Drew,
I have direct personal experience with this when I was a TVRO installer up here in Alaska.
Before the mid-1980's TV-satellites pointed their antennas at mid America around Kansas - Nebraska. Due to Alaska being not only at the far northern fringe but also western edge of the beam, signals were down around 6 to 10 dB (from memory). This meant that to receive the signal in Alaska one needed at minimum a 12 to 14 foot dish. IN Barrow (Lat=70) it took 16 to 20 foot dishes pointed a few degrees above the horizon (7-deg max due south). As time went on the satellite industry re-pointed some of the satellites to better favor Alaska and Hawaii resulting in being able to use 8 to 10 foot dishes. Today we get ku-band sat-TV with the use of a 30-inch dish (you use an 18-inch dish in the lower-48). We find that we need a 1-1.2 m dish to overcome rain/snow fading, though.
OK how does this relate to P4? For far-north or far-south stations, it will require careful ham station antenna location that can see a clear low horizon elevation angle and probably more antenna gain to overcome being on the fringe of the satellite antenna "footprint". If the sub-satellite (straight down) position on the equatorial orbit is too far east or west of one's local longitude, there will be no view above the horizon for the extreme latitude stations.
This will have no technical cure. So hopefully the orbit positions that can be obtained will be favorable to the maximum population. I would expect P4A and P4B will ride to mid-America and European positions. The Pacific sat probably would be the last launched if one were trying to reach the maximum ham population centers (only logical).
So you can see why Alaskan satellite operators are hoping for the launch of P3E and Eagle. Otherwise we may be in for a long wait till P4C! PS: I'm taking the liberty of assigning the designations P4A, P4B, P4C (not AMSAT terminology).
Following the saga with interest - and hope! 73, Ed - KL7UW
At 08:50 AM 12/14/2007, Andrew Glasbrenner wrote:
I noticed the new release of SATPC32 12.7 includes Intelsat spacecraft in one of the keplerian/satellite options. You can scroll through them and get an idea of the possibilities and range of footprints. Real life performance will be, as Bob suggests, dependent on our antenna pattern. Other services are usuable from the poles, such as Inmarsat, given enough gain and a clear horizon. MTI uses this as a selling point for their phone with the 4 ft dishes we S-band types are so fond of. So we might work fairly well out to the edge, again, dependent on the antenna.
73, Drew KO4MA
From: Robert McGwier [email protected]
We do not know the answer yet. Our request is for multiple payloads, covering with subsat over Atlantic, Pacific, and Central U.S. We would need one over the Indian Ocean to cover the 2 pi radians of the equator with antenna pattern. The north and south pole would be left out so I am sure the emperor penguins and polar bears would be upset!
Bob
Simon Brown wrote:
Where would this GEO be positioned? Even rough information would be interesting.
Simon Brown, HB9DRV
Sent via [email protected]. 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 [email protected] ======================================
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.
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Edward Cole Sent: December 14, 2007 1:43 PM To: Andrew Glasbrenner Cc: amsat-BB Subject: [amsat-bb] Re: Phase 4 versus Eagle
Drew,
I have direct personal experience with this when I was a TVRO installer up here in Alaska.
Before the mid-1980's TV-satellites pointed their antennas at mid America around Kansas - Nebraska. Due to Alaska being not only at the far northern fringe but also western edge of the beam, signals were down around 6 to 10 dB (from memory). This meant that to receive the signal in Alaska one needed at minimum a 12 to 14 foot dish. IN Barrow (Lat=70) it took 16 to 20 foot dishes pointed a few degrees above the horizon (7-deg max due south). As time went on the satellite industry re-pointed some of the satellites to better favor Alaska and Hawaii resulting in being able to use 8 to 10 foot dishes. Today we get ku-band sat-TV with the use of a 30-inch dish (you use an 18-inch dish in the lower-48). We find that we need a 1-1.2 m dish to overcome rain/snow fading, though.
OK how does this relate to P4? For far-north or far-south stations, it will require careful ham station antenna location that can see a clear low horizon elevation angle and probably more antenna gain to overcome being on the fringe of the satellite antenna "footprint". If the sub-satellite (straight down) position on the equatorial orbit is too far east or west of one's local longitude, there will be no view above the horizon for the extreme latitude stations.
This will have no technical cure. So hopefully the orbit positions that can be obtained will be favorable to the maximum population. I would expect P4A and P4B will ride to mid-America and European positions. The Pacific sat probably would be the last launched if one were trying to reach the maximum ham population centers (only logical).
So you can see why Alaskan satellite operators are hoping for the launch of P3E and Eagle. Otherwise we may be in for a long wait till P4C! PS: I'm taking the liberty of assigning the designations P4A, P4B, P4C (not AMSAT terminology).
Following the saga with interest - and hope! 73, Ed - KL7UW
At 08:50 AM 12/14/2007, Andrew Glasbrenner wrote:
I noticed the new release of SATPC32 12.7 includes Intelsat spacecraft in one of the keplerian/satellite options. You can scroll through them and get an idea of the possibilities and range of footprints. Real life performance will be, as Bob suggests, dependent on our antenna pattern. Other services are usuable from the poles, such as Inmarsat, given enough gain and a clear horizon. MTI uses this as a selling point for their phone with the 4 ft dishes we S-band types are so fond of. So we might work fairly well out to the edge, again, dependent on the antenna.
73, Drew KO4MA
From: Robert McGwier [email protected]
We do not know the answer yet. Our request is for multiple payloads, covering with subsat over Atlantic, Pacific, and Central U.S. We would need one over the Indian Ocean to cover the 2 pi radians of the equator with antenna pattern. The north and south pole would be left out so I am sure the emperor penguins and polar bears would be upset!
Bob
Simon Brown wrote:
Where would this GEO be positioned? Even rough information would be interesting.
Simon Brown, HB9DRV
Sent via [email protected]. 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 [email protected] ======================================
_______________________________________________ Sent via [email protected]. 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
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
Folks it will be our ham antennas and our bands. True the sat will most likely be facing North America. How does Direct TV do it? Point straight down or at a slight angle? So we will have propagation like any other sat pointed at the earth only better?
Les W4SCO
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
Andrew Glasbrenner expunged ([email protected]):
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.
I guess it comes down to what we expect the groundstations to have for gain.
If we assume an AO-40 class station, it probably won't make a difference. If we're talking about some sort of handheld data device, that may be different. We don't need quite the same amount of gain that XM radio or Sat TV would require, from the groundstation perspective.
-Steve N1JFU
Have to agree with Drew even if this reduces signal levels at extreme latitudes. I would assume that the P4 centered on the NA&SA would boresight the equator with a beam chosen to match the earth's apparent angular size = arcsin (8000/23500) = 19.9 deg. which corresponds with an antenna with 19.5 dB. At 2.4 GHz an 18-inch dish has about 19.7 dB gain. Such a footprint would only be 3 dB down at the poles.
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 [email protected] ======================================
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 [email protected] ====================================== _______________________________________________ Sent via [email protected]. 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
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, [email protected] 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 [email protected] ====================================== _______________________________________________ Sent via [email protected]. 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 [email protected] ======================================
At 04:13 AM 12/16/2007, Edward Cole wrote:
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.
I'd agree there. While I don't currently have the capability of U uplink, I could easily add the appropriate transceiver to my collection. I already have V band capabilities. The final ingredient would be to build some suitable antennas.
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).
Agreed. One practical path to HT access I see would take a leaf out of the VoIP book, a ground station to access the bird and a network of local repeaters for user access. That scenario's probably most useful for emergency use, where a portable repeater with satellite access can be brought in to an affected area to provide long haul comms to the rest of the world, in parallel with HF circuits. Similar ideas could be used to link the area for data transmission as well. As for direct HT access, well as you say, we are up against the laws of physics here, 38000km is a LONG way, even with a line of sight path.
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).
L is a good choice for the uplink, not as sure about S band these days. You would require antennas with a clean radiation pattern and reasonable satellite elevation, with all of the 2.4 GHz devices around. X band is another downlink option that is of interest. Antenna size would be nice as well, and since the target is fixed, the antenna can be securely fixed to point at the nearest bird in the constellation. When it comes to dishes, for me, smaller is more practical, which suggests higher frequencies (C, X, etc).
73 de VK3JED http://vkradio.com
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.
Art, KC6UQH
----- Original Message ----- From: [email protected] To: "Edward Cole" [email protected] Cc: "amsat-BB" [email protected] 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:
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 [email protected] ====================================== _______________________________________________ Sent via [email protected]. 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
Sent via [email protected]. 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
kc6uqh wrote:
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.
Art, KC6UQH
You always do. Vote in the director elections. You get three or four votes.
Bob
"WE" will be where our "host" is located and need to point from there the best we can. I assume we will know this info before launch? So whether or not we can aim for a certain spot is unknown until then.
At 02:59 PM 12/14/2007, you 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.
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Edward Cole Sent: December 14, 2007 1:43 PM To: Andrew Glasbrenner Cc: amsat-BB Subject: [amsat-bb] Re: Phase 4 versus Eagle
Drew,
I have direct personal experience with this when I was a TVRO installer up here in Alaska.
Before the mid-1980's TV-satellites pointed their antennas at mid America around Kansas - Nebraska. Due to Alaska being not only at the far northern fringe but also western edge of the beam, signals were down around 6 to 10 dB (from memory). This meant that to receive the signal in Alaska one needed at minimum a 12 to 14 foot dish. IN Barrow (Lat=70) it took 16 to 20 foot dishes pointed a few degrees above the horizon (7-deg max due south). As time went on the satellite industry re-pointed some of the satellites to better favor Alaska and Hawaii resulting in being able to use 8 to 10 foot dishes. Today we get ku-band sat-TV with the use of a 30-inch dish (you use an 18-inch dish in the lower-48). We find that we need a 1-1.2 m dish to overcome rain/snow fading, though.
OK how does this relate to P4? For far-north or far-south stations, it will require careful ham station antenna location that can see a clear low horizon elevation angle and probably more antenna gain to overcome being on the fringe of the satellite antenna "footprint". If the sub-satellite (straight down) position on the equatorial orbit is too far east or west of one's local longitude, there will be no view above the horizon for the extreme latitude stations.
This will have no technical cure. So hopefully the orbit positions that can be obtained will be favorable to the maximum population. I would expect P4A and P4B will ride to mid-America and European positions. The Pacific sat probably would be the last launched if one were trying to reach the maximum ham population centers (only logical).
So you can see why Alaskan satellite operators are hoping for the launch of P3E and Eagle. Otherwise we may be in for a long wait till P4C! PS: I'm taking the liberty of assigning the designations P4A, P4B, P4C (not AMSAT terminology).
Following the saga with interest - and hope! 73, Ed - KL7UW
At 08:50 AM 12/14/2007, Andrew Glasbrenner wrote:
I noticed the new release of SATPC32 12.7 includes Intelsat spacecraft in one of the keplerian/satellite options. You can scroll through them and get an idea of the possibilities and range of footprints. Real life performance will be, as Bob suggests, dependent on our antenna pattern. Other services are usuable from the poles, such as Inmarsat, given enough gain and a clear horizon. MTI uses this as a selling point for their phone with the 4 ft dishes we S-band types are so fond of. So we might work fairly well out to the edge, again, dependent on the antenna.
73, Drew KO4MA
From: Robert McGwier [email protected]
We do not know the answer yet. Our request is for multiple payloads, covering with subsat over Atlantic, Pacific, and Central U.S. We would need one over the Indian Ocean to cover the 2 pi radians of the equator with antenna pattern. The north and south pole would be left out so I am sure the emperor penguins and polar bears would be upset!
Bob
Simon Brown wrote:
Where would this GEO be positioned? Even rough information would be interesting.
Simon Brown, HB9DRV
Sent via [email protected]. 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 [email protected] ======================================
Sent via [email protected]. 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
Sent via [email protected]. 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
[email protected] wrote:
"WE" will be where our "host" is located and need to point from there the best we can. I assume we will know this info before launch? So whether or not we can aim for a certain spot is unknown until then.
At 02:59 PM 12/14/2007, you 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.
We will know long in advance of the launch where our subsat point will be. Intelsat will then do station keeping. As we are selected for a launch, we will be able to tell what the planned subsat will be. We will tell all of you what it is when our launch partner tells us we can. In addition, we will calculate where on the earth will be illuminated. We will calculate how much degradation there will be for users on the limbs of the earth so they can size their antennas, etc. accordingly. AMSAT is designing and will make available the terminals for the ACP. I remind that with this bird we no longer need rotors.
You will see in my upcoming journal columns that we have two flight opportunities for SDX next year. It was almost a third on a Cubesat but that is the way things go some times.
We have purchased the necessary development to enable build of code for the entire SDX and ACP in prototype form. The SDX will contain the "ultimate" HELAPS and this will be designed using the real modulator which will be worked out with Marc Franco (N2UO). We are expecting both efficiencies and linearity never thought possible a few years ago and deliverable only with the DSP based HELAPS riding on board.
We have two Lyrtech boards which have TI DSP chips and FPGA to enable us to do the work. These boards produce and use IF and we can set them up to operate on 10.7 MHz easily. We are using rapid prototyping tools that I get from work so we can quickly demonstrate this capability.
Howard has been continuously improving the SDX/Leila implementation and I want to be able to start development on the HELAPS modulator and radar pulse subtracter.
The same boards with the FPGA will enable us to build the wideband digital modulator and polyphase filter bank demodulators for the ACP in a reduced number of channels form to allow for easy algorithm development. Don't worry about all of this jargon for now. It will all be made clearer in my columns and demonstrations during the coming year.
We are only doing prototype work for now on the ACP and will only work on the IF and baseband processors for the linear transponder because we don't know the size of the linear transmitter yet. Eagle will be ~50w and Intelsat will be LOUD if we get the power we have requested and the efficiencies we expect. The ACP, even though it is all microwave, will be a hard limiting transmitter and very efficient.
Bob
participants (8)
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Andrew Glasbrenner -
Edward Cole -
kc6uqh -
R.Haighton -
Robert McGwier -
sco＠sco-inc.com -
Steve Meuse -
Tony Langdon