[amsat-bb] Re: (no subject)

[Robert Bruninga]

> For the [below] mentioned reason the answer C 
> ( To avoid limiting the signal of the other 
> users ) stands correct. 

But only because B is also true. Because the satelite
transmitter power is limited to 1 watt.  If the Satellite's
power was not limited, then the relative powers of the uplink
stations would not matter.  

I agree that the proper "concept" we are teaching here is C.
But B is a very poor choice for a "wrong" multiple choice
question.  Option B should not be listed.

> -----Original Message-----
> From: amsat-bb-bounces at amsat.org 
> [mailto:amsat-bb-bounces at amsat.org] On Behalf Of i8cvs
> Sent: Wednesday, February 13, 2008 9:56 PM
> To: Clint Bradford; AMSAT-BB
> Subject: [amsat-bb] Re: (no subject)
> 
> ----- Original Message -----
> From: "Clint Bradford" <clintbrad4d at earthlink.net>
> To: <amsat-bb at amsat.org>
> Sent: Tuesday, February 12, 2008 7:24 PM
> Subject: [amsat-bb] (no subject)
> 
> > Is everyone satisfied with this exam question?
> >
> > E2A08 What is the primary reason for satellite users to
limit their
> > transmit ERP?
> > A. For RF exposure safety
> > B. Because the satellite transmitter output power is limited
> > C. To avoid limiting the signal of the other users
> > D. To avoid interfering with terrestrial QSOs
> >
> > I just find its Answer B "incomplete" ...
> >
> >
> > Clint Bradford, K6LCS / KAF3359
> > 909-241-7666
> 
> Hi Clint, K6LCS
> 
> In my opinion question B is not incomplete but it is useful 
> for an exam
> because it is deceitful to decide in favour of answere C or 
> not and infact:
> 
> The primary reason for satellite users to limit their 
> transmit EIRP is not
> because the satellite transmitter output power is limited (B) 
> but only to
> avoid limiting the signal for the other users (C)
> 
> Lets work an example considering a tipical linear transponder 
> for CW and
> SSB like those used for many OSCAR satellites.
> 
> AGC threshold   = -77 dBm
> AGC dinamic range = 50 dB
> Output level above the AGC threshold  = + 30 dBm = 1 watt
> 
> Now suppose that you are the only user with an EIRP of 1000 
> watt arriving
> at the satellite receiver with a signal  level of just - 77 
> dBm i.e. the
> signal level at wich the AGC start to be operational.
> 
> In this condition the transponder output power will be 1 watt 
> only for you.
> 
> Now suppose that I come up with you at the same time arriving
at the
> satellite receiver with the same level of - 77 dBm  and we
both send a
> stady carrier
> 
> In this condition and since the transponder is linear you 
> will get 0.5 watt
> and I also will get 0.5 watt i.e. 1 watt in total because the
total
> available power from the satellite linear transponder will be 
> splitted in
> equal parts between you and me.
> 
> Now suppose that you only increase your EIRP by 10 dB i.e. 
> you transmit
> with 10.000 watt EIRP
> 
> In this condition your signal level at the satellite receiver
will be
> - 67 dBm and so you will activate the AGC going into it's 
> dinamic range
> decreasing the satellite sensitivity by 10 dB for me.
> 
> Since I cannot increase 10 time my EIRP my signal level will 
> be now barely
> audible into the noise but you will get about the total power
from the
> satellite transponder i.e. about 1 watt only for you and a 
> few mW only for
> me
> 
> In any case your increase of EIRP x 10 time in power has not 
> created the
> condition to increase the total transponder output power wich 
> stand the same
> 1 watt but you have only reduced the satellite receiver 
> sensitivity by 10 db
> for me and for the other users.
> 
> For the above mentioned reason the answere C ( To avoid 
> limiting the signal
> of the other users ) stand correct.
> 
> 73" de
> 
> i8CVS Domenico
> 
> 
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