RTLSDR - a poor ham's spectrum analyzer

"DVB-T dongles based on the Realtek RTL2832U can be used as a cheap SDR [Software-Defined Radio], since the chip allows transferring the raw I/Q samples to the host, which is officially used for DAB/DAB+/FM demodulation. The possibility of this has been discovered by Eric Fry (​History and Discovery of RTLSDR) [...]

This is a short description, which I have taken over from the osmocomSDR forum.

So what is the trick ?

Usually, a DVB-T dongle is used for digital TV and radio receiption when connected to a PC.
It is using the software package provided by the dongle's manufacturer.
As the dongle uses the USB 2.0 interface, a driver is required which is provided with the manufacturer's software.

With a modified USB driver, you can pick up the sampled data from the DVB-T dongle and process it on your own hand using an SDR software.
And using an additional driver package you may also set the dongle's tuner from the SDR software.

For demodulation of digital modes, you may loop the audio output of your SDR software to a decoder program running on the same PC hardware.
That's it.

Your investment:
- less than 20 US$ for a DVB-T dongle with the proper chip set *
- freeware package for SDR software and the digital modes demodulationin commonly used in ham radio

What you get:
- a spectrum analyzer with up tp 3.2 MHz real-time bandwidth
- a multi-mode software-defined broad-band receiver
- both with a frequency range from down to ca. 22 MHz to up to ca. 2200 MHz *
  * see the above osmocomSDR forum for the proper dongles which cover different frequency ranges

Drawbacks:
- only 8 bit of dynamic range
- limited blocking close to strong RF signals
- no pre-selection filters, design is rather optimised for small antennas

This is the current setup:

DVB-T dongle Dexatek DK DVB-T Dongle (Logilink VG0002A)
Frequency range: 22 - 1100 MHz (Tuner Fitipower FC0013)

PC hardware / software
Laptop with 1.4 GHz Pentium M single core, 1 GByte RAM
USB 2.0 interface with 1 m extension cable to the DVB-T dongle
Windows XP Professional Service Pack 3
general
SDR package
the free SDR# (pronounced "SDRsharp")
which I can recommend if you run the SDR package on a rather old single-core PC hardware
It offers built-in demodulators for
- AM (
Amplitude Modulation) ⇒ used in short-wave broadcasting and air traffic
- NFM (
Narrowband Frequency Modulation) ⇒ used in short-range communication and VHF ham bands
   The bandwidth can be adjusted for further demodulation with separate digital-mode packages

- WFM (Stereo Wideband Frequency modulation) ⇒ used in broadcasting
   A decoder for RDS (Radio Data System) is included
- DSB / LSB / USB
(Double- / Single-Side-Band Modulation) ⇒ used on amateur radio short-wave bands
   The bandwidth can be adjusted for narrow Morse Code (CW) transmissions
ADS-B-only
SDR package
the free ADSB# (pronounced"ADSBsharp")
for decoding of aircraft transponder signals on 1090 MHz, see below
demodulator packages: freeware only:
adsBscope works together with ADSB#
for visualization of the received and decoded aircraft transponder signals
AFSK1200DEC.exe AFSK (Audio frequency-shift keying) 1200 Bd.
Used by amateur radio hams for packet radio,
APRS (
Automatic Packet Reporting System) and telemetry.
DSTAR.exe DSTAR (Digital Smart Technologies for Amateur Radio), a digital amateur radio standard for voice and data transfer.
Due to the propriery codec, so far only the the header of the messages can be decoded.
But this is sufficient to see
- Who is calling CQ ?
- Who are the QSO partners ?
- Is there any activity at all on my local DSTAR repeater ?
  (i.e. "Does it make sense to buy a DSTAR equipment ?")
FLDIGI.exe Multi-mode decoder which supports the common digital amateur radio standards used on short-wave bands, such as
- Radio Teletype  (various RTTY modes)
- Phase Shift keying (various PSK modes)
- various multi-carrier modes (such as Olivia, Contestia, Throb, Thor, MT63,...)
- WeatherFAX (various Weather FAX modes) ⇒ used by maritime weather services
SORFMON.exe POCSAG decoder, a standard previously used in commercial pager systems.
When the pager services where shut-down, Amateurs used the surplus hardware and modified it for the 70 cm ham band.
In Germany 439.9875 MHz is used for POCSAG in ham radio.
WACARS.exe
ACARS (Aircraft Communications Addressing and Reporting System) decoder for air traffic status reports.


That is what I could achieve so far:


long-term WSPR monitoring on 28 MHz or 50 MHz with minimum hardware effort, power consumption < 5 W:
- e.g. Raspberry Pi 1  (the old single-core model)
- the above RTL-SDR with an adeqaute low-pass filter, blocking the VHF FM broadcast band
- software implementation by VA2GKA, as described here
- see my hardware setup with additional EMC filtering:


- WSPR stations received on 10 m after 2 weeks of continous operation in the 2017 short-skip season:

Spectrum monitoring of my 28 MHz WSPR beacon:
- look for in-band spurious signals,
- quick-check of signal-decoding without setting up the big RF-rig

50 MHz ham band openings during the Es season:
- see the various beacons coming out of the noise
- the entire band on a glance, click on the spectrum peaks for listening
- run the PSK multi-decoder and see what's going on

70 MHz ham band openings during the Es season:
- the band is assigned in several european countries
- amazing signals when the ionisations of the Es layer is really high

Traffic monitoring of the local APRS-repeater DBZU- on 144.800 MHz,
tools as described in the above setup:


Traffic headers monitoring of the local DSTAR-repeater DBESS on 145.7625 MHz,
tools as described in the above setup:




This is what I am looking forward to do:

NOAA weather satellite reception:
137.300 MHz / 137.500 MHz / 137.620 MHz

ISS packet radio transponder reception
FM SSTV downlink Downlink 145.800 MHz
AX.25 1200 Bd AFSK Packet Radio downlink 145.825
MHz



Things that are possible from a technical point of view
 (But beware the legal restrictions of your country !):


Air-plane transponder data monitoring, such as:
- ACARS (Aircraft Communications Addressing and Reporting System) on 131.725 MHz (Primary channel in Europe),
 
tools as described in the above setup:
 

- ADS-B (Automatic dependent surveillance-broadcast) on 1090 MHz,
  tools as deescribed in the above setup:
 

Pager services, such as:
- POCSAG
- FMS






back to start