Following my previous observation of TRITON-1, I’ve captured another pass (Observation #14840214) for PRATHAM (41783) with my station (4950 - jp7dvx).
Once again, the waterfall shows very clean Doppler curves (around +12 kHz). Since the status is “Unknown” again, I am curious: is this characteristic signal behavior for PRATHAM, or am I catching another “unexpected visitor” passing through the same frequency band?
Your insights on how to identify these signals would be greatly appreciated.
I just want to add some information to your interpretation of this observation.
If all is set well, and the TLE for the satellite you are observing matches the satellite, your satnogs station is compensating the frequency “drift” caused by the speed of the moving object. So, a valid observation should be as close to a straight line as possible.
This also causes terrestial signals which are being picked up on that same frequency. do shift with that compensation and cause a doppler curve in the waterfall results.
So the signal showing is not the satellite but could be caused by anything local, even some radiation from an Internet / network router.
For example, from my S-band station, this is a valid one, because the Optsat is classified and does not get a daily tle update
while this one is failed, this is a local signal which follows the tuning doppler and is a locally received signal.
Last one https://network.satnogs.org/observations/14725401/
Shows the satellite in the center, which makes it valid, and also shows some local signal being moved over the waterfall because of the doppler tuning.
Thank you so much for the brilliant explanation! That really is an eye-opener.
So, because the SatNOGS system compensates for the satellite’s Doppler shift, a true satellite signal shows up as a straight line, while my local interference gets wrapped into that beautiful “Doppler curve.”
Using a mobile antenna on my second-floor balcony definitely makes me vulnerable to picking up local noise sources like network routers, but now I know that I’m essentially visualizing my home’s local RF environment being warped by orbital tracking!
I really appreciate you taking the time to share this technical insight. It makes tracking so much more fun.
Thank you so much for the brilliant explanation! That really is an eye-opener.
So, because the SatNOGS system compensates for the satellite’s Doppler shift, a true satellite signal shows up as a straight line, while my local interference gets wrapped into that beautiful “Doppler curve.”
In fact, looking at one of my other recent observations (Observation #14840228 for NOAA 6), I noticed that even the decoded data tab was full of random “E” and “T” strings (like E E E U EE, A TEEEE E). Now it all makes total sense—the CW decoder was simply mistaking my local noise curves for Morse code!
Using a mobile antenna on my second-floor balcony definitely makes me vulnerable to picking up local noise sources, but now I know that I’m essentially visualizing my home’s local RF environment being warped by orbital tracking.
I really appreciate you taking the time to share this technical insight. It makes tracking so much more fun!
Inspired by this, I’m thinking of adding a proper bandpass filter right before the dongle to clean up the frontend. I’ll be very curious to see how the waterfall changes on my next passes!
Thanks for following up! Just to clarify, my current RX antenna is mounted on the indoor side of my second-floor balcony window—specifically, indoors just behind a double-pane glass door. Because of this, it tends to pick up various local electronic noises around the house.
That’s why I’m really hoping the upcoming bandpass filter and LNA will help clean things up!
Is there no way to place the antenna outside . Over here in the EU the double pane glass appears to contain metal damp coating between the layers keeping the temperature inside but that also effects the reception.
I don’t disagree on the choice of filter and LNA but if you could only have the antenna on the outside of the window that would make a great improvement. There are cable guides which fits between closed window, however they usually come with F type connectors, but all that helps moving the antenna out a bit helps a lot !
By the way, one big reason I usually keep things indoors is our brutal winter snow here in Hirosaki! A previous antenna got completely crushed and snapped by heavy snow, so I have a bit of PTSD from that.
That’s why I’m hoping the upcoming filter and LNA can save the day without me having to brave the snowdrifts quite yet!
