Subj : Re: Getting Started
To   : Warpslide
From : Vk3jed
Date : Mon Aug 17 2020 20:11:00

-=> On 08-16-20 21:05, Warpslide wrote to alterego <=-

 Wa> It does seem like a pretty scary mountain.  Right now I'm trying to

Some of us have scaled that mountain and are here to be your Sherpa.  We know
the lie of the land and the pitfalls. :)

 Wa> figure out why it's called the 2 metre band & the 70cm band, it doesn't
 Wa> seem to be because of antenna lengths...


Actually, it's the wavelength.  So a bit of theory to get you going.

Radio waves travel at the speed of light - 300,000,000 metres/second (it's
actually easier to use metric - sorry Americans ;) ).

Radio waves are a combination of oscillating electric and magnetic fields that
cycle periodically from 0 to maximum + value, back to 0, then maximum and
finally back up to 0.  This is called a cycle.  The frequency is the number of
these cycles per seconf, which has a special name - Hertz (1 Hz = 1
cycle/secon).

The wavelength is how far the signal travels in one cycle.  In other words,
wavelength (L) = 300,000,000/frequency(f)

The "2 metre" band extends from 144 to 148 MHz (M means 1 million).  Using the
formula above:

L = 300,000,000/144,000,000.  Now because there's a lot of zeros, we can
simplyfy this formula:

L = 300/f(MHz).

L = 300/144 = 2.08m  (at the lower edge of the band).

And at the upper edge:

L = 300/148 = 2.03m

Pretty close to 2 metres, hence that's where the name from!.

Similarly for 70cm.  That band runs from 420 or 430 to 450 MHz (depending where
you are).  Let's use 440 MHz as a sample frequency.

L = 300/440 = 0.68m or 68cm.  That's close enough to 70cm. :)

Hope that helps! :)


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