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Re: Orbit 250 apogee



Hello Wayne,

My comments are interspersed below.

----- Original Message -----
From: "Estes Wayne-W10191" <W10191@motorola.com>
To: <amsat-bb@AMSAT.Org>
Sent: Wednesday, May 16, 2001 12:33 PM
Subject: [amsat-bb] Orbit 250 apogee


> It was also my first experience with LEILA.  That thing is really picky.
> Here are my observations about LEILA:
>
> 1. With my (less than optimum) receiving setup LEILA likes to make the
siren
> tone just when I can start to hear my downlink well.  I can't run more
than
> about 10W (after cable loss) into a 30 element CP yagi without getting the
> attention of LEILA.

That actually seems about right from what has been published in the Journal
which shows a 100w EIRP should provide a 23db SNR at the AO40 U-rx.
>
> 2. For a few minutes before I shut down the radio I was doing other things
> while still tuned to the frequency of my last QSO.  There were no stations
> on that frequency, but the LEILA siren came on several times.  Did anybody
> else hear the LEILA siren on an empty channel?

I've heard this also on an earlier orbit.  In may case I had been calling CQ
in CW running 3w into a 12 element yagi or about 50w EIRP a few minutes
earlier but the frequency had been clear for a bit over a minute.

> 3. It appears that people uplinking on 23cm can get MUCH stronger
downlinks
> (than people uplinking on 70 cm) without triggering the LEILA siren tone.
> I'm not sure it's reasonable for LEILA to completely eliminate AGC on the
> 70cm uplink because that doesn't permit decent downlink signal strength.

There may be some imbalance between the to ul receiver outputs but a review
of the tlm archive doesn't show the 23cm rcvr AGCs being hit hard if at all.
Also bear in mind how the full system operates.  Driving AO40's ul AGC
primarily acts to keep the offending downlink signal from getting any
stronger.  It does this by reducing the effective sensitivity of the ul
rcvr.  As a result, the aligators aren't really that much stronger, but they
prevent the lower powered stations from accessing the satelllite.

> I asked this question a week ago and didn't get an answer:  Will the
"final"
> S-band downlink use more power and/or a higher-gain antenna?

There are two s-band tx which operate at 50w pep each.  The difference is
the s1 tx/antenna has about 8-10db more gain.  What the tlm for times that
s1 is turned on.  If the squint angles are good you'll be able to see the
effects of the extra gain.  Conversely, if the squint is bad, you'll also
see the impact of being off the bore site of a narrower antenna pattern.

I hope this helped.

73s,
Lee-KU4OS


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