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

[Glenn C. Lasher Jr.]

On Thu, 28 Mar 2002, Jeff Hubbs wrote:

> 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.

True.  It's a little under 1/4 wavelength across.  Normally, if you are
using this kind of frequency to talk to a satellite, you are talking to a
LEO satellite (shortening the line-of-sight) and also you would not use a
dish, but rather an "eggbeater" antenna or a quad of some variety, the
emphasis being on putting up an unpolarized signal.  The quad antenna
would give you increased directionality, based on the same principles as a
yagi, except that unlike a yagi, the quad is unpolarized.

> Below 30MHz?  That's in mobile territory; you'd be using a whip antenna,
> more than likely.

Close.  CB is 27MHz, that's definitely mobile territory.  The 10m ham band
is 29'ish.  These are both proven as fairly practical for mobile
operations.  They are both easier to operate from a fixed base, however,
because a truly good antenna for these bands is quite tall to put on a
vehicle.  I generally consider mobile territory to be 27MHz up through
about 2GHz.  Anything above that is too line-of-sight restricted, and
anything below that requires a mondo antenna.

Not to say it isn't done.  I do know an extra-class ham operator who has a
"screwdriver" antenna on the back of his car, and he can operate in all of
the ham bands with it from 160m (2MHz) through 6m (52MHz).  This is pretty
much all of the skip territory.  It's not an especially efficient antenna,
but it works well enough.

Back to satellite, I cited 146MHz (the 2m ham band) as probably the very
lowest frequency you would want to use for satellite (maybe a little lower
for the government bands around 136MHz or aviation just below that, but
that's gotta be it), partly because these frequencies are almost always
above the MUF, and, of course, there is the focusing problem you mentioned
above, and which I had neglected in my previous comments.  You are right
to point out that it's far easier to focus a high frequency than a low
one.

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


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