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How long is a wavelength ? Larry ;)


stacysound

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Hey Larry - How long is a wavelength for a block 21 system?

 

In your white papers on Comparing Diversity Reception Techniques.

 

"The Audio Switching design illustrated here follows the logic that if one antenna has a multipath problem, the other antenna is not likely to have a problem at the same time. This requires that the antennas be separated by at least a half wavelength of the operating frequency (preferably even more)."

 

How would one figure that out? Looking forward to another outstanding lesson in RF...

 

http://www.lectrosonics.com/Support/Wireless/comparing-diversity-reception-techniques.html

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wavelength = velocity divided by frequency.

 

The velocity of light (RF) is 186,000 miles per second (Stacy is in Texas) or within a few percent of a billion feet per second. So if you like doing things in your head the wavelength of a 1 GHz signal (1000 MHz) is very close to one foot. Then 300 MHz would be 3.3 times longer or 3.3 feet. Then 500 MHz is a frequency half of 1000 MHz or twice as long a wavelength or 2 feet. So just do 1000/MHz or 1000 divided by MHz. Just remember lower frequencies are longer as a reality check on doing inverses in your head. For our frequencies, a wavelength is always greater than a single foot.

 

Remember this is a full wavelength. A half wavelength at 1000 MHz is a half foot. At 500 MHz it is one half of 1000/500 or one foot.  

 

For users not in the anti-metric USA, use 300 MHz as a 1 meter wavelength and go from there. Then 600 MHz is half a meter and so forth.

 

All this is in vacuum or air.  RF is slower in coax so wavelengths are about  60% to 80% of open air, i.e., 1 GHz is 0.7 feet long.

Best Regards,
Larry Fisher
Lectrosonics

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