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[ale] OT: How fast is your connection, and how much do you pay?



Glenn C. Lasher Jr. wrote:

>On Tue, 26 Mar 2002, Charles Marcus wrote:
>
>>I believe that the wattage is very small - a friend of mine has one,
>>and I seem to remember reading something somewhere about his, and
>>thinking that it was really small.  I guess it is the high freq that
>>makes it usable.
>>
>
>Quite the contrary.  Higher frequency tends to work against you in
>propagation matters.  The reason why you can use very low power levels on
>satellite are twofold.  First, you are using a very high-gain antenna, in
>the form of a parabolic reflector (i.e. the dish).  Second, you have an
>almost-completely unobstructed line-of-site.  Given such an unobstructed
>line-of-site, you can have satellites operating on 144-148MHz (ham radio
>frequencies) just as easily as on 30GHz, if not more so.
>
Yeah, but the dish is only so big, so as frequency goes down, the 
directionality and therefore gain of the antenna on boresight goes down. 
 At 148MHz, an 18" dish is only between 1/4 and 1/5 of a wavelength 
across, so wouldn't that be a little like visible light vs. a virus (my 
point being that the dish would not be an effective reflector)?  I'm 
having trouble accepting the idea of satellite uplinks at those kinds of 
frequencies using an 18" dish.  

>
>The only physical requirement with respect to frequency and reaching a
>satellite, is that the frequency be high enough that it is not reflected
>back by the upper layers of the atmosphere.  Such reflection is called
>"skip" and is responsible for shortwave radio being able to have the
>tremendous reach that it does (worldwide communication without satellites
>or cable is possible on shortwave).
>
>The exact frequency varies, but is usually below 30MHz.  Sometimes it
>ventures as high as 80MHz, sometimes as low as 7 or 8MHz.  If you want to
>look it up, it is referred to as the "Maximum Usable Frequency" or MUF.
>Of course, usability here refers to usability for skip, which
>counterindicates usability for satellite.
>
Below 30MHz?  That's in mobile territory; you'd be using a whip antenna, 
more than likely.

>
>
>
>--
>glasher at nycap.rr.com
>You've been programmed by the Illuminati not to see the word "".
>
>
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