[amsat-bb] Update on FunCube-3 / EO-79 Interference

Wouter Weggelaar wouterweg at gmail.com
Mon Nov 14 19:18:38 UTC 2016

Dani, you are right.

What you are seeing is the combination of the attack and decay time of
the AGC with a strong signal.
You can see the AGC bringing the noise back up as soon as the carrier is gone.
The transponder is fast-attack and slow decay on the AGC.

Since the downlink passband is a bit stronger as compared to
FUNcube-1, you can now more clearly see the passband.

Wouter PA3WEG

On Sun, Nov 13, 2016 at 6:20 PM, Dani EA4GPZ <daniel at destevez.net> wrote:
> El 13/11/16 a las 17:55, Scott escribió:
>> I have uploaded a screen shot of my waterfall showing how the wideband
>> stream comes & goes in response to activation of the transponder at:
>> https://dl.dropboxusercontent.com/u/31460496/ham/2016-11-13--EO-79.png
> Hi Scott,
> I think that what you're seeing is just the noise floor of the
> transponder. I have no experience with FUNcube-3, but your picture looks
> very much like the noise floor I have seen on FUNcube-1. On overhead
> passes, it's quiet noticeable, even with only a 3 element yagi.
> Keep in mind that (usually) a linear transponder is running all the
> time. It doesn't have to be activated by an uplink signal.
> In general, AGC action may cause the transponder's noise floor to vary
> with input signals. One expects that if there are strong signals the
> transponder's noise floor will become weaker. This behaviour depends on
> lots of design parameters, so this need not always be the case.
> 73,
> Dani EA4GPZ.
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