[amsat-bb] Re: Phase 4 versus Eagle
kc6uqh at cox.net
Sat Dec 15 11:01:22 PST 2007
The 2M /70cm is not the best choice on a satellite 23,000 miles away. 2M
suffers from galatic noise, 70cm is siginificantly better. 1 to 2 GHz is
considered optimum for SETTI work. Best choice is 902-928 up and 1.2 GHz
down. Next best choice is 2.4 GHz or 70cm up for satellites not centered
over North America.
P4 will bring us, no Doppler, no tracking, no spin rotation, fixed dishes.
Something we have yet to experience in satellite communications.
It has my vote if I have one.
----- Original Message -----
From: <sco at sco-inc.com>
To: "Edward Cole" <kl7uw at acsalaska.net>
Cc: "amsat-BB" <amsat-bb at amsat.org>
Sent: Saturday, December 15, 2007 7:04 AM
Subject: [amsat-bb] Re: Phase 4 versus Eagle
> 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.
> Les W4SCO
>>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
>>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-
>> >>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
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