[amsat-bb] Re: Phase 4 versus Eagle
sco at sco-inc.com
Sat Dec 15 07:04:08 PST 2007
if I could work AO40 with a small S band dish and 7.5 ft 70cm crossed
yagi at 40,000 km why can't i work P4 much easier? P4 will not move
and from what i read it will have how many times as much power as
AO40? ... 4x, 6x, 8x?
is the "problem" here the fact that some want to engineer a sat so
users on the ground can use a handheld HT as a sat phone? If that is
the real reason then the solution seems simple. FORGET that idea. The
antenna setup I describe for AO40 minus the tracking (since it won't
be required) seems more than adequate and could be setup within 20
minutes for emergency use. If AO40 could hear me with 50-100 watts of
power (from the ground station) why can't P4? if we could put
antennas on AO40 to hear me why can't we do that on P4? or are we
again trying to build a sat that can hear a 5 watt HT
(groundstation)? if so forget it.
with a fixed GEO location to aim at, with high power for the
downlink, with no need to worry about station keeping, what is the
"real" problem in designing a sat that will work wonderfully?
Ground station: Ft-847, preamps, M2 crossed yagis and small dish(s)
and computer. If we can't design a sat to work on P4 to work with
that given the resources on (the sat host) then there is something
wrong. That is my opinion.
>I would guess that at 145 and 435 MHz the satellite antennas will not
>be large enough to produce 20 dB* of gain, so only a percentage of
>their signal will hit earth with a larger amount radiating uselessly
>into space. The reverse issue for the satellite Rx antenna; only a
>small percent of the beam will see earth signals. This means mode UV
>(old Mode-B) will require larger ground station
>antennas. Calculating this is straight forward path-link
>calculations. One can plug in the range and Tx power (say 50w) and
>receiver sensitivity (-145 dBm) to come up with antenna gain requirements.
>No I will not do that for you this time - hint I have a calculator on
>my webpage that a clever person could modify - check out
>Mar's Reconnaissance Orbiter (MRO) Radio Test at the bottom of:
>How does the range to Geostationary orbit compare with apogee on
>AO-13 or AO-40? I think you will find that a standard AO-13 mode-B
>antenna system will be adequate (depending on the power and antennas on P4).
>73 Ed - KL7UW
>*Note: on 144 MHz my eme array produces 21.3 dBi gain (a bit large
>to install on a satellite)
>At 12:00 PM 12/14/2007, Andrew Glasbrenner wrote:
> >>Probably a good pointing spot would be where XM and Sirius Point their
> >>antennas - just about on the Canadian Border close to Winnipeg- Manitoba
> >>Robin VE3FRH.
> >Probably not if we care about covering the Southern Hemisphere. We
> >really don't know enough even to speculate, but this likely won't be
> >a spot beam like the Ku and C band transponders use. Range will be
> >less than AO-40, so the earth is a fairly big target still.
> >73, Drew KO4MA
>Ed - KL7UW
> BP40IQ 50-MHz - 10-GHz www.kl7uw.com
>144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w
>DUBUS Magazine USA Rep dubususa at hotmail.com
>Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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