Observation 314679: LILACSAT 2 (40908)


Regarding Observation 314679

In the last few weeks, I have been able to pick up several passes of LilacSat-2 in which the transponder was turned on. Generally, they look pretty typical - lining up right in the middle of the waterfall for the entire pass. Tonight, I attempted to work the satellite myself, and was finally successful (barely) at making a contact with K4KDR. Came back inside and checked my vetting queue and was presented with this. What the heck? Was it downlinking off-frequency for half the pass?



Is that your transmitter?


That’s the first thing I thought:

“there I am, keying up on the downlink frequency again”

But no way, had I done that, I would’ve blown out the RTL-SDR. I was standing at the end of my driveway, about 50 feet from the SatNog antenna, transmitting at 10 watts through an Arrow II.

This was from the spacecraft, I think.


Here’s another instance of the same thing. Only barely visible at the beginning of the pass:


In this one, I purposely keyed up on the downlink frequency (at only 5 watts!), and sure enough I wiped out the receiver.

[edit] also to note, I was announcing frequently (probably 10 times throughout the pass), and that doesn’t seem to be visible, so I doubt the ghost image in the original post is a harmonic or something like that.

Interesting with this pass, is the downlinking telemetry is indicative of FM transponder mode, but neither me nor K4KDR were able to get in.


the only FM voice I hear is you testing. The other on the waterfal seems to be some type of FSK beacon. The blurbs look the same and are at equal spacing. maybe the bird has changed modes.


No, this is the telemetry style when the sat is in FM voice mode. Typically it does this until it “hears” an uplink, then it stops downlinking telemetry. When it it is “telemetry only” mode, the bursts are very short, and resemble APRS packets (although I’m not completely sure what modulation is used).


Could it be you forgot to set a PL Tone on your uplink sonits not hearing you?


My understanding is that there is no PL tone required.


Interesting. This observation:

is centered on the 437.225 4k8 telemetry channel, yet there is no telemetry seen on that frequency. There is, however, that FM downlink-like signal at about 200s about 10 kHz below the expected tlm frequency. The same pass that I observed (centered on the 437.200 fm downlink frequency) shows the fm repeater on (or what is typically visible when it is on):


and I can almost make out that rogue output that is clearly seen in the 317712 observation.

I wonder what is going on, here.