# RF basics

Discussion in 'Radio and Wireless' started by Rajinder, Nov 6, 2019.

1. ### Rajinder

531
9
Jan 30, 2016
Hi,
I am new to rf design. I have been given a project that uses a 868MHz rf chip.
Are there any good sites for beginners with minimum maths?
Also what is carrier frequency, frequency deviation, preamble. Lastly, how does crystal selection select the frequency i.e..868MHz?

2. ### duke37

5,364
772
Jan 9, 2011
Try to find some basic books on radio frequency principles.
A steady RF signal, the carrier frequency, conveys no information other than the sender has money to spare.
The carrier can be modulated by altering the ampltude of the carrier. This is used on long wave, medium wave and short wave.
The carrier can be modulated by changing its frequency, This is used for VHF/FM.
Above this, digital modulation is used which is a mixture of modulation tecniques.
The frequency deviation is the amount of frequency wiggle.

Crystals are single crystals of quartz which vibrate at a frequency determined by their size. They can be used to generate a frequeny or to select a portion of a complex signal. 868MHz is too high for a crystal so if this frequency is needed, A frequency of one sixteenth of this may be generated and then multiplied by sixteen to get 868MHz

3. ### Rajinder

531
9
Jan 30, 2016
Thanks for the help.
I have a couple of more questions please:
1. Why are standing waves undesirable?
2. How do you design a PCB antenna for 50R?

4. ### Harald KappModeratorModerator

11,662
2,697
Nov 17, 2011
They aren't always, read the discussion here.
There are many ways to do this.

5. ### duke37

5,364
772
Jan 9, 2011
Standing waves will dissipate energy.
Standing waves will present a different impedance depending on the position of the wave. Altering a cable length may change or even stop the equipment working.

6. ### bertusModerator

2,029
763
Nov 8, 2019
Hello,

This is a copy of a post I made at AllAboutCircuits.
The US Navy Electricity and Electronics Training series.
https://the-eye.eu/public/murdercub...US_Navy_Electricity_and_Electronics_Training/
There is also the US Navy Electronics Technician series:
https://the-eye.eu/public/murdercube.com/Electronics/Electronics/US Navy Electronics Technician/
And the US Navy Information Systems Tech Training:
https://the-eye.eu/public/murdercub...cs/US_Navy_Information_Systems_Tech_Training/

Bertus

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7. ### bertusModerator

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Nov 8, 2019
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8. ### Rajinder

531
9
Jan 30, 2016
Thanks for the help.