CRA Calculator. Jul 09, 2003 · Coax Cable Loss. The relation between the R, Zo, and amount of power division is given by the following formula. Example 25. The advantage of using coax for a 1:1 choke-balun is the constant Z0 of 50 ohms. 0. For our present purpose, we may model the structure as. **Note: Like our stripline impedance calculator, all of our RF calculators allow SI prefix input. where. Linkedin. Micro Coax & Twinax Cable Specifications 20Ω Coax Cable – 26 AWG 50Ω Coax Cable – 34 AWG Ω Coax Cable – 36 AWG50 Ω Coax Cable – 38 AWG 85Ω & 100Ω Twinax Cable – 30 AWG 85 Ω & 100 Twinax Cable – 32 AWG 75Ω Coax Cable – 38 AWG 100Ω Twinax Cable – 30 AWG Board-to-Board Assemblies = Eye Speed ® Coax = Eye Speed Twinax. This connection steps down the high antenna impedance to. The formula for the length of the matching section is as follows: Q-Match Coax (in feet) = 246 x [velocity factor] / Frequency (MHz). Attenuation (dB/100 ft , @ 400 MHz). In fact, striplines often make components such as band-pass filter's more accurately, with more symmetric roll-off and no lower cutoff frequency. Coaxial cables are commonly used for transmitting electrical signals, including RF (radio frequency) signals. ε 0 = 8. This formula is used to calculate the VSWR from the given return loss. The length of the cable makes no difference whatsoever in regard to the characteristic impedance. If a short section of a 50 ohm cable has a 75 ohm impedance, then 33% of the voltage signal will be reflected at each end of the 75. In summary, if you have a transmitter with an output impedance of 150 ohms and you want to use a cable with an impedance of 75 ohms, you need to make sure your load impedance is equal to the cable impedance. The impedance of a coaxial cable is a critical parameter that characterizes its electrical properties. Grover, Dover Publications, 2004 . 850c-0. Input. Output values are rounded to the second decimal place. 9. For my loop, the length of the matching section worked out to: 16. When the bend radius is exceeded it alters the characteristic impedance of the cable. MiniVNA or MFJ-269 or similar). The cable input. 1: Determining the inductance of coaxial line. A differential cable is usually constructed with a UTP, STP, STQ or twin-axial configuration and achieves 100-Ω differential impedance. Example: Calculate the distributed capacitance and inductance, impedance and a cutoff frequency of a coaxial cable RG-58 with the following characteristics: inner. I might add that if you're looking to calculate the electrical impedance of a circuit, they have a separate impedance matching calculator and a PCB impedance calculator for various PCB-mounted conductors. Note that these calculations are theoretical and engineers and technicians will probably never have the. Scroll down to find formulas for determining attenuation, wavelength, characteristic impedance, time delay, and more. Quarter Wave Transformer Impedance Calculator. Wi-Fi 7 will enable consumer, enterprise, Industry 4. Provides an impedance matched 50 ohm coaxial connection for two receivers when feeding signal from one active antenna, or when combining two different antennas (L. In summary, the design process for the coaxial probe placement is simple: Select an operating frequency and stackup. e. , some amount of incident power will reflect the source in a practical system). DX Engineering Coaxial Cable Reference Chart LMR-240 50 ohm Cable LMR-240 Ultraflex 50 ohm Cable LMR-400 & 400 DB 50 ohm Cable LMR-400 Ultraflex 50 ohm Cable Indoor/Outdoor Peak Power 5. The concept of Shield Transfer Impedance (Zt), introduced by S. which can be algebraically solved for Z 0 as: Z 0 = Z a Z b. Transformed through the antenna side capacitor (adjusted to 139. CAPACITANCE Property of a coaxial cable to store electric chargeCable Coaxial Coaxial cable Loss In summary, if you have a transmitter with an output impedance of 150 ohms and you want to use a cable with an impedance of 75 ohms, you need to make sure your load impedance is equal to the cable impedance. c is the speed of light 299,792,458 m⋅s −1,. Calculate the edge input impedance for the antenna. To use the calculator you first need to measure the impedance (resistance + reactance(j)) of your antenna, this can be done with an antenna analyzer (i. 854187817620. Plugging this into the equation we calculate the cable length. Off-center coax. ) using the high and low frequency approximations. But it is not applicable to large and non-symmetrical cable-connector system as. 124 in), type of insulation is polyethylene with the relative permittivity of 2. Any other impedance at the output causes an impedance transformation because the SWR is not 1:1. The Smith Chart achieves this by superimposing a grid on S11 that maps load impedance. on the calculator devide 29. The characteristic impedance of an infinite transmission line at a given angular frequency is the ratio of the voltage and current of a pure sinusoidal wave of the same frequency travelling along the line. Calculate the impedanceCharacteristic Impedance (Zo) 50 (±2) ohms. The CST Cable Studio Impedance Calculator can be started from Cables > Impedance Calculator. Brown part is the copper itself. Now, to calculate the necessary line length: assuming that our cable has a velocity factor of 0. A cable can be modelled with KVL using 0 Ohms or some small DC resistance for all frequencies from DC to about 1/10th of a wavelength of the cable length and also at 1/2 wavelength and all. HELP. As such, the outer (braided) conductor completely. The Pi (pad) RF attenuator calculator allows you to determine the Resistor values (R1 & R2) for a Pi attenuator. 5dB loss per 100 feet at 146 MHz). We at everything RF have developed a RF Connector Frequency chart that can be used as a reference chart to tell you the max frequency (cutoff frequency) of each connector type. where. 80 for typical two-wire lines and coaxial cables. 125 MHz. CALCULATION OF Kr WHEN LENGTH IS APPROACHING OR EXCEEDING λ/2. It has an inner 7-stranded bare copper. Gamma matching online calculator. age and current in a cable of supposedly infinite length. 39 ohm line, cut for the frequency of operation (between the antenna and your cable) you'd end up with a perfect match. d is the diameter of the inner conductor of the coax cable; units of D and d must be the same,. The loss tangent introduces a "real" conductance which is calculated from the susceptance by multiplying by loss tangent. The feedpoint impedance at the design frequency is about 100 ohms, so full wave loops are often fed with an impedance-matching section made from a piece of. This online reflection coefficient to VSWR calculator calculates the VSWR by entering the reflection efficient Γ (= value between 0 & 1). 2. × 10 −12 F/m is the. In an RF system, when power is sent from the source to load, there are three main parameters to be considered: (1) incident power. “468” is the constant used to convert frequency in MHz to feet. See also this excellent PDF by Audio Systems Group, which shows the impedance of a $75Omega$ coaxial cable rising to $1000Omega$ at 1 kHz, and almost $10kOmega$ at 1 Hz. How to calculate the dimensions or diameter of coaxial feed as per impedance of the equilateral antenna. As we know that the definition of the return loss of a system is the ratio of incident power to. The cable dictates how much current initially flows based (mainly) on its inductance, capacitance and resistance. This is the only way to calculate the total impedance of a circuit in parallel that includes both resistance and reactance. We have a conflict in statements here where formula 6. 2. where. The impedance is maintained so long as L/C is maintained. Lcoax ≈ μ0μrL 2π ln( D d) L c o a x ≈ μ 0 μ r L 2 π l n ( D d) Where: Lcoax L c o a x = inductance of the coaxial cable in henries (H) μ0 μ 0 = permeability of free space = 4π×10 −7. Γ = Reflection coefficient. By understanding the formula and utilizing the calculator, professionals can determine the characteristic impedance of coaxial lines, ensuring proper impedance matching and efficient signal transmission. The cable is a transmission line (read more here) and it will transport a signal properly ONLY when the input and output of the cable/transmission line is TERMINATED by the proper impedance ! So a 50 ohm coax cable needs a source with a 50 ohm output impedance and it needs a 50 ohm load at the other end of the cable. EEWeb offers a free online twisted pair impedance (transmission line) calculator. . ε 0 = 8. If there is an insulator around the wire then this. εr = Dielectric constant of the insulator. 1. R w = Terminating resistance between two. RF calculations and RF conversions include metric-standard, link budget, coax cable, power, attenuation, frequency and many more. × 10 −12 F/m is the. $endgroup$ –RG316 Coax Cable. 191Ω. Zc = characteristic impedance of cable-above-ground transmission line. It is around 30cm cable. CCTV & Security Cable. When a balanced source is to be isolated from an un-balanced load, the impedance matching transformer is referred to as a balun. 85419 x 10. ε 0 = 8. 4 in. For this example, assume perfect conductors and a lossless dielectric with relative permittivity ε r = 2. Scroll down to find formulas for determining attenuation, wavelength, characteristic impedance, time delay, and more. Commercial Electric 25 ft. Question 17. “468” is the constant used to convert frequency in MHz to feet. Ze is the external earth loop impedance. the combined velocity factor will be around 0. 6 . . 7mm. You can use these cables with a 50 Ohm. Maximum Operating Voltage (Vrms) 4000. for chosen frequency. Suitable for VHF (~1. So, if the Propagation Velocity is 70%, it means that the signal. e. This may not seem much of a loss but look at the Power Compensator again and you will see that 100w from your transmitter would have to be increased to 108. This tool is designed to calculate the inductance of a coaxial cable if its dimensions are provided. Characteristic Impedance (Zo) 50 (±2) ohms. If the antenna feedpoint is 50 ohms (such as a gamma match of a beam antenna) using 75 ohm coax as the main. Injecting a current transient into one side of a microstrip or coax transmission line causes a voltage to appear across only one of the two conductors. 81, giving an impedance of 120. All Answers (17) The attached formula is used to calculate the characteristic impedance of coaxial probe, where: (d) is the inner diameter of coaxial probe. 854187817620. the total current in the input coaxial cable is real for a set of positions along the cable, which permits matching at these points using the techniques considered in the rest of this problem. I leave it to other sources to provide the complex equations needed to precisely model coaxial cables. The area just becomes the effective area, so for the inner shell, 2πaδ 2 π. Triax Cable. 3. Some systems use 75 Ω; this latter value is more appropriate for high-speed digital signals. 114 GHz. ε 0 = 8. D is the inside diameter of the coax cable shield,. This works from DC to 1. × 10 −12 F/m is the. Coax Conn Rx Cable and connector impedance The characteristic impedance of a cable and its connec-tors should match the impedance of the transmitter and receiver. HELP. Capacitance Cond-to-Shield Nom. This model computes the electric and magnetic field distribution inside of the coaxial cable. WhatsApp. 5nF. 4w. In-Ear Sensors Record Health Metrics From Brain Activity and SweatDistributed Inductance (L') For a coaxial cable, the inductance per unit length L' in henries per meter (H/m) is defined as. 035 in), outer conductor diameter 3. 854187817620. D is the inside diameter of the coax cable shield,. With superior signal integrity and low loss transmission, RG400 coax. The following formula is used to calculate the cut-off frequency, lower & higher operational frequency of the rectangular waveguide. In the limiting case of infinite load impedance, theBecause a coax operates in TEM mode — with the electric and magnetic fields normal to the direction of propagation along the cable — modeling a 2D cross section suffices to compute the fields and the impedance. 2. By inputting the necessary values into the. For coaxial cables the characteristic impedance will be typically between 20 and 150 ohms. The return loss of a system is defined as the ratio of incident power to reflected power and is measured in dB. This calculator calculates the impedance of a coaxial cable. 336: 360 = 0. Explore the Coaxial Cable Calculator, a handy tool for calculating various parameters of coaxial cables such as impedance, capacitance, inductance, and cutoff frequency. To use the calculator you first need to measure the impedance (resistance + reactance(j)) of your antenna, this can be done with an antenna analyzer (i. 557 GHz. 85, and using a speed-of-light figure of 186,000 miles per second, the velocity of propagation will be 158,100 miles per second. The deterioration of Kr above 8 MHz is spectacular. Here's a quick line loss calculator to use Note that the simple program used for this web page gives a very close approximation for additional losses due to SWR. ABOUT US. RG6 Coaxial Cable in Black. These helpful formulas can be used to calculate expected phase change of Dynawave coaxial cables for any given temperature range, as well as for an array of uses for cable assemblies. UsefulFormulas. Location. Figure 2 - Fast pulses measured at the end of the coaxial cable using an oscilloscope without impedance matching. output power, and size requirements. For a coaxial line, the electric fields extend in a radial direction from the center conductor to the outer conductor. Distributed Inductance (L') For a coaxial cable, the inductance per unit length L' in henries per meter (H/m) is defined as. Output values are rounded to the second decimal place. This formula is from the following reference. TF-047; SF. It's primarily intended for radio and data communications. Image 1, "matched") : Cable is impedance matched with 50 Ohm. a = r = 0. The coaxial cable, along with the balanced two-wire, is the most common type of transmission line used in RF communications. For example, if you wish to input "25000000", just type "25M" instead. Hence, the return loss is always lower than the ideal system (i. The length of a half-wavelength dipole can be calculated by the given formula: L =. R1 is the resistance of the line. In fact, striplines often make components such as band-pass filter's more accurately, with more symmetric roll-off and no lower cutoff frequency. Unlike cable used for mains or other power transfer, the impedance of a coaxial cable is not affected by its length. e. R = l σA R = l σ A. Coax Cable Formula. 035 in), outer conductor diameter 3. 405 inches and a voltage rating of up to 1000 Vrms. 240 DIA) Solid Copper center conductor Foam Polyethylene Dielectric Aluminum Tape outer conductor Both of the cables are inside a bigger one: The black part is the isolation. 96. It is important to determine the characteristic impedance of a twisted-pair cable because this impedance should match the impedance. The length of the dipole is usually one-half of the wavelength of the RF signals. DX Engineering Coaxial Cable Reference Chart LMR-240 50 ohm Cable LMR-240 Ultraflex 50 ohm Cable LMR-400 & 400 DB 50 ohm Cable LMR-400 Ultraflex 50 ohm Cable Indoor/Outdoor Peak Power 5. The use of a standardized impedance makes RF design much more practical and efficient. G = 2πσ ln(b / a) Figure 2. This topic describes a technique for calculating the impedance of a waveguide. To find the termination resistance that matches the characteristic cable impedance, connect a 200Ω potentiometer at the cable end and tune it until no reflections occur. (141) $17. On Figure 5, the. The inner and outer. Suitable for VHF (~1. The impedance can be calculated by the following formula. The coaxial cable, along with the balanced two-wire, is the most common type of transmission line used in RF communications. 11. Choose from 50 Ohm, 75 Ohm, 93 Ohm and 95 Ohm coaxial cables or 78 Ohm and 100 Ohm Twinax cables. For the air-filled cables typically used in high-power applications, this corresponds to a characteristic impedance of about 30 Ω. 5. September 8, 2022. Calculate the attenuation and power handling capability of coaxial cables using the online calculator by Times Microwave Systems. 56 X 10-7 H/m, Capacitance =. Altium's built in impedance calculator shows the trace impedance at 34 ohms not 50 ohms. The impedance of the coax is a relationship of the capacitance per unit length and the inductance per unit length. **Note: Like our stripline impedance calculator, all of our RF calculators allow SI prefix input. It has an inner copper weld wire (CW) or copper-clad steel (CCS) conductor (carrying the electrical signal), which is enclosed by an insulation layer typically made of air space Polyethylene (ASP). Resistance in this calculator formula for pi attenuator is measured in Ohms. Equation. MEDIUM VOLTAGE SHIELDED CABLE PARAMETER CALCULATOR. This calculator calculates the impedance of a coaxial cable. To calculate the impedance of a coaxial cable with a diameter of 0. Distributed Inductance (L') For a coaxial cable, the inductance per unit length L' in henries per meter (H/m) is defined as. Impedance: 50 Temp: -55, 200. 3. For the students of scientific history, this is the same Oliver Heaviside who formulated Maxwell’s equations in the vector form that we are familiar with today; first used the term “impedance”; and. A coaxial cable is designedCoaxial cable, or coax (pronounced / ˈ k oʊ. COAXIAL CABLE IMPEDANCE CALCULATOR Calculates the characteristic impedance of a coaxial cable given its dimensions. A microstrip is a type of transmission line in which a strip of a conducting material like copper is mounted on a dielectric material and routed to a ground plane. The formula for the length of the matching section is as follows: Q-Match Coax (in feet) = 246 x [velocity factor] / Frequency (MHz). 25 inches and a dielectric constant of 2. This robust cable is flexible, suitable for burial, and appropriate for use over a wide temperature range. diameter Schedule 40 PVC form. for a typical polyethylene-insulated cable. Where, RL = Return loss in dB. 336 ° (degrees) that is a portion of a 360° angle. This is the online directional coupler calculator that calculates the coupling (dB), coupling loss(dB), insertion loss (dB), and directivity (dB) of a directional coupler by entering the value of input power P1 (dBm/Watt(s)), output power. 0. Cutoff wavelength and frequency. The 3. For practical applications, please visit manufacturers’ websites and consult their data. A slot or gap with a conducting coating on a dielectric substrate makes up a slot line, a form of transmission line comparable to CPW. Ns = Number of turns in Secondary coil. Characteristic Impedance Calculation For Typical RG58U Coaxial Cable The plots below show the characteristic impedance Zo for a coaxial cable with typical RG58U characteristics (cables from different manufacturers differ somewhat in the exact physical dimensions, dielectric constants etc. c is the speed of light 299,792,458 m⋅s −1,. diameter coax (RG-8 or LMR-400) coil wound on a 5 in. Customers can choose to either buy cable in bulk or use our large selection of coax types to construct custom cable assemblies. The above formula is another form of the familiar equation: Z (squared) = Zo X Zr. 900c. We recently corrected a problem with the cut-off frequency calculation for single dielectric, which was pointed out by Andrew (thanks!) It will calculate characteristic impedance of coax that contains up to five concentric dielectrics!You can find online coaxial cable impedance calculators that accept inputs of outer diameter dielectric width, inner conductor diameter width and either the dielectric constant or velocity of propagation (VoP, the speed at which RF propagates through the cable conductors) values to calculate the intrinsic impedance of the coax. If you'd insert a 1/4 wave section of 27. Picking it interactively in the 3D view and. 6/1. If it's safe to assume that both drivers have an output of the same amplitude, we can even calculate the loss introduced by the cable: 20×log(1. As the name suggests, the length of this transmission line if fixed at a quarter of the wavelength (λ/4). 15 mm (0. Of course - our simple dipole calculator to assess the length of the device. Coax Impedance (Transmission Line) Calculator. Phasing & Matching Lines How to measure coax stub lines, produce coaxial impedance transformation lines, Baluns and how to stack and match with coax lines; Coax & Splitter Online Calculator Coaxial Line Impedances Online Calculator, Intro to Power Splitters and Power Splitter Dimensioning Online Calculator; Symm. 6 Ohm/1000ft (47. Coaxial Cable Attenuation. c is the speed of light 299,792,458 m⋅s −1,. . These cables usually consists of an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield and an outer covering. ) using the high and low frequency approximations above for Rc and Lc. where. ElectronicsForU. However, the twisted. From my memory, cable splitters (such as for splitting a cable tv coax cable into two televisions) provide impedance matching to prevent signal reflections, etc. These two cables will transform the impedance for maximal power transfer. The reflected voltage is used to calculate the impedance while the round-trip signal time is used to calculate either the dielectric constant of the transmission line or the length of the transmission line, depending on which of the. R = Zo (K + 1/K) Where, K2 = P3 / P2; (P3 - power at port 3) (P2 - power at port 2). Terminating the cable with a 50 Ω resistor still causes a negative reflection , although of much smaller pulse height (Figure 5). Use the frequency and layer thickness/Dk value to determine the antenna size. d is the diameter of the inner conductor of the coax cable; units of D and d must be the same,. æ k s /), is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric (insulating material); many coaxial cables also have a protective outer sheath or jacket. Here, you can utilize the online calculator to ascertain the impedance of a coaxial cable in ohms for a specific circuit. 15 mm (0. The 50 ohm characteristic impedance of my coax is only "characteristic" if it's terminated with $ 50 + 0j$ load. 398Ω. Gamma matching allows you to match such a dipole with a 50-ohm coaxial feeder. Also known as RG-400 or RG400 cable, this premium coaxial cable is designed to meet the demanding requirements of high-frequency applications. The cable dictates how much current initially flows based (mainly) on its inductance, capacitance and resistance. Among the commonly used connectors for 50 Ω coaxial cable is the venerable PL-259, available from Amphenol RF as the 83-1SP-1050 (Figure 5), as well as the wideband Type N, such as the VNS30-2051. The trick is that I'm trying to use 75Ω RG6 coax for the matching section (because it is relatively inexpensive and low-loss), but I want a 50Ω impedance at the feed point. The epsilon_r of the cable isolation is 2 so total electric permittivity is 2 * 8. Thus, for this system, VSWR = 1:1 (i. where. 49 m. 124 in), type of insulation is polyethylene with the relative permittivity of 2. R2 is the resistance of the protective conductors. The standard impedance choice for systems requiring low attenuation is 75 Ohm. It can for instance vary from the standard 50 ohm. They are used in a wide range of applications including antenna connections. This applies to generalized S. Micro-coaxial cables. You can perform the calculations, but by changing the outer diameter in Figure 3 by just two millimeters, you will find that the coaxial cable’s impedance changes from 75 ohms to 46 ohms. Values range between 0. For discussion of impedance matching of the voltage source to the transmissionJul 22, 2019. The use of a standardized impedance makes RF design much more practical and efficient. Coax Impedance Calculator – EEWeb Community. Model # Y278784 SKU # 1000724874. where. 5nF. Cutoff Frequency of Upper Mode: 13. coaxial cable. ε 0 = 8. In the application, the reverse calculation is also available, finding the width and length of the strip according to the given characteristic impedance and the electrical length of the T-line. WhatsApp. The coax cable is RG-8X. For example, if you wish to input "25000000", just type "25M" instead. 8542*10^ (-12). Disconnect both ends of the cable from their connections. where. Cable Capacitance (pF/ft) 20. Good enough, because the calculation for 15 m of typical coax with 6. This example is for LMR-600 which is very low. Micro-coaxial cables. 854187817620. Use RG 58 cable (or any 50 ohm cable) You will ear the. e. 5 mm Coaxial Connector is designed to be relatively rugged. The cutoff frequency is the frequency up to which the system functions efficiently. Coaxial Impedance Calculator. U. The impedance of a coaxial cable is determined by its physical. Use the frequency and layer thickness/Dk value to determine the antenna size. i cant find the datasheet though it has part number 473-872-03 Rev A1 Mfr 64023. Insulation service. 07 m. μr μ r = relative permeability. In electrical engineering, the reflection coefficient is a parameter that defines how much of the electromagnetic wave is reflected due to the impedance discontinuity in a transmission path. This calculator calculates the impedance of a coaxial cable. e. 5dB loss per 100 feet at 146 MHz). 854187817620. 5 ohms. There are many single-stub matching network calculators, but almost all of them assume that the impedance of the matching network is the same as the feed point. 9913 and LMR-400 are popular “low-loss” RG-8 types. The ferrites are held in place by foam tape. The impedance of the coax is a relationship of the capacitance per unit length and the inductance per unit length. It assumes that the wave is traveling at the speed of light which is the case for most wireless signals. In fact, striplines often make components such as band-pass filter's more accurately, with more symmetric roll-off and no lower cutoff frequency. Visit to learn more about our other electrical engineering tools. Test the length of the cable by placing a multimeter probe on each end of the cable, touching the center wire emerging from the coaxial connector. Characteristic Impedance Nom. Calculate the impedanceThe correct way to consider impedance matching in transmission lines is to look at the load end of the interconnect and work backwards to the source. d is the diameter of the inner conductor of the coax cable; units of D and d must be the same,. RF Calculators. 1 7. The parameter scale of the X and Y axis of the oscil-loscope screen are 20 ns/div and 200 mV/div. ) and i notice that a lot of people use RG 6 or tv cable, all 75 ohm impedance, causing a mismatch and a loss of +/- 15 @ 25 % reception. This tool will help you find the inductance for a given length of coax cable. e. d is the diameter of the inner conductor of the coax cable; units of D and d must be the same,. Characteristic Impedance Calculation For Typical RG58U Coaxial Cable The plots below show the characteristic impedance Zo for a coaxial cable with typical RG58U characteristics (cables from different manufacturers differ somewhat in the exact physical dimensions, dielectric constants etc. Z = R + jX, where j is the imaginary component:. 3. This coaxial cable calculator determines the distributed capacitance and inductance of a coaxial cable, its impedance and cutoff frequency for a given cable geometry, and relative permittivity or velocity factor. Pasternack RG178 flexible coax cable is 50 Ohm and has a PTFE dielectric. These cables usually consists of an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield and an outer covering. The coaxial cable is so fundamental that Oliver Heaviside patented it in 1880, just a few years after Maxwell published his famous equations. 7mm. More consistent results will usually be obtained by using a dedicated cable joiner or a plug and socket with the same impedance as the cable. & Baluns Symmetrising Devices. The most common values of coaxial cable impedance are 50 and 75 ohms. It is around 30cm cable. This is the only way to calculate the total impedance of a circuit in parallel that includes both resistance and reactance. An example follows.