An Intuitive Tutorial on SDR, The Frequency Domain and IQ Data

Over on his website P. Lutus has written up a useful article that introduces us to some common SDR hardware (RTL-SDRs, upconverters and the HackRF), mentions some common SDR software, and then dives into some SDR theory explaining concepts like the frequency domain and IQ sampling.

The theory sections in particular are explained quite intuitively with animated and interactive graphs that really help with visualizing the math. The explanations are short and not math heavy, so if you have half an hour you can learn some of the basic theory behind making SDRs work.

IQ Visualized on an interactive graph.
IQ Visualized on an interactive graph on P.Lutus' blog post.

SDR# Dark Mode Plugin

A few days ago Eddie MacDonald released his Tuner Knob plugin for SDR#. Today he's released a new plugin called "SDR# Dark Mode" over on our forums. This plugin is very simple in that is just makes the SDR# interface black, which should be better on the eyes those using the app at night. The plugin also adds two other options which allow you move the tuning toolbar to the bottom of the screen and remove all padding to save some screen space. The three options in the plugin are:

"Night Mode" or "Regular Mode" - allowing the app to be black or not
"Bottom Tool Bar" - allows you to place the radio control tool bar on the top or bottom of the app
"Remove Padding" - remove the 10px border around all the controls giving you a tiny amount of more workable space.

The plugin can be downloaded from the file uploaded on the third post on the announcement thread.

Normal Mode

Normal Mode

Dark Mode + Remove Padding

Dark Mode + Remove Padding

Dark Mode + Remove Padding + Toolbar on Bottom

Dark Mode + Remove Padding + Toolbar on Bottom

SDR-Console V3 Beta Now Released: Console Server Now Available

SDR-Console V3 is the latest in the line of the free SDR-Console software packages from developed Simon Brown. Recently SDR-Console V3 left its 'preview' software status and moved into 'beta' production status. 

SDR-Console is a general purpose SDR program similar to other software like SDR#, HDSDR and SDRUno. SDR-Console V3 however sets itself apart by being one of the most feature rich packages with goodies like advanced DSP and NR options, frequency favorite lists, IQ recording and playback with reverse and fast forward, built in CW Skimmer and satellite tracker, independent receiver control with matrix view, signal history export, a recording scheduler, remote server and in the future support for SDRs with transmit capability.

SDRConsole V3 Beta Supported Radios
SDRConsole V3 Beta Supported Radios

One interesting feature released with the beta version is the SDR-Console server, which allows you to use an SDR remotely over a network such as a local LAN or over the internet. We tested the server on our local machine. After setting up the server account, adding an RTL-SDR radio definition and installing the server Windows service we were able to successfully connect and receive flawlessly. The server appears to limit the maximum bandwidth to 1 MHz.

SDR-Console and the server currently support multiple SDR hardware including the RTL-SDR. SDRplay have blogged about support for their line of RSP products too, and have also created a public internet connected RSP1A demo which anyone can connect to and use (assuming that you have a decent enough internet connection). A list of public Console V3 servers can be found by clicking on the 'SDR Space' button when adding a 'V3 server' radio definition in SDR-Console V3. Currently there are multiple locations and SDR hardware publically available including ELAD FDM-S1's, SDRplay units, Airspy HF+'s as well as RTL-SDR's. We tested a few remote servers and were able to easily connect to most of them and get good smooth throughput.

SDR-Console V3 can be downloaded here.

Current Console V3 Servers
Current Console V3 Servers

Below we show a screenshot of SDR-Console V3 Beta 1 receiving from a remote SDRplay RSP1A with multiple IF channels selected and with matrix view active on a second screen.

SDR-Console V3 Beta 1 Receiving Remote RSP1 in Matrix View
SDR-Console V3 Beta 1 Receiving Remote RSP1 in Matrix View

Also check out the post the swling.com blog did on the beta release to see an additional perspective and some example videos of SDR-Console V3 in action.

More Reviews and Discussion on the Airspy HF+

Recently a few more reviews of the HF+ have been released and we list some of them below for those thinking about purchasing one.

SDRPlay RSP-1A vs. Airspy HF+ on Shortwave and Medium Wave

In this video icholakov compares the RSP-1A with the HF+ on shortwave and medium wave reception. He writes:

Comparing reception of two popular SDR Receivers using the same antenna at 5 PM local time. Short wave and medium wave frequencies. Using the same SDR Console 3 software for both. I have not ced enough variances using different usb cables and different host laptops to say that in this case the two are pretty much on par. The laptop running RSP-1A happened to have a better audio profile but that's the laptop not the sdr. I only see a noticeable difference when receiving the low power 10 Watt Travel Information radio from the Florida Turnpike on 1640 kHz. I assume that it is coming via ground wave.

Airspy HF+ vs Elad FDM-S2 Weak Signal Comparisons

In this guest post on the swling.com blog Guy Atkins put up a number of audio samples recorded from the HF+ and FDM-S2. The audio samples were not labelled with the radio they came from and he asked readers to vote on which audio sample sounded better. A week later he released the results which showed that the HF+ and FDM-S2 had mostly 50/50 votes, indicating that one did not really sound better than the other.

Airspy HF+ Review - A Nice SDR Receiver

In his blog post Roi Huberman shows a few examples of the HF+ in action and briefly compares it against his SDRplay noting the better dynamic range.

Airspy HF+ Broadcast FM Selectivity Check

In this video by YouTube user stereo11 the selectivity of the HF+ is tested by attempting to receive weak far away stations that are very close to a powerful local station on the frequency spectrum. The HF+ and the SDR# software is able to easily reject the strong station once the IF is adjusted. 

Overview of the HF+

This YouTube video by Radio-Noticias revista española de radioafición is in Spanish, but can be decently autotranslated using YouTube captions to English. It provides a good overview of the HF+ design and features.

Airspy HF+ MW Overload Problems

All the reviews we've seen so far have praised the HF+ heavily, but it's worth noting that it seems that a few HF+ owners are experiencing significant overloading problems. These are typically users that live very close to powerful MW AM transmitters.

However, the good news is that it seems that a recent firmware patch fixes this issues. The firmware update with instructions can be found at the bottom of the HF+ page on the Airspy site. The firmware update involves opening the case and briefly shorting two pads so it is only really something to do if you are experiencing problems in the first place. It also appears that performing a simple hardware mod helps too.

Previous Reviews

In the past we reviewed the HF+ ourselves and that review can be found here. You can also search our previous posts for various other HF+ reviews that we've posted about before.

Video Tutorial: Setting up DMR Decoding with SDR#, DSD+ and an RTL-SDR

Over on YouTube user Tech Minds has uploaded a useful video which shows how to set up DMR decoding with SDR#, VB-Cable, DSD+ and an RTL-SDR dongle. He also uses the DSD plugin for SDR# which makes controlling the command line DSD+ software a little easier. If you are interested we also have a short tutorial on DMR/P25 decoding available here. The video starts from downloading and installing the software, and explains every step very carefully, so it is a very good starting video for beginners.

DMR (aka MotoTRBO or TRBO) is a digital voice protocol used by Motorola radios. Software like DSD+ is required to listen to it, but it can only listen in if the signal is unencrypted.

Tech Minds has also uploaded several other tutorial videos to his channel over the last few months including guides on how to set up the ham-it-up upconverter, ADS-B tracking, using a Raspberry Pi to create a FM transmitter and more.

Visual Tuner Knob Plugin for SDR#

Thank you to Eddie MacDonald for submitting his new SDR# plugin to us via our forums. Eddie's plugin is called the 'Tuner Knob Plugin', and simply enables a visual tuner knob on the screen for adjusting the frequency. This plugin could be useful especially for those running SDR# on touchscreen tablets or laptops. To install the plugin copy the .dll file to the SDR# directory and copy and paste the magicline.txt into the plugins.xml file. We tested the plugin on our PC and found it to run well.

We have uploaded the plugin here for all to download.

Eddie writes about the plugin:

Programming the plugins is not so easy considering their is very little documentation and few examples on the net. There may be a few bugs I have not caught (but i hope i have caught them all.)

This DLL was compiled and tested on a Windows 7 x64 machine and the DLL is compiled for both x86 and x64 platforms. I have tested it on SDR# Version v1.0.0.1635

I am not certain which previous versions it may or may not run on. However, being built on the 4.6 .Net framework it should work with Win7 on.

I built this plugin because i got tired of holding down buttons and waiting for the frequency changes. I figured this was a simpler method (even though some people hate rotary style controls on windows) It works exceptionally well with a touch screen.

As previously mentioned in the forum post I created the 'remote' to test my programming for future plugins for DSP

While some may not find a use for the remote I made it this way for my wife who like to cruise the dial and just see what she can pick up.

Tuner Knob Plugin for SDR#
Tuner Knob Plugin for SDR#

Some more information about the Airspy HF+ R3 Bypass Modification

At the beginning of this month we posted a review by Bjarne Mjelde who reviewed the MW DXing performance of the Airspy HF+. One thing he found was that by performing a simple capacitor bypass modification, the performance of the HF+ below 15 MHz could be significantly improved. Over on the SWLing blog we've seen a post that gives a bit more information for those wanting to perform the R3 bypass modification on their HF+'s. There Yousseff, head of the Airspy team wrote:

During the early phases of the design R3 was a place holder for a 0 ohms resistor that allows experimenters to customize the input impedance. For example:

  • A 300 pF capacitor will naturally filter the LW/MW bands for better performance in the HAM bands
  • A 10µH inductor would allow the use of electrically short antennas (E-Field probes) for MW and LW
  • A short (or high value capacitor) would get you the nominal 50 ohms impedance over the entire band, but then it’s the responsibility of the user to make sure his antenna has the right gain at the right band
  • A custom filter can also be inserted between the SMA and the tuner block if so desired.

R3 and the nearby resistors have been intentionally left outside of the RF shield, and their size was picked to be big enough to allow anyone to play with them. You will notice the size difference with the rest of the components.

In general, unless one knows what he’s doing, it’s not recommended to alter a working system. “If it’s working, don’t fix it”. But, we are hobbyists, and not doing so leaves an uncomfortable feeling of something unachieved. Most brands addressing the hobby market leave some tweaks and even label them in the PCB.

The main purpose of the HF+ is the best possible performance on HF at an affordable price. This is to incite HAMs to get started with this wonderful technology while using an SDR that isn’t worse than their existing analog rig.

The MW/LW/VLF crowd may have slightly different requirements, but that can be addressed by shorting a resistor.

The HF+ Mod (Edited by Bjarne, original photo by Nils Schiffhauer)
The HF+ Mod (Edited by Bjarne, original photo by Nils Schiffhauer)

Running a NAS, Torrentbox and ADS-B RTL-SDR Server all on the same Raspberry Pi 3

Most readers are familiar with the Raspberry Pi 3 and how it can be used with RTL-SDR applications such as ADS-B reception. However, one does not need to dedicate an entire Pi 3 to a single task as they are more than powerful enough to run multiple applications at once.

Over on his blog 'Radio for Everyone' Akos has uploaded a tutorial that shows how he set his Raspberry Pi 3 up as a simultaneous Network Attached Storage (NAS), Torrentbox  and ADS-B server. A NAS is simply a hard drive or other data storage device that can be accessed easily over a network instead of having to be connected directly to a PC. A torrentbox is a device such as a Raspberry Pi 3 running torrent software so that you can download torrent files 24/7 without needing a PC on all the time.

Akos' tutorial shows how to set everything up from scratch, starting from writing the Raspbian SD Card and connecting to it via SSH. He then goes on to show how to install the torrent software, set up the NAS and finally set up ADS-B reception.

Pi 3 as a NAS, torrentbox and ADS-B server.
Pi 3 as a NAS, torrentbox and ADS-B server.