Mike Comer @mike_n8wc
@kb6nu great info! Back to radio after several years. Enjoy how the internet has enhanced enjoyment of a great radio hobby.
Mike Comer @mike_n8wc
Back in May, I purchased a DVB-T mini-dongle to play around with software-defined radio (SDR). Unfortunately, I purchased the wrong type of dongle, and I couldn’t get it to work with any of the SDR software packages out there. The reason for this is that it the dongle did not use the Realtek RTL2832U.
A couple of months ago, I purchased another dongle, this time making sure to purchase the correct one. As you can see from the Amazon ad at right, this dongle cost less than 15 bucks. When I first got it, I was able to get it to run with the Windows laptop I was using down in the shack, but wasn’t able to get it to work with the Mac I use in my office. So, I put it aside, meaning to get back to it sooner or later.
Well, later came on Sunday, as about a foot of snow fell on outside. I downloaded an OSX port of the SDR program gqrx, and in short order, I was actually up and running, and listening to FM broadcast stations here in Ann Arbor. Very cool! I have since used it to listen to not only FM broadcasts, but also the local repeaters and the NOAA weather station on 162.55 MHz.
At first, I was pretty disappointed with the performance. That was the fault of the antenna, though. The antenna that came with the dongle is pretty much useless. What I did was to cut off the whip, solder on a couple of alligator clips and clip the coax to an FM broadcast dipole that came with a stereo I bought ages ago. If you don’t want to do this, you can purchase adapters cable, like the one shown at right, which have an SO-239 on one end and the MCX right angle connector, which plugs into the dongle on the other end.
That greatly improved the performance on FM broadcast as well as on 2m. I had planned on clipping to the 450-ohm ladder line J-pole that I have to see how it improves reception on 2m, but haven’t gotten around to that yet.
While gqrx is a nice program, it does have some limitations. For example, you cannot set up “memories” and switch between them. So, switching frequencies can be somewhat of a hassle. It would also be nice to have a scan feature, so that I could set it up just like I do my handheld and scan all the local repeater frequencies. The good thing is that this program is still very much under development.
The support is really good, too. There is a gqrx Google Group where I got a very quick answer to a newbie question.
What else can you do with this dongle? Quite a bit as it turns out. Yesterday, while composing another blog post, I learned about an RTL-SDR spectrum analyzer using a BeagleBone Black, which I already happen to have, and its 7? Touchscreen cape. Again, very cool.
For quite a while now, I’ve been thinking about what I should do about software-defined radio (SDR). For one thing, I’d like to write about it here on KB6NU.Com. For another, I’d like to learn more about it – how it works, what’s available, etc.
I”ve decided that short of writing a book about the topic, I’m not going to try to write something comprehensive, but instead just little bits about SDR as I come across them. So, with that in mind, here’s some SDR stuff that I’ve come across recently.
- DVB-T Mini Digital TV USB Stick Dongle. Based on an exchange of e-mails on the AMRAD mailing list, I recently purchased one of these little dongles. Apparently, a bunch of AMRAD members purchased this unit at a recent hamfest, and they’ve all been having fun with them.Unfortunately, it looks like I purchased the wrong one. This design is not supported by the commonly available SDR software. The dongles that are supported use the Realtek RTL2832U chip, so look for that before purchasing.
Coincidentally, one of the guys here in Ann Arbor, purchased a FunCube Pro dongle at Dayton and brought it down to the museum Saturday. It costs significantly more ($150), but it will tune 150 kHz to 1.9 GHz. It will be fun to compare the two.
- SoftRock, Peaberry. A couple of months ago, I purchased a SoftRock Lite II kit from someone who hadn’t gotten around to building it and decided that he was probably never going to get around to it. Well, of course, I haven’t gotten around to building it yet, either, but I do hope to get to it sooner rather than later.I have since come across the Peaberry line of kits. The Peaberry SDR V2 kit looks interesting. For $150, you get a multi-band SDR transceiver.
- RTL-SDR.Com. This blog covers a wide range of topics including how to receive all kinds of different transmissions with DVB-T dongles that use the RTL chips. One recent article compares SDR using the RTL dongles and the FunCube Pro dongle.
Three more things I found while Twittering and using Google+.
Stay Connected to Your Broadband – an Improved ADSL Filter. I have a DSL line here, and have never had any RFI problems. In Great Britain, however, their broadband lines seem to be susceptible. This 2010 article shows you how to build a filter that will fix that right up.
Learn circuits and electronics from MIT. The Massachusetts Institute of Technology is putting a lot of courses online, and you can take them for free! This course, Circuits and Electronics, is the core course for all undergraduate electrical engineering (EE) and electrical engineering and computer science (EECS) students. Before you jump into this, realize that they say it will require about ten hours per week, and you need to know some basic calculus and linear algebra. This is an academic class, after all.
Open Hardware Journal. From the first page:
Open Hardware means sharing the design of physical or electronic objects with the public, similarly to Open Source software. The right to use, modify, redistribute, and manufacture, commercially or as a non-profit, is granted to everyone without any royalty or fee. Thus, Open Hardware designers hope to enrich society by developing a library of designs for useful objects that everyone can make, use, and improve.
The second issue features an article on the TAPR’s High-Performance Software-Defined Radio (HPSDR) project, which now includes over a dozen building blocks that can be used to assemble a high-grade 100 kHz to 55 MHz software-defined radio.
En route to the Teacher’s Forum, I passed by the Antenna Forum, which looked to be very popular. There were guys standing out in the hallway trying to hear the presentation.
The Teacher’s Forum has been moderated by Carole Perry, WB2MGP, for as long as I can remember. She always has good speakers. This year, the lineup included Gordon West and Bob Heil.
One idea that I picked up is to use a flashing light or LED to demonstrate the idea of duty cycle. By hooking it up to a variable duty cycle oscillator, you could vary the amount of on time versus the amount of off time, and this would make a very good visual demonstration.
This year’s presenters mostly talked about teaching kids. This fall, I plan to teach a class for seniors. If it goes well, I’m thinking that I could talk about that class at next year’s teacher forum.
In the afternoon, I attended the Software-Defined Radio Forum. This forum was also packed. We first heard about the new FlexRadio 1500, which is a $650 SDR. Its output is only 5W, but this looks like a real bargain.
Next up was Lyle, KK7P, from Elecraft. He gave us the Elecraft perspective on what an SDR is and what it’s not. It was interesting, but not very technical.
After Lyle, the TAPR VP (whose name and call I forget) talked about developments with the SDR projects at TAPR. My initial impression is that while all of these developments are well-done, it’s still much less expensive to simply buy a Flex 1500. I haven’t checked the specs, though, to see if they are comparable.
Finally, there was a talk on MacHPSDR, a native Mac implementation of a receiver for OpenHPSDR hardware. I wish that I’d been able to stay, as I am a Mac person, but I had to leave. Despite the availability of this software, you really do need to have a PC to run a software-defined radio. I don’t expect this to change in the near future.
Well, that was certainly enough for one day. On Saturday, there were some equally interesting forums, including forums on RTTY, SSTV, antenna-modeling software, and the AMSAT forum. Despite this, I decided to not attend a single one and walk the fleamarket and visit vendor booths. More about that in the next post.
At $1,600, this kit is a little on the expensive side for most amateurs, but it’s an interesting indication of where things are going….Dan
Colorado Electronic Product Design, Inc. Introduces New Digital Radio Kit
Boulder, Colorado – August 29, 2008 â€“
Colorado Electronic Product Design (CEPD) introduces a digital radio kit consisting of three configurable printed circuit boards.
The Digital Radio Kit (DRK) is intended to aid in the development and test of algorithms and signal processing applications including:
- Digital radio, modulator/demodulator development
- Software defined radio
- High speed data acquisition and signal processing
- Audio data acquisition and signal processing
The system combines a PCI card, an FPGA signal processing card, and a down converting digital radio card. All three cards have connectors allowing them to stack, forming a digital radio system. The kit will operate in standalone mode or the PCI card can be attached to a computer.
The standard configuration for the digital radio card is the 75MHz to 150MHz band. The digital radio card is capable of transmitting and receiving RF signals. Filters, Low Noise Amplifiers, and mixers are socket-ed to simplify frequency changes. The card includes a frequency synthesizer LO and mixers for up and down conversion for transmitting and receiving. The card utilizes a 13-bit, 210 million samples per second (MSPS) analog-to-digital converter (ADC), a 14-bit, 400 MSPS digital-to-analog converter (DAC) and an audio codec.
I swapped some e-mail with these folks, and they assure me that with some component replacements, the DRK will cover HF frequencies. There is more information, including a block diagram, at http://www.cepdinc.com/DRK.htm