RadioBanter - View Single Post

January 15th 05, 06:11 AM

In article , (Jeffrey Herman)
writes:

Len Over 21 wrote:

...
NTSC color subcarrier is exactly 3.579545454545454545454545....
MHz. :-)

With the correct integer divisor and correct integer multiplier, it
comes out to 500 KHz fairly exact.

"Fairly exact"? What's that mean?

Heh heh heh...as "exact" as you can calibrate it to some
accepted standard of frequency.

Hint: It isn't W1AW. :-)

Any repeating decimal can be written as a rational number, a/b.
That particular decimal above is exactly 315/88: Set that decimal
equal to N. Since two digits repeat, multiply both sides of the
equation by 10^2; we now have: 100N = 357.9545454... Next, subtract
the first equation from this second one; all the repeating 54 pairs
cancel due to this subtraction, giving us 99N = 354.375, a
terminating decimal. To eliminate the decimal point, multiply
both sides by 1000: 99000N = 354375. Now divide both sides by
99000: N = 354375/99000. This fraction simplifies to N = 315/88.
Hence, that original repeating decimal, 3.579545454... is exactly
equal to 315/88.

Note that if you have a repeating decimal with 3 repeating digits,
you'd multiple both sides of the initial equation by 10^3, etc.

Suggestion: Why don't you expound over in the math newsgroup?

On the other hand, how would you get a "fairly exact" color burst
oscillator on-frequency and keep it that way?

You have to understand the ELECTRONICS part in order to do
that. That ties into "RADIO." Get the connection? It's peachy
keen to know all about continuing fractions and stuff but let's
look at the number "88." Factoring it out results in an 11.
If you are generating, say a color burst frequency, that 11
would be in the numerator, not the denominator. That implies
a MULTIPLIER of 11. [ever have to build a frequency
multiplier?] A multiplication of 11 is a bit hard to do even
though GE (among others) solved it with tubes back about a
half century or so in the past. [I can tell you how they did it
even if it isn't explained in the ARRL Handbook]

Hint: 56.818 181 818 ... KHz is involved. How?

The numbers only APPEAR to relate, but the numbers aren't
oscillating and generating RF. Try to stay focussed HERE.

So...how much RF have you done up at Ku-Band territory?