Re: P3D testing

• Subject: Re: [amsat-bb] P3D testing
• From: "John P. Toscano" <tosca005@xxxxxxxxxx>
• Date: Tue, 19 Sep 2000 17:02:08 -0500

```Franklin Antonio wrote:
>
> At 01:27 PM 9/19/2000 -0400, Howie DeFelice wrote:
> >Does anyone know if during the transmitter/receiver testing they are
> >characterizing transponder gain ? In other words, if we know the receiver
> >gain and noise figure, the antenna gain, and the transmitter gain for each
> >band, we can assemble a matrix that would allow us to calculate a link
>
> I have repeatedly asked this question, and have carried on a long exchange
> of email with the P3D builders.  So far, I have had no success.  They seem
> not to grok the notion of "transponder gain".  Their responses always
> contain an explanation that the notion of transponder gain is meaningless
> because the transponder has AGC.  I'm glad to see that there is someone
> other than me who is interested in this subject.
>
> I think it's pretty important to know the transponder gain.
>
> I wish you luck.
>
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Hmmm...  Seems like a pretty easy concept to grok to me.  But failing
the existence of any such published figure, maybe we can calculate
it ourselves.  What is the minimum signal strength needed at the
satellite receiver to generate an intelligible signal?  What is the
transmitter output?

transmit power output
Transponder gain = -----------------------------

i.e., if the receiver needs 50 microwatts and the transmitter is
50 watts (totally bogus figures, I presume, just pulled out of
the vacuum of space or the vacuum between my ears), then the
transponder gain = 50 / (50 x 10^-6) = 10^6 = 1,000,000 = 60db.

Naturally, each receiver may have a different sensitivity and each
transmitter may have a different power output, so the transponder
band pair.

So, are those figures (receiver sensitivity and transmitter power
output) published?

John (KBØZEV)

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