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(meteorobs) Further Clarification of ELF, VLF, LF, etc.



My apologies if my words below appear to be going way off-topic; but I
thought that perhaps some on the list might want a bit more clarification
of frequency bands as regards the terms actually used.

At 07:51 AM 1999-07-02 -1000, Jim Bedient wrote:
>Here's the official titles: 
>
>Band   Frequency    Wavelength
>
>ELF     <3 Khz        >100 km
>VLF   3 - 30 kHz  100 km - 10 km  
>LF   30 -300 kHz   10 km - 1 km 
>MF  0.3 - 3 MHz   1000 m - 100 m    
>HF    3 - 30 MHz   100 m - 10 m  
>VHF  30 - 300 MHz   10 m - 1 m 
>UHF 0.3 - 3 GHz      1 m - 10 cm 
>SHF   3 - 30 GHz   10 cm - 1 cm
>EHF  30 - 300 GHz   1 cm - 1 mm

Actually, when electronics-types want to get more specific about the ELF
and VLF frequencies, we usually separate them further by using the
following terms:

0 Hertz (Hz): DC (much of the time, we "RF" types also refer to "digital"
signals as "DC" even if the digital signals are actually very, very fast
and could more-correctly be called "RF"!)

1 to 30 Hz: subaudible (below the usual human hearing frequency range)

30 Hz to 300 Hz: also subaudible (below the usual human speech frequency
range, but most humans can easily hear frequencies within this frequency
range)

300-3000 Hz: audio (because this is the usual human speech frequency range)

3 kHz-30 kHz: ultrasound (above usual human hearing range; this is the
range where your dog perks up his ears when you blow his whistle!)

From 30 kHz to 300 MHz, we use the terms that Jim listed in the table
above. But at 300 MHz, many of us consider the UHF band to extend from 300
MHz to only 1000 MHz (1 GHz); then, we usually refer to anything between
about 1 GHz and 18 GHz as just "microwaves". Anything from about 18 GHz  on
up to several hundred GHz is normally referred to as the "millimeter" wave
bands. The designators SHF and EHF aren't used too much in actual practice.
And in actual practice, we don't often exactly-define a frequency to be
"ultrasound" or "audible" when it sits right on the edge of both: instead,
depending upon the context in which we are talking, we might say EITHER
ultrasound OR audible!

In the "professional" and military world, there are letter designators for
the various bands from 30 MHz on up through the millimeter wave bands; for
example:
1 to 2 GHz: L band
2 to 4 GHz: S band
4 to 8 GHz: C band
8 to 12 or 12.4 GHz: X band
12 or 12.4 to 18 GHz: Ku band
Then there are numerous millimeter wave band letter designators, such as K,
Ka, W, etc., which are used to define the many millimeter-wave bands from
18 GHz up to 300 GHz. Anything above 300 GHz is usually considered
"lightwave".

So, if you think back to your old satellite dish receiver and remember that
it was called "C band", you can see that it apparently operated somewhere
between 4 and 8 GHz; actually, it was somewhere around 6 GHz. And perhaps
you had a later satellite dish system called "Ku band"; it operated in the
13 GHz band. There were also other satellite systems about 20 years ago
that used frequencies in the 3.7 GHz region which were often referred to as
"C-band" because 3.7 GHz is close enough to the 4 to 8 GHz region; but in
reality, those systems should have, and sometimes were, been referred to as
"S-band" systems.

More detailed info on this whole topic of what's a "frequency",
"wavelength" and "band" is available in numerous places on the web, I'm sure.

As one more aside: there are certain narrowband segments of the VHF, UHF,
microwave and millimeter-wave bands which are idea for radio-astronomy
because the resonant frequency of certain elements, such as hydrogen,
helium and oxygen occurs within those bands. Radio-astronomy actually
"listens" for signals from galaxies that are generated by large clouds of
those elements on specific frequencies. In radio meteor work, we have no
such "resonant" frequencies for which we can listen, other than the
electrophonic sounds of this thread. Instead, we listen for other
radio-frequency signals which are reflected from meteors burning up in the
atmosphere. Since meteors don't generate RF "sounds" by theirselves, a
transmitter is necessary, whose reflected signal is then detected.

Clear skies (except here in New England: we NEED the rain!!),
SteveH
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