAMPLE A coaxial cable has a capacitance of 90 pF/m and a characteristic impedance of 50. The addition of a 1:1 balun between your feedline and your present 4:1 balun may help. Performance Figure 3 shows the far-field elevation plots for frequencies of 7, 14, 21 and 28 MHz. Take the time to tune the antenna– no tuner is required nor should one be used. Whatever real gain an antenna might have, using high loss transmission lines (e. LMR-240UF coax is higher-loss but well shielded and lightweight, making it useful for the vertical run up lightweight masts. 12: Close-ups of the installation with the feedline spacers. Double check all elements for proper length and centering on the boom, then secure them in place with epoxy. This was done to avoid attenuation caused by running the feedline near or along metal surfaces. So, why is the selection of feedline so important? Fir. max size 160/80 loop • Total length of coax, may need to avoid varactors altogether Strong signal. This antenna weighs over 7,000 lbs (3175 kg) of 8 bay batwing at 850 ft. In the absence of common-mode currents, then the optimum feedline length is 0, because a longer feedline only increases your feedline losses. A “balun”, a device which blocks common mode currents from the feedline, is often employed. The feedline is RG-58 at a random length of about 40 feet. I was having a real bad time with the elevated radials of my 160m antenna=. 405 diameter or larger low-loss coax above 1. My question is this: just how important is a choke balun when using a ground-mounted HF (for 40M) quarter-wave vertical antenna with 32 quarter-wave buried radials?. This was done to avoid attenuation caused by running the feedline near or along metal surfaces. This is because any type of open wire. There is no significant difference between the two types RG-58 cable has less loss at a given frequency RG-8 cable has less loss at a given frequency RG-58 cable can handle higher power levels * T9B11 Which of the following types of feedline has the lowest loss at VHF and UHF? 50-ohm flexible coax Multi-conductor unbalanced cable Air-insulated. In my opinion, 1/2" Heliax is the minimum acceptable feedline--although I would try to keep the length of the feedline as short as possible. I expect to use three dipoles (one for each band), all coming together in the middle and fed with a single feedline through a 1:1 W2AU-type balun. The coax used is RG-174. Attach the antenna to the TV through the coaxial cable. Here are a few examples. Closeup of the feedpoint area ofthe 1296-MHz Cheap Yagi. To avoid, put ferrite beads on the coax at the feedpoint, or use 3-5 turns of coax (1″-2″) taped together at the feedpoint. There is only one rule for coax length: Use the shortest practical length possible to go from radio to antenna. The cable cut-off length is 80 1/4". Since 5/8 wave length antenna is no longer matching the transmission line impedence, a feeding coil must be added between the antenna and the feedline so that the antenna can match the impedence of the tranmission feedline. Ensure that the wire and the foil do not make contact. Home; End fed wire antenna calculator. An apparatus has an improved antenna pattern for a cross dipole antenna. To determine the proper length of coax, use the following formula:. Additionally special care was taken when the feedline was routed through windows to get it into the house. If I slope the feedline to my house entry point, the 450 ohm feedline length will need to be about 100-110' which should keep it non-resonant for any HF bands. 3, but they do have a bearing on the applications shown in Fig. * The longer the feed line, the higher the signal loss. While studying this question enroute to writing an article on "A Slightly Off-Center-Fed Diople" in QST for September 2019, I learned that connecting the feedline to the antenna at a current node will essentially prevent the antenna from taking power at that frequency. the supplied coax jumper cable, or a similar 50 ohm coax cable rated 125 watts or higher. For fixed stations, coaxial hardline is probably the best choice. Choosing a Feedline Choke Feed line chokes/line isolators for coax fed dipoles, verticals, beams, slopers, loops, windom, OCF, and yagi antennas Definition. lower on all bands, due to the additional loss of the coax feedline, which is 25m of RG213. RG-8X is popular these days because it is light and easy to handle. The other configuration, is one I plan to write more about later. 046 in radius AWG 16 Velocity Factor. NOTE: Coax center conductor attaches to the “Long section” feed point. Take the time to tune the antenna– no tuner is required nor should one be used. In closing a Safety Precaution. The length of is not arbitary but critical to its successful operation. It uses insulated, stranded copper-clad steel wire with a breaking strength of 50 kg, and a Teflon-insulated SO-239 coax jack with gold contacts. 2 shows a couple of possible examples - RF toroid cores over the coax and a coil of coax near the feed-point. (Not shown. Previous Work This antenna system is based largely on previous work done by amateurs for decades, using feedline segments of carefully-selected length for matching two feedlines. >So, let say you are using RG-8 >It has a vol. 'VB-8 coaxial cable from Decibel Products Corp. Following are the benefits or advantages of Coaxial Cable: * Due to skin effect, coaxial cable is used in high frequency applications (> 50 MHz) using copper clad materials for center conductor. However, this conclusion would be warranted only for cases in which the coax end was either free or was isolated by some attenuation device to the degree that it acted like a free end. I) Tune up the transmitter in the normal way into a 50 -ohm dummy load (if 50 ohm coax is used between the transmitter and the FC-902). It's just for coax only. The length is just enough to serve as a U-bolt keeper bar. A “balun”, a device which blocks common mode currents from the feedline, is often employed. Three 8 Oz fishing weights for launching into trees. At lowest swr/ reactance the frequency displays the 90 degree frequency under test, Simply shorten coax carefully in small increments until you are at the degree/ frequency you need. Every feedline is also an impedance transformer all along every 180-degrees of its length. The transition from coaxial cable to integral feedline is seamless. The weight saving is massive!. There are many rules-of-thumbs for lengths of dipole to avoid and lengths of parallel feedline to avoid. I was having a real bad time with the elevated radials of my 160m antenna=. Take the time to tune the antenna– no tuner is required nor should one be used. readout on MFJ. Once you are satisfied with the overall length of the radiator, lace the end of the wire through the end insulator as shown in Fig. Inside the coax, current I1 flows on the outside surface of the centre conductor, and current I2 flows on the inside surface of the shield. Herman, you may have common-mode current on your feedline (RF coming back to your radio on the coax braid). I use a power divider consisting of a half wavelength of 35 ohm impedance feedline to match a pair of 50 ohm yagis phased on 2m to feed a long length of 50 ohm feedline to the shack. The Antenna Coax Feedline is a 20' length of RG59 Coaxial Cable. The following DOS IMAXGRAF. install common mode chokes on the coaxial feedline and preamp power cable bury cables about 12 inches deep for optimum null depth Avoid re-radiated signals from nearby antennas and power lines locate the antenna as far as possible from other antennas and power lines The “Magnetic” Loop is a specialized antenna. , 3184 Quebec st. In addition to length, the frequency of the signal has a huge effect on the overall loss of the coax. Cut the dipole wire to be a little longer than the computed length - it's easier to cut wire than to extend it!. With openwire feedline we may also incur common mode current. To avoid problems matching or feeding any dipole antenna with high impedance lines, keep the lines around the length in the green area of the chart below. Don't use anything but. The term used to describe the general idea of keeping the feedline and antenna separate is 'decoupling. I was having a real bad time with the elevated radials of my 160m antenna=. Simply put, the coax is losing 8. 72 meters (rounded up to two decimal places) Once you have your length of wire for your desired band you will need to cut the wire in half again for (one for each side of the dipole). IF the antenna itself is resonant (which is the object of "tuning" an antenna) it will read the same at the end of the 20 feet or the short jumper. 73, Pete N4ZR Hi Sante, I once had three parallel dipoles (I think for 40, 20 and 15) using one coax feedline and one balun, mounted so that the three wires were only a few inches apart (using wooden spacers, a real low-tech installation). Use a "liquid" (plastic) electrical tape product to seal the coax connector rear end--and the coax junction once you install the feedline. Signal resistance increases with feedline length. The right picture shows a gap coupler of size G that has a width equal to that of the resonator and feedline center trace, W. 25in of RG-174 the coax end is reached. the supplied coax jumper cable, or a similar 50 ohm coax cable rated 125 watts or higher. Avoid lengths where then antenna becomes one wavelength long an any frequency you intend to use. This can be a store-bought balun or you can get the proper choke coils to add to your coax just below the existing balun. 300W carrier it gets plenty HOT, but I will be listening on 160 and 80 and operating on 20 and 40, and I thought that the 4:1 balun would be easier and ladder line be a lighter feedline than coax. Antenna manufacturers often tell their customers to cut their coax feed lines to a specific length in order to get a good match. To remove the case, simply take off the four screws on each side. Feedline Lengths: The feedline length is also an important part of a "friendly" antenna design. This is a good length since it keeps it well off the ground while still providing some slack for movement. You can obtain or construct an external 4:1 balun to make the transition from your twinlead feedline to a short length of coax, then bring the coax into the house via a single feedthough hole if you'd like. RG-8X is popular these days because it is light and easy to handle. Unless you model your own scenario in some detail, it is probably a good idea to strive for a dipole length of 35% of a wavelength or longer. From there it goes directly to a four output distribution amp (at least on paper). Additionally special care was taken when the feedline was routed through windows to get it into the house. Introduction. 50 feet of LMR-400-UF (Ultra-Flex) to go from the antenna mast to the operating station. Ca= lculated the attenuation based on the loss and then used the SWR121 to te= st the same length of coax at the same freq. The RG-174 was connected to a signal generator supplying 14. Due to the repositioning of the feed point I had to shorten the feedline. FEEDLINE LENGTH: Long ago I was taught (personally) by Lew McCoy, W1ICP (SK) that the optimum length of the feedline should be:. Total length (in meters) = 5. For instance, to work 40m be sure the antenna is at least 10m or 33' long. EXAMPLE A coaxial cable has a capacitance of 90 pF/m and a characteristic impedance of 50. Their antenna designs have inspired other companies to also rethink their own antenna systems. There is only one rule for coax length: Use the shortest practical length possible to go from radio to antenna. You can choose to just live with it, as many certainly do, or you can buy or build a "balun" (a balanced-to-unbalanced transformer) to place at the feedpoint to. Coaxial cable commonly used for Amateur Radio has an impedance of 50 ohms while ladder line impedances can vary from 300 to 600 ohms. circuit occurs in the feedline. The theory behind the "good" and "bad" length designations are based on impedances that are. While studying this question enroute to writing an article on "A Slightly Off-Center-Fed Diople" in QST for September 2019, I learned that connecting the feedline to the antenna at a current node will essentially prevent the antenna from taking power at that frequency. While this may appear to fix the problem, it doesn't fool most automatic controllers. The feedline connects to the Antenna Connector on the assembly. The required physical lengths are shorter as determined by the velocity factor of the feedline. At this point the center conductor is extended with a 7ft 8. From there it goes directly to a four output distribution amp (at least on paper). That’s because the feedline acts as an impedance transformer, and converts what might be an unmanageable im-. 64 for each leg). There is some need for both practical engineering and theoretical understanding. The gain on a dipole is reference or ZERO. A “current mode” balun or feedline choke can consist of some number of turns of the coax cable in free space, or around a ferrite or powdered iron core, forming an inductor. Feedline Length An alternative means of reducing the reactance at the terminals of any coupler is to change the length of feedline from the antenna to the coupler output terminals. The ground wire is about 11 feet long. Connect the coaxial line from the relay box to the “RELAY BOX” SO-239 connector. The following DOS IMAXGRAF. Since 5/8 wave length antenna is no longer matching the transmission line impedence, a feeding coil must be added between the antenna and the feedline so that the antenna can match the impedence of the tranmission feedline. If you need to add feedline to this antenna, feedline lengths near 65 feet, 130 feet, and so on, should be avoided for ease of tuning on the 80 meter band. frequency near 4. 1/2" Heliax is a good quality cable and the losses show that. Disadvantage of this last, it is harder to bend. Results were less than a te= nth of a dB difference. I've also seen l14-inch hardline soldered to the driven element. I didn't find there was much, if any interaction among them. A “current mode” balun or feedline choke can consist of some number of turns of the coax cable in free space, or around a ferrite or powdered iron core, forming an inductor. There are multiples types of ununs and baluns. If you connect a coax feedline straight up to a dipole antenna, the shield of the coax absolutely will radiate. Once you are satisfied with the overall length of the radiator, lace the end of the wire through the end insulator as shown in Fig. NOTE: Weather seal the coax fitting by covering it with neoprene or resistant compound. Here are a few examples. Antenna performance will be crap if you don't, regardless of the coax length. Since the electric and magnetic fields (of the stub system) are in air, I think. For example, a vertical with properly sloped radials is around 50 ohms. I decided on 37 feet of 300 Ohm ladder line as an acceptable non-resonant length for the feedline. 25in length of regular 18AWG covered stranded wire. Not including your time and gas for the trip to the store, you've spent about $115. Like a fuse, they are designed to break the connection when a sudden burst of energy comes across them. Start practicing with this loop, it doesn't have to pass the feedline, so a little deformation is permitted. I expect to use three dipoles (one for each band), all coming together in the middle and fed with a single feedline through a 1:1 W2AU-type balun. Keep coiling the counterpoise back and checking the SWR until you find the length that gives the lowest SWR. Connect a 50-ohm antenna feedline coax to the ANT 1 jack on the back of the AT-100Plus, and optionally connect a second antenna feedline to the ANT 2 jack. With this knowledge in hand, we can avoid feedline lengths that increase feedline currents. Coaxial cable consists of an inner conductor with an insulated covering (dielectric), which is then covered with a braided wire or foil sheathing (shield). Center-fed dipoles experience current nodes when the feedpoint is any even multiple of the frequency on which the length. Coax feedline chokes (and impedance transformers) all have an unbalanced input and are made with several output options dependent on whether the output is balanced or unbalanced. ) perform consistently well. If you run into matching problems on some bands, try another balun ratio (e. This can improve the situation considerably. Use fingers only to tighten. Over 50% of installation problems are coax/connector problems. 120’ of RG-8X Coax feedline @ 144mHz loss = 4. The AT-100Pro is designed to interface directly with many popular ICOM and Yaesu transceivers,. (Not shown. Take the time to tune the antenna– no tuner is required nor should one be used. By the way, which is the best coax to use ? 50 or 75-ohms ?. I might suggest using a dipole of about 35cm length (two 17cm lengths of copper wire attached to inner and outer of the bottom end of your coax). The required physical lengths are shorter as determined by the velocity factor of the feedline. The feedline can be either coax or open wire/TV twinlead. The theory behind the "good" and "bad" length designations are based on impedances that are. For longer runs, use an ultra- low loss cable, such as Belden 9913, to reach the antenna site, then use RG-8X. To avoid problems matching or feeding any dipole antenna with high impedance lines, keep the lines around the length in the green area of the chart below. For the best efficiency, the long coaxial cable run should be from Point A to Point B, keeping the influence of the antenna impedance mismatch from affecting the coaxial cable feeder. There is no significant difference between the two types RG-58 cable has less loss at a given frequency RG-8 cable has less loss at a given frequency RG-58 cable can handle higher power levels * T9B11 Which of the following types of feedline has the lowest loss at VHF and UHF? 50-ohm flexible coax Multi-conductor unbalanced cable Air-insulated. For maximum power transmission, 50 Ohm coax cables are used to match the RF PA's output impedence. That should be good enough for a repeater, right?" Well, not necessarily. The Coaxial Feedline Serves As A Tuned Circuit That Creates The Necessary Counterpoise. Normally, in the case of normal (balanced) dipoles, we try to avoid this from happening. Say your feedline from the shack to the center of your dipole requires a 100 foot run of coax. This cable is readily available, easy to install, and will perform well for rooftop runs of up to 60 or 70 feet at 50 MHz. the unbalanced feed than to try to correct it. This is usually the antenna tuner. Amateur Radio transceivers are designed to work with an impedance of 50 ohms, so you must use 50 ohm coax, or find a way to convert the 300 to 600 ohm impedance of ladder line to 50 ohms. I allowed about 3 feet for "feedline" (to the left of the choke). Side Feed : If the designer desires the “Mast Any Length” of figure 1 to be much longer, perhaps becoming the guyed antenna support all the way to ground, a pipe-T may be placed near the bottom. The only difference is that the shield of the coax is grounded, and the ladder line is not, so it acts in common-mode to bring in and radiate induced RF. Wire Lengths for Various Band Combinations. 'VB-8 coaxial cable from Decibel Products Corp. With openwire feedline we may also incur common mode current. The reason for 5/8 antenna. d) Treat the cable gently when routing it through the vehicle. Place the RT 100 near the feedpoint and the virtually eliminate all feedline loss due A dipole antenna designed for one frequency can function over a broader frequency range with a manually or automatically adjusted antenna tuner. A generator uses a power source such as a fuel-powered motor or (some say, rarely) a perpetual motion machine, to generate power. 5Mhz and 30Mhz. 046 in radius AWG 16 Velocity Factor. If I slope the feedline to my house entry point, the 450 ohm feedline length will need to be about 100-110’ which should keep it non-resonant for any HF bands. 2 M - STEREN 205-750: Telephone Cords - Amazon. One 40 foot RG-58C/U coax feedline with PL-259 connectors Two 20 foot RG-58C/U transmission lines, one with BNC and the other with PL-259 connectors 3 each nylon heaving lines / halyards. max size 160/80 loop • Total length of coax, may need to avoid varactors altogether Strong signal. 357 Mc to be exact. should try to buy quality feed line, avoid the small-diameter coaxial cables for runs greater than 50 feet up to 30 MHz, and seal the points where moisture can enter the line. These losses are not significant in the short line length used in Fig. Screw the PL-259 on the end of your coaxial cable to the SO-239 connector on the matching unit. The coaxial feedline is attached as follows: center conductor to the hook of the "J" pole and shield to the opposite side of the "J" as shown in above. The common configuration for the G5RV is ladder or window line for a certain length and then coax to the shack. acknowledged, but that doesn't necessari- ly mean that your Stray will be appearing in QST. Picture two telephone poles (or towers) with the support points for the individual dipoles several feet apart vertically along the two poles/towers. of the antenna employ 50-Ohm coaxial cable as the feedline. of runtime on coax be equivalent to a length of 1. So I built one for the new 60 meter band. There are multiples types of ununs and baluns. The longer the length of a piece of coaxial cable, the more signal is lost. I use a power divider consisting of a half wavelength of 35 ohm impedance feedline to match a pair of 50 ohm yagis phased on 2m to feed a long length of 50 ohm feedline to the shack. An-tenna action will also cause a voltage to be impressed along the length of the cable, which can appear as a common-mode component on the signal conductor(s). The cable cut-off length is 80 1/4". For illustration purposes, let's say that the 80-meter dipole will run. (Avoid 130, 260 ft). Check your feedline (including new ones) with a dummy load placed at the antenna end of the coax. The reference impedance and the cable impedance show a 16:1 ratio. 5 MHz (for non-amateur use), coax fed, without the use of traps or a tuner. 73, Pete N4ZR Hi Sante, I once had three parallel dipoles (I think for 40, 20 and 15) using one coax feedline and one balun, mounted so that the three wires were only a few inches apart (using wooden spacers, a real low-tech installation). With the view to establish a quick and easy multi-band antenna deployment for portable and camping operations a simple long wire antenna with an earth or earth plus counterpoise arrangement with a 9:1 voltage unun including a tuner or simply with a tuner is one possible solution. Once you are satisfied with the overall length of the radiator, lace the end of the wire through the end insulator as shown in Fig. 75ohm coaxial cable (cable TV) for the descent to the issuer. Attach the coaxial cable to the balun. For a 100' length of 600 ohm, homebrew feedline, you'll spend about $36-$40 for spreaders (IF you can still purchase them) and roughly $65-$80 for a 500' roll of 14ga stranded wire. (260m) and about 1000 ft. 698 71/90= 7. Amateur Radio transceivers are designed to work with an impedance of 50 ohms, so you must use 50 ohm coax, or find a way to convert the 300 to 600 ohm impedance of ladder line to 50 ohms. Proper grounding is essential for lightning protection. The antenna will still perform very well, even with the feedline at this angle. I bought 10 meters of RG58 coaxial cable and I've made 24 turns on a Ø 120 PVC pipe using the whole length of it. 67' inverted V dipole with the apex at 30'. At one end, short (solder) the coax shield to the center conductor of the RG-8 and the remaining pig tail to be connected (soldered) to. However, this conclusion would be warranted only for cases in which the coax end was either free or was isolated by some attenuation device to the degree that it acted like a free end. Having 30 feet of coax coiled up in a corner will reduce the effectiveness of the antenna dramatically. In my search I've read suggestions of using 18 to 21 Feet of coax cable for a 1. Cut a length of 120 inches of RG-59/U and put PL-259 connectors and UG-176 reducers on each end of the coax. Choosing a Feedline Choke Feed line chokes/line isolators for coax fed dipoles, verticals, beams, slopers, loops, windom, OCF, and yagi antennas Definition. This is usually the antenna tuner. The counterpoise can be accidental and not physically obvious, such as the outside of a coaxial cable's shield, parallel currents on a balanced feedline, or currents on a mast or metallic support. A common thought of many is since this is coaxial cable, we need velocity factor adjustments. What I can tell you, per your question, is to change the SWR by changing the length of the coax, you're not changing SWR at the feedpoint where the antenna meets the coax - what appears we're doing is now an impedance transformation of using the coax as a feedline and hence the transferring of Resonance to more of an Impedance Transformation. However it will take whatever your feedline can take and you can throw into it. Finally, try to use a tuner design that has been optimized for this type of antenna. Reduce the gain control on the transmitter to a minimum, and place the transmitter in t tstandbyt. This can improve the situation considerably. A microwave antenna assembly is disclosed. As another EZNEC exercise, hang a 6-foot wire (representing the coax shield) at a current null point in your favorite quad DE and watch the pattern change for the worse. You can figure that you will lose some of your signal in the coax going up to the antenna, and you will lose some of your received signal strength coming back down when the antenna is used for receiving. Coax is OK, as long as you understand impact of loss on the bands to be used on… • Try to make antenna length at least ½ wavelength of lowest frequency. End fed wire antenna length. Use a Balun or Feedline Choke. As we discussed on the first page of this article, a length of wire or coax that is 1/4 wavelength long is an impedance inverter. Of course cost is also an important consideration. Coaxial cable consists of an inner conductor with an insulated covering (dielectric), which is then covered with a braided wire or foil sheathing (shield). At one end, short (solder) the coax shield to the center conductor of the RG-8 and the remaining pig tail to be connected (soldered) to. A wavelength on this line is about two-thirds of its free-space length. Imperveon 50-ohm cable from Times Fiber Communications, 358 Hall Ave. 2:1) then try moving the band switch up and down one position and repeating steps 2) - 5). So, there’s really no winning here, is there? However, some useful solutions could be: Use an antenna that’s 50 ohms, not a dipole. You'll lose a good 2 dB just from the ohmic losses, and even more if your antenna isn't very nearly a PERFECT impedance match to that of the coax - and that's figured at 14 MHz. , Wallingford, CT 06492. Every feedline is also an impedance transformer all along every 180-degrees of its length. Typically, the impedance of the radio and the coax feedline are the same and constant (e. While studying this question enroute to writing an article on "A Slightly Off-Center-Fed Diople" in QST for September 2019, I learned that connecting the feedline to the antenna at a current node will essentially prevent the antenna from taking power at that frequency. A more common 80 or 100 feet of RG-8 style coax laying on the ground outside the house might produce a much higher interaction, and loss. It allows you to compute the effects of loss through different types of coax with any frequency, line length, or power level. - On 144MHz you can get away with just using equal PHYSICAL lengths of phasing lines (assuming you are using the same velocity factor of cable for all cables). So I built one for the new 60 meter band. The RG-174 was connected to a signal generator supplying 14. For example, a vertical with properly sloped radials is around 50 ohms. The balun should be located near the tuner, keeping the coaxial cable between it and the tuner as short as possible. I am using LMR-600 UltraFlex coax for the rotator loop and feedline connection to this antenna. But then, you no longer have a G5RV. Connect a 50-ohm antenna feedline coax to the ANT 1 jack on the back of the AT-600Pro, and optionally connect a second antenna feedline to the ANT 2 jack. Basically the 75 ohm side of this transformer (BNC connector) is connected to the 50 ohm output of the radio and the 50 ohm side (F-Connector) of the transformer is connected to the 75 ohm feed line or load. Picture two telephone poles (or towers) with the support points for the individual dipoles several feet apart vertically along the two poles/towers. A more common 80 or 100 feet of RG-8 style coax laying on the ground outside the house might produce a much higher interaction, and loss. Cut the dipole wire to be a little longer than the computed length – it’s easier to cut wire than to extend it!. A generator uses a power source such as a fuel-powered motor or (some say, rarely) a perpetual motion machine, to generate power. The weight saving is massive!. Inside the coax, current I1 flows on the outside surface of the centre conductor, and current I2 flows on the inside surface of the shield. The "Best" Random Wire Antenna Lengths - Blogger. If you have to, the W2DU is a choke balun (beads around the feed coax) that mounts at the feed point; it works well, with minimal losses, since it is not a voltage balun. Well, immediate suspension of my amateur radio license for starters, followed by confiscation of all my amateur radio equipment! Seriously, I can't remember exactly what it was that was said, something like avoid either 1/4 or 1/2 wavelength lengths of cable, at the operating frequencies you wish to use. As we discussed on the first page of this article, a length of wire or coax that is 1/4 wavelength long is an impedance inverter. Leads to the element are short and direct. One such conclusion is that we can avoid coaxial cable common mode currents by avoiding line lengths that are odd multiples of 1/4 wavelength. Connect a 50-ohm antenna feedline coax to the ANT 1 jack on the back of the AT-100Plus, and optionally connect a second antenna feedline to the ANT 2 jack. This is true no matter how many series traps, isolating devices or systems, or common mode suppression devices, installed at the feedpoint. It's just for coax only. Normally, in the case of normal (balanced) dipoles, we try to avoid this from happening. >102" whip and 102" coax x the volocity factor of the coax. 5 MHz (for non-amateur use), coax fed, without the use of traps or a tuner. The following DOS IMAXGRAF. 82 of some foam insulated coax on 144. These losses are due to the resistance of the wire, dielectric losses, etc. At high frequency, as gets larger, the values of R and G becomes less significant in comparison with L and C. 5MHz; an 88′ dipole is 31% of a wavelength at 3. Unless you model your own scenario in some detail, it is probably a good idea to strive for a dipole length of 35% of a wavelength or longer. Place the RT 100 near the feedpoint and the virtually eliminate all feedline loss due A dipole antenna designed for one frequency can function over a broader frequency range with a manually or automatically adjusted antenna tuner. I've also seen l14-inch hardline soldered to the driven element. Step 1: Attach the Coax Feedline to the connector facing the wall. People seem to spend a lot of time messing with the length of antenna or feedline trying to get an acceptable SWR on multiple bands. A feedline should be chosen based on the length of the cable run and the frequency of the signal. On to the tests! Comparing a small, unidirectional active antenna with directive beverages from 225 to 500 meters long is a bit like comparing a family sedan with a racing car - and half expecting the former to win. Of course, if you decide to use 50 ohm coax to avoid this problem, then you get a similar mismatch at the antenna, 50:72. FEEDLINE LENGTH: Long ago I was taught (personally) by Lew McCoy, W1ICP (SK) that the optimum length of the feedline should be:. Imperveon 50-ohm cable from Times Fiber Communications, 358 Hall Ave. Total length (in meters) = 5. An-tenna action will also cause a voltage to be impressed along the length of the cable, which can appear as a common-mode component on the signal conductor(s). d) Treat the cable gently when routing it through the vehicle. Antenna performance will be crap if you don't, regardless of the coax length. As another EZNEC exercise, hang a 6-foot wire (representing the coax shield) at a current null point in your favorite quad DE and watch the pattern change for the worse. In free air space, the wavelength (in feet), is 492 / Freq (in Mhz). If you really want to get nutty, try using 110VAC lamp cord ("zip" cord) as a feedline. The results are only approximations based on EZNEC and must be fine-tuned to perfection in reality. HF: Half wave dipole fed with the one coaxial cable feedline. If you are building a “resonant feedline antenna,” where you are defining the active antenna element with an inductor on the feedline, then Q matters. 2 M - STEREN 205-750: Telephone Cords - Amazon. Install lugs on coax as shown in figure 4 and weatherproof with electrical tape. For longer runs, use an ultra- low loss cable, such as Belden 9913, to reach the antenna site, then use RG-8X. Certain lengths of coax can be used as a conjugate match to match two unequal impedances and is required in SPECIAL cases but never in normal everday one-antenna systems. At lowest swr/ reactance the frequency displays the 90 degree frequency under test, Simply shorten coax carefully in small increments until you are at the degree/ frequency you need. One “high visibility” heaving line / halyard. The following DOS IMAXGRAF. Here is a list of favored Dipole lengths:* 40 to 41 meters - 132 to 135 ft. You can choose to just live with it, as many certainly do, or you can buy or build a "balun" (a balanced-to-unbalanced transformer) to place at the feedpoint to. 25in length of regular 18AWG covered stranded wire. These are described in the ARRL Handbook and in the ARRl. As for feedline I'm using identical 3' lengths of RG6/U and am trying to find a low loss high quality splitter to feet it to. ⚫ install common mode chokes on the coaxial feedline and preamp power cable ⚫ bury cables about 12 inches deep for optimum null depth ⚫ Avoid re-radiated signals from nearby antennas and power lines ⚫ locate the antenna as far as possible from other antennas and power lines The “Magnetic” Loop is a specialized antenna. In some versions, this coax acts as a broadband feedline balun instead of the usual transformer type. In the absence of common-mode currents, then the optimum feedline length is 0, because a longer feedline only increases your feedline losses. In closing a Safety Precaution. The feedline was terminated in a BNC plug, which you can see loosely coiled for storage at the left.