Identify as much information as you can about your piece of cable prior to discussion: Characteristic impedance. Mar 26, 2009. Hence, the return loss is always lower than the ideal system (i. . for a typical polyethylene-insulated cable. 3. 4. If the impedance of the load matches that of the source, impedance matching is not required, and the balun has a 1 : 1 impedance ratio. 295+j32. 5 Surge Impedance (ohms): 35. D is the inside diameter of the coax cable shield,. The return loss of a system is defined as the ratio of incident power to reflected power and is measured in dB. Example 25. Figure 2 - Fast pulses measured at the end of the coaxial cable using an oscilloscope without impedance matching. The calculator allows you to automate the calculation of losses in a coaxial cable. The cable dictates how much current initially flows based (mainly) on its inductance, capacitance and resistance. Gamma matching allows you to match such a dipole with a 50-ohm coaxial feeder. 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. Length of the half-wave section λ g /2: mm. A-INFO carries hundreds of RF cables all in-stock and available for same-day shipping worldwide. 1. Why these values? One explanation is that the value of 50 ohms was selected because a coaxial cable with polyethylene dielectric with relative permittivity ε r = 2. Calculation of complex impedance. These calculations for Pout (Power out in watts) are for an input of 50 watts. 7 - 29. The coax cable is RG-8X. Z0 = Characteristic impedance. An air-spaced cable would shift signals at the speed of light c. Nist, KQ6QV has free software for calculating arbitrary transmission line impedance, as well as transmission. The history of 50 Ohm impedance goes back to the late 1920s/early 1930s, when the telecom industry was in its infancy. 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. Lower VSWR means lower reflection power (good impedance matching); thus, power transfers to load will be high. Step by Step Procedure The 125 ohm cable is connected at the end of a regular 50 ohm RG-213 cable. The impedance of the coax is a relationship of the capacitance per unit length and the inductance per unit length. The following formula relates the return loss and VSWR. We have a conflict in statements here where formula 6. L L = length of the coaxial cable. If, on the other hand, a < δs or merely ∼ δs, then current density is significant throughout the wire, including along the axis of the wire. C = Shunt capacitance per unit length. If I place a trans-match between the rig and the feed, then I'm tuning the feed line. 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. ) Type (RG-58, RG-6, etc. The impedance of a coaxial cable is determined by its physical. 40 GHz. 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. Semi-rigid coax (new for June 2021!) Triax (new for August 2023!) Coax cable vendors . d is the diameter of the inner conductor of the coax cable; units of D and d must be the same,. Lower VSWR is always desirable for a system. Summarizing: The power handling capability of coaxial transmission line is optimized when the ratio of radii of the outer to inner conductors b / a is about 1. Attenuation (dB/100 ft , @ 400 MHz). This calculator helps you calculate the characteristic impedance of a coaxial cable given its dimensions. Transmission line impedance is an important aspect of RF electronics, as it greatly influences the quality of a signal. 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. Our RF and microwave calculators and converters will provide the figures you need for your radio frequency engineering needs. Operating above the cut-off frequency that results in interference in signal propagation. 854187817620. Calculate the attenuation and power handling capability of coaxial cables using the online calculator by Times Microwave Systems. Maximum Operating Voltage (Vrms) 4000. Quarter Wave Transformer Impedance Calculator. Where we basically use the effective area instead. A quarter wave transformer is used to match two transmission lines with different impedances. and Canada (866) 727-8376 International +1 (949) 261-1920point along a transmission line with a general load impedance. These are considered to be standardized impedance values with cables readily available. 2. R = Zo (K + 1/K) Where, K2 = P3 / P2; (P3 - power at port 3) (P2 - power at port 2). 05+j51. For my loop, the length of the matching section worked out to: 16. c is the speed of light 299,792,458 m⋅s −1,. This arrangement minimizes coupling between the coils. Check the velocity factor for bare copper, which is 0. 2. 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 formula is this: -. Plugging this into the equation we calculate the cable length. 2. One pole (rod) is continuous with a length of λ/2 and the other is split at the center. 0. Calculates Delay, Velocity Factor, Effective Dielectric Constant and Characteristic Impedance of a PCB track. 66 kW Black TPE Jacket (. 35dB. R = l σA R = l σ A. In summary, the design process for the coaxial probe placement is simple: Select an operating frequency and stackup. This online reflection coefficient to return loss calculator calculates the return loss (dB) by entering the reflection efficient Γ (= value. com If it. Wireless Converters and Calculators. Good enough, because the calculation for 15 m of typical coax with 6. Due to its geometry, the coaxial cable impedance requires you to know the inner wire's diameter and the outer shielding. 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. Taking the square root of 22,500 yields 150 Ω for a characteristic line impedance. 718. × 10 −12 F/m is the. The resistance of such a wire is given by Equation 4. Coaxial cables are commonly used for transmitting electrical signals, including RF (radio frequency) signals. This online reflection coefficient calculator calculates the reflection coefficient (Γ) by entering the value of the characteristic impedance Z o (in ohms. thus a big transmission line can have the same impedance as a small transmission line if one is scaled in proportion from the other. Now, to calculate the necessary line length: assuming that our cable has a velocity factor of 0. You can select the unit of measurement for the coaxial cable's inner diameter,. A Coaxial cable is a type of cable that is used to make transfer RF/Microwave signals. 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. Get precise results by providing the outer diameter, inner diameter, and relative permittivity. d is the diameter of the inner conductor of the coax cable; units of D and d must be the same,. d d = coaxial cable inner diameter. 124 in), type of insulation is polyethylene with the relative permittivity of 2. 4w. 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. Characteristic Impedance Calculator. 3. 5 Surge Impedance (ohms): 35. 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). 6 dB/100 m yields 1 dB. Example: Calculate the distributed capacitance and inductance, impedance and a cutoff frequency of a coaxial cable RG-58 with the following characteristics: inner. The impedance morphs from 50 ohm to sqrt (R/jwC) as frequency lowers. Free Windows program for calculating the loss and impedance transformation. Output values are rounded to the second decimal place. where. where. com Coax Cable Impedance Calculator Where, d = The outside diameter of the inner or center conductor. However, the nominal refer-ence impedance of the analyzer is 50 + j0 Ω, rather than the complex characteristic impedance of the cable. Another way is to use ladder line. Z = R + jX, where j is the imaginary component: √(-1). This causes an impedance mismatch at each staple location resulting in micro-reflections. Then ta ke the potentiometer and measure itsI have a passive GNSS antenna with a 6" 1. Picking it interactively in the 3D view and. WhatsApp. e. South East Ontario. 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. Coaxial Cable Attenuation. e. D is the outer diameter of the cable. The coax cable has a capacitance as a result of the gap between inner conductor and outer shield of the cable. d is the diameter of the inner conductor of the coax cable; units of D and d must be the same,. 1. 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. Coaxial Cable Calculator. Note that these calculations are theoretical and engineers and technicians will probably never have the. 405 inches and a voltage rating of up to 1000 Vrms. 6 Coaxial Line. Gamma matching is the most commonly used matching device used for a planar dipole in the Yagi-Uda antenna. For a coaxial line, the electric fields extend in a radial direction from the center conductor to the outer conductor. Any change of L/C when passing through connectors results in a reflection of energy from the mismatch. A differential cable is usually constructed with a UTP, STP, STQ or twin-axial configuration and achieves 100-Ω differential impedance. The RG-6 cable I used had a velocity factor of 66 percent. The impedance of this antenna is around 300 Ω, so you may want to use a 4 : 1 transformer or a λ/4 long piece of 150 Ω coaxial cable to match this impedance to 75 Ω. Schelkunoff in 1934, is a very convenient parameter for the prediction and control of EMI coupling through cable shields. If we calculate the inner and the outer impedance using formula Z=R+j (XL-XC), where XL=j2pifL, and. It assumes that the wave is traveling at the speed of light which is the case for most wireless signals. They are used to protect systems from receiving a signal with a power level that is too high to process. 8 Ohm, Inductance (L) = 2. The Pi attenuator (Pi pad) is a specific type of RF attenuator circuit which resembles the shape of the Greek letter for Pi. Cable Capacitance (pF/ft) 23. pr is the relative permittivity of the material the cable is made from. Engineers were designing air-filled coaxial cables for radio transmitters designed to output kW worth of power. Distributed Inductance (L') For a coaxial cable, the inductance per unit length L' in henries per meter (H/m) is defined as. DUT (cables and connectors), inaccuracy could be a prob-lem. 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. Coaxial cables transmit signals through the center wire. Facebook. d is the diameter of the inner conductor of the coax cable; units of D and d must be the same,. Calculate the attenuation and power handling capability of coaxial cables using the online calculator by Times Microwave Systems. which can be algebraically solved for Z 0 as: Z 0 = Z a Z b. The relation between the R, Zo, and amount of power division is given by the following formula. As such, the outer (braided) conductor completely. This page allows you to calculate the impedance required for a 1/4 wave (electrical) section of line. 35dB. As the name suggests, the length of this transmission line if fixed at a quarter of the wavelength (λ/4). Distributed Inductance (L') For a coaxial cable, the inductance per unit length L' in henries per meter (H/m) is defined as. Click on any RF calculator below to get started. Z = R + jX, where j is the imaginary component:. Wall Thickness Calculator; Glossary of Aerospace Terms; Guides and Product Information;. In fact, striplines often make components such as band-pass filter's more accurately, with more symmetric roll-off and no lower cutoff frequency. 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. The calculator will output the characteristic impedance, cut-off frequency, capacitance per unit length, inductance per unit length, and velocity of propagation in. The distance in time between adjacent pulses is 35. A length of 13. e. Martin and Mendenhall (1984) proposed to use an addi-tional braid (i. Now, let us investigate the physical meaning of return loss. age and current in a cable of supposedly infinite length. Someone once asked us for an equation for calculating the characteristic impedance of off-center coax. 1: Determining the inductance of coaxial line. 191Ω. Attenuation (dB/100 ft , @ 400 MHz). Since we might as well find the impedance per length, we can study the expression: Rl = 1 σA R l = 1 σ A. To understand how a coax loss calculator works, you. MiniVNA or MFJ-269 or similar). R = l σA R = l σ A. The cable dictates how much current initially flows based (mainly) on its inductance, capacitance and resistance. c is the speed of light 299,792,458 m⋅s −1,. The first plot shows the Impedance in Cartesian form, the second the absolute Value of Impedance and the third the Phase. Transmission lines Transmission line concepts and an online transmission line calculator by Owen Duffy, VK1OD. . It has an inner 7-stranded bare copper. CALCULATION OF Kr WHEN LENGTH IS APPROACHING OR EXCEEDING λ/2. As can be seen from the calculation results, the impedance remains at 50 Ohms with the cable fitted. The fabrication procedure for slot lines is the same as that for microstrip lines. Executive Summary. In the case of an ideal microstrip, where one of the conductors is infinitely. The inductance of a coax cable can be. Nom. 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. Example. Where: Z = the 1/4 wave coax line impedance, Zr = terminating resistive impedance (antenna) ( input resistive impedance as read on the RF impedance bridge at the end of the 1/2 wave line). Coax Impedance Calculation. 2. The epsilon_r of the cable isolation is 2 so total electric permittivity is 2 * 8. 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. 0815 λ (wavelength, lambda or Wave) The physical length L is 0. 04 feet = (246 x . Return loss (RL) is the ratio of the reflected power to the incident power, in decibels (dB). 85419 x 10. 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. where. 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. ε 0 = 8. For practical applications, please visit manufacturers’ websites and consult their data. For coaxial cables the characteristic impedance will be typically between 20 and 150 ohms. Brown part is the copper itself. 0815. Zs = Ze + (R1 + R2) Z s = Z e + (R1 + R2) Where Zs is the line-earth loop impedance. Eq 1 assumes that the reference impedance of the mea-suring instrument equals the com-plex characteristic impedance of the cable. The cable length is 3. . D is the inside diameter of the coax cable shield,. 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. . This is a required field. The following calculator computes the resistance, inductance, inductive reactance, capacitance, charging current, and surge impedance for medium voltage shielded power cables. The attenuation per unit length (basic loss) in a coaxial cable (dB/m) at radio frequencies can be approximately determined by the formula: k2 — factor, characterizing the loss in the dielectric of the internal insulation, proportional to the frequency. 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. D is the inside diameter of the coax cable shield,. Coax Impedance Calculator – EEWeb Community. 39 ohm line, cut for the frequency of operation (between the antenna and your cable) you'd end up with a perfect match. The entry unit of frequency can be modified, the output wavelength is calculated in meters. The velocity factor of a foam insulated cable depends on the production technology and varies from manufacturer to manufacturer. 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. 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. CRA Calculator. 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…. Same-day shipping if you order in the next hours!. 5). Sep 3, 2018. Coaxial cable combiners with ferrite cores are often used to combine the output powers of power amplifiers intended for wideband applica-tions. . Interestingly, a piece of transmission line can be used as a transformer. 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. Bend Radius is the minimum radius that a Radio Frequency (RF) coaxial cable can be bent to without damage. 854187817620. 4w to achieve 100w at the aerial. A note regarding the impedance transformation being classified as 1:4 rather than 4:1. 035 in), outer conductor diameter 3. 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. Outer Shield DCR Nom. It is around 30cm cable. What we call attenuation or loss is a decrease in the power of a signal or signals, usually measured in decibels. D (mm) Er d (mm) Impedance Notes: Optimal D/d ratio for breakdown voltage is 2. It is also relatively straightforward to calculate the inductance per. The example structure is a standard RG6 coaxial cable. Surge Impedance Calculation 35 100 0. Fairview Microwave's Coaxial Cable Impedance Calculator allows you to enter the Outer Diameter Dielectric width, Inner conductor Diameter width and either the Dielectric. RF Calculators. . Also known as RG-400 or RG400 cable, this premium coaxial cable is designed to meet the demanding requirements of high-frequency applications. Ns = Number of turns in Secondary coil. This ratio represented in dB is called as Return Loss. Good enough, because the calculation for 15 m of typical coax with 6. It is horrible! At the compromise value of 50 ohms, the power has improved a little. Now we can add the resistances from the inner and outer shell since they're in series. More. The waveguide width determines the lower cutoff frequency and is equal (ideally) to ½ wavelength of the lower 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. This formula is from the following reference. 405 inch. d is the diameter of the inner conductor of the coax cable; units of D and d must be the same,. While commonly constructed using printed circuit boards, this structure can also be built using other materials as long as there is a conductor separated from. ) using the high and low frequency approximations. in both cases, the speed and the Characteristic Impedance depend upon logarithms of the ratio of two distances in the cross. RF calculations and conversions include metric-standard, link. FL connector I have a 2" microstrip transmission line to the RF input of my GPS receiver. The parameter scale of the X and Y axis of the oscil-loscope screen are 20 ns/div and 200 mV/div. RF calculations and RF conversions include metric-standard, link budget, coax cable, power, attenuation, frequency and many more. The functionality of a coax loss calculator is straightforward, yet it provides critical information for ensuring optimal performance. 035 in), outer conductor diameter 3. If there is an insulator around the wire then this. ) using the high and low frequency approximations above for Rc and Lc. - 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. It is widely used for data communications and telecommunications applications in structured cabling systems. 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. 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. Equation. The capacitance value varies with the spacing of the conductors, the dielectric constant, and the. The TV Broadcasting Industry chose to use the 75 Ohm standard for coaxial cable in SDI video. Print - Advertisement - This calculator. **Note: Like our stripline impedance calculator, all of our RF calculators allow SI prefix input. Of course - our simple dipole calculator to assess the length of the device. 1: 300 Ω 300 Ω twin-lead. 1 7. A rectangular waveguide is commonly used for the transport of radio frequency signals. A series of RF calculators for radio frequency engineers. The 50 ohm characteristic impedance of my coax is only "characteristic" if it's terminated with $ 50 + 0j$ load. Although widely applied to. Grover, Dover Publications, 2004 . 302 times larger than the diameter of the inside conductor. As the name suggests, the length of this transmission line if fixed at a quarter of the wavelength (λ/4). The relative permittivity of the medium ϵr ≈ 1 ϵ r ≈ 1 for the. The following formula is used to calculate the impedance of a coaxial cable. It supports both balanced and unbalanced lines. 11. 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. 5 to 21. Sensor Fusion Comes to RetailNext: Interview with Alexei Agretchev . 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. f 2 = Upper operational frequency in GHz. Two come to mind: RG58 has a Vf of 0. 65. 66 kW Black TPE Jacket (. Coaxial cable specifications often include the velocity factor, which is typically between 60% and 90% (1). 2. 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. d is the diameter of the inner conductor of the coax cable; units of D and d must be the same,. LOGIN. 2. 5. The advantage of using coax for a 1:1 choke-balun is the constant Z0 of 50 ohms. frequency: f = DC - 100Hz f = 1kHz f = 100kHz Zo: Zo = R G Zo = L C Zo = R ωC Zo. 336: 360 = 0. Maximum Operating Voltage (Vrms) 4000. There are three main classes of characteristic impedance for coaxial cables : 50 Ω, 75 Ω and 95 Ω. Now it's time to look at the generic formula for α D: We plug in Gprime and Z 0 into this and get attenuation in Nepers /meter: If. ε0 = permittivity of free space = 8. where. where. Then use the LCR Meter and measure the inductance at the open end of the cable. I leave it to other sources to provide the complex equations needed to precisely model coaxial cables. 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. It has an inner 7-stranded bare copper. 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. on the calculator devide 29. The formula for the. Coax Inductance Description. Coaxial Cable Calculator. 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. Enter the Outer Diameter (D), Outer Diameter (d), and Permittivity. Characteristic impedance = R + jωL G + jωC− −−−−−−−√ R + j ω L G + j ω C. Triax Cable. Wi-Fi 7 will enable consumer, enterprise, Industry 4. Some systems use 75 Ω; this latter value is more appropriate for high-speed digital signals. e. Cable Capacitance (pF/ft) 23. There are more than 75 different RF Coaxial Connectors that can be used in wireless systems. ) Published under the terms and conditions of the. RG178B/U part number from Pasternack is a RG178 coax cable that is flexible. ε = dielectric constant = ε0 * εr. From my measurement I got data as below: From that table, we can see that there is significant impedance of the cable. Coax Impedance Calculator. 854187817620. 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. The most commonly used twisted pair cable impedance is 100 ohms. 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). Frequency to Wavelength Calculator. Get. UsefulFormulas. 3. 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. The Pi attenuator consists of one series resistor and. 336 by 360, = 0. It can for instance vary from the standard 50 ohm. 5 ohms, so the coax cable's Zo should be 25 ohms (i. 20. It is the output connection that determines whether a choke is a balun or unun. . The following formula is used to calculate the cut-off frequency, lower & higher operational frequency of the rectangular waveguide. The length of the cable makes no difference whatsoever in regard to the characteristic impedance. Suitable for higher power (~1800 watts) at HF. f 1 = Lower operational frequency in GHz.