EIRP

link budget

The link budget is a calculation involving the gain and loss factors associated with the antennas, transmitters, transmission lines and propagation environment, to determine the maximum distance at which a transmitter and receiver can successfully operate

Micro Wave

Micro Wave Communication:

A communication system that utilizes the radio frequency band spanning 2 to 60 GHz

Radio frequency

Radio frequency (RF) is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals. RF usually refers to electrical rather than mechanical oscillations

Understand Latitude and Longitude

Latitude lines are imaginary lines on the earth's surface. They run east and west around the globe and tell you your distance north or south of the Equator.

Think of latitude like the rungs of a ladder (ladder sounds a lot like latitude). Latitude lines run east and west, but they tell how far up (north) you can go or how far down (south) you can go.

Longitude lines are imaginary lines on the earth's surface that run from pole to pole around the globe and tell you your distance east or west from the Prime Meridian.

When you think of longitude, think of long, tall telephone poles (because longitude lines run from pole to pole). Longitude lines run north and south, but they tell how far east you can go or how far west you can go. 

In the field of mathematics, circles are measured in degrees. There are 360 degrees in a circle. Since the earth is basically circular, it was decided to measure latitude and longitude in degrees also.

The first latitude line was the Equator (equally distant between the north and south poles). It is the largest of all latitude lines. All other latitude lines are measured in degrees north or south of the Equator. There are a maximum of 90 degrees of latitude to the north or the south of the Equator.

The first longitude line was the Prime Meridian. Any meridian could have been chosen as the Prime Meridian because they are all exactly the same. The Prime Meridian was selected by international agreement at the International Meridian Conference called by President Chester Arthur in October of 1884. Representatives from 25 nations met in Washington, D.C. All other longitude lines are measured in degrees east or west of the Prime Meridian. There are a maximum of 180 degrees on longitude to the east or the west of the Prime Meridian.

It is approximately 70 miles between two latitude lines. For more accuracy in location, degrees can be divided into smaller parts. One degree can be divided into 60 minutes (') and one minute can be divided into 60 seconds ("). We will not use minutes or seconds of latitude and longitude in this course.

SNR Vs Fade Margin

A radio receiver tuned to a particular frequency channel will receive whatever is transmitted on that channel plus any receive whatever is transmitted on that channel plus any background noise. If the strength of a transmission is significantly stronger than the noise, then the receiver is able to effectively ignore the noise – the transmission (normally called the “signal”) has a good-signal-to-noise ratio. If the signal is of similar strength as the background noise, the receiver will not be able to discriminate the signal from the noise – this is a poor-signal-to-noise ration or SNR.

When a data message is modulated onto a RF signal, the ability to demodulate the message depends on the background noise. As a signal gets closer to the noise level, the demodulated data has more errors, as the noise makes it harder to determine if a demodulated bit of data is a 1 or 0. These errors are called “bit-errors”, and the error rate (errors per total bits) is the bit-error-ratio or “BER”.

The sensitivity of a radio receiver is the lowest RF signal that it can detect reliably – generally quoted at a specified BER. The “data sensitivity” is the lowest RF signal that the receiver can demodulate a data message with very low level of external noise.

Data sensitivity is normally expressed at a particular BER.

A transmitted signal can vary in strength. During rain or fog, the radio signal is attenuated (decreased) by the denser air. In a thunder storm, the transmitted signal will decrease, and the noise level will increase – this could turn a low BER into a high BER.

A SNR of 5dB means that the average signal measurement is 5dB stronger than the average noise level. Unfortunately radio noise is often much less than receiver sensitivity, so SNR is not particularly relevant.

A more common term that is relevant is the “Fade-Margin” – how much can a radio signal decrease (or “fade”) before the receiver can no longer demodulate data. Fade margin is the difference between the transmitted signal and noise or receiver data sensitivitiy, whichever is greater. It gives a measurement on how much the signal needs to "fade" before it becomes unreliable. The fade margin should be measured on a fine day.

For modern industrial wireless products, a fade margin of 10dB is adequate - this gives enough margin for loss of signal or increased noise during poor weather of high solar activity. An installation will work reliably with a lower fade margin, however not all of the time.