Can someone explain to me why it is a bad thing for the satellite to have too much uplink power to it?
Even if you send a huge amount of power up, I don't see how it could damage the satellite, by the time it reaches the sat, the power would be so low.
Is this only something for the linear birds, does it apply to FM satellites as well?
Thanks Skyler KDØWHB
Hi Skyler,
There are two issues:
The first issue is the automatic gain control in the satellite passband. Linear transponders only have a limited amount of power available to spread across the 20 kHz - 100 kHz passband, so the gain needs to be limited to keep the transponder output linear. When a very strong signal is in the passband, everyone else's signal is weaker. For example, I can usually receive my own signal (using 5 watts from an FT-817 to an Arrow) about S8 above 5-10 degrees on FO-29. On Field Day, it was tough to get a decent signal even above 40 or 50 degrees because of all the high power stations in the passband. Your signal should be no stronger than the beacon.
The second issue is how it could damage the satellite. The issue is when an aging satellite's power system (such as AO-7 or FO-29) can't manage to provide the full power ordinarily needed to run the satellite. In AO-7's case, too strong of a signal can bring the voltages available to the transponder down to a point where it can cause the satellite to switch modes. In FO-29's case, strong signals in the passband while the satellite is in eclipse could cause the battery voltages to drop to a point where the satellite would shut off to preserve the batteries.
This doesn't apply to FM satellites, but using a lot of power to dominate the satellite by using the FM capture effect to keep weaker signals out is considered poor practice.
Remember that the FCC amateur service regulations require the use of the minimum power necessary to conduct communications. The regulations also require you to not cause harmful interference to other amateur stations. Using excessive power on a linear transponder violates both of those provisions.
Also remember that when we're talking about "excessive power" that's ERP, not actual output. Even 500 mW could be excessive power if you're using a huge antenna array and the satellite is right overhead. I have heard stations use the excuse that they are only running 2 watts when called out for pounding the transponder with an excessively strong signal. Well that might be too much, turn it down more. If your radio doesn't allow you to turn the power any lower, you may need to add an attenuator pad to your station.
Also, a CW signal is much harder on a linear transponder than an SSB signal because a CW signal at keydown is full power, where a SSB signal only reaches full power on voice peaks.
73,
Paul, N8HM
On Sun, Jul 26, 2015 at 11:03 AM, Skyler F [email protected] wrote:
Can someone explain to me why it is a bad thing for the satellite to have too much uplink power to it?
Even if you send a huge amount of power up, I don't see how it could damage the satellite, by the time it reaches the sat, the power would be so low.
Is this only something for the linear birds, does it apply to FM satellites as well?
Thanks Skyler KDØWHB
-- Skyler Fennell amsatnet.info KDØWHB [email protected] _______________________________________________ Sent via [email protected]. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Thanks for taking the time to answer, that makes sense.
I only have FM capability currently, but that is good to know for when I get to SSB.
On Sun, Jul 26, 2015 at 9:24 AM, Paul Stoetzer [email protected] wrote:
Hi Skyler,
There are two issues:
The first issue is the automatic gain control in the satellite passband. Linear transponders only have a limited amount of power available to spread across the 20 kHz - 100 kHz passband, so the gain needs to be limited to keep the transponder output linear. When a very strong signal is in the passband, everyone else's signal is weaker. For example, I can usually receive my own signal (using 5 watts from an FT-817 to an Arrow) about S8 above 5-10 degrees on FO-29. On Field Day, it was tough to get a decent signal even above 40 or 50 degrees because of all the high power stations in the passband. Your signal should be no stronger than the beacon.
The second issue is how it could damage the satellite. The issue is when an aging satellite's power system (such as AO-7 or FO-29) can't manage to provide the full power ordinarily needed to run the satellite. In AO-7's case, too strong of a signal can bring the voltages available to the transponder down to a point where it can cause the satellite to switch modes. In FO-29's case, strong signals in the passband while the satellite is in eclipse could cause the battery voltages to drop to a point where the satellite would shut off to preserve the batteries.
This doesn't apply to FM satellites, but using a lot of power to dominate the satellite by using the FM capture effect to keep weaker signals out is considered poor practice.
Remember that the FCC amateur service regulations require the use of the minimum power necessary to conduct communications. The regulations also require you to not cause harmful interference to other amateur stations. Using excessive power on a linear transponder violates both of those provisions.
Also remember that when we're talking about "excessive power" that's ERP, not actual output. Even 500 mW could be excessive power if you're using a huge antenna array and the satellite is right overhead. I have heard stations use the excuse that they are only running 2 watts when called out for pounding the transponder with an excessively strong signal. Well that might be too much, turn it down more. If your radio doesn't allow you to turn the power any lower, you may need to add an attenuator pad to your station.
Also, a CW signal is much harder on a linear transponder than an SSB signal because a CW signal at keydown is full power, where a SSB signal only reaches full power on voice peaks.
73,
Paul, N8HM
On Sun, Jul 26, 2015 at 11:03 AM, Skyler F [email protected] wrote:
Can someone explain to me why it is a bad thing for the satellite to have too much uplink power to it?
Even if you send a huge amount of power up, I don't see how it could
damage
the satellite, by the time it reaches the sat, the power would be so low.
Is this only something for the linear birds, does it apply to FM
satellites
as well?
Thanks Skyler KDØWHB
-- Skyler Fennell amsatnet.info KDØWHB [email protected] _______________________________________________ Sent via [email protected]. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership.
Opinions expressed
are solely those of the author, and do not reflect the official views of
AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite
program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
I dont know the answer, that is why I'm asking.
AO40 would send a tone when someone would overpower it. does any of these sats do the same?
John
You were not sufficiently specific so I am going to assume you are speaking of a linear transponder. In that case there is a finite amount of SHARED power. If you are a greedy alligator and you put a huge bunch of power into the spacecraft you get all the downlink power and the other users disappear into the noise.
FM birds it's mostly irrelevant unless you overload and then you just sound like crap. On Jul 26, 2015 9:04 AM, "Skyler F" [email protected] wrote:
Can someone explain to me why it is a bad thing for the satellite to have too much uplink power to it?
Even if you send a huge amount of power up, I don't see how it could damage the satellite, by the time it reaches the sat, the power would be so low.
Is this only something for the linear birds, does it apply to FM satellites as well?
Thanks Skyler KDØWHB
-- Skyler Fennell amsatnet.info KDØWHB [email protected] _______________________________________________ Sent via [email protected]. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
participants (4)
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John Becker -
Paul Stoetzer -
Robert McGwier -
Skyler F