Wireless: More Ch 4

Jerry's been yakkin quite a bit.  Showed us some different types of antennas in class.

Reviewed pictures/graphs showing filters and what is blocked. 

Wavelength (meters)( λ) = 300/F MHz - remember this, it'll be on the test and used.  

Extra Credit ops-              Ham Fest in Severville 9/29 50points

                                        LOPSA meeting 10/2 30points

Digressions links, unsure where they fit in, but looks important.
Dipole Antennas

Cell Phone Booster

Notes from class (such as it is) after the break.

**Look for the links, I'm going to try to start adding in the websites that Jerry is pulling up that actually relate to the subject.**


Antenna Sizes and Shapes

(continued)

• Patch antennas

– Emit an RF energy beam that is horizontally wide but vertically taller than that of a yagi antenna

– Considered a semi-directional antenna

– Often used to send RF energy down a long corridor

– Some are designed for installation on building walls

• To send an RF signal in one direction away from the structure

– One common application for patch antennas is in cellular telephony

Signal Strength and Direction

• Distance between the transmitter and receiver

– Determines the strength of the signal

• Transmitters produce a finite amount of RF energy

– For most applications, active antennas can be extremely expensive

• Omnidirectional antenna divides strength of signal in a 360-degree circle around the antenna

• Free space loss

– RF waves tend to spread away from the source of the signal (the antenna)

He went over antenna patterns at this point, kinda skipping ahead, but he mentioned using this stuff for the test.  Yay.  

How Antennas Work

• Understanding antennas requires in-depth knowledge of physics, mathematics, and electronics

Wavelength

• Length of a single RF sine wave

• Determines the size of an antenna

• Full-wave antenna

– Antenna transmits and receives a signal most efficiently at a specific frequency

• When it is as long as the full length of the wave

– In most cases, this is not practical

• For practical reasons, antennas are more commonly:

– Half-wave antennas, quarter-wave antennas, or eighth-wave antennas
Constructing a 5/8 Wavelength Vertical Antenna


Antenna Performance
• Antenna performance
– A measure of how efficiently an antenna can radiate an RF signal
• Design, installation, size, and type of antenna can affect its performance


Radiation Patterns
• Antenna pattern
– Graphic developed by measuring the signal radiating from the antenna
– Indicates the direction, width, and shape of the RF signal beam coming from the antenna
• Antennas emit signals in two dimensions
– Horizontally and vertically
• Antenna specifications almost always state the vertical beam angle that a particular antenna emits

(add pictures here)

Antenna Polarization
• Antenna polarization
– Orientation of the wave leaving the antenna
• Vertical polarization
– Sine waves travel up and down when leaving antenna
• Horizontal polarization
– Sine waves travel from side to side on a horizontal plane
• Most efficient signal transmission and reception is experienced when both antennas are equally polarized


**Next time:  Will be starting on Antenna Dimensions**