This arrangement minimizes coupling between the coils. 5 in. My thoughts: The source sees from DC to approximately 300 kHz 117 Ohm Real Component (as 2x50 Ohm + 10*1. 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. In the amplifier design, above, the goal is to transform an output load of 50 ohms down to 12. Choose from 50 Ohm, 75 Ohm, 93 Ohm and 95 Ohm coaxial cables or 78 Ohm and 100 Ohm Twinax cables. The RG-6 cable I used had a velocity factor of 66 percent. The Smith Chart achieves this by superimposing a grid on S11 that maps load impedance. where. RF Coax Cable Assembly Designer Fairview Microwave's Coaxial Cable Impedance Calculator allows you to enter the Outer Diameter Dielectric width, Inner conductor Diameter width and either the Dielectric Constant or Velocity of Propagation (VoP) values in order to calculate the impedance of the coax. This is a required field. This is the only way to calculate the total impedance of a circuit in parallel that includes both resistance and reactance. Generally, a wave is reflected back. Micro-coaxial cables. where. 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. Ns = Number of turns in Secondary coil. RG12 Coaxial Cables are a type of coaxial cable commonly used for high-frequency signal transmission in telecommunications and networking applications. diameter Schedule 40 PVC form. Taking the square root of 22,500 yields 150 Ω for a characteristic line impedance. Figure 4 shows calculated results on a 5m long good quality single braid coaxial cable, 1 meter above ground, with perfect 360° contact at connector backshell. Coax Impedance Calculator. But it is not applicable to large and non-symmetrical cable-connector system as. September 8, 2022. 7mm. The epsilon_r of the cable isolation is 2 so total electric permittivity is 2 * 8. To ensure a quality signal travels the length of the cable a metal shield is needed. × 10 −12 F/m is the. Telegram. 854187817620. 36Ω), the impedance is: Transformed through 25 feet of RG-8 coaxial cable to 111. Two come to mind: RG58 has a Vf of 0. The characteristic impedance of a. Np = Number of turns in the primary coil. Altium's built in impedance calculator shows the trace impedance at 34 ohms not 50 ohms. on the calculator devide 29. S. Transformed through the antenna side capacitor (adjusted to 139. CCTV & Security Cable. 124 in), type of insulation is polyethylene with the relative permittivity of 2. On the shield is written COAXIAL CABLE 5C-2V 75 ohm. Calculation Dielectric Outer Diameter: Inner Conductor Diameter: Result: Pasternack carries hundreds of coaxial RF cables all in-stock and available for same-day shipping worldwide. × 10 −12 F/m is the. The device output impedance is usually low at high power levels; so, to match this impedance with a standard 50-ohm load, coax-ial-line transformers with specifiedThe cut-off frequency of the coaxial cable represents the maximum upper operating frequency of the cable. Note: The value of μr in this calculator has been taken as 1. RG-58/U, Belden 8240: RG-58C/U, Belden 8259: MHz: dB/50 ft:The square root of 15 (feed point) times 50 (normal coax cable) is 27. As the name suggests, the length of this transmission line if fixed at a quarter of the wavelength (λ/4). 75 Ohm Coax Cable. 232 Ohm/1000ft (761 Ohm/km) 14. Capacitance Cond-to-Shield Nom. 405 inches and has a maximum working voltage of up to 5000 Vrms. 5nF. Insulation service. 14. for chosen frequency. The Smith Chart graphically maps S11=reflection coefficient= (ZL-Z0)/ (ZL+Z0) to Load Impedance (ZL), normalized to Z0 (source impedance = center of chart). The standard impedance choice for systems requiring low attenuation is 75 Ohm. . The distance in time between adjacent pulses is 35. お知らせ：2023年11月23日（木）～24日（金）は米国祝日のため、受注のタイミングにより通常納期より2～3営業日多く頂戴する場合があります。50 ohms is used because it is the impedance of the coaxial cable, except audiovisual applications is 75ohms, and so we avoid having to use an impedance matching circuit to connect the PCB to the outside. 7 - 29. 5 dB. Apr 22, 2009. 854187817620. The characteristic impedance of a coaxial cable with a dielectric is then and the propagation velocity of a wave is, where c is the speed of light In free space, the wavelength of a wave with frequency f is For a polyethylene-insulated coaxial cable, the propagation velocity is roughly 2/3 the speed. Calculate the edge input impedance for the antenna. The inductance of this structure is of interest for a number of reasons – in particular, for determining the characteristic impedance of coaxial transmission line, as addressed in Section 3. From then on the dips occur when the cable is an odd number of quarterwaves, or the distance between each dip is caused by an additional half-wave. These cables would also span long distances, reaching hundreds of miles. 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. thus a big transmission line can have the same impedance as a small transmission line if one is scaled in proportion from the other. Maximum Operating Voltage (Vrms) 4000. 5 mm Coaxial Connector is designed to be relatively rugged. Over time properties of standard coaxial type cables have been standardized. The TV Broadcasting Industry chose to use the 75 Ohm standard for coaxial cable in SDI video. From then on the dips occur when the cable is an odd number of quarterwaves, or the distance between each dip is caused by an additional half-wave. 1 7. The most common values of coaxial cable impedance are 50 and 75 ohms. High return loss means low reflected power, so high return loss is good for a system. TF-047; SF. VSWR = Voltage standing wave ratio. Where L is the length of the dipoles. 5dB loss per 100 feet at 146 MHz). I leave it to other sources to provide the complex equations needed to precisely model coaxial cables. Distributed Inductance (L') For a coaxial cable, the inductance per unit length L' in henries per meter (H/m) is defined as. 20. the combined velocity factor will be around 0. The relative permittivity of the medium ϵr ≈ 1 ϵ r ≈ 1 for the. d is the diameter of the inner conductor of the coax cable; units of D and d must be the same,. The distance in time between adjacent pulses is 35. For the air-filled cables typically used in high-power applications, this corresponds to a characteristic impedance of about 30 Ω. To calculate the impedance of a coaxial cable with a diameter of 0. Note that in the case of a dipole with an approximate feedpoint impedance of 70 to 75 ohms, fed with RG-6 or other 75 ohm coax, only one 75-to-50 ohm 12th-wave transformation is needed, at the shack entry end of the feedline. Wi-Fi 7 will enable consumer, enterprise, Industry 4. Coax Inductance Description. Early in my explorations of electricity, I came across a length of coaxial cable with a label of “50 ohms” printed along its outer sheath (Figure below). ) 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. 718. , some amount of incident power will reflect the source in a practical system). FL connector I have a 2" microstrip transmission line to the RF input of my GPS receiver. Microstrip traces and coaxial cables (coax) are two special cases of two-conductor transmission line structures. During transmission, the antenna is fed at the center terminals of the two rods. 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. The "trick" to doing the multi-dielectric calculation is to note that capacitance of multiple concentric. V is calculated by integrating the electric field along a path from the. When a balanced source is to be isolated from an un-balanced load, the impedance matching transformer is referred to as a balun. For my loop, the length of the matching section worked out to: 16. d is the inner diameter of the cable. The term “impedance matching” is rather straightforward. Picking it interactively in the 3D view and. Coax impedance is the square-root of the ratio of inductance/length divided by capacitance/length: Note that because the ln (D/d) term is a ratio, you can just as well use ln (R/r), and in either case the dimensional units don't matter. From the u. Length of the three-quarter-wave section 3λ g /4: mm. This online reflection coefficient calculator calculates the reflection coefficient (Γ) by entering the value of the characteristic impedance Z o (in ohms. e. 8 Ohm, Inductance (L) = 2. Now, to calculate the necessary line length: assuming that our cable has a velocity factor of 0. This causes an impedance mismatch at each staple location resulting in micro-reflections. How to calculate the dimensions or diameter of coaxial feed as per impedance of the equilateral antenna. 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. 6 Coaxial Line. It needs to be terminated with a connector designed for the correct impedance, as well as the coaxial cable size and shielding. The transmission line is terminated in a load impedance of 50 . This allows the signal to remain intact and not bleed out like it would without the shield. 15 mm (0. Insulation service (cable tray, conduit, direct burial, etc. REGISTER. ε 0 = 8. 3. Most professional engineers and technicians will never have the need to calculate the capacitance, inductance, or impedance of a coaxial cable since they are usually. 4w to achieve 100w at the aerial. 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. Pasternack's Coaxial Cable Impedance Calculator allows you to enter the Outer Diameter Dielectric width, Inner onductor Diameter width and either the Dielectric Constant or. 65. 5. Values range between 0. Coax Impedance Calculation. For my loop, the length of the matching section worked out to: 16. Suitable for higher power (~1800 watts) at HF. See Figure 2. Same-day shipping if you order in the next hours!. 191Ω. Customers can choose to either buy cable in bulk or use our large selection of coax types to construct custom cable assemblies. When the load impedance is mismatched to the source in a 1 : N imped-The calculator now shows that for the length of coax the loss is 0. It is widely used for data communications and telecommunications applications in structured cabling systems. The Velocity of propagation (Vp) of a cable is the speed at which an electrical signal can propagate through the cable in comparison to the speed of light. Cutoff Frequency of Lowest Order Mode: 6. VSWR is defined as the ratio of the maximum to minimum voltage on a loss-less transmission line (expressed as 3. Frequently, it becomes necessary to match. CRA Calculator. The 50 ohm characteristic impedance of my coax is only "characteristic" if it's terminated with $ 50 + 0j$ load. ε 0 = 8. Characteristic Impedance Nom. To calculate impedance, we first calculate the voltage between conductors and the current flowing in the inner conductor. The Pi (pad) RF attenuator calculator allows you to determine the Resistor values (R1 & R2) for a Pi attenuator. It matters (used to matter) to telephone. 10. The above formula is another form of the familiar equation: Z (squared) = Zo X Zr. Equation. Gamma matching is the most commonly used matching device used for a planar dipole in the Yagi-Uda antenna. Calculation method of the triaxial b method transfer impedance value: where a means = 20log 10 (S 21) represents the measured attenuation loss, a cal represents the composite loss measured during calibration, Z 0 represents the impedance of the signal generator and receiver, usually 50 Ω, and represents the coupling length of the tested. These cables usually consists of an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield and an outer covering. Gamma matching online calculator. Coaxial cable characteristic impedance Calculator and formula. An example of a wire microstrip might most often be found in prototypes or reworked boards where a wire is used over the top of pcb or copper clad material. A little more generally, a quarter-wave section of transmission line of impedance Z 0 converts between two impedances Z a and Z b: Z 0 / Z a = Z b / Z 0. cally short cables, these answers can be very different. This frequency to wavelength calculator helps you determine the wavelength of a waveform based on the frequency. 6 . This will also provide the time delay the cable provides for a signal and also the capacitan…Coax Cable Transmission Line Models. Coaxial Cable Impedance Calculator allows you to enter the Outer Diameter Dielectric width, Inner onductor Diameter width and either the Dielectric Constant or Velocity of Propagation (VoP) values in order to calculate the impedance of the coax. 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. The characteristic impedance will be displayed in Ω. 0 at Check Nearby Stores. For example, if you wish to input "25000000", just type "25M" instead. The impedance of a coaxial cable is determined by its physical. Model # Y278784 SKU # 1000724874. 04 feet = (246 x . 0:1, 2. 5 to 21. Identify as much information as you can about your piece of cable prior to discussion: Characteristic impedance. After all, if there is a mismatch of the antenna with this cable, the signal will be reflected before it enters to the cable. Designing a Current-Mode-Controlled Buck Converter in LTspice by Robert Keim. 6 . 191Ω. “468” is the constant used to convert frequency in MHz to feet. For this example, assume perfect conductors and a lossless dielectric with relative permittivity ε r = 2. A graphical representation of this insight uses the so-called Smith chart [1]. As such, the outer (braided) conductor completely. For example, if you wish to input "25000000", just type "25M" instead. The formula for the. 336: 360 = 0. HELP. The transmission line is terminated in a load impedance of 50 . 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. 40 GHz. 854187817620. Rectangular Waveguide Sizes. 240 DIA) Solid Copper center conductor Foam Polyethylene Dielectric Aluminum Tape outer conductorBoth of the cables are inside a bigger one: The black part is the isolation. S. 9. The operation of this. Calculate impedance from resistance and reactance in parallel. Coaxial cable combiners with ferrite cores are often used to combine the output powers of power amplifiers intended for wideband applica-tions. The. We are bespoke cable designers and manufacturers and we struggle to hit accurate designs on Coaxial Cables. RF Attenuator Basics & Selection. Now, let us investigate the physical meaning of return loss. 405 inches and has a maximum working voltage of up to 5000 Vrms. Attenuation (dB/100 ft , @ 400 MHz). Although widely applied to. 8542*10^ (-12). Return loss (RL) is the ratio of the reflected power to the incident power, in decibels (dB). Calculation Dielectric Outer Diameter: Inner Conductor Diameter: Result: Pasternack carries hundreds of coaxial RF cables all in-stock and available for same-day shipping worldwide. Here, the inductance of the cable is. 124 in), type of insulation is polyethylene with the relative permittivity of 2. Feed line chokes are a special case of impedance transformer with an input/output impedance ratio of 1:1. This tool is designed to calculate the inductance of a coaxial cable if its dimensions are provided. ,100 % power transferred from a source to a load via a transmission line/cable). Calculate the attenuation and power handling capability of coaxial cables using the online calculator by Times Microwave Systems. The twisted pair helps create a more uniform inductance and capacitance per unit length of wire to ensure a constant impedance, by keeping the return path as close to the signal as possible. e. Coax Impedance Calculator. 85419 x 10. We have a conflict in statements here where formula 6. 16 mm]The loss tangent introduces a "real" conductance which is calculated from the susceptance by multiplying by loss tangent. TF-047; SF-047; PT-047; IB 047; XF 045; SpaceFlight; SiO2; High Power; Radiating Cables. From my measurement I got data as below: From that table, we can see that there is significant impedance of the cable. These calculations for Pout (Power out in watts) are for an input of 50 watts. For a coaxial line, the electric fields extend in a radial direction from the center conductor to the outer conductor. Scroll down to find formulas for determining attenuation, wavelength, characteristic impedance, time delay, and more. 80 for typical two-wire lines and coaxial cables. The Pi attenuator (Pi pad) is a specific type of RF attenuator circuit which resembles the shape of the Greek letter for Pi. Use RG 58 cable (or any 50 ohm cable) You will ear the. = cthe speed of the voltage/current signal on the cable is the speed of light. This is actually a general way to express impedance, but it requires an understanding of complex numbers. Therefore, in this case, one cannot do without measurements, the calculator shows a certain average value. 9 mm (0. One online calculator tool that seems to work well and gives expected results is Coaxial Cable Impedance Calculator. Choose from 50 Ohm, 75 Ohm, 93. a = r = 0. Looking at the datapoints and moving back from the antenna (75. Outer Shield DCR Nom. If we look again at the example of the coaxial cable and leave it open at the end, achieving a characteristic impedance of ~377 Ω does not relate to anything about the fields. Explore the Coaxial Cable Calculator, a handy tool for calculating various parameters of coaxial cables such as impedance, capacitance, inductance, and cutoff frequency. Explore the Coaxial Cable Calculator, a handy tool for calculating various parameters of coaxial cables such as impedance, capacitance, inductance, and cutoff frequency. Visit to learn more about our other electrical engineering tools. Permeability (µ) is assumed to be 1. The distance between the first two dips (deltaF) is 99 MHz. Shown is a typical “ugly balun” widely described onIMPEDANCE - Impedance is a term expressing the ratio of voltage to current in a cable of infinite length. $egingroup$ I am wondering if the coaxial cable part from the antenna to the filter can be thought as the 50 ohm input series impedance. c is the speed of light 299,792,458 m⋅s −1,. Coax Cable Formula. (141) $17. 8 ns. WR90 Specifications. The velocity factor of a foam insulated cable depends on the production technology and varies from manufacturer to manufacturer. Zo = the impedance of the feed line. 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. D D = coaxial cable outer diameter. They are used in a wide range of applications including antenna connections. The quality of an impedance match can be expressed mathematically by the reflection coefficient (Γ). The cable length is 3. × 10 −12 F/m is the. Find a length of coaxial cable and bring it with you to class for discussion. It is important to determine the characteristic impedance of a twisted-pair cable because this impedance should match the. R w = Terminating resistance between two. Figure 3. I leave it to other sources to provide the complex equations needed to precisely model coaxial cables. Note that these calculations are theoretical and engineers and technicians will probably never have the. Step by Step Procedure The 125 ohm cable is connected at the end of a regular 50 ohm RG-213 cable. 405 inches and a voltage rating of up to 1000 Vrms. Simply select the quantity of convergence points, adjust the length and select the cable from the menu to create a bill of materials will be generated - showing the minimum amount of items required to configure a system. 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. Simply put, the coax is losing 8. Coax velocity factor of popular coax cable types is published in many places. 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. 9 mm (0. Choose from a variety of cables and get started now!. 557 GHz. D is the inside diameter of the coax cable shield,. When attaching a 200 Ω balanced antenna to a 50 Ω unbalanced (coaxial) cable, connect the high impedance (200 Ω) balanced antenna to the high impedance side of the transformer, and the low impedance (50 Ω) unbalanced end to the low impedance side of the transformer. Tuesday, October 31, 2023. Impedance: 50 Temp: -55, 200. By inputting the necessary values into the. Polar or rectangular grids only allow direct reading of S11. P B = Power output of Port 3. Cable Capacitance (pF/ft) 23. Coaxial Cable Calculator. 95 metersA microstrip width calculator can calculate the width of a microstrip. 5 ohms. 1,857. Attenuation (dB/100 ft, @. 3. What is the characteristic impedance of twisted pair cables? 100 ohms. 150MHz) = 300m/s / 7. Scroll down to find formulas for determining attenuation, wavelength, characteristic impedance, time delay, and more. 854187817620. The parameter scale of the X and Y axis of the oscil-loscope screen are 20 ns/div and 200 mV/div. **Note: Like our stripline impedance calculator, all of our RF calculators allow SI prefix input. 2. From my measurement I got data as below: From that table, we can see that there is significant impedance of the cable. Due to its geometry, the coaxial cable impedance requires you to know the inner wire's diameter and the outer shielding. The twisted pair helps create a more uniform inductance and capacitance per unit length of wire to ensure a constant impedance, by keeping the return path as close to the signal as possible. A 50Ω coax has an impedance of 50Ω whether it's one metre or one kilometre long. The RG6 Coaxial Cable tops out at 75 Ohms and sweep tested at 3GHz. The formula is this: -. 1. 10. Geometriy is not that critical. 25 provides minimum signal loss at about 50 ohms and at the same time it can carry large power for a given. ε 0 = 8. Figure [Math Processing Error] 7. Line Type: Belden 8215 (RG-6A) Belden 8237 (RG-8) Belden 9913 (RG-8) Belden 9258 (RG-8X) Belden 8213 (RG-11) Belden 8261 (RG-11A) Belden 8240 (RG-58) Belden. is required to do the impedance transformation from 50 ohms to 292 ohms at 146 MHz. Coaxial Cable Impedance Calculator. 5 mm Coaxial Adapters. Now, let us investigate the physical meaning of return loss. 2,210. Calculation of complex impedance. 035 in), outer conductor diameter 3. The RG-63/A/B/U is a 125-ohm coaxial cable with an overall diameter of 0. Understanding coax can be helpful when working with it. It has an inner 7-stranded bare copper. As can be seen in the following graphs, the only time a 1:1 choke-balun accomplishes a 1:1 transformation is when it sees 50 ohms at its output. c is the speed of light 299,792,458 m⋅s −1,. The cutoff frequency is the frequency up to which the system functions efficiently. Of course - our simple dipole calculator to assess the length of the device. 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. 9)dB = 1. The input impedance of such a dipole is typically less than 50 ohms and may have a reactance. Calculator (1) computes that a reactance of 200 Ohms at 1. Here is my measurement to a piece of RG6 cable. An example follows. ABOUT US. 36Ω), the impedance is: Transformed through 25 feet of RG-8 coaxial cable to 111. RF Attenuators are components that reduce the amplitude level of an incoming signal. Distributed Inductance (L') For a coaxial cable, the inductance per unit length L' in henries per meter (H/m) is defined as. Example 7. 15 mm (0. C = Speed of light. 9913 and LMR-400 are popular “low-loss” RG-8 types. 05+j51. × 10 −12 F/m is the. More. 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. Where: Zo = Characteristic impedance in ΩDistributed Inductance (L') For a coaxial cable, the inductance per unit length L' in henries per meter (H/m) is defined as. 900c. The cable dictates how much current initially flows based (mainly) on its inductance, capacitance and resistance. Layout of the three coils. Characteristic Impedance of a cable calculation: You May Also Like. 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. 336 ° (degrees) that is a portion of a 360° angle. . In fact, striplines often make components such as band-pass filter's more accurately, with more symmetric roll-off and no lower cutoff frequency. 49 m. This means the cables need to be. - Example: 2nd mode in coaxial cable is a dipole TE 11-mode - This dipole mode changes polarity twice around cable circumference - Approximation: Use average circumference 11= =𝜋∙ + 2 - In coaxial line the TEM-mode is the dominant mode - The corresponding wavelength equals the cable circumference C, but at which radius? 11= vpoint along a transmission line with a general load impedance. 8 MHz needs a coil of 18 µH. The quality of an impedance match can be expressed mathematically by the reflection coefficient (Γ). 11. R = Zo (K + 1/K) Where, K2 = P3 / P2; (P3 - power at port 3) (P2 - power at port 2). Wilkinson Power Divider Calculator. Figure 3. Pasternack's RF calculators and conversions section provides engineers valuable and easy-to-use tools ranging from complex mathematical formulas to simple conversions. Characteristic Impedance Calculator. Coaxial Cable Calculator. You can calculate it with the following equation: Z (z) = V (z)/I (z). Z0 = Characteristic impedance. This example is for LMR-600 which is very low. How is the turn ratio calculated? The turn ratio of the RF transformer is calculated by using the following formula. 302 times larger than the diameter of the inside conductor. The flexible types (9913F and LMR-400UF) are preferred, particularly for rotatable antennas. Coaxial cable characteristic impedance Calculator and formula. a = outside radius of inner conductor (inches) b = inside radius of outer conductor (inches) c = speed of light in a vacuum = 299,792 km/s = 186,282 mi/s. 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. This calculator calculates the impedance of a coaxial cable.