I’m having a really hard time getting my new station up and running. I’m using a Raspberry Pi 3+ and RTL SDR Blog v3 dongle. Gain is set to 44.6 dB in the Satnogs client. For the preamp, I’m using a 40 dB pasternack model, hooked up to a mag-mount antenna.
I know the antenna is not the best: a vertical 1/4 wave dual-band mag mount, same thing you’d stick on your car. It’s also stuck to a cookie sheet outside my window on the second story, so it’s got a clear view of only the north half of the sky. But I’ve heard XI-IV and CUTE cubesats plenty of times with a hardware radio on a mag mount. A proper eggbeater antenna should be arriving in the mail soon.
I’ve only seen actual satellite data from NOAA 18 way in the beginning, and nothing since. Observation. I haven’t seen any other signs of satellites on any of the passes, even the NOAA ones that were marked automatically good. Observation page.
I’ve swapped the preamp between a 20dB model and a 40dB model several times in the past week, but the waterfall display always looks the same, it doesn’t get brighter/dimmer. I’ve tested the hardware preamps on a network analyzer, and they are working fine. Also I’ve changed the gain on the RTL SDR from around 20 to 30 to 44.6 several times and the waterfall stays the same color. What’s up with that?
What gain settings for the RTL SDR do other omnidrectional stations use? I’m assuming a 40dB preamp is enough gain.
Any other thoughts on what I might test? Thanks in advance!
It might already be too much gain!
Start without preamp and a gain setting somewhere around 30 with an rtlsdr.
You can use an interactive SDR application on your PC in combination with rtl_tcp running on the Pi to tune your setup. See https://wiki.satnogs.org/Adjusting_the_SatNOGS_Client
Skip the ‘kalibrate’ part at the beginning.
+1 on lower the gain. You can see that setting the gain lower here https://network.satnogs.org/observations/241603/ which is 36.4 you can see the signal and get better result on decoding.
The waterfall, after some changes on plotting, is adaptable so you are not going to see any difference on colors but only in the scale next to the waterfall. For example compare https://network.satnogs.org/observations/241603/ and https://network.satnogs.org/observations/246403/ the first goes from -10 to -70 and the second goes from 0 to -60.
About the NOAA observations, they are auto-vetted as good, because there are decoded data on them. The decoder wouldn’t decode if there was nothing there, so you got something but it’s not visible in waterfall as the gain was too high, making the noise floor to cover the signal.
@DL4PD, less gain worked! Thanks for the tip. I’m running RF gain now of 28.0 with no preamp, and I’m getting some signals. All of the passes from UTC 2018-09-13 are in this configuration, link. I should have also mentioned that the coax run is about 3 meters.
There are a lot of local signals that are very strong, I wonder what those are? Spurs or noise from the RTL SDR or raspberry pi? See passes https://network.satnogs.org/observations/248178/ and https://network.satnogs.org/observations/248184/ . How should I mark those passes? I would mark them as Failed because nothing was decoded.
With regards to the Adjusting_the_SatNOGS_Client wiki page, I think that is only for finding the PPM offset? Should I be concerned with frequency offsets yet? I’m just trying to get the power levels in the right ballpark. I can tune around with gqrx, but local stations are not a problem. I have access to good test equipment, I might try putting a weak CW tone into the RTL SDR and see where the noise floor is.
@fredy thanks for the tip about the waterfall colors. I’m assuming the units are dBm not dB? Is it possible to make the colors absolute instead of relative, so we can color-compare different station configurations, and also different stations? This way it would be easy to see that I had too much gain, and also compare to other stations that have the same antenna as you.
Although you didn’t have a decoding on those, they should still be vetted as “good” since the satellite transmitter is clearly active and visible in the waterfall.
You can check this page on the wiki on how to vet/rate observations based on results. The main concept is that Good/Bad are counting against the Transmitter (and thus Satellite) success rate, while “Failed” (vs Good and Bad) count negatively on the Ground Station success rate. (e.g. an obs rated “Bad” would be +1 for the station and -1 for the Transmitter)
and btw once again welcome to SatNOGS Network @bklofas !
Thanks for the info on rating observations. With my gain problems somewhat sorted, and my new antenna arriving soon, I should have a bunch more successful passes soon.
Bryan (personal response from an emailed inquiry about my station),
Be prepared to be underwhelmed:
Antennas are homemade, and as you can probably see by some of my waterfalls - the circular polarity is questionable at best. However, the effort seems to at least work somewhat, so I’ve left it as is. ALL of my antennas are in my attic, which is about 20ft above ground level. Roof is just wood construction and asphalt shingles.
Feedline for the satnogs antennas are only about 10 feet long (RG-8X), and I do not use any LNA (I’ve got a cheapo RTL-SDR LNA in my amazon basket, and I’ll order it one of these days). Gain setting in satnogs setup is 48.0 (I am indeed using a V3 RTL-SDR.com dongle).
Not sure about IF/BB gain settings - I’m assuming they are at default values because I haven’t touched them.
Let me know if you have any other questions.
the issue of initial tuning and gain setting has been a bit of a pain for newcomers since we switched to an adaptive waterfall. I wonder if there would be a way to switch that off for initial testing?? @fredy @surligas ?
We discussed this on the chat channel the other day, and it would be relatively easy to write out waterfall statistics (mean power level, etc) to the metadata that’s stored with an observation. That could be useful to keep track of how the gain is changing.
@K3RLD Thanks for the info on your station.
It’s super interesting seeing all the different values for omni stations. You’re running no hardware preamp and 48dB of RTL gain with almost no coax loss, Burns Fisher has a 20dB hardware preamp with no RTL gain and a few dB of coax loss, I’m currently running a 20dB preamp with 8dB RTL gain with no coax loss. All omni antennas of varying types, so they should be within 5 dB or so.
@cshields and @cgbsat this would be very helpful. With absolute waterfall measurements it would be easy to do SNR measurements also. Then picking a CW satellite and doing a quick link budget would let me know how my station is doing. This comment is also a good push for me to register and get onto IRC, haha!!
@bklofas: Note that you can join IRC also via Matrix in the browser, https://riot.im/app/#/room/#satnogs:matrix.org
I do not know if this is so easy. To measure the power you need a frequency span of the transmitted signal. This of course depends on the transmission scheme and assuming that the signal is perfectly centered.