Re: [amsat-bb] get a clue...

["Lee" <lee-fl@xxxxxxxxxx>]

----- Original Message -----
From: "i8cvs" <domenico.i8cvs@tin.it>
To: "Lee" <lee-fl@cfl.rr.com>; "AMSAT-BB" <amsat-bb@AMSAT.Org>; "Kevin
Schuchmann" <kschuchm@pacbell.net>
Sent: Tuesday, December 17, 2002 9:00 AM
Subject: R: [amsat-bb] get a clue...


>
> The problem is that many radio operators in the passband instead to
> disregard those stations using very high level downlink through the L-band
> congratulates instead with those L-band operators for their strong signals
> and they are happy to make QSO hearing strong signals so that the pile-up
> over a 6 dB or more signal over the beacon is higly populated and
> continuously operating particularly when the moon is not in range for some
> EME operators.

Exactly my point Dom.  There are many people being lead astry into thinking
their receiving arrangement is adequate because they hear these MB+6db
stations with a usable SNR.  Unfortunately what they don't hear is the
stations operating properly 10db below the beacon because the local noise
floor is too high.  Further if they don't understand that they are only
hearing the L-band stations and try to uplink on U-band they will inevitably
run excessive amounts of power trying to hear themselves.

> > 2. The L-band rx AGC does not restrict users of this band to the
> recommended
> > MB-10db signal level.  As a result some stations attempt to achieve the
> same
> > excessive levels using the 70cm uplink resulting in decreased U-Rx
> > sensitivity.
>
> Stations using excessive 70 cm uplink power cannot achieve the same
> excessive level of those using L-band because LEILA put  a notch and
> the siren to the U-band offending signals for level just 8 dB belove the
> beacon. If i use the U-band uplink i cannot desense the U-band receiver
and
> i cannot desense the L-band receiver at all because of the above LEILA
> limitations.

Clearly from the AGC data there are uplink signals being sent that have the
effect of reducing the receiver sensitivity for everyone else.  From what I
have seen LEILA operates at the IF level.  This appears to be after the U-Rx
AGC.  As a result even though LEILA notches out the offending station's
downlink, the uplink will continue to drive the AGC.  It is not hard to
imagine a station who copies the the MB+6db stations with a 10db SNR but
can't find his U-band uplink and continues to turn up his transmit power
without even hearing LEILA' s warning siren.

> Normally my 70 cm and 23 cm TX are ON all the time and some time i prefere
> to use the U-band uplink but as soon LEILA get a notch on me i can switch
> immediately to the L-band and i can continue to discusse with my friends
> even with a stronger signal over the LEILA siren using the L-band uplink !

Perhaps I'm missunderstanding what you are saying here.  Why not set a good
example and just reduce power to the proper level rather than switching
modes and further exceeding the recommended operating condition?

> > Take a look at some AO-40 AGC data downloaded from the archive for this
> > month.
> > http://home.cfl.rr.com/lmclamb/ao40agc1202.html
> >
>
> A test of desensing  was made by G3WDG, DJ1KM, 4X1AS and my self some
monts
> ago and this indicates that using U-band the SSB is mostly affected by
LEILA
> and that CW or a steady carriers like SSTV are  less affected  by LEILA
for
> example.

I believe you are exactly right on this Dom.  The result is the high AGC
values shown in the telemetry data.  As a result, other stations must run 5
times as much power to overcome the 7db of AGC which exsists over 50% of the
time.

73,
Lee-KU4OS


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