Tagged: rtl2832

Discovery Dish 1420 MHz Hydrogen Line Feed Tested with a WiFi Grid Dish

Thank you to Alex P for writing in and sharing with us his detailed evaluation of the Discovery Dish 1420 MHz hydrogen line feed when paired with a low-cost 1m WiFi grid dish. The goal was to see how well this near off-the-shelf setup performs as a hydrogen line radio telescope. The Discovery Dish feed integrates the dipole very close to the internal LNA and filters to minimize losses, uses a weather-sealed enclosure, and is built around a low-noise Qorvo QPL9547 amplifier, which has a very low noise figure at 1420 MHz.

Alex used 4NEC2 with a simple geometry approximation to analyze the beam pattern and also experimentally determined the optimal feed-to-dish spacing for the WiFi grid. The results show that the Discovery Dish feed significantly outperformed a more standard feed + external LNA setup.

Alex also shows how he uses aluminum foil, or conductive foam, to shield the feed from all signals during a background correction scan. Generally, for background correction scans, we recommend pointing towards a cold area of the sky (any area far away from the Milky Way with little to no hydrogen), but Alex prefers this method.

Discovery Dish 1420 MHz Hydrogen Line Feed Tested on a WiFi Grid Dish
Discovery Dish 1420 MHz Hydrogen Line Feed Tested on a WiFi Grid Dish

Building a DIY Off-Grid Weather Station with a Raspberry Pi and RTL-SDR Receiver

Thank you to Vinnie for writing in and sharing with us his home made Raspberry Pi based off-grid weather station, which uses an RTL-SDR to receive data.

Being somewhat disappointed with a cheap all-in-one weather station's data, lack of local storage and customisation possibilities, Vinnie decided he could do better and build his own custom solution instead. While working on an existing Raspberry Pi based ADS-B station that he had already deployed, he realised that the hardware was largely underutilised and would make an ideal platform for additional RF decoding tasks.

By adding a second RTL-SDR dongle and using the popular rtl_433 software, Vinnie was able to receive and decode data from an Ecowitt WS90 all-in-one outdoor weather sensor. Unlike many consumer weather stations, the WS90 operates as a simple one-way RF transmitter with no cloud dependency, making it ideal for local SDR-based decoding and long-term data ownership.

All weather data is received locally over RF, decoded into JSON, processed on the Raspberry Pi, and stored locally without relying on third-party cloud services. Rainfall totals, daily highs and lows, and historical trends are calculated entirely in software, giving full transparency and flexibility over how the data is handled. A simple web dashboard then displays current conditions and recent history on the local network.

The entire system runs in Docker containers alongside the ADS-B feeder, keeping services isolated and easy to maintain. Optional one-way data sharing to weather aggregation services can be enabled if desired, but the station functions fully offline by default.

In his post, Vinnie has written an in-depth overview of the hardware choices, RF decoding, data pipeline, and software architecture behind the project, including why certain sensors were chosen and how rainfall is calculated from raw impulse data. The code is all opensource and available on his GitHub.

Vinnie's Outdoor ADS-B + Weather Station, and the Ecowitt 90 Weather station.

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New RTL-SDR Blog Forum Active

We've just activated a brand new RTL-SDR Blog forum based on the Discourse platform, and we will be retiring the old phpBB boards. If you have any questions or want to share anything relating to RTL-SDRs, SDRs, or the radio hobby in general, please feel free to log on and make a post.

For troubleshooting questions, please be sure to include as much detail as possible about the issue, such as exact error messages, what you are trying to achieve, and ideally add screenshots showing your settings. Also, please remember that for questions relating to specific software, you will probably get the best help by asking in discussion groups specifically for that software, or by emailing the authors of those programs directly.

We've decided to retire the old phpBB forums due to excessive spam that has proved extremely difficult to combat. phpBB has limited plugins available that actually work for spambot detection. We've tried adding captchas, technical barrier questions, using spambot block lists, spambot blocking services, and setting a high security setting on Cloudflare. But nothing has been able to stop the new ChatGPT/AI powered spambots.

These spambots are particularly insidious because they ask legitimate-sounding questions to start a discussion and may even reply with legitimate-sounding responses. Later, once trust has been established with humans and the forum spambot detection software, they will start posting spam links, and editing old posts to include subtle spam links.

The new forums are based on Discourse, and are available here https://rtl-sdr.discourse.group/

Based on our previous experience, Discourse is a much more modern platform and has much better natural spambot protection, so spambots shouldn't be a problem on that platform.

If you've been a fan of these forums, please make an account on our Discourse forum. Thanks!

As usual, for inquiries relating to RTL-SDR Blog product faults, or shipping issues, please email us directly at [email protected] with your order ID number included for direct help.

The old forums will stay up for archival reasons, but they will be locked from now on.

DSDPlus Public Release Updated & Fast Lane Changes

The team behind DSDPlus has recently uploaded a new public release version 2.547. The last public release was version 1.101, released several years ago. Up until now, only DSD+ Fastlane customers have had access to the new version.

The new version adds new programs like FMP, which can be used to receive the FM signal from an RTL-SDR, Airspy or SDRplay SDR and transfer it to DSD+ over TCP. Previously, a program like SDR#, or SDR++ would have to be used along with audio piping software like VB Cable.Β 

Also introduced are numerous enhancements, including a single-receiver trunk-tracking mode that eliminates the need for dual SDR setups, a site loader GUI for rapid tuning and system selection, significantly expanded digital protocol support such as full P25 Phase II TDMA voice following, encryption algorithm and key ID detection, and GPS/AVL location and mapping capabilities. Hardware integration has also improved with features like bias-tee control for RTL-SDR Blog dongles, serial-targeted device selection, and smoother TCP-linked operation between DSD+ and FMP components.

The full list of changes can be found in the "Notes.txt" file in the DSDPlus zip file. The Radio Reference Wiki also has a summarized changelog.

The team also notes that they are now closing new signups to the DSD Fastlane program. FastLane was a program that allowed users to pay a small fee to receive the latest updates. They note that the program will remain active for users who have already signed up.

DSD Plus V2 Public Release with FMP24
DSD Plus V2 Public Release with FMP24

rtl_haos: An rtl_433 to Home Assistant Bridge

Thank you to Jaron McDaniel for writing in and sharing with us the release of his open source software called "rtl_haos". rtl_haos is a 'drop-in' bridge that turns one or more RTL-SDR dongles into Home Assistant friendly sensors via rtl_433 and MQTT. Jaron writes:

I just finished a tool that that bridges data received from rtl_433 into Home Assistant friendly entities. Basically allowing you to integrate anything rtl_433 can see into Home Assistant.

Basically you clone the git to a Rasberry PI, configure it for your MQTT server, plug in a RTL-SDR or two and you'll see entities with icons and units automatically assigned to whatever rtl_433 discovers.

This tool allows you to connect older and cheap non-Wi-Fi connected sensors to Home Assistant, which typically communicate to a base station via wireless ISM band signals. Home Assistant is an open-source home automation platform that integrates and controls household devices such as lights, sensors, and actuators.

rtl_haos Overview
rtl_haos Overview

Frugal Radio: Using a 25 Dollar PC for Decoding with SDRs

Over on YouTube, Rob from the Frugal Radio channel has uploaded a video showing that you don't need to shell out thousands for a capable PC to run your SDR. Robs finds five second-hand Dell Optiplex 9020 PCs advertised for just $25 each, and shows how each PC is powerful enough to run multiple SDR decoders at once, and run three monitors.

He notes that these PCs are a bargain as they come with a 4th gen Intel i5, 8GB RAM, and a 256 GB SSD. And they even come with Windows 10 Professional pre-installed.

Later in the video Rob shows what each of his $25 PCs is doing. He shows how PC1 decodes five digital trunk systems with RTL-SDRs and runs SDR++ with an Airspy. And how PC2 decodes P25 trunk systems and runs the PDW pager decoder.

Rob notes that deals on these second-hand Dell Optiplex 9020 PCs are easy to find on eBay as these are common ex-corporate PCs.

25 dollar 24/7 SDR PCs for the Shack

An Overview of 2025 SDR Black Friday Deals

Below, we're collating the best Black Friday sales we could find on SDR and related products.

If you find any other good sales for SDR or related products, please post in the comments!

RTL-SDR Blog

We're currently offering $5 of V3 dongles (including the V3c) on Amazon. The sale will last until Monday 1 December, and only while stocks last.

RTL-SDR Blog V3 Dongle + Antenna Kit: US$47.95 US$42.95 (Link)
RTL-SDR Blog V3 Dongle Only: US$37.95 US$32.95 (Link)
RTL-SDR Blog V3c Dongle Only: US$39.95 US$34.95 (Link)

We also want to add that in December, the price of V4 dongles will be raised, due to rising chip costs, and dwindling R828D stockpiles, so buying now is purchasing while essentially on sale.

We're also participating in the Airspy 25% sale with the YouLoop listing on our store. The sale takes the price down from $39.95 to $29.96.

Airspy

Airspy offers low-cost RX-only SDRs. Airspy is holding a 25% off Black Friday sale. Black Friday is usually their biggest discount of the year. The sale is offered by their official iTead store and by most resellers. Links to their sales are platforms available here https://airspy.com/purchase

Airspy R2: US$169.00 $126.75
Airspy Mini: US$99.00 US$74.25
Airspy HF+ Discovery: US$169.00 US$126.75
Airspy SpyVerter R2: US$49.00 US$36.75

SDRPlay

SDRplay offers low-cost RX-only SDRs. There do not appear to be any direct Black Friday deals from SDRplay, but on Ham Radio Outlet, the SDRplay nRSP-ST and DUO units are on sale. The RSPdx-R2 and RSP1B appear not to be on sale.

SDRplay nRSP-ST: $499.95 $399.95
SDRplay DUO: $299.95 $249.95

FlexRadio

FlexRadio offers high-end SDRs aimed at ham radio users. They are currently running a Black Friday deal as shown in the screenshot. https://www.flexradio.com/products/categories/black-friday/

Ham Radio Prep Course

While not physical SDRs, some people interested in getting their amateur radio licence in the US may be interested in this study course, which is discounted for Black Friday. https://hamradioprep.com/black-friday

They have various course bundles on sale, but this screenshot is of the full bundle.

halow_scanner: An RTL-SDR Based 802.11aH HaLow Channel Scanner

Over on GitHub we've recently noticed the release of halow_scanner, a Python script that uses an RTL-SDR to scan the 802.11ah (WiFi HaLow) channels in the sub-GHz spectrum to determined which channels have the least noise/interference.

Unlike standard WiFi, which operates outside of the RTL-SDRs range at 2.4 GHz+, 802.11ah operates in the sub-GHz ISM bands, which RTL-SDRs can easily receive.

Use of these lower frequencies gives 802.11ah HaLow excellent signal penetration, making it useful for long-range, low-power IoT devices. With 802.11ah HaLow links, several kilometers can be achieved.

The software's features include:

  • πŸ” Scans all 802.11ah HaLow channels in the US 902-928 MHz band
  • πŸ“Š Supports multiple channel bandwidths: 1, 2, 4, and 8 MHz
  • πŸ“‘ Uses RTL-SDR for spectrum analysis
  • 🎯 Identifies the cleanest channel with lowest noise floor
  • πŸ“ˆ Provides detailed power spectrum measurements
  • ⚑ Fast scanning with averaging for accuracy
Comparison Between regular WiFi and 802.11ah HaLow. Source: https://www.gateworks.com/802-11ah-halow-long-range-low-power-wireless-for-iot/
Comparison Between regular WiFi and 802.11ah HaLow. Source: https://www.gateworks.com/802-11ah-halow-long-range-low-power-wireless-for-iot
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