[amsat-bb] Re: (no subject)
bruninga at usna.edu
Thu Feb 14 05:56:10 PST 2008
> 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
> > 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
> 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
> 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
> - 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
> satellite transponder i.e. about 1 watt only for you and a
> few mW only for
> 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
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of
> the author.
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