Category Archives: Radio

What is slew rate?

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The slew rate is the maximum rate at which the output voltage can change. This is especially relevant when amplifying sound waves using an op amp.

slew rate is the maximum change in voltage that can be achieved per second. The unit typically used is V/μs.

For example, a slew rate of 0.5 V/μs would be calculated using this formula:

2 x π x f x V = Slew rate (V/s)

So in this case you’d first convert 0.5 V/μs to 500 000 V/s.

Then to find the maximum voltage for a 1KHz signal you’d use this formula:

500 000/ (2 x π x 1000) = 15.71 volts.

This also means that a 1KHz signal can have an amplitude of 15.71 volts.

To put this into context, the human range of hearing is 20Hz to 20KHz. Therefore when amplifying audible sound you could have an amplitude of up to 3.98volts with this slew rate. Meaning that this op amp would be suitable for a 20KHz signal with an amplitude of 3.98 volts or less.

However when amplifying a 40KHz signal (a typical ultrasonic frequency), you’d only be able to achieve an amplitude of 1.989 volts. meaning that this op amp would only be suitable for 40KHz frequencies with an amplitude below 1.989 volts.

 

 

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Wavelength & Frequency calculations

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This equation allows you to calculate wavelength from frequency, and frequency from wavelength.

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freq

In this equation:

lambda

(lambda) represents wavelength (in metres).

 c         represents the velocity of light (which is approximately 3.00×108 m/s).

 f         represents frequency (in hertz).

 

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Wavelength is the distance between two peeks of the signal.

frequency is the number of oscillations in one second.

 

Cellular/mobile phones and networks

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Cellular refers to the structure of the network that phone uses. With cellular phone being the North American term for a mobile phone.

Cellular networks are broken up into cells, these cells are defined by base stations and the distance to which they propagate coverage. In them, radio waves are used instead of physical connections to transmit incoming and outgoing signals. Each base station is allocated a band within the Ultra High Frequency (UHF) portion of the radio frequency spectrum. Adjacent cells must not use the same transmission frequencies, as their areas of propagation overlap, and would cause interference. However, Non-adjacent cells are far enough away for their to be no overlap and frequency re-use is feasible.

Each base station has a limited number of uplink and downlink frequencies, to allocate to phones connecting to the network (making a call). However, because only a comparatively small amount of people are ever connected to a call at any one time, this limit is rarely every reached. An example of when an instance of this has occurred would 7/7 London Bombings, where a large part of the O2 network in London was shut down to everyone (excluding members of emergency services), so as to prevent the system from overloading and crashing calls.

For the 2012 London Olympics, pre-emptive measures were taken to ensure that the network could accommodate the increased number of uses that would be using it. Additional base stations were set-up temporarily around the area at which the Olympic grounds were.