[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: Reason for uplink power!!


Interesting charts.  I compared them to last nights operating notes.  I had
my downlink running about 1-1/2 s-unit below the beacon using between 400
and 600 w ERP [9-15w Tx power].  Early in the pass I had fairly good signal
back to myself [S2 for S-0.5 noise floor], but after 0900 utc there were
unusual fades occurring and in general my signal level was down on the
s-meter with the same uplink power.  This surprised me since my squint was
better later [~3 deg].

Now the stations I talked to reported I had a good signal at this time???
Your plot of AGC showed higher in the early part of the pass.  Later there
were several times the noise floor really jumped when there were no signals
on the frequency.  Seemed like the transponder noise rose.

I did not trigger LEILA for the first hour, but occasionally toward MA 40+
both I and the station I was talking with triggered LEILA a few times.
There was much less activity then.  I tuned around later to hear many more
cw stations than ssb.  Guess LEILA was lonely and wanting some company to
visit...or the threshold had been set lower later.

I also experienced carriers on the frequency or tuning thru, and a couple
cases of people transmitting either ssb or cw on top of the existing QSO,
which suppressed our signals [AGC?].  I was able to find my down link
fairly easily in the beginning by listening to the beacon [2401.299] to
determine the doppler offset [-24 KHz at 0744 utc] then picking a clear
receive freq. [IF] up band a ways and calculating my listening freq [Frx =
2278.005 - IF].  Then by calculating my transmit freq. [Ftx = Frx -
2836.990] and adding the doppler offset to the transmit freq. [since it is
an inverting xponder], my Tx was within a couple KHz.  That saved a tedious
xmtr tuning with potential interference to others.

Thanks for the very informative AGC plot.
PS:  The above Rx conversion factor [2278.005] takes into account my LO
error of 5 KHz

At 07:44 PM 7/21/2001 +0200, you wrote:
>Hi sat-ops,
>based on the information of the command team, I plotted a comparison for
>the U-Band AGC on the orbits 256(1st transponder period) and orbits
>330+331 (running xpndr period). 
>Many ops complained about the bad rx sensitivity of this 2nd period. The
>reason seems to be a non-optimum LEILA2 setting. During first period,
>LEILA1 was active and produced mean AGC levels of around 5 dB. With the
>actual setting of LEILA2, some hams managed to drive the AGC to 15-20
>dB! So remember your uplink pwr from the last couple of days and reduce
>10dB.. this will be it after the proper LEILA setting has been loaded!
>This is not the fault of the AO-40 RX nor of the cmd teams (by the way:
>great job!).
>Somebody is just driving the AGC up.. and he won't notice.. because he
>is still 7 dB  below the MB (this is how the AGC limit is set..). 
>My advice: 
>1. find out how long you can increase your ERP while monitoring your
>2. if you found the compression point, go back 1/2 to 1 s-levels.. 
>3. this way YOU are not the one driving the AGC.. repeat after every
>Of course, after commisioning of LEILA2, this will be all obsolete.. so
>don't flame me to long for this.. ;-)
>73s and see you on the bird!
>Achim, DH2VA
>Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
>To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org