I have some free time today and will go to the addison after this course. i looked at their onlie inventory (UGH! PDFs!) ... they dont SEEM to have lmr-400 ... if that was to be the case ... what would be the best alternative?
thanks
lawrence
From: "Loren Zemenick" <[EMAIL PROTECTED]> To: "Wireless" <[EMAIL PROTECTED]>, "Brian Lloyd" <[EMAIL PROTECTED]> Subject: RE: [BAWUG] Microwave propagation speed versus air temperature Date: Wed, 27 Aug 2003 08:21:39 -0700
I am thinking of refraction at a temperature gradient, analogous to a simple
optical lenses. Ducting depends upon refraction also but to keep the radio
energy in a duct, analogus to optical fiber. With a temperature gradient I
imagined a situation similar fishing with a spear. An fish is not located
where it appears because of refraction at the air-water interface. Pointing
a second set of antennas to follow the bent beam might improve the signal.
>BTW, they didn't use diversity reception, they used a voter that selected which signal was the more useful.
I assumed the voter you previously mentioned is the equivalent of diversity reception.
Loren Zemenick
-----Original Message----- From: Brian Lloyd [mailto:[EMAIL PROTECTED] Sent: Wednesday, August 27, 2003 7:22 AM To: Loren Zemenick Subject: Re: [BAWUG] Microwave propagation speed versus air temperature
Loren Zemenick wrote:
> Tropospheric ducting may be an overstatement.
But it is the effect you are hoping to exploit. Tropospheric ducting is the
effect caused by an inversion causing the wave front to bend and
more-or-less follow the curve of the earth. It depends on the part of the
wavefront in the warmer air to propagate faster thus causing the whole
wavefront to bend. Get it just right and you can talk to Hawaii from SoCal
with 100W on 144 MHz. Been there, done that.
> I am trying to calculate the angle of refraction when the beam passes > through a temperature inversion. I have a 5 mile link that has a > ridge-top end-point 1200 feet above it other end-point on the vally > floor. If the effect is large enough, I want to set up a second pair > of 24dBi antennas and use antenna diversity.
Oh, I think I see what you are driving at. At 5mi wouldn't expect the
effect to be too substantial. At 80 mi it was. (Ref my comments previously
about MMDS in SoCal from mountain top to mountain top). They had to figure
it out by trial and error as the results were not consistent. Eventually
they figured out where to put the second dish lower on the tower in order to
have consistent links.
BTW, they didn't use diversity reception, they used a voter that selected which signal was the more useful. --
Brian Lloyd 6501 Red Hook Plaza, Suite 201 [EMAIL PROTECTED] St. Thomas, VI 00802 +1.340.998.9447 - voice +1.360.838.9669 - fax GMT-4
-- general wireless list, a bawug thing <http://www.bawug.org/> [un]subscribe: http://lists.bawug.org/mailman/listinfo/wireless
_________________________________________________________________
MSN 8 helps eliminate e-mail viruses. Get 2 months FREE*. http://join.msn.com/?page=features/virus
-- general wireless list, a bawug thing <http://www.bawug.org/> [un]subscribe: http://lists.bawug.org/mailman/listinfo/wireless
