[BC] Re: Wind and STL Mutes

[Broadcast List USER]

This is a well known phenominom.  This is why the "phone company"  
nearly ALWAYS uses space diversity on the receive end of microwave  
paths, especially long ones.

This is why we will ALWAYS specify 0.6 to one Fresnel Zone clearance  
in even UHF STL paths (950 MHz).  The signal wanders around.  It does  
not go in a straight line.

I don't think this is why the highly compressed (digitally) STL  
encoders fail though.  I have seen this myself, and we ended up  
giving up capacity for the reliability of a wide band, composite,  
analog STL.

A lot of things make the BER go up, including that 1968 GTO that just  
drove up the the transmitter site (STL receive site).  It just seems  
too sensitive to me, when we can go to a much higher frequency with a  
much higher bandwidth and get real two way wide band digital  
connectivity, and have STL, T-1, and telephone with extra channels  
for RPU and other useful services (for us).

I hate the Drunken Bat, but Canopy seems to be a very nice product.

--chip

On Feb 5, 2009, at 5:03 PM, broadcast-request at radiolists.net wrote:

> Message: 1
> From: "r.j.carpenter" <rcarpen at comcast.net>
>
> A friend at NOAA in Boulder, CO, once had a research project [about
> 1970+] to measure the effect of atmospheric turbulence of free-space
> optical paths. They set up a narrow-beam laser on the mesa field  
> station
> north of Boulder and a receiver on the hill behind the Radio  
> Building in
> south Boulder, a distance of about ten miles. The path was clear, but
> right across the center of Boulder. The receiver allowed them to  
> measure
> how far the beam was deflected by the dielectric constant  
> variations due
> to turbulence.  The answer was "quite a bit".
>
> I can't find exactly the right reference, but this gives an idea.
> http://www.opticsinfobase.org/ao/abstract.cfm?id=19956
>
> Agreed that this was optical and not UHF, and it was CW and they  
> didn't
> measure apparent path length changes as mentioned by  
> RichardBJohnson. I
> think it brings up the question of how narrow is your transmitting  
> beam.
> This in addition to the time/propagation delay issue mentioned by  
> Richard.
>
> bob carpenter