Les,
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@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
73, 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@hotmail.com ====================================== _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
73, 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@hotmail.com ======================================