Hi Pete,
Yes, there are several ways to represent frequencies:
1) Absolute units of Hz. For example 60 Hz, or 32.768 kHz, or 3.579545 MHz, or
9.192631770 GHz. Note some modern texts use s⁻¹ (1/s or s-1) instead of Hz or
Hertz. Or, you can always show your age and use cps (cycles per second).
2) Arithmetic error from some nominal value. For example 3 Hz above 1 MHz, or
17 Hz below 40 GHz. Your frequency is 10 MHz plus 0.005 Hz, or 5 mHz
(milli-Hertz) too high.
3) Relative, or geometric error. For example, 60 Hz with 1% error, or 32.768
kHz with -10 ppm error, or 10 MHz with +0.5 ppb error. Note these errors values
are unit-less. The general form is F = F0 x (1 + E) where F0 is the nominal
frequency and E is the relative error.
In your example 10.5 MHz is 10 MHz x (1 + 0.05). Note carefully
the decimal point; 10.000 000 005 MHz is 10 MHz x (1.000 000 000 5) so E = 0.5
ppb.
In most cases one need only specify the relative error since F0 is either
implied or irrelevant. For example, if you multiplied your oscillator to 1 GHz
or divided it down to 1 PPS the relative frequency error would remain 0.5 ppb.
3½) When using percents, ppb (parts per million), or ppb (parts per billion) is
not convenient, you can always use scientific notation. So instead of 0.5 ppb
(or 500 ppt) it's more common to see 5e-10. This is much more informative than
saying 10.5MHz and making the poor reader count each of the zeros.
In summary,
10.5 MHz
5 mHz above 10 MHz
+0.5 ppb error
+5e-10
/tvb
- Original Message -
From: g4...@btopenworld.com
To: time-nuts@febo.com
Sent: Monday, July 23, 2012 1:50 PM
Subject: [time-nuts] Shorthand
Is there a commonly accepted shorthand for a frequency, say 10MHz, generated
at the maximum accuracy of the lab generating it?
ie instead of writing 10.5MHz?
Pete
G4GJL
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