Since we might as well find the impedance per length, we can study the expression: Rl = 1 σA R l = 1 σ A. The Smith Chart achieves this by superimposing a grid on S11 that maps load impedance. Output values are rounded to the second decimal place. 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. A differential cable is usually constructed with a UTP, STP, STQ or twin-axial configuration and achieves 100-Ω differential impedance. 3pF) in the tuner to 111. 900c. The first plot shows the Impedance in Cartesian form, the second the absolute Value of Impedance and the third the Phase. If one 50 Ohm line is split into two 50 Ohm lines, the two will appear as a single 25 Ohm line (two 50 Ohm lines in parallel). 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. × 10 −12 F/m is the. D is the inside diameter of the coax cable shield,. In a nut shell the characteristic impedance of a coax cable is the square root of (the per unit length inductance divide by the per unit length capacitance). This can cause an impedance discontinuity where the join is made. Z 0 = Characteristic Impedance of the overall system. 1 7. Email. Now we can add the resistances from the inner and outer shell since they're in series. As such, the outer (braided) conductor completely. 150 MHz start by calculating the freespace wavelength… Wavelength(Freespace-7. Lumped Port Impedance - User Specified The complex impedance Z s, defined when the port gets created, serves as the source impedance of the S-matrix of the lumped port. Coaxial cable characteristic impedance Calculator and formula. coax cross section. 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. SIC = Dielectric constant of the cable insulation (Table-3) = cthe speed of the voltage/current signal on the cable is the speed of light. 8 Ohm, Inductance (L) = 2. 20. 557 GHz. For any cable type, it is equal to the reciprocal (1/x) of the square root of the relative permittivity of the cable’s insulation. The formula for the length of the matching section is as follows: Q-Match Coax (in feet) = 246 x [velocity factor] / Frequency (MHz). Coax cable loss table and charts – NASA. 0815. I've added the formulae to my answer. R2 is the resistance of the protective conductors. D is the inside diameter of the coax cable shield,. Coax Impedance Calculator | Sivers IMA. 3. “468” is the constant used to convert frequency in MHz to feet. How is the turn ratio calculated? The turn ratio of the RF transformer is calculated by using the following formula. VSWR (voltage standing wave ratio, sometimes pronounced "viswar"), is the ratio of the maximum standing wave amplitude at one node to the minimum. This online reflection coefficient to return loss calculator calculates the return loss (dB) by entering the reflection efficient Γ (= value. 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. 5nF. 1: Determining the inductance of coaxial line. There are countless. Gamma matching is the most commonly used matching device used for a planar dipole in the Yagi-Uda antenna. Frequency to Wavelength Calculator. 5 ohms. 302 times larger than the diameter of the inside conductor. 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. (D) is the outer diameter of coaxial. This calculator is designed to calculate the characteristic impedance of a microstrip - a flat conductor suspended over a ground plane with a dielectric between them (see diagram below). 50 Ohm Coax Cable. 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. VSWR (Voltage Standing Wave Ratio) and Return Loss both measure the same parameter i. ε 0 = 8. This is a required field. The functionality of a coax loss calculator is straightforward, yet it provides critical information for ensuring optimal performance. 15 mm (0. Mar 26, 2009. . Coaxial cables are extremely useful transmission lines as the coaxial nature of the transmission line provides relatively efficient transmission from DC to a cut-off frequency, which is a function of the geometries of the coaxial components of the cable. Formulas. where. In a nut shell the characteristic impedance of a coax cable is the square root of (the per unit length inductance divide by the per unit length capacitance). COAXIAL CABLE IMPEDANCE CALCULATOR Calculates the characteristic impedance of a coaxial cable given its dimensions. 2. thus a big transmission line can have the same impedance as a small transmission line if one is scaled in proportion from the other. Distributed Inductance (L') For a coaxial cable, the inductance per unit length L' in henries per meter (H/m) is defined as. The coaxial cable, along with the balanced two-wire, is the most common type of transmission line used in RF communications. If the cable is 50 ohms it means that the impedance driving the cable must be 50 ohms and that the termination impedance at the output of the cable must also be 50 ohms. ε 0 = 8. . 7 - 29. Coax Impedance Calculator. Input. Same-day shipping if you order in the next hours!. This robust cable is flexible, suitable for burial, and appropriate for use over a wide temperature range. “Inductance Calculations” , F. Attenuation (dB/100 ft, @. The relative permittivity of the medium ϵr ≈ 1 ϵ r ≈ 1 for the. RF calculations and conversions include metric-standard, link. Facebook. 4. Geometriy is not that critical. Explore the Coaxial Cable Calculator, a handy tool for calculating various parameters of coaxial cables such as impedance, capacitance, inductance, and cutoff frequency. R is resistance per metre, L is inductance per metre, C is parallel capacitance per metre and G is parallel. Coax Impedance Calculation. 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. Coaxial cable is a two-conductor cable made of a single conductor surrounded by a braided wire jacket, with a plastic insulating material separating the two. 405 inch. RF calculations and RF conversions include metric-standard, link budget, coax cable, power, attenuation, frequency and many more. For discussion of impedance matching of the voltage source to the transmissionJul 22, 2019. If that transmission line is 1/4 wave long, it's called a quarter-wave transformer, and it makes whatever's at the end of it look like the conjugate impedance. The Smith Chart graphically maps S11=reflection coefficient= (ZL-Z0)/ (ZL+Z0) to Load Impedance (ZL), normalized to Z0 (source impedance = center of chart). This calculator is able to calculate the impedance, delay, inductance, and capacitance of a coaxial cable. where. Permeability (µ) is assumed to be 1. 1: 300 Ω 300 Ω twin-lead. εr = Dielectric constant of the insulator. D is the inside diameter of the coax cable shield,. A Coaxial cable is a type of cable that is used to make transfer RF/Microwave signals. 398Ω. . You can use either a 1:1 balun or a choke balun at the feed point of the antenna or where the balanced part of the system meets the unbalanced part. Show Me Cables' high quality RG6 quad shield coaxial cable consists of an 18 AWG solid bare copper. **Note: Like our microstrip line impedance calculator, all of our RF calculators allow SI prefix input. **Note: Like our stripline impedance calculator, all of our RF calculators allow SI prefix input. This tool will help you find the inductance for a given length of coax cable. 56 X 10-7 H/m, Capacitance =. Choose from 50 Ohm, 75 Ohm, 93. For example, connecting coax cable to a dipole antenna. 035 in), outer conductor diameter 3. **Note: Like our stripline impedance calculator, all of our RF calculators allow SI prefix input. The parameter scale of the X and Y axis of the oscil-loscope screen are 20 ns/div and 200 mV/div. the cable is Tensolite (Carlisle) brand (came all the way from USA, not China) came already with BMA connectors soldered on both end. 854187817620. But for a practical transmission system with load, there will be a small impedance mismatch that will lead to a small amount of incident power reflected back to the source. On Figure 5, the curve shows the test results of a 5m coaxial cable where the shield has been is intentionally spoiled by a 10cm pigtail. Useful. 295-49. Microstrip traces and coaxial cables (coax) are two special cases of two-conductor transmission line structures. it has double shielding, outer layer is stranded/woven wires, inner layer is metal strip wrapped in spiral, PTFE look alike. 854187817620. Using our own calculators which, for impedance, is based on the formula above (which is the same as the calculator in the tool section of this site) our characteristic impedance turns out about 8% - 10% higher than calculated. Any coaxial cable filled with air has a wave impedance of ~377 Ω, but this does not at all help to make the open piece of coaxial cable a good antenna. 13-1. √ 50*12. Figure 2 - Fast pulses measured at the end of the coaxial cable using an oscilloscope without impedance matching. Transformed through the antenna side capacitor (adjusted to 139. Plugging this into the equation we calculate the cable length. 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. 6 . Fiber calculators and tools. ε = dielectric constant = ε0 * εr. Example: Calculate the distributed capacitance and inductance, impedance and a cutoff frequency of a coaxial cable RG-58 with the following characteristics: inner conductor diameter 0. 15 mm (0. D is the inside diameter of the coax cable shield,. 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. The coaxial cable (coax) is one of the most ubiquitous transmission line structures. Simply put, the coax is losing 8. This will also provide the time delay the cable provides for a signal and also the capacitan…Coax Cable Transmission Line Models. Where, RL = Return loss in dB. This online reflection coefficient calculator calculates the reflection coefficient (Γ) by entering the value of the characteristic impedance Z o (in ohms. 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. They are used in a wide range of applications including antenna connections. Frequently, it becomes necessary to match. High return loss means low reflected power, so high return loss is good for a system. Terminating the cable with a 50 Ω resistor still causes a negative reflection , although of much smaller pulse height (Figure 5). These cables would also span long distances, reaching hundreds of miles. A rectangular waveguide is commonly used for the transport of radio frequency signals. 81, giving an impedance of 120. Np = Number of turns in the primary coil. This example is for LMR-600 which is very low. 9 mm (0. The input impedance of such a dipole is typically less than 50 ohms and may have a reactance. 10. ε0 = permittivity of free space = 8. The cable length is 3. for chosen frequency. D is the inside diameter of the coax cable shield,. d is the diameter of the inner conductor of the coax cable; units of D and d must be the same,. The velocity of propagation along the wire is 2x108 m/s. HELP. 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). Over time properties of standard coaxial type cables have been standardized. RG12 Coaxial Cables are a type of coaxial cable commonly used for high-frequency signal transmission in telecommunications and networking applications. Coax Impedance Calculator. Coax Impedance Calculator – EEWeb Community. ) using the high and low frequency approximations. 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. Output values are rounded to the second decimal place. 3. 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. UsefulFormulas. The RG-6 cable I used had a velocity factor of 66 percent. Bend Radius is the minimum radius that a Radio Frequency (RF) coaxial cable can be bent to without damage. Note that the very first dip is where the cable is less than 1/4 wavelength. If the antenna feedpoint is 50 ohms (such as a gamma match of a beam antenna) using 75 ohm coax as the main. If you use the formulas in the table below you will calculate a VSWR of 1. Taking the square root of 22,500 yields 150 Ω for a characteristic line impedance. EXAMPLE: INPUTS: Outer diameter = 36 , Inner diameter = 10 , Relative permittivity =2. This causes an impedance mismatch at each staple location resulting in micro-reflections. An example follows. D is the inside diameter of the coax cable shield,. 85419 x 10. Coax Cable Formula. 854187817620. Select the cable type from the available options. Cable Capacitance (pF/ft) 23. Semi-rigid coax (new for June 2021!) Triax (new for August 2023!) Coax cable vendors . 35dB. The advantage of using coax for a 1:1 choke-balun is the constant Z0 of 50 ohms. As the name suggests, the length of this transmission line if fixed at a quarter of the wavelength (λ/4). They also have an impedance of 75 ohms, which is a standard for coax cable used in the broadcast industry. Thus, for this system, VSWR = 1:1 (i. 0815 × W × V (velocity factor of the cables). The 3. The capacitance of a one conductor shielded cable is given by the formula below: Where: C = Total capacitance of the cable (microfarads) I charge = Charging current of the cable. 9 Ohm/km) 29 pF/ft (95 pF/m) 50 Ohm 70% Voltage UL Voltage Rating Voltage Rating 30 V (UL AWM 1637) 750 V (Mil-Spec) Mechanical Characteristics. 398Ω. milked on braid method) to make outer con-ductor of the outer coaxial system instead of using an outer tube (IEC 62153-4 Annex C). For my loop, the length of the matching section worked out to: 16. Now, let us investigate the physical meaning of return loss. 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. Cutoff Frequency of Lowest Order Mode: 6. Where L is the length of the dipoles. There are more than 75 different RF Coaxial Connectors that can be used in wireless systems. Question 17. 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. Linkedin. and 1/12 λ of 75Ω coax. Get precise results by providing the outer diameter, inner diameter, and relative permittivity. 25 inches and a dielectric constant of 2. c is the speed of light 299,792,458 m⋅s −1,. Polar or rectangular grids only allow direct reading of S11. The measure of this reflected power is called as return loss. Here, the inductance of the cable is. Wilkinson Power Divider Calculator. REGISTER. It is important to determine the characteristic impedance of a twisted-pair cable because this impedance should match the impedance. Impedance: 50 Temp: -55, 200. 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). diameter coax (RG-8 or LMR-400) coil wound on a 5 in. To understand how a coax loss calculator works, you. Calculate the edge input impedance for the antenna. 2. Suitable for VHF (~1. Our RF and microwave calculators and converters will provide the figures you need for your radio frequency engineering needs. in both cases, the speed and the Characteristic Impedance depend upon logarithms of the ratio of two distances in the cross. The transmission line is terminated in a load impedance of 50 . Suitable for higher power (~1800 watts) at HF. 15 mm (0. In the case of coaxial cables, impedance is expressed in terms of "ohms impedance". 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. R = Zo (K + 1/K) Where, K2 = P3 / P2; (P3 - power at port 3) (P2 - power at port 2). This can be achieved by regulating the inner and outer diameter of the coaxial cable, along with the. 15 mm (0. Suitable for higher power (~1800 watts) at HF. ε 0 = 8. 96. #2. You can convert the 75 Ohm coaxial cable to 50 ohm coaxial cable or vice versa by adding a Balun (Balanced Unbalanced) having impedance =sqaureroot of (75*50) Or in other way you can use a transformer or a parallel resistor circuit . Jan 15, 2022. You can select the unit of measurement for the coaxial cable's inner diameter,. ) using the high and low frequency approximations. Same-day shipping if you order in the next hours!. Along the slot line, the electromagnetic wave encounters the substrate and the air, which serve as its transmission medium. The. is required to do the impedance transformation from 50 ohms to 292 ohms at 146 MHz. You can use these cables with a 50 Ohm. For example, if you wish to input "25000000", just type "25M" instead. Polar or rectangular grids only allow direct reading of S11. They are used to protect systems from receiving a signal with a power level that is too high to process. I used 100m for l. D (mm) Er d (mm) Impedance Notes: Optimal D/d ratio for breakdown voltage is 2. d is the diameter of the inner conductor of the coax cable; units of D and d must be the same,. Quite often, it is desirable to verify your calculations of the charac-The characteristic impedance of a coaxial cable is determined by the inductance and the capacitance per unit length; Zo = √(L/C). Distributed Inductance (L') For a coaxial cable, the inductance per unit length L' in henries per meter (H/m) is defined as. . “468” is the constant used to convert frequency in MHz to feet. This frequency to wavelength calculator helps you determine the wavelength of a waveform based on the frequency. A Rectangular Waveguide is a conducting cylinder of rectangular cross-section used to guide the propagation of waves. the built-in transfer impedance calculator, which extracts the impedance from the geometric characteristics of the shield. Engineers were designing air-filled coaxial cables for radio transmitters designed to output kW worth of power. 0, medical, smart city, and other applications that are impractical or impossible with other wired and wireless technologies, providing twice the bandwidth and three times the speed of Wi-Fi 6, deterministic network support, and more…. When a balanced source is to be isolated from an un-balanced load, the impedance matching transformer is referred to as a balun. Impedance mismatch of 75 Ohm Cable. It’s simply defined as the process of making one impedance look like another. 66 kW Black TPE Jacket (. 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. The following formula is used to calculate the cut-off frequency, lower & higher operational frequency of the rectangular waveguide. Coax Impedance (Transmission Line) Calculator. 8542*10^ (-12). ) Published under the terms and conditions of the. Pasternack's RF cable impedance measurement tool Coaxial Cable Impedance Calculator allows for the calculation of the impedance of the coax. Ns = Number of turns in Secondary coil. Altium's built in impedance calculator shows the trace impedance at 34 ohms not 50 ohms. For this example, assume perfect conductors and a lossless dielectric with relative permittivity ε r = 2. The VSWR/return loss calculator from Pasternack will find VSWR, return Loss, mismatch loss, and the reflection coefficient given any one of the listed input types. ε 0 = 8. 6/1. 14. The Smith Chart graphically maps S11=reflection coefficient= (ZL-Z0)/ (ZL+Z0) to Load Impedance (ZL), normalized to Z0 (source impedance = center of chart). You can calculate it with the following equation: Z (z) = V (z)/I (z). Wall Thickness Calculator; Glossary of Aerospace Terms; Guides and Product Information;. For any cable type, it is equal to the reciprocal (1/x) of the square root of the relative permittivity of the cable’s insulation. Conductor DCR Nom. 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. Twisted pairs are used with balanced signals. 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 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. However, the nominal refer-ence impedance of the analyzer is 50 + j0 Ω, rather than the complex characteristic impedance of the cable. f if the frequency of the RF signals. $endgroup$ –RG316 Coax Cable. 2. If you would use different values, the signal would reflect and distort itself. 0:1). on the calculator devide 29. Input the inductance of the pair or coaxial cable in μH/m. For example, if you wish to input "25000000", just type "25M" instead. Coaxial cable specifications often include the velocity factor, which is typically between 60% and 90% (1). This is actually a general way to express impedance, but it requires an understanding of complex numbers. Here it is: For outer diameter D, inner diameter d, and eccentricity c: Z0= [60/sqrt (ER)] x acosh [ (1/2)x (D/d+d/D-4c^2/ (dxD)] We entered the equation into Excel, and sure enough, if c=0 you get the same exact impedance you get from the. The 3. 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. Distributed Inductance (L') For a coaxial cable, the inductance per unit length L' in henries per meter (H/m) is defined as. Maximum Operating Voltage (Vrms) 4000. 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. We have now proven by measurement that the LOAD Termination, Signal Generator and Coaxial Cable all have. The use of a standardized impedance makes RF design much more practical and efficient. 854187817620. 3. Conformable Cable. Attenuation (dB/100 ft , @ 400 MHz). Calculate impedance from resistance and reactance in parallel. This relation is also the case for finite transmission lines until the wave reaches the end of the line. REGISTER. where. × 10 −12 F/m is the. This online reflection coefficient to VSWR calculator calculates the VSWR by entering the reflection efficient Γ (= value between 0 & 1). TF-047; SF-047; PT-047; IB 047; XF 045; SpaceFlight; SiO2; High Power; Radiating Cables. The RG-8A/U is a 50-ohm coaxial cable with an outside diameter of 0. MiniVNA or MFJ-269 or similar). 9)dB = 1. 405 inches and has a maximum working voltage of up to 5000 Vrms. The coaxial cable's diameter conduction allows for. The development of the expressions for L and R is more involved, as there will be current in the interior of the inner conductor. R = l σA R = l σ A. This online reflection coefficient to return loss calculator calculates the return loss (dB) by entering the reflection efficient Γ (= value. Out of Stock Online. A length of 13. VSWR is defined as the ratio of the maximum to minimum voltage on a loss-less transmission line (expressed as 3. Set Parameters as Desired. The distance in time between adjacent pulses is 35. CCTV & Security Cable. 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. Coaxial cable is typically rated to operate at 50 or 75 ohms so the scale should be at or greater than these ratings. The area just becomes the effective area, so for the inner shell, 2πaδ 2 π. The term coaxial refers to the inner conductor and the outer shield. - 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. RG-8 and RG-213 (50 ohm); and RG-11 (75 ohm) are about 0. 336 by 360, = 0. The term “impedance matching” is rather straightforward. WR90 Specifications. The coax is a good way to create a transmission line. In the limiting case of infinite load impedance, the Because 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. (141) $17. A typical coax cable has 50 ohm characteristic impedance above about 1 MHz but that doesn't mean that's the impedance that the source sees because, if the load isn't 50 ohm then the "seen" impedance isn't 50 ohms and reflections will be present. In fact, striplines often make components such as band-pass filter's more accurately, with more symmetric roll-off and no lower cutoff frequency. Although this sounds somewhat crude and primitive, I have watched technicians perform such an “operation” several times with very good success. D is the inside diameter of the coax cable shield,. It needs to be terminated with a connector designed for the correct impedance, as well as the coaxial cable size and shielding. 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 coax cable has a capacitance as a result of the gap between inner conductor and outer shield of the cable. 718. The length of the dipole is usually one-half of the wavelength of the RF signals. Wireless Converters and Calculators. Maximum Operating Voltage (Vrms) 4000. 2 OUTPUTS: Impedance = 51. Linkedin. d d = coaxial cable inner diameter. 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. . 10. The length of the coaxial cables is 29. Jul 09, 2003 · Coax Cable Loss. in both cases, the speed and the Characteristic Impedance depend upon logarithms of the ratio of two distances in the cross. The formula for the length of the matching section is as follows: Q-Match Coax (in feet) = 246 x [velocity factor] / Frequency (MHz).