I wanted to share my failure (thus far) to determine why my garage door opener doesn't work when it's below ~50f and the light is on. I thought it was interference from the LED bulbs, so I replaced them. That didn't work so I bought a plug-in shop light and an adapter to turn the light socket into an outlet, so the light source can be far away from the antenna - no luck.

So I decided to get more technical. I dug out the RTL-SDR I bought ten years ago and installed SDR++. I was hoping to find interference from the light or opener in the range of the emitter, but I didn't.

First, I had to find where my two clickers emitted. That's the waterfall you see. The two blips on the left are the newer (2 years) emitter, and that mess on the right is the older (20 years) one that is usually in my car. Yeah, wtf.

Now, I'm just a chemist, but that looks sloppy as hell. Not only is it sloppy, the freq. changes when I tilt the emitter. What could cause the frequency to drift when I rotate the device? There's nothing lose in there, it's a very simple circuit.

At least I knew where to look for interference, but when I took my laptop out to my garage, I found no evidence whether the light was on or off, but I have to hold the new emitter just inches away from the antenna to get it to work when the light is on - the old one won't work at all until the light times out. This remains true even when there are no lights connected.

So I'm no closer to making the door work. I think I'll try improving the antenna, which is currently just a wire hanging from the opener.

Hey everyone,

I’m currently running an NESDR Smart v5 with SDR++ from the top floor of my house (in the Montreal area).The antenna is on the window sill. Right now, my setup feels exactly like a car radio; I can mostly just pick up standard FM/AM broadcast stations and maybe 2 weather stations

I see other frequency spikes popping up on the waterfall, but they are too weak to pull in clearly. I'm using the stock bundled antennas (including the 22-inch telescoping whip), but I want to upgrade my system's "power" and reception range without building a massive, serious base station.

What are some small, budget-friendly things I can buy or DIY to instantly improve my reception?

I'm looking for things like:

• Cheap Antenna Upgrades: Are there simple, affordable antennas (like a portable dipole kit or a mag-mount car antenna) that work way better than the stock ones?
• LNA / Signal Boosters: Would a cheap inline Low Noise Amplifier (LNA) help boost these weak signals, or will it just overload my dongle?
• DIY Tricks: What can I do with cheap materials (like speaker wire or baking sheets for a ground plane) to squeeze more performance out of what I already have?

Just looking for some fun, low-cost modifications to help me hear more out there. Thanks!

Some of you saw my earlier posts about getting raw I/Q out of the Semtech LR2021 (the LoRa chip on the LilyGO T-Display-P4). Spent the last couple days poking at the limits and figured I'd share what I found.

The tuning range is way wider than the datasheet says - 100 MHz to 2.74 GHz and streams 16-bit I/Q. Which is the most significant finding, but I’ll go more into detail below and have lots of info on the repo - https://github.com/SAMS0N1TE/lr2021-sdr

Live decoding (P25, POCSAG, FM) is in LakeShark if you want the handheld side: https://github.com/SAMS0N1TE/LakeShark

Datasheet claims 150 to 960 MHz and 1.5 to 2.5 GHz. I didn't have a signal generator handy for every band so I used the board's own 40 MHz clock harmonics as markers. Tune to N+10 kHz, then N+30 kHz, and if the tone moves by exactly 20 kHz it's real RF and the synth is locked. Every step from 120 to 2720 MHz tracked except 2440, which was just buried in wifi. Below 100 MHz image cal fails and you get nothing. 100 MHz works (still flags IMG_CAL but tracks). 2740 MHz works, and at 2756 and up the PLL won't lock. So that gets you the top of FM broadcast, all of airband, the 1 to 1.5 GHz gap, and 2.5 to 2.7 GHz. Keep in mind these are leakage markers, so this proves the chain works there, not how sensitive it is. Also one board, one antenna. Your module might be different.

Sample rate tops out at 250 ksps. The I/Q rate is 4x whatever LoRa bandwidth you set. 125k and 250k are clean. 500k overflows the FIFO in about 2 ms and 1M in under 1 ms. That's not really the chip's fault, 500 ksps of 16 bit pairs is 2 MB/s which is the entire 16 MHz SPI bus before overhead. A tighter read loop or a narrower sample format (if the ROM has one) might push it. I've done 6+ minute runs at 125k with zero loss, haven't done long runs at 250k yet.

For gain I ran a weak HackRF carrier at 433.92 and stepped through manual gain. Steps 1 to 5 see nothing, 12 or 13 is where you want to be, boost adds maybe a dB. Chip AGC matches step 13 on weak signals but was about 20 dB worse SNR on a strong one, so a host side AGC picking a fixed step would beat it. Image rejection came out around 41 dB.

BLE works natively. The chip has its own Bluetooth LE packet engine and I hadn't touched it until now. Set it up for LE 1M on the advertising channels and it just started pulling ads. About 500 to 800 valid packets in 10 to 12 seconds per channel, 24 to 32 distinct devices. Coded and 2M heard nothing but nothing nearby was using them, so those are untested, not broken. There's also 802.15.4 (Zigbee/Thread), FLRC, wM-Bus and LoRa ranging in there that I haven't tried yet.

Repo has the probe tools, raw CSVs and the method if anyone wants to reproduce on their board. Would really like to know if other LR2021 modules hit the same edges.

Features

• 📡 Automatic scanning: hops across your frequency ranges (118–137 MHz by default) and stays on a range while someone is talking.
• 🎙️ Records every call: each transmission is saved on its own, with a short pre-roll so the first word isn't cut off.
• 🗣️ Voice detection: a built-in speech detector separates real voice from data bursts, dead carriers, tones and noise.
• 🎧 Play in the browser: click a waveform to seek, or turn on auto-play for new calls.
• 💾 MP3 and WAV: voice calls are saved as MP3 automatically; any recording can be downloaded as MP3 or WAV.
• 🌈 Spectrum page: live spectrum, waterfall and activity history, plus a spectrogram of every signal that was not recognised as voice.
• ✈️ Voice only: ACARS and VDL2 data channels are ignored by default.
• ⚙️ Web settings: device, gain, ranges, thresholds and MP3 options, all from the browser.
• 🖥️ Single native program: C++17, no Python, runs as a desktop app or headless server on Windows and Linux; open it from any phone or PC on your network.

Tell me, while I was waiting for the car, this map appeared on the dongle graph. Tell me, we have a digital weighing machine. If there's a theft going on with the remote, how can we catch it?

The battery on my old laptop died, so I gutted the pack and wired salvaged lithium cells to a BMS inside the chassis. It powers an ESP32 and an Ra-02 (SX1278) LoRa module running Meshtastic 2.7.15, through a buck converter set to 5V. There’s also a small battery level indicator on the lid.
Phone connects over Bluetooth fine, and I’m using the laptop itself as a Linux box to flash and configure.
• Clean up the wiring (it’s a prototype mess right now)
• Add an inline fuse
• Test range with a proper antenna
Any suggestions on power design or antenna placement are welcome. First time putting a node inside a laptop shell.

I recently brought a new rtl sdr v4 from robu to learn rf and find new things now i want to study the weather monitoring using these things

AIS Trail (https://map.aistrail.com) is a free live ship map, open to volunteer receivers anywhere. If you run an AIS receiver, one more output line adds your station.

• About a minute, no account: https://app.aistrail.com/stations/new
• AIS-catcher over HTTPS: -H https://api.aistrail.com/feed userpwd station:<KEY> gzip on interval 10
• Or plain UDP from rtl_ais, AIS Dispatcher, OpenCPN, kplex or Signal K
• Your station gets a public page counting the ships it heard first, with coverage and uptime; founding badge for the first 20; optional email if it goes quiet
• Non-exclusive, stop any time, no IP addresses stored. To be upfront: the data also goes into our paid data service, which keeps the map free. Terms: https://aistrail.com/legal/stations/

Questions welcome.

I have an Airspy HF+ Discovery and a MLA loop antenna. While tuning a frequency and getting a lot of noise, I can squeeze the SDR in my palm, and the noise will disappear and the signal improves. What's up with that? Faulty SDR? Not a showstopper, just annoying. I feel like my SDR might not be performing to its optimum.

Adding gain when you’re near a strong transmitter often makes things worse, not better. Past a certain point you’re just overloading the front end harder.

A preselector helps, but gets complicated fast when you’re monitoring a wider range rather than one specific band. Wider bandpass means more interference gets through, narrower bandpass limits what you can cover.

curious how people here actually handle that trade-off. Do you prioritize front-end filtering and accept the coverage limits, or stay wideband and work around the weak-signal performance hit?

Disclosure: I work in defense electronics.

​Hi everyone,

​I’m facing an issue with my PlutoSDR. It was previously stuck in DFU mode, and I successfully flashed the official firmware from Analog Devices.

​Now, the device is recognized properly by the computer and shows up in the system, but it is not receiving or reading any signals at all (completely flat).

​Has anyone encountered this issue before, or knows a reliable fix for it? Also, if anyone has the specific or original firmware/recovery files for this model, I would greatly appreciate it if you could share them.

​Thanks in advance for your help!

Hi everyone, I’ve been thinking for a while about buying an affordable SDR receiver, mainly to get started with HF radio listening. I don't think I want to use the dongle for VHF or UHF frequencies for the time being. I plan to use the receiver with a YouLoop or MLA30+ antenna.

As I mentioned, I don't want to spend too much, so I’ve been looking at options like the RTL-SDR V3, RTL-SDR V4, RTL-SDR V4L, and HTOOL SDR6 (which, from what I gather, is also based on RTL-SDR technology).

After doing some research, I’d prefer the V4 because it has an upconverte (which I understand improves HF reception compared to the V3's direct sampling) but I also noticed the V4L, which costs a bit less; given my limited budget, that might be preferable.

I would also like to try connecting it to the CB/11m antenna on my roof (using a PL-259 to SMA adapter) to get better reception on the 27 MHz band, provided it is feasible or advisable; I’d prefer to buy the receiver and run this test first, then get the loop antenna later so I don't have to spend a large amount all at once. However, it isn't strictly necessary: ​​if it turns out not to be a good idea, I’ll simply wait and buy the loop antenna at the same time as the dongle.

What do you experts think about these receivers? Which ones would you recommend, considering the price-to-performance ratio?

Thanks in advance for your help.