Re: [amsat-bb] Contacts on AO-10

[K5OE@xxxxxxx]

You guys offer some very good observations about my favorite (and most 
frustrating) DX satellite.  Let me add my $0.02 worth to the dialog:

john@newnorth.ca (VE8EV) writes:

> The interesting part about all this is that I could not detect deep fading 
of 
> the received signal other than that associated with the loss of power when 
> the sun falls on the end of the spacecraft.  Given the above, the satellite 
> must be using the *omni* antennas rather than the high gain antennas as was 
> previously believed.  If the high gain antennas were in use there should be 
> much more deep and regular fading of the signal as the satellite rolls/
> tumbles on its axis.
>  Comments?

I have suspected this for a long time:  during perigee passes, when not in 
complete fade, the entire "shadow" of the satellite is available for two-way 
communication.  I have had many QSO's 20 to 30 minutes long while the bird 
will move from 240 degrees to 90 degrees in azimuth while carrying on 
continuously with stations in California, Florida, and Tennessee.  If the 
high gain antenna was in use at this close range (less than 10,000 km at 
times), I doubt this would be possible (due to the narrow beamwidth of the 
high gain antennas) and the fading from tumbling would be far, far worse.

jono@enteract.com (KE9NA) writes:

>  1.) The polarization of the signal sometimes changes quite rapidly.  This
>  applies to both uplink and downlink.  According to Mike, KF4FDJ, as the
>  satellite wobbles, it ends up messing with the polarization of the signals
>  or what the antenna sees.  So as the bird tumbles, the polarization 
switches
>  due to the position of the antennas.  If you have antennas that can be
>  switched, this is good.  If not, you may be assuming the bird is not
>  workable because either your downlink or uplink signal or both are in
>  completely opposite polarizations from what you need.  I have seen this 
many
>  times myself.

This could not be more  accurate.  I started out working AO-10 with linear 
antennas and later used smaller (less gain) switchable CP antennas.  Many of 
my DX contacts were just barely above the noise and the ability to switch 
both antennas to the (for the moment) favored polarity often made the 
difference in being able to complete a QSO.  FWIW, the bird is easier to hear 
than to hit:  if you don't have > 500 W ERP, contacts beyond 30,000 km will 
be very difficult.  

>  2.) The fades are not necessarily due to lack of sunlight but also position
>  of the antennas due to the wobbles.  There was a pass into Europe about a
>  month ago that I remember well.  When I could hear myself well on the bird,
>  I was very weak into Europe.  Then it would switch and the bird would fade
>  for me and be open towards Europe.  As the bird tumbles, it seems the
>  antennas are pointing in different directions so you might not be in the
>  maximum portion of the antenna's beamwidth at any given time.

Another very accurate observation.  I figured out a while ago that 
transmitting during the fade when I could not hear my own signal was quite 
often successful to both Asia and Europe--I would hear them responding to me 
when the downlink returns on my end.  The trick is to keep transmitting all 
through the fade until you hear your own signal start to come back, then you 
will be able to hear them respond.  This seems to only come into play when 
the bird is pretty far out there, not during perigee passes.

markg@pptnet.com (KB3CWS) writes:

> Maybe you're lucky, but I get the regular fades also. I just noticed the
>  "temporary eclipse" fades the past couple of days which is different from
>  normal fading. Also, when the fade goes away, the signals are awfully 
strong
>  for an omni antenna.

I think it is just a factor of the proximity of the satellite.  The 
inverse-square law applies to this satellite more than any other bird we have 
available.  The signal strength difference between 10,000 km and  40,000 km 
is 24 dB!  

One final observation about eclipse (like Tony Langdon, I visually observe 
the sat shadow v. the sun's terminator in WinOrbit to know when it is in/out 
of eclipse):  the satellite loses power instantaneously upon moving 
completely into the Earth's shadow (I don't want to quibble about the 3 or 4 
seconds of Mickey Mouse sounding audio when that happens).  The same is true 
when it returns to sunlight:  within seconds the bird is at full strength 
signals.  I find it interesting that there does not appear to be any 
observable degradation or build up of power required from the solar cells, 
indicating the batteries add nothing to the transponder's power.
 
73,
Jerry, K5OE
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