0 Fault Resolution, Display Resolution, and Max Distance. A scientific calculator with a log function helps to solve the equation. However, just remember better return loss is indicated by bigger return loss numbers, and that is better for your antenna. Calculating coax loses due to dielectric loss tangent. Fig. The Power Sensor method is the configuration for measuring cable loss and requires that both ends of the cable be accessible. This is an easy measurement to make and it's a good idea to do this measurement when installing new cables. How to measure a coax lines resonance frequency Any quarter lambda of coax line acts as a resonate circuit. Thus, the one-way attenuation for the cable is α(dB/m) = 1 l(m) 10 loga/b(dB/m) (C.15) Thus, the attenuation of a cable of length l and characteristic impedance Z 0 is obtained by plotting the input impedance Z i in a Smith chart nor-malized to Z 0. VSWR readings can easily be converted into return loss in dB using this online resource at Telestrian. It is then connected to the far end of the feeder (perhaps up a tower) and the SWR is measured in the shack. This effect can be used to measure the loss of a cable. A good power meter will measure power to an absolute accuracy of 5 to 10% but will measure a power difference more accurately. 2. This needs to go between the transmitter and the power meter. Decibels (dB) determine the relationship in signal strength between two sources. Make a note of the readings and then you can check your cable every year or two to see if its loss remains constant. Measure the full-strength signal with an appropriate meter; to measure radio signals, for example, a radio signal power meter indicates the strength of radio waves at a particular location in units of milliwatts, microwatts or similar units. The difference is twice the cable loss so the cable loss is 0.3 dB. In this instance, you measure the attenuated signal at the output end of the long cable. With speed of light as c = 299792458 m/s I figure as velocity factor v = 0.77 at 14 MHz. In a worst case scenario, all of the measurement errors would be at their extremes in the same direction and add constructively. There are several ways to do measure cable loss. Often times this is a know measurement from the manufactor. Three or four layers has better immunity from interference and is more sturdy and durable, but is a little more expensive and less flexible than dual shield. You will need to know the velocity factor of the coax cable being measured. This increase in loss can arise as a result of disruption to the braid or screen, and as a result of changes to the dielectric. Repeat the test and check the transmitter output indicated. In our case we used a, Professional engineers seldom use VSWR as a measurement as return loss is more useful. The steps of this method are given below: First, you have to locate the area where the coax cable is distributed. You can use This arrangement minimizes coupling between the coils. Insertion loss measures the energy absorbed by the transmission line in the direction of the signal path in dB/meter or dB/feet. The BOXA-TEST has a 5:1 load and this was used to measure the cable loss. There are several possible problems: poor connections, physical damage to the cable, degraded performance due to water ingress. ... Return Loss in dB) INTSAT 220 Elite. These rather special conditions give a theoretical infinite VSWR. This mode was designed to measure 50 ohm cables, but measures differential mode loss in many types of 50 ohm transmission line transformers and choke baluns, as well as loss in 50 ohm attenuator pads. The nominal characteristic impedance is 50 Ω, and the electrical length of this cable segment is 0.385 wavelength. Choice of the mismatched load is important if good results are to be achieved. The Belden catalog shows this to be 1.4 dB/100 ft, so the matched loss of our cable segment should measure 1.4/4 = 0.35 dB. In this mode, the MFJ-259B LCD indicates frequency and coax loss in dB. Transmission line losses are dependent on cable type, operating frequency and the length of the cable run. The calculator now shows that for the length of coax the loss is 0.35dB. Use the formula for finding the decibels as a ratio of the power of the signals to calculate the exact value of the loss. to measure the matched loss of the cable at 10 MHz. Decibels (dB) determine the relationship in signal strength between two sources. A mismatch will reflect (return) some power. this method of measuring loss is perfectly okay in the shack but is less useful if the cable run is in-situ with the two ends some distance apart. Return loss is the power loss due to a signal travelling to the end of a line and being reflected back. If you are doing this, also make a note of how you made the measurement - especially what equipment you used. Professional engineers seldom use VSWR as a measurement as return loss is more useful. Coaxial cable connected to the antenna provide a stronger signal. The ferrites are held in place by foam tape. I transmitted a signal with 12dBm power and I connected through the coaxial cable to the oscilloscope. Typically, for a device or a system, return-loss is measured at the input or at the output.