[amsat-bb] Re: Phase 4 versus Eagle
kl7uw at acsalaska.net
Sat Dec 15 09:13:15 PST 2007
I probably was not clear on this. That is also my assumption for
mode-UV since there are unknown factors like sat power and antenna
gain at this point. Since there does exist (hopefully not all have
dissembled their stations) a lot of mode-UV stations from the
AO-13/AO-40 era designing to that capability would make sense to me.
For the HT orientation, the mw digital mode-SC (CC-rider update) is
probably the correct approach. If this disappoints the HT - Leo
crowd, I would point out that there ARE some physical realities to
consider that may not make P4 as accommodating as a Leo (400km vs
But my intuition tells me that mode-LS is probably a better main comm
frequency for satellite users. That will require gain antennas
(20-dB) and moderate power (5-10w).
Just my two cents at this early what-if stage.
Ed - KL7UW
At 06:04 AM 12/15/2007, sco at sco-inc.com wrote:
>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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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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