Why SDR?
About two years ago, I spent a couple of months using a Scanner, beginning to learn the basics about aerials and how to target different bands. Priorities changed and I needed to sell the equipment to free up some money and ever since I have been looking for a cheap way to start 'Scanning' again.Over the weekend, I stumbled upon the concept of Software Defined Radio. A very cheap, versatile and adaptable method of receiving a large spectrum of radio broadcasts.
From what I understand, this method should also be somewhat portable as I live in a very developed area of the town and very quickly learned in previous attempts that there is a large amount of noise present, therefore, the end aim would be to be able to have a setup that I could take to a more open area to use in addition to a 'home' setup.
As I am approaching this from zero knowledge, I thought it would be useful to document the process for anyone that might be thinking of starting the same project. It will also be a useful record for myself of the process and wins/fails!
The basics (as I understand them so far):
The whole concept of SDR is based around the use of a USB DVB-T Dongle. If you haven't heard of these before, they are the USB devices, (not much larger than some USB memory sticks) that are sold to allow you to receive Digital TV transmissions in the EU and watch them via a Computer. I purposefully use the term Computer as they can be used with a traditional 'PC' running windows or linux, a MAC, and even some smartphones. Usually these DVB-T Dongles come with supplied software and a simple aerial.The way SDR works is to take the functionality of the DVB-T Dongle to receive radio transmissions and then couple this with custom designed drivers and software to allow the user to receive and decode transmissions across a much wider spectrum than the devices were originally sold to do. I would hesitate to say that they weren't designed this way as development so far shows they are very capable of a wide range of reception.
SDR is commonly referred to as RTL-SDR, this is because the majority of USB DVB-T Dongles that are used, are based on the RTL2832U Chipset.
My very first 'concern' after reading all I could about implementation so far, was the lower end of the radio spectrum that these devices can receive. For example, the specifications of the most commonly available unit in the UK, one with the R820T Tuner chip, are to receive between 24MHz to 1850MHz, obviously dependent on the aerial used. Whilst I am interested in operation across all the frequencies, I would like to be able to scan the HAM frequencies used in the UK and further afield, for example, the 40 and 30 metre bands, 7MHz and 10MHz respectively.
With a bit more research, it appears I am not alone in this and there are a number of descriptions of circuits, kits, part and fully built 'Upconverter' units that combined with one or more antennae, should allow reception of these lower frequencies.
I understand that this is already getting way ahead of myself, but I am always careful when looking at a technology that I am going to be able to later adapt it to my needs without having to start completely over.
I am currently researching a lot of information from the RTL-SDR Wiki at: http://rtlsdr.org/start
Now to get started! I need to choose and find a supplier for the basic DVB-T Dongle and an aerial that will give me the widest frequency coverage as cheap as possible for initial testing.
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