RTLSDR

EDIT: It was pointed out below by u/lukmly013 that SDR++ supports RTL-SDR directly. I have removed the rtl_sdr driver app and it works.

So, it is as simple as downloading the SDR++ app and enabling the USB-C port. No need to mess around with the driver app and its security settings.

This is a PSA as I could not find online whether a GrapheneOS would be able to run an SDR dongle or not.

I was skeptical about this working because GrapheneOS has several hardened security features and does not allow root access. ~~Since the RTL-SDR dongle is a USB device that requires coordination between a "driver" app and second SDR app I wasn't sure if such a configuration would work.~~

Conclusion: It does work!

I am using a USB-C to USB 3.0 OTG adapter and the rtl-sdr blog v4 dongle with a generic antenna. My phone is a Pixel 7.

The SDR app I have used is SDR++: https://github.com/AlexandreRouma/SDRPlusPlus/

~~The driver required is "Rtl-sdr driver", available via F-droid: https://f-droid.org/packages/marto.rtl_tcp_andro/~~

Both of these can be downloaded via Obtainium.

As for the phone settings:

Under "Security" settings, make sure the USB-C port is not set to "Off" or "Charging-Only".

In that same menu, if you see the sub-menu "USB peripherals", make sure that new USB peripherals are allowed. In my case I am almost sure that I had this sub-menu before, but I don't see it anymore.

~~In the app info menu of the Rtl-sdr driver app (long-click on app icon), toggle to ON the "Exploit protection compatibilit mode"~~

You should now be able to open the SDR++, click play, and find some bands.

This was enough to get the RTL-SDR to work in my phone.

Hopefully someone else finds this useful.

I’ve been working on improving performance and portability of my V-dipole for NOAA weather satellite reception.

Previously, I had the antenna mounted to a PVC pipe stuck in the dirt in my backyard at the appropriate 0.44~ish meters.

Today, I tried it in the front street with a new free standing mount. Despite being at the appropriate height, SNR was terrible unless I physically touched the antenna rod connected to the center conductor. Also, there’s already a ferrite choke on the cable close to the antenna.

I’m trying to work out how much could be different between my front road and backyard. Is it possible that the layer of asphalt is not acting like an appropriate ground plane mirror? Should I create a physical ground plane? For the record, grass was wet and asphalt was dry.

I’ve ordered a cheap NanoVNR to investigate, but in the meantime, I thought I’d ask since I only get so many chances to test the antenna.

Took me a few days to get around to it, but here's two SDRs tuned to 137.9125MHz (frequency for APT from NOAA18) and 152MHz (frequency I found with some pager traffic).

Though there wasn't always a perfect correlation (I assume there are other pager frequencies in use), there were definitely instances where a pager message corresponded perfectly with the broadband signal dip at the APT frequency. This is a solid 10+ MHz away and through a SAW filter, so I suspect the dip is less overloading the SDR and more some internal gain adjustment? I had auto-gain turned off.

Either way, it doesn't seem to impact my APT signal reception, it's just an odd quirk.

Everyone knows helix antenna is needed for capturing NOAA satellite images, due to circular polarization of the signal, right?

As I was listening to ISS APRS repeater (with great success!), I noticed NOAA 19 would pass over me shortly. Since the dipole was already set up outside, I decided to give it a go.

Software used:

• GQRX to capture the audio
• Gpredict to know when to start the recording, and to compensate for the doppler shift
• noaa-apt to convert the audio file to an image

Hardware used:

• RTL-SDR.com branded USB dongle
• 3 lousy USB extension cords
• "Bunny ear" retractable dipole antenna that I got in a bundle with one of the SDRs

Now, there is not much to see in the image, but I sure as hell can spot some clouds there, and that's much more than I actually expected!

I've had a sdr sitting in my drawer for a few months now (was going to use it to sniff for weather stations near me to feed to my home assistant)

Didn't end up going in that direction, but I would like to play around with it!

Where are some good places to start, what are your use cases?