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Re[2]: AO-40 AGC study,please read it!



Hallo Estes,

Wednesday, January 15, 2003, 4:26:35 PM, you wrote:

> Has anybody identified the cause(s) of sudden drops in the AO40 downlink
> signal strength?  I'm talking about when everything is working fine, and
> then the signal SUDDENLY drops by ~10 dB for ~30
> seconds, and then SUDDENLY returns to "normal".  The duration of the drop
> is longer than a typical LEILA attack, and I can't hear a LEILA siren when
> I tune up and down a few kHz.

> What do you guys with panoramic receivers see in the passband when everything
> suddenly drops 10 dB?

I am one of these guys with panoramic receiver, and it rather often
happens to me, that my signal becomes suddenly much weaker as you
describe above. It is not everything what suddenly drops but a 10 kHz
width only. Then I can see LEILA acting above or below my frequency
in a distance of approx. 5 kHz so that I cannot hear the siren. But it is
quite obvious that LEILA is causing a notch on my signal as long as
it is acting. I have observed two durations of LEILA, one of only few
seconds and the other of more than 2 minutes. I don't know what
influences the duration.

> Has anybody noticed a geographic pattern when this
> occurs and doesn't occur?  I suppose this
> could be caused by an extremely powerful SSTV or RTTY station.
> Or perhaps the offending signal is NOT a ham?

I have the impression that LEILA comes more often up if the satellite
is over USA, but it also happens, if it covers nothing of USA. In no
way I have observed any connection with SSTV or RTTY stations. LEILA
very often comes up on frequencies without any activity. I have often
observed it around 2401.410 - 430, where is no activity at all (why
not, BTW?). Some people suspects that LEILA becomes triggered by short
pulses which cannot been heard or seen on the panoramic display.

73,
 Reinhard (aka René)
 DJ1KM                            

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