[Premium-Rx] real basic question on stability etc.

[Ben Dover]

>At 05:52 PM 9/1/2005 +0100, you wrote:
>Hi Tom
>
>That's a very big surprise - which hare-brained idiot allowed that one to 
>happen?  There's supposed to be a band plan organiser called the ITU for 
>the planet - did they really allow such a cock-up?  Which digital satellite 
>phone system shares this with NOAA?  Or was it a legacy 
>Earth-Satellite-Earth communications band plan and someone forgot?
>
>Interesting that such mistakes occur in this day and age of "well aware of 
>issues people"
>
>Best regards
>
>John G8 BSD
>
>

Hi, John.

I found out about the staellite phones by accident. 

Tuning the band I got a lot of FSK data signals I couldn't identify. They were
clearly coming from satellites; they showed Doppler shift, and had definite
AOS / LOS (Acquisition / Loss Of Signal) periods.

At first I thought them to be some sort of "next generation" weather bird, and
hit the net to find out who was running them.

I finally found a website that showed spectrum allocations for the band,
and the
truth became clear.

>From the nature of the signals (short bursts of digital data) I don't think
these
are the actual voice stream; they're more likely control signals to the
phones.

I think that the phones were allocated to the band after the weather birds
were 
already there; the satellites have been there since the early 1960s.


Re. frequency allocation problems; in your part of the world (England)
there are
even more severe problems in the 137 MHz weather bird band.

The currently most popular hobbyist weather satellite receivers, Icom
PCR-100 and
PCR-1000, are essentially wideband scanners with little front end
selectivity. That
makes for BAD problems in the crowded VHF spectrum.

I don't know if it's an allocation error or if it's adjacent channel
overloading but 
most British WX satellite enthusiasts report SEVERE problems from pager
base stations!


Over here, we're lucky on that score. I used to have an adjacent channel
overloading 
problem here; the Sun Prairie Police Department base station is about a
half mile 
away from me on 151 MHz, and every time they came on my GAsFET preamplifier
at the
antenna would overload BADLY. The cure in my case was a workshop session
with a hunk
of large diameter copper pipe (a scrap of 3.125" broadcast transmission
line scavenged 
from work) and a butane torch to construct a cavity for 137 MHz! Beyond
that tho, US
satellite nuts are fortunate to not have much in the way of high power
terrestrial
interference either in or that close to the bird band.


73's,

Tom, W9LBB