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R: Noisy signal this morning on AO-40 around MA=160



Hi Charlie G3WDG,

As you already know i experienced the strong noisy signal on orbit 1287
beginning MA 158 when i started my activity at about 08:33 to day august 20

As usually while operating i was monitoring the passband on my panoramic
receiver sweeping 100 KHz with the MB in the center.

At first the noisy signal appeared centered just 35 KHz belowe the MB,it was
about 30 KHz wide,it was 6 dB stronger than the MB and its gaussian shape
was moving very slowly up in frequency in to the S2 passband.

At first i belived it was a local digital interfering signal but moving the
antenna up and down i soon realized that the radiating source was AO40

At 08:56 the interfering signal was covering completely the MB and it was
completely impossible to receive it for about 10 minutes.

The interfering signal was than drifting slowly up toward the center of the
CW and SSB passband rendering all modulation distorted and QSO difficult
even using high power uplinking in L1 band

The MB and SSB signals where weaker than normally due to the AGC fixed
at around 10 dB in the L1 band as decoded by Charlie G3WDG

Since the interfering signal was moving up in frequency in to the S2
passband i switched the scan wide of my panoramic receiver to 50 KHz/div
allowing to monitor 500 KHz with the MB on the left.

As soon the interfering signal was moving up to 2401.550 KHz than it dropped
about 15 dB belove the MB level and desappeared completely as soon it was
close to 2401.600 KHz

At this point about MA 181 at 10:12 UTC the L1 sensitivity becomes nominal
again and signal level in to the S2 passband where strong as normal.

Conclusion:

It seams that a powerfull interfering signal was radiated in to the L1 band
and it was slowly drifting down in frequency so that it appears drifting up
in to the S2 band due to the effect of the inverting transponder.

The above has been experienced in the same orbit also by  GW3XYW, G3WDG,
DJ1KM, WC9C and iT9UJY

If this happens again it should be very interesting to switch off the L1
receiver for some minutes living ON the L2 receiver to monitor the effect in
to the S2 passband and the L1-RX AGC by telemetry in order to establish if
the interfering signal is radiated from the earth or internally generated
somewhere by AO40 itself.

73" de

i8CVS Domenico

----- Original Message -----
From: Charles Suckling <charles.suckling@ntlworld.com>
To: <amsat-bb@AMSAT.Org>
Cc: <g3ruh@jrmiller.demon.co.uk>; <w4sm@cstone.net>
Sent: Wednesday, August 20, 2003 11:04 AM
Subject: [amsat-bb] Noisy signal this morning on AO-40 around MA=160


> Anyone else experiencing a strong noisy signal around the beacon this
morning?
>
> Telemetry decode is affected sometimes, but on good blocks I can see the
L1
> agc is high,  at around 10dB.  Maybe QRM on L-Band?
>
> Pity FEC wasn't on!
>
> 73
>
> Charlie G3WDG
>
>
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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