Update on FunCube-3 / EO-79 Interference
Yesterday I reported on my observation of a possible 25k-wide data stream interfering with amateur CW & SSB on FunCube-3 / EO-79 (QB50P1). I was not able to decode the data nor did I see any obvious match for a source (terrestrial nor another satellite).
On today's 16:14 UTC pass over the USA East Coast, I saw the same wideband stream resembling telemetry data but would like to add to yesterday's comment.
From watching numerous hams attempt to find their downlink signal or in
some cases make successful SSB or CW contacts, it became obvious that the "data" stream that I was seeing was only present when someone was actively transmitting through the transponder. No carrier on the uplink/downlink - no wideband signal. But when there was an SSB or CW signal present, the wideband stream would begin also.
Please note that the match is not EXACT... sometimes there was a slight delay in the appearance of the wideband stream when the transponder was activated. But when you watch it "live", the relationship was obvious.
I am not even remotely familiar enough with how a liner transponder works offer any technical explanation for this behavior, but just wanted to add my observations to the conversation.
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
73,
-Scott, K4KDR Montpelier, VA USA
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.
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 [email protected] 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. _______________________________________________ Sent via [email protected]. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
participants (3)
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Dani EA4GPZ -
Scott -
Wouter Weggelaar