Discussion in 'Electronic Basics' started by AssTelescope, Dec 26, 2004.

2. ### Watson A.Name - \Watt Sun, the Dark Remover\Guest

I think that this size dish is too small for the 2.4 GHz that the can
antenna is putting out. Probably a lot of the signal just goes out the
back and is wasted.

3. ### Clarence_AGuest

???
At 2.4GHz a full wave is .00041 inches. The reflector will work just fine!
getting it at the focus is more of a problem.

4. ### Watson A.Name - \Watt Sun, the Dark Remover\Guest

You'd better recalculate that wavelength. More like it's a bit less
than 5 inches. And that antenna dish was made for frequencies much
higher than 2.45 GHz with wavelengths much shorter.

5. ### Larry BrasfieldGuest

In my universe, the wavelength in free space is more
like 4.9 inches at 2.4 GHz. I'm willing to believe c
how you post here from over there.

6. ### Clarence_AGuest

SB 4.1 inches....... !
Yes, bad copy.... The point was that the reflector is made for 8 to 10GHz, so
it will work. IF the feed is at the focalpoint.

7. ### Clarence_AGuest

Gee, I guess I shouldn't try to convert from meters to inches in my head...
12.5 mm IS closer to 4.9 inches.

8. ### John GGuest

12.5 mm is 0.4921259 inches on this planet and has been since the French
invented the metre.

But then the metre is an unknown standard in the USA isn't it?

9. ### TerryGuest

Nope: Ignoring the banter. It's 4.9 inches!

At 2.4 gHz One Wavelength = 300/2400 = 0.125 metres = 12.5 centimetres

Centimetres!
(A typical 6" 8" doorway is roughly two metres or two hundred centimetres
high).
And one hundred centimetres is roughly 39.3 inches.
So 12.5/100 x 39.3 = 4.9 inches.

But the 'probe' that launches and receives the signal would presumably be
one quarter wavelength? To match the 50 ohm feed line?
So probe length (inside the can and hopefully at the dish focal point?)
would be 4.9/4 = 1.23 inches approx?????????

The dish being 'too small', having been designed for 10 gigahertz would have
only a portion of the capture area . It would therefore exhibit a 'loss' or
'lower gain' at 2.4 gHz? Possibly expressed in decibels?

f w
m.hertz centimetres
300 100 (One metre)
600 50
1200 25
2400 12.5
4800 6.25
9600 ` 3.125

Here in Canada we are becoming pretty well bilingual in regard to metric or
non-metric.
We measure building materials both ways. Gasoline in litres and distances in
kilometres. Car engines in may countries have been measured in litres/ccs
for years! Radio wavelength which is inversely related to frequency has been
measured in metres almost from the word go.
I've never heard of radio station frequency or wavelength measured in feet
or miles?

Terry.

10. ### Clarence_AGuest

One quarter the size would reduce the gain by about 6db. Still substantial!
Can't spell it, but it MUST be the way to go?
BTW, you buy 'petrol' in liters, distance is approximated in Kilometers, and
all are convertible to usable numbers with care if the person doing it isn't
too tired!

Seems pretty easy to tweak you guys. >)
However 'metric meters' are a rather recent invention. Feet and inches were
used since the invention of radio. Before that "Cubits" "fathoms" and
'leagues' were the standard!

11. ### Tom MacIntyreGuest

No it isn't...12.5 cm is 4.9-whatever inches.

Tom

12. ### Clarence_AGuest

Perhaps you mean 4.9212598?

13. ### John GGuest

Wrong again.

Whatever you think, 12.5 mm is really 0.4921259 inches.

Yes the wavelength at 2.4 gigahertz is 4.92 inches or 12.5 CENTIMETRES
but I was replying to the conversion in the previous post which was
MILLImetres to inches

14. ### Watson A.Name - \Watt Sun, the Dark Remover\Guest

I think you had better try again - practice makes perfect. 4.9 inches
is right, but 12.5 mm is about a half inch. Try 12.5 CM.

15. ### Watson A.Name - \Watt Sun, the Dark Remover\Guest

No, it is not. Rulers and tape measures come with both scales.
So the ultimate question is, "Wot's Your Real Problem?"

16. ### Watson A.Name - \Watt Sun, the Dark Remover\Guest

Well, the way I figured it is 3x10^8 / 2.45x10^9 = .12245 meters =
12.245 CM

..12245 * 39.37 = 4.82 inches.

Of course, that xdoesn't take into account that the speed of light is a
bit less in the antenna, so it's maybe 5% too long.