Tuesday, April 2, 2013

Satellite AO-07 Spectrum Plots

Following on the screenshots of satellite VO-52's downlink spectrum (previous post), here are some photos of what Oscar 7's downlink looks like when viewed with a software-defined radio (the FUNCube Dongle Pro+).  AO-07 was in Mode B (UHF up, VHF down) at the time.

This particular pass (4/2/2013 1315z) was North to South:

And I started taking the screenshots when AO-07 was already high in elevation towards the east.   You can see the three strong "noise" bands (145.926, 145.941, and 145.958 MHz) of the satellite within the transponder downlink (145.924-145.964 MHz):

In this photo, a station can be seen calling CQ at around 145.950 MHz.  It's interesting to see how the SSB transmission affects the three noise bands.  We hear how excessive uplink power can cause the transponder to start "FMing", and this is a mild example of how a transmission in one part of the passband can affect signals in another:

In the next frame, you can still see the SSB transmission at 145.950 MHz, but you can also see an interesting "glitch" that affected the whole passband for around 15 seconds:

Some sort of signal (rapidly increasing in frequency) was heard by the satellite in the next photo, and you can see how it disrupted the three noise bands as it went by.  This is possibly another example of how the whole transponder passband can be affected by a single signal.  The "offending" signal is the orange diagonal line:

As AO-07 continued south, it's signal started to become weaker.  You can see my SSB CQ calls at 145.949, followed by a call in CQ below:

As the satellite got lower, signals were weaker, but my SSB CQ calls were still clearly visible:

Eventually the satellite was just a degree above the southern horizon:

And even then my SSB CQ call and CW ID is visible in the spectral plot:

When Oscar 7 got to -0.6 degrees (below the horizon), the three "noise bands" are entirely gone, along with any trace of signal from my uplink:

1 comment:

  1. I saw it was going to make a decent pass earlier today, and the most recent status showed it was in Mode A, so since I had my Flex 5000 up and running, I tuned it to 29.450, and waited.

    Didn't see anything, so I tuned to 29.502 to look for the beacon, and didn't see anything, even though the satellite was in the sun.

    It must have switched modes, so I'll try again another day.


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