Hello, i recently put up my antenna on my roof, it’s a turnstile cross-dipole 137-152MHz.
I tried listening to NOAA satellites just by putting the RTL-SDR into my computer and i saw a little bit of data come through ( it was a bad pass, but i at least confirmed i got something )
Now when trying to listen via satNOGS, i get nothing.
Here’s an example of what i get:
https://network.satnogs.org/observations/11689282/
Does anyone have any ideas what could be the issues?
Thank you in advance
I guess i should’ve provided some more information, i’m using RTL-SDR v4 on a RPI 5
The antenna is mounted on a chimney and i have a cable that runs 5m from the antenna to my RPI, the cable connection works, as stated before.
Antenna
I notice a lot of values being reported “null” in your metadata and the one most hitting my eye is:
Thank you so much!!!
I changed the gain to 30 just to test about 3 minutes before my next pass and i actually got something.
https://network.satnogs.org/observations/11689718/
Now how could i optimize the best gain value? I read the wiki about it, but it didn’t help me much, is trial and error the best approach?
Excellent result for now ! By looking at the image you appear to be somewhere in Italy ? Might even be Greece …
For checking the best gain setting it’s recommended to stop the running satnogs station and start some SDR software like gqrx, sdrpp or, depending on headless system, rtl-tcp server on the satnogs station and some client on another system.
By running sdr rx software you can adjust the gain as high as you barely see the noise lever rise in the waterfall. If you raise the gain with 3 dB and the noise floor raises more as this 3 dB your gain is to high (my general rule…)
Do you have any experience with SDR software ?
You’re close, the station is in Slovenia and no, i have no experience with SDR software.
On what kind of system are you running the satnogs station ? Something with a desktop environment ?
Not really, RPI lite OS, meaning no desktop.
You wrote you did put the rtl-sdr in your computer so you must have some SDR software experience ?
Oh well i know as much as my friend told me 
I used SDR++, that’s really the only software i have experience with, could i use that to identify the ideal gain?
Yes you can,
Below a table with on the first row SDR++ values when you use a RTL-SDR and the second row is the corresponding SatNOGS (Soapy) gain value.
RTL-SDR gain Values:
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6
Alright can someone explain me some satNOGS settings?
I’m taking inspiration from this observation, they got a really good image:
https://network.satnogs.org/observations/11697821/
This is my latest observation, it’s getting better but i still need to adjust the gain:
https://network.satnogs.org/observations/11694125/
This is what i’ve managed to decode from it, would like to point out bad signal at the start and finish, the disturbance can be seen on my waterfall, the signal is very messed up at the end
this is their metadata:
{
}
I have a couple questions:
Thank you for taking your time to read all of this
I think your results are getting better and the image looks better as what I can receive over here in the Netherlands in a very crowded environment.
Keep in mind the other observation has a station at >400 m ASL so that might be in a very quiet reception area.
The other settings from the metadata I am not going to explain. The RSp sdr device has completely different gain settings, as can been seen in “other settings” and “dev args” so that’s impossible to compare with your device / device settings.
Move the rtl-sdr to the PC with sdr software. Try if a gain of 40 is not just a bit to high , amplifying just a bit more noise which you see in your image.
@saltysoldier23. I have a couple of SDRPlay RSPdx’s that I use for normal satellite work. I don’t use them on my SatNOGS stations……so I can’t answer all your questions. Below is my understanding of some of the SDRPlay settings and features and how to use them.
In regards to the SDRPlay gain settings, the SDRPlay has a RF amp and an IF amp. The way they work is that they run full gain but use an attenuator to reduce the gain. Hence the RFGR (RF Gain Reduction) and IFGR (IF Gain Reduction). This means that a Gain Reduction of 5 is only a small attenuation (ie still lots of signal).
This is very different (back-to-front) to most SDR software which has a gain control where 0 is minimum gain. Some have both RF and IF gains but they tend to use 0 as a minimum gain.
Some SDR software tries to combine these two gain settings into a single gain figure using some sort of translation. I have a vague recollection that the RTL-SDR has both a RF Gain and an IF Gain but the drivers tend to use the single gain figure. I think the SatNOGS Gain-Mode: “Settings Field” is used to switch from a single gain mode to the dual gain mode.
With regards to sample rates for the SDRPlay devices. They have a number of Sample Rates that are default. If you choose something else the software does some trickery to get it to the required sample rate. You can use SoapySDRUtil to find the rates. They are 200kHz, 300kHz, 600kHz, 1.536MHz, 5.0MHz, 6.0MHz, 7.0MHz & 8.0MHz. I understand that these sample rates are also tied to a bank IF Filters and the sample rate sets the filter bandwidth. So this means selecting one of these sample rates/ bandwidths is generally the best option. Typically you want something a little bigger than the bandwidth of your signal so you don’t get hit by adjacent channel noise. I tend to use 1.536MHz for general use but something smaller may be better for SatNOGS.
The dev_args are generally switches that can turn on/off various features of your particular SDR. I don’t use these much so am not really familiar with each. The Bias-Tee is often done separately (ie not via this method). There is more than one way to skin a cat!!!. I tend to run my satellite system with AGC turned off. I am not sure if you are overriding the RFGR and IFGR with a AGC, Have a play with removing that setting. I have never enabled the DAB Notch setting, but have a play removing that also.
Finally LNA’s. The noise figure of a radio system is generally most influenced by the first amplifier that the RF signal comes upon. The noise figure of most SDR’s is not that good. Often around 3-6dB….some are worse. Adding a bandpass filter and a LNA with a good noise figure (less than 1dB) will improve the overall sensitivity of your system. The gain is less important. In fact you may need attenuators to make sure it does not overload your SDR front end if the gain is too high. You can wind back the SDR gain to help with this…but if it is overloaded it you need to reduce the signal level.
This is what I have gleaned about the SDRPlay SDR’s over the years. I hope it helps.
John VK4JBE
Thank you, this was very insightful!
Firstly i’ll to find the right gain ( good NOAA passes don’t care about my work schedule so i haven’t had a chance yet )
That probably won’t make the signal perfect, but will help at least. I’ll try to temporarily remove the metal chimney that is nearby, i’m suspecting that is reflecting a lot of garbage into my antenna.
I’ll also have a look at some LNA’s since i see a lot of noise in the waterfall.
Thank you everyone for taking your time and helping me
Will keep this post updated with my findings!
