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RTL Software Defined Radio
hardware : by Tommy - May 9th 2013, 10:56PM
hardware
Last week I got my newest toy in. It's a USB DVB RTL Receiver featuring the Realtek chipset beloved by radio enthusiasts. The chip functions by receiving radio signals and converting them to audio streams which the computer can decode/demodulate using software. The software tells the chip what frequency to tune to, and demodulates the signal. This concept is known as a Software Defined Radio or SDR for short.

The Realtek is cheap and agile enough to tune a wide range of frequencies (52 MHz-2200 MHz). Thanks to free (as in beer) software like SDRSharp, the "work" of setting up this complex sounding setup is almost trivial. (Especially if you use the install script in the downloads section of SDRSharp. Other websites can show you how to setup a trunking radio scanner for police/fire/EMS in your area. [So long as your local fire responders don't use a trunked P25 Phase II system])

If you're looking to get started, check out this USB DVB Dongle (any RTL2832U receiver should work). I would also recommend getting an antenna pigtail so you can use a bigger/better antenna for whatever frequencies you want to receive.

tags: radio sdr rtl

( Comments : 1 | Full article )

 
Ham Radio PDF Archive
radio : by Tommy - March 26th 2013, 04:11PM
radio
The other day I went looking for an old issue of the once-free publication WorldRadio Online, but had trouble finding all the issues in a single repository. I decided to make myself one once I found all the files. So here it is: www.n5dux.com/ham/pubs

WorldRadio used to be a very low key, cheap publication about amateur radio. The kits and homebrew articles were worth a look. WorldRadio had a small following but when the much larger CQ magazine offered to buy-out WorldRadio, the owners of WorldRadio gave in. CQ has far more advertising dollars to support their publications (CQ, CQ-VHF and PopComm) - for them, it's a business wrapped around a hobby. WorldRadio was more of a hobby wrapped around a hobby.

So CQ Magazine bought the small WorldRadio, moved their "lifetime subscription" members to a one or two year CQ magazine subscription (crummy deal) and made WorldRadio into a free, online-only publication titled WorldRadio Online. (A move that jilted many of the older, not-quite-so-tech-savvy readership.) Many of the longtime readers said it was the end of WorldRadio, some said it was the start of online publications for ham radio. Both were right. WorldRadio Online was a great monthly treat because it was free. The transition to online was made easier in that the reader wasn't having to pay for it. The content got watered down somewhat as CQ wasn't making much money on the project, but you get what you pay for: no complaints. Still, longtime readers still said the end was near for WorldRadio. In October 2011, they were proven more correct. WorldRadio Online became a paid-for, online-only publication. The once-free PDFs were taken down and any new content would have to be paid for. I'm unaware of any widespread fanbase of the now online-only paid publication which can only mean it's a matter of time before the publisher pulls the plug on the project altogether.

Also succumbing to similar commercial/financial pressures is the European publication HamMag.

Continue reading...

tags: WRO WorldRadio HamMag Ham Radio

( Comments : 0 | Full article )

 
7400 Oscillator
hardware : by Tommy - January 21st 2013, 10:51PM
hardware
I recently came across a schematic that showed how to build an oscillator using the NAND gates inside a 7400 chip. After poking around online, looking for the 7400 (and not some variant) I learned the LeTourneau University College of Engineering has a parts supply closet with a whole stash of them for 5 each. (I've known about the parts closet for quite a number of years, but only recently discovered a tall filing cabinet full of most commonly used ICs. (No NE602 or 612s, I'm afraid, but that's another post for another time.)

So, with my 7400 in hand, I was able to breadboard an oscillator using the "colorburst" crystal at 3.579 MHz. The oscillator emits a square wave at the fundamental frequency, so harmonics abound. In fact, just through playing around with another receiver, the 3rd harmonic at ~28.632 MHz is considerably stronger than the others that fall in the ham bands. (All higher harmonics are just above the ham bands, though I may be able to pull them back down with a variable capacitor in series with the crystal.) I need to do some range testing on this to see just how far I can get on the various bands.
My next trick is to build a bandpass filter network to dampen the harmonics down to legal levels. Then, I'll have a bona fide transmitter, though very, very low power. Perhaps a final amplifier is on the drawing board next.

tags: electronics diy radio

( Comments : 1 | Full article )

 
Parallax Propeller
programming : by Tommy - July 21st 2012, 11:20AM
programming
I recently picked up a Propeller Board of Education from my recent trip to Parallax, Inc to teach the Teachers' Institute for the ARRL. The Propeller is Parallax's latest microcontroller platform that offers far more than the old beloved BASIC Stamp could. Digging back through my old posts, I found my initial review of the Parllax BASIC Stamp from 2006. (Little did I know that about 5 years later I'd begin teaching classes on the Stamp, visit Parallax HQ, and befriend the author of the "What's a Microcontroller" book (among other titles).)

The Propeller is a programmable multicore microcontroller that can be programmed in Assembly, Spin (an Object-Based programming language that I'm still learning), or, most recently, Standard C. The multicore design lends itself well for many, many projects, chief among them is robotics. Now your creations can take in and process loads more data at once. And with robotics, the more sensory input your bot has, the better equipped it will be to handle various tasks.

I just recently began to fully grasp the power of the little Propeller chip. Once the relative simplicity of utilizing the 8 cores available (known as "cogs"), the possibilities begin to multiply and compound one atop the other. My initial reluctance to the Propeller was the Spin language. The operators seem a bit foreign compared to the C-style languages I've been comfortable with for so long. The various code sections also seemed confusing initially. After reading through the tutorials posted on the learn.parallax.com website, I was up and running in a relatively short amount of time. I also took advantage of the Propeller Manual (pdf) and Programming the Propeller with Spin (pdf). While both offer great starting points, be sure to reference the learn.parallax.com site first - the Programming the Propeller text has its weaknesses.

Continue reading...

tags: microcontroller parallax propeller boe

( Comments : 0 | Full article )

 
Map Overlays
programming : by Greg - April 26th 2012, 03:58PM
programming
Since long long ago the military has used maps and graphic symbols to plan and implement combat plans. So to plan a mission, you need a MGRS topographic map, a blow up of the same map covering your Objective, and enough laminate overlays to fill a small car. I love arts and crafts just like the next guy, but is the sales guy at the mall gets a touchscreen tablet, why cant we get planning software. My list of needs: -a topographic version of Google Earth with Military Grid ref System -variable zoom and contour intervals -ability to capture snapshot the desired map -several tabbed 'layers' that I can toggle on and stack as needed -simple drawing tools -a tactical symbol database, one that recognizes the symbol I'm trying to fat finger and inserts it for me. That is all.

tags: military, maps, planning

( Comments : 0 | Full article )

 
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