
Welcome to the World of Software Defined Radio (2016) - robputt
http://www.robertputt.co.uk/welcome-to-the-world-of-software-defined-radio.html
======
qubex
DVB-T type devices such as the one referred to in this article are indeed
remarkably flexible but keep in mind that they are only able to receive. In my
case, that quite rapidly exhausted my curiosity.

I'm now eagerly awaiting delivery of a LimeSDR
([https://www.crowdsupply.com/lime-
micro/limesdr](https://www.crowdsupply.com/lime-micro/limesdr)), one of
several hacker-friendly radio peripherals that can both receive _and send_ (in
the LimeSDR's case, in full duplex mode) because of course having a
transceiver is a whole different ball-game. GnuRadio can serve as the logic of
both receivers and transmitters.

Of course depending on country, frequency and transmitted power you may
require licences to operate.

~~~
ptero
I recently read here that a Raspberry Pi can be turned into an SDR transmitter
by attaching a wire to a pin. On paper, the specs look impressive (for a
$20-$30 device), but I would love to know the RF quality of the resulting
waveform.

I cannot find the discussion, but the info is here: [http://www.rtl-
sdr.com/tag/rpitx/](http://www.rtl-sdr.com/tag/rpitx/)

~~~
th0ma5
As an Amateur Extra I've used a Pi to transmit WSPR 24/7 and was once heard in
New Zealand from Ohio. No amplifiers even...

~~~
j_s
Just to triple-confirm, there was no additional hardware besides the Pi? I'm
assuming at least some sort of antenna was involved...

Any links to write-ups/HOWTO's would be tremendously appreciated!

~~~
billh
You will need a antenna that is resonant on the frequency you're transmitting
on for any hope of the signal leaving the immediate proximity of the Pi. It
would also be a very good idea to filter the signal coming out of the Pi to
reduce the strength of any frequency spurs accompanying your Pi generated
signal and to keep your transmission legal.

This is a pretty good write up of using the Pi as a wspr transmitter:
[https://github.com/JamesP6000/WsprryPi](https://github.com/JamesP6000/WsprryPi)

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trishmapow2
SDR and RF in general has always felt like black magic for me, but the
availability of cheap hardware and wife software selection makes this
accessible to everyone. For newcomers I recommend the RTL-SDR subreddit,
plenty of great resources. My latest venture is a jam and replay attack on
keyless entry systems eg vehicles, project page is here:
[https://github.com/trishmapow/CC1101-FSK](https://github.com/trishmapow/CC1101-FSK)

~~~
bjt2n3904
Not gonna lie. As a radio guy, our terminology is messed up. My favorite
though is using superlatives.

Low Frequency (LF), Medium Frequency (MF), High Frequency (HF).

You'd think that maybe HF is WiFi, but you gotta remember these terms were
invented back in the early days of radio. HF is between 3 and 30 MHz.

You have Very High Frequency and Ultra High Frequency, but that only takes us
to 3 GHz. 5 GHz Wifi is technically SHF -- or Silly High Frequency.

But we also refer to these frequency bands in terms of MHz, or if we feel like
it, wavelengths. Since radio signals travel (effectively) at the speed of
light (m/s), we can multiply Hz (1/s) by a distance and get wavelength. (c = f
* l). 144 MHz then is the 2 meter band, or VHF as we call it.

Confused yet? Wait until we start talking about baseband and I/Q signals!

~~~
flashdance
> 5 GHz Wifi is technically SHF -- or Silly High Frequency

For those curious, op's right and it actually is SHF, but it stands for Super
High Frequency. I don't understand humour, only RF (and even that, barely).

[https://en.wikipedia.org/wiki/Super_high_frequency](https://en.wikipedia.org/wiki/Super_high_frequency)

Here's a fun semi-relevant science experiment you can do at home: running a
microwave will kill nearby wifi and bluetooth connections. Isn't that strange?

Try it with a par of bluetooth headphones right now!

~~~
NightlyDev
I really don't know much about radio, but I have never experienced that the
microwave have noticeably affected wifi or bluetooth.

Is it something that is only likely to happen with older and less isolated
microwaves?

~~~
flashdance
Most people aren't using wifi near running microwaves, so it's hard to notice.
Some microwaves leak more than others, but none of them are required by the
fcc not to interfere with 2.4ghz wifi. The FCC says that they can actually
leak an unlimited amount of radiation at that frequency [1], although
obviously if it's high enough to start cooking people standing nearby other
agencies than that the will get involved.

I bet ya an upvote that yours still leaks enough. One thing to try is to put
your phone next to the microwave and place your bluetooth headphones or
speaker riight at the limit of its range. Turn on the microwave and see what
happens!

[1] [https://www.ecfr.gov/cgi-bin/text-
idx?SID=c7be03a4f7b02514ce...](https://www.ecfr.gov/cgi-bin/text-
idx?SID=c7be03a4f7b02514cea89421fc363794&mc=true&node=pt47.1.18&rgn=div5#se47.1.18_1305)

~~~
EvanAnderson
I once worked at a site that had the Wi-Fi access point for one side of the
office in the break room. There was, of course, a microwave in the break room.
There were frequently complaints around the lunch hour that the Wi-Fi didn't
work well, though strangely it worked earlier and later in the day.

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payne92
For a device that can transmit as well as receive, consider HackRF:
[https://github.com/mossmann/hackrf/wiki](https://github.com/mossmann/hackrf/wiki)

It's been out for a while.

The newer option is LimeSDR, which just shipped:
[https://www.crowdsupply.com/lime-
micro/limesdr](https://www.crowdsupply.com/lime-micro/limesdr)

(Note that you need to comply with all local laws regarding transmitting).

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TKinNC
There is a glaring error at the beginning of this article under the "things
you cannot do with SDR."

"Listening in on the conversations of Ham operators."

In the US at least, there are many VHF/UHF Ham bands easily received by SDR. I
use an Airspy on Mac OS X, and although the software is terrible, there is
plenty to listen to.

~~~
mikestew
Maybe they were thinking HF (High Frequency), which is what's used for long
distance/international contacts and what many people think when they think
"ham radio". AFAIK the USB stick receivers can't receive HF. But that's a
hardware limitation, not SDR limitation. There exist SDRs that can do HF, they
just don't cost $15.

~~~
BenjiWiebe
Actually the latest RTL-SDR has a software switch for direct sampling. Which
isn't great quality, but with an indoor wire antenna in the basement (!) I
received JT65 transmissions from 47 states in the course of a few evenings.
Hawaii, Vermont, and Alaska are the ones I missed. However, I did hear
Hawaii... On SSB!!

------
KGIII
This thread could use this link:

[http://websdr.ewi.utwente.nl:8901/](http://websdr.ewi.utwente.nl:8901/)

Basically, it is an SDR for multiple users and an online interface. It's RX
only, of course. More options are available at websdr.org but the above is my
favorite.

Caution, it can be a huge time sink.

------
coin
> mhz

Should be written using the proper SI prefix, MHz. There's a huge difference
between the milli (m) prefix and mega (M).

------
bosky101
Relevant...

Listen to Radio from around the globe

[http://radio.garden/live/](http://radio.garden/live/) (drag the map to tune
in)

~~~
lioeters
This is really wonderful, thank you for the link. I'm enjoying now a radio
broadcast from..Malawi. The diversity of voices around the world, the ease of
moving and focusing on stations - one of the best things I've seen on the web.

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codazoda
Is there a similarly priced and sized SDR that can both receive and transmit?

Having received my ticket recently, I'd love to try some digital ham radio
modes without spending a fortune.

~~~
billh
There is the LimeSDR Mini that is currently being croudfunded[1]. For $140 USD
you would be hard pressed to find anything like it that would give you full
duplex across that frequency range. I own the full size LimeSDR device and it
has been a great piece of hardware for playing around with.

1\. [https://www.crowdsupply.com/lime-micro/limesdr-
mini](https://www.crowdsupply.com/lime-micro/limesdr-mini)

~~~
platz
Lime has the best hardware/specs at their price points, but their software
toolchain is atrocious; just trying to do simple tasks in GNURadio is so
flaky/error prone

------
jballanc
...wrong thread...

~~~
lima
Wrong thread :)

~~~
jballanc
Wow...no idea how that happened...

------
dogruck
Reminds me of this ye old project at MIT
[http://www.sds.lcs.mit.edu/SpectrumWare/home.html](http://www.sds.lcs.mit.edu/SpectrumWare/home.html)

