One technique to reduce the reflected signal from the input or output of any device is to place an attenuator before or after the device . The attenuator reduces the reflected signal two times the value of the attenuation, while the transmitted signal receives the nominal attenuation value.
How do you solve for VSWR?
The VSWR definition states that the VSWR is equal to the maximum voltage on the line divided by the minimum voltage . The voltage fluctuations come about as a result of the voltage components from the forward power and the reflected power summing together.
What affects VSWR?
Although the term VSWR is normally used, both the voltage and current standing waves can cause issues . ... This means that a poor match between the feeder and antenna will result in a high SWR which causes the output to be reduced and hence a significant loss in transmitted power.
Why VSWR should be less than 2?
The range of values for VSWR is from 1 to ∞ . A VSWR value under 2 is considered suitable for most antenna applications . The antenna can be described as having a “Good Match”. So when someone says that the antenna is poorly matched, very often it means that the VSWR value exceeds 2 for a frequency of interest.
Is lower VSWR better?
The VSWR is always a real and positive number for antennas. The smaller the VSWR is, the better the antenna is matched to the transmission line and the more power is delivered to the antenna.
What can cause high VSWR?
High VSWR is often due to testing with very broadband, high-power, and poorly matched loads . It is best to avoid this situation as much as possible, however, sometimes this condition is unavoidable as testing must still be done.
Is VSWR dependent on frequency?
The magnitude of those losses are dependent on the type of transmission line, and its length. They always increase with frequency . For example, a certain antenna used well away from its resonant frequency may have an SWR of 6:1.
What is bad VSWR?
Poor VSWR/ Return . Loss can damage transmitters, reduce the coverage area, and lower data rates . For instance, a return loss of 10 dB means that 10% of the total power is not radiated and (if the transmitter is still running) that the coverage area is 10% smaller than the transmitter power settings might imply.
What is a good VSWR ratio?
A VSWR of less than 1.5:1 is ideal , a VSWR of 2:1 is considered to be marginally acceptable in low power applications where power loss is more critical, although a VSWR as high as 6:1 may still be usable with the right equipment.
Can VSWR be negative?
Summary. It is possible to have ρ>1 . VSWR calculated from ρ is singular where ρ=1, and will yield negative VSWR where ρ>1.
Is high return loss Good?
The measurement of the amount of light reflected back toward the source is called return loss, and it is expressed in decibels (dB). This measurement parameter is always a positive number, and a high return loss is a favorable measurement parameter that generally correlates to a low insertion loss.
Is S11 return loss?
In practice, the most commonly quoted parameter in regards to antennas is S11. S11 represents how much power is reflected from the antenna, and hence is known as the reflection coefficient (sometimes written as gamma: or return loss. ... This accepted power is either radiated or absorbed as losses within the antenna.
What is a good S11 value?
This is the origin of the rule of thumb, that the maximum acceptable value of S11 for an interconnect structure is about -13 dB : If S11 is smaller than -13 dB, we will not see the impact from these reflections on the transmitted signal. However, if S11 is larger than -13 dB, then expect to see some impact on S21.
Why is VSWR bad?
VSWR not only affects the efficient transmission of power but can have a severe effect on the transmitted audio . As a result of a mismatch, there is a portion of the RF signal that is reflected back towards the transmitter. When this reflected signal reaches the transmitter, it is reflected back towards the load.
What if my SWR is too high?
For instance a SWR too high ( over 3:1 ) all over the band can be an indication of a bad part or junction, poor ground or poor location. An SWR too low over the whole band (1:1 for all 40 channels) can indicate a low efficiency antenna or lossy component. Safe operation of your CB should be with an SWR of 2:1 or less.
Where is VSWR used?
It is often used in association with meters used to detect the standing wave ratio . Both current and voltage rise and fall by the same proportion for a given mismatch. VSWR: The VSWR or voltage standing wave ratio applies specifically to the voltage standing waves that are set up on a feeder or transmission line.
