[amsat-bb] Why too much uplink power is bad
electricity440 at gmail.com
Sun Jul 26 15:44:02 UTC 2015
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 <n8hm at arrl.net> 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.
> Paul, N8HM
> On Sun, Jul 26, 2015 at 11:03 AM, Skyler F <electricity440 at gmail.com>
> > 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
> > 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
> > as well?
> > Thanks
> > Skyler KDØWHB
> > --
> > Skyler Fennell
> > amsatnet.info
> > KDØWHB
> > electricity440 at gmail.com
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electricity440 at gmail.com
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