Your first receiver
By the end of this chapter, you know which receiver to start with, where to buy a genuine one, and which antenna to start with.
Nothing here needs installing, and there is nothing to type.
Have a receiver already? Skip to Installing Substation, or to A first scan if Substation works with it already.
A USB SDR
A USB SDR is a receiver small enough to plug into a USB port, with a socket for an antenna. It takes its power from the port, and sends its IQ samples to the computer over the same connection.
The best known began as something else. RTL-SDR Blog's About RTL-SDR tells how: mass-produced USB sticks for watching digital television on a computer, built around Realtek's RTL2832U chip, turned out to hand over their raw IQ samples, and with a driver written for them they became software-defined radios at a fraction of what one had cost. An RTL-SDR is any receiver built on that chip. Nobody owns the name, so anyone can make one, and many do. An RTL-SDR only receives: it cannot transmit.
The receivers Substation works with
Substation works with a wide range of receivers. It speaks directly to any RTL-SDR and to the HackRF One, and to any other receiver that has a driver for SoapySDR, a library that speaks to many makers' receivers in one way, such as a LimeSDR or a PlutoSDR. It reaches the two Airspy receivers that way too, by names of their own. A later chapter sets a receiver up through SoapySDR from what it reports about itself.
Five receivers have been tested with Substation. As their makers give them:
| Receiver | Range | Bandwidth |
|---|---|---|
| RTL-SDR Blog V3 or V4 | 500 kHz to 1.766 GHz | up to 2.4 MHz on the V3, 2.56 MHz on the V4 |
| HackRF One | 1 MHz to 6 GHz | up to 20 MHz |
| Airspy R2 | 24 MHz to 1.7 GHz | up to 9 MHz |
| Airspy HF+ Discovery | 0.5 kHz to 31 MHz, and 64 to 260 MHz | up to 660 kHz |
A receiver's range is the lowest and highest frequency it tunes to, and its bandwidth how much of that range it hands over at once. Every one of them reaches the 2m band. The band is 2 MHz wide, so an RTL-SDR holds all of it at once, and the HF+ Discovery about a third.
They differ in how finely they measure, too. Each IQ sample is made by an analogue-to-digital converter, an ADC, which turns the signal into numbers of a fixed size: 8 bits on the RTL-SDRs and the HackRF One, and 12 on the Airspy R2. More bits give more dynamic range, which is how far apart in strength a loud signal and a quiet one can be while both are still heard. With 8 bits, a strong station nearby can swamp weak ones in the same bandwidth.
- The RTL-SDR Blog V3 and V4 are RTL-SDRs that RTL-SDR Blog redesigned for radio rather than television. Each has an oscillator that keeps its tuning steady as it warms up, and an aluminium case that keeps it cool. Both are low-cost, general-purpose receivers, good enough for most scanning of the very high and ultra high frequencies, VHF and UHF, where most of the bands Substation ships are.
- The HackRF One, from Great Scott Gadgets, reaches the highest frequencies and hands over the widest bandwidth of the five. It can transmit as well as receive, though Substation only ever receives.
- The Airspy R2 suits weak signals and wide bands in VHF and UHF, measuring more finely than an RTL-SDR.
- The Airspy HF+ Discovery is built to hear very weak signals with strong ones nearby. It covers the high frequencies, HF, up to 31 MHz, and part of VHF, but less than a megahertz at once.
Not every receiver reaches every band the same way. The V3 and V4 reach the 2m band, CB radio and the bands above them. Below 24 MHz are three of the bands Substation records out of the box, the 80m, 40m and 20m amateur bands. The V3 reaches those in a mode of its own, direct sampling, which RTL-SDR Blog's driver switches to by itself below 24 MHz, and the V4 through a converter built into it, which needs nothing switching on. Neither has yet been tested with Substation on those bands.
An RTL-SDR Blog V3 or V4 first
Start with an RTL-SDR Blog V3 or V4. Either suits this guide, whose first scan is of the 2m band.
- The V3 is in stable production, its maker says, and sold alone or with a dipole antenna kit, which its maker calls great for beginners. Of the two, it is the one its maker sells today.
- The V4 is no longer made, because the tuner chip it needs has run out, though its maker's resellers may still have some. Its maker gives it better filtering than the V3, so strong broadcast stations are less likely to swamp what you are listening to.
Its maker now sells a V4L, or Lite, in the V4's place, with a different tuner chip that needs newer drivers. It has not been tried with Substation yet, so this guide does not suggest it.
Buying a genuine one
Clones are sold under these names. RTL-SDR Blog warns that receivers in blue or green cases, in silver cases with four screws, or advertised as "Pro" are not its own, and that many listings of the V4 on marketplace sites are fakes, most of them a copied V4 case with a V3 clone inside. Buy from a maker's own shop, or from a reseller the maker lists:
- RTL-SDR Blog: its store page, which lists its own shop, its official eBay and AliExpress stores, and resellers in many countries, the UK among them.
- Great Scott Gadgets: the authorised resellers on its where to buy page.
- Airspy: the distributors on its purchase page, among them Itead Studio, its official manufacturing partner.
An antenna to start with
A receiver hears only what its antenna picks up, and an antenna picks up best the frequencies its length suits.
- The V3's kit is a dipole, an antenna of two equal arms, here telescopic so you can lengthen or shorten them for a band, with a cable and mounts to put it where it receives best. Its maker says it receives signals from the ground and from VHF satellites, and that it is made for portable and temporary use outside, not in poor weather.
- The HackRF One comes without an antenna, and its maker recommends its ANT500 to start with.
- For the HF+ Discovery, Airspy sells the YouLoop, a loop antenna for HF and VHF.
A later chapter works out how long an antenna should be for the band you scan, with a command Substation installs.
The next chapter installs Substation, and the driver your receiver needs.