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: [email protected] [mailto:[email protected]] 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" [email protected] To: [email protected] 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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