Tuesday, 30 July 2013

Beginner - Hardware

Updated Nov 15, 2016

What is Software Defined Radio?

In Software Defined Radio, your computer is doing the hard work; the most affordable SDRs are RTL-SDR dongles, which can be used to receive signals between 0.1 to 2200 MHz depending on model.
MHz is the number on your car radio, it is the frequency of the signal. When you listen to Radio 96FM you are “tuning” to 96 million Hertz (M is million).
You can use the stick for audio and data reception, weather satellite reception, local music radio and many other uses.

What you need

1. Computer / Laptop
2. USB cable and RTL Stick
3. Antenna adaptors
4. Coaxial cable
5. Antenna


Computer / Laptop

Can be a laptop or a desktop, all it needs is an USB port. For example, I tested all equipment and software on a 7-year old Dell laptop with Windows 7 - all works fine.
If you bought your laptop in the last 3-4 years, chances are all software will run smoothly.

RTL – SDR Stick (RTL2832U & R820T or R820T2 Tuner)

The RTL stick puts the signal into your computer using your USB port. Costs from 6 to 40 dollars.

Antenna Adaptors / Cable ends

Adaptors connect the dongle, cables and the antenna to each other.
If you want to disconnect the antenna, you will need adaptors.
MCX: Commonly used on older dongles. You push it in. If you have no adapter, you can cut the small antenna cable that came with the stick, and splice it into your antenna cable – see below.

AIS, antenna, RTL-SDR, Software Defined Radio, 820T, testing, review, DIY guide

BNC: Bayonet type, ready-made scanner antennas use this. You push, then turn this. CCTV also uses this, so if you have a wholesale / electrical shop in town they might have them.
AIS, antenna, RTL-SDR, Software Defined Radio, 820T, testing, review, DIY guide


F-type: Screw-type, used for satellite TV, UPC/Sky modem connectors. 
AIS, antenna, RTL-SDR, Software Defined Radio, 820T, testing, review, DIY guide


SMA: Screw-type, used on marine radios, Icom equipment etc.

AIS, antenna, RTL-SDR, Software Defined Radio, 820T, testing, review, DIY guide

Others (SO-239 and N-type): myriad variations exist, most common are SO-239 and N-type. They are super-sized screw-type connectors. If you can get them, use them.
BNC and F-Type can be bought everywhere because they are used for CCTV, TV and Satellite installations.

Cables (called coaxial cables or coax)


AIS, antenna, RTL-SDR, Software Defined Radio, 820T, testing, review, DIY guide

Every cable has numbers written on it, like RG 59U, and/or 75 Ohm. You need 75 Ohm cable to connect antennas to the stick – luckily, satellite and TV cable is fine. Unless you ask specifically for radio cable you will probably get 75 Ohm cable, called RG59.
If the area you’re in has TV you can buy coax cable somewhere. 10 metres/30 foot works out to around 10 - 15 euros, but shops also sell it by the metre. Electrical wholesalers are the cheapest.
The Ohm thing: the resistance of the cable. Try to use 75 Ohm. Scanner antennas, your marine radio and handheld VHF antennas are also 50 Ohm – they work with the stick.
Thicker cable with better shielding/less signal loss is more expensive, and normally used for long cable runs e.g. mast-mounted antennas.

AIS, antenna, RTL-SDR, Software Defined Radio, 820T, testing, review, DIY guide

Do not lose sleep over cable; use what you can afford or get locally.


Antennas / Aerials



Center conductor whip antenna – cost of 1 metre copper wire.

Construction:
  1. Measure from the end of the coax the required length.
  2. Cut the insulation lengthwise.
  3. Peel off the braid and outer plastic shell, then cut it off. 
  4. Only the centre wire inside the plastic shell remains. 
  5. Connect the other end to the RTL stick, start receiving signals.

Centre-loaded Magnetic Antenna

Works flawlessly; being wide-band means that you can receive from CB radio 30 MHz to Airplane ID signals at 1090Mhz. An antenna for 90% of the signals you want to receive. 
Being a ready-made antenna it comes with a BNC connector. Connect to RTL stick with MCX-SMA and SMA-BNC adapters, or a dedicated pigtail.

Discone antenna


Looks like a hedgehog, but offers the best sensitivity. Windage might be an issue, other than that it is the best / most expensive option for reception. A bit conspicuous, also a good antenna for terrestrial digital TV reception.

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