[amsat-bb] Re: Phase 4 versus Eagle

Edward Cole 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 
37,600km range).

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.
>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:
>>   http://www.kl7uw.com/raseti.htm
>>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
>> >>73
>> >>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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