The $75 iGate – (geek skills required)

I have successfully created an APRS iGate using a Raspberry PI, RTL-SDR, mini WiFi adapter, SD card, and 5v micro-USB power supply.


I used several set of instructions from the internet including Marco Kubon’s blog post, Jason Fitxpatrick’s How-to-Geek wifi article, ReadiesCards thread on mini-httpd, ¬†and various debugging techniques that are best found by using Google if and when a problem exists.

The only reason I have the HTTP server integrated into the iGate is to make it easy to check the logs using any web browser, including from my iPhone and iPad. All maintenance is done using SSH. Like I said, “geek skills required”.

The hardware is all commonly available:

FYI: The cheaper and more common R820T based RTL-SDR dongles may work but I started with one of those and had issues. Then I switched to the E4000 tuner and managed to get things working. I did not go back and try to get the R820T based dongle working. Read into that what you want but given how much time I wasted on this project, I have not had the energy or desire to do more experimenting.

The one thing I will conclude with is that I do not yet¬†fully trust this iGate. It seems stable but more than once – while getting the system working – I’d start up the software and it would not receive any messages. I think most of the issues are the lousy test antenna but I won’t know until I drop this in place of my stable 2m-radio based iGate.

Raspberry Pi RTL-SDR iGate – it works!

Raspberry Pi, RTL-SDR, and PoE

Time to retract my opinion that you can’t make an iGate with an SDR and a Raspberry Pi. It turns out you can if you have the right software defined radio.

The most common RTL-SDR (USB radio receiver dongle) is the current crop of offerings which use the R820T chip for its tuner. These are also the least expensive at $10-$15 when ordered from any of the Chinese or Taiwanese vendors. The harder to find version uses an older E4000 tuner. These are also more expensive and many buyers have reported receiving a “free upgrade” when ordering the old style. Needless to say this causes problems since you really need the old E4000. In addition to looking for “E4000″ in the description, also look at the frequency range. It should be 50Mhz – 2200Mhz.

I finally took a chance and ordered a different RTL-SDR which claimed to be a real E4000 design. It didn’t look like any of the pictures others had posted for the “real deal” but the vendor claimed these were real. After 24 days on a boat, the little things arrived.

I tested them and they reported they had the E4000 tuner. The final test was to plug it into the Raspberry Pi, load the software test, and see if I could receive APRS messages.


The final packaging is not complete but the design uses PoE (power over Ethernet) and mount the small package near the base of the antenna and only run an Ethernet cable to it.

Nick, the Catahoula, discovers snow

Nick turns two in February. Given he started life in Arkansas and went to New York in June and then came to Virginia in September of his first year, he had not seen snow before. Initially he didn’t want to go outside. That didn’t last long !

An iGate using a RTL-SDR

An iGate is a simple base station which receives APRS messages over the air and transfer them to the internet. A simple iGate uses a radio receiver, a terminal node controller (converts modulated audio to a data), and a computer. The source data is modulated into audio, transmitted, received, and then demodulated back to data.

All of the iGates I've built have used a traditional radio. This time I tried using a Software Defined Receiver or SDR. These are strange cheap little decides. They are marketed as digital TV receivers but they support an extremely wide frequency range.

It all started with an internet article that described using an SDR with a Raspberry Pi. I don't know what the author was smoking but it doesn't work. (I take it back – read here) It will generate underrun errors. A Google of the error and either SDR or Raspberry Pi and there are lots of reports and no answers. I used my primary computer and SDR Sharp software to verify the dongle and antenna. Then I switched to the XO laptop which has just enough juice to make it all work. The steps are geeky enough but here is the cliff notes edition …

  • install the necessary computer tools and libraries
  • “git” the source for rtl-sdr
  • build and install rtl-sdr
  • run rtl_fm and pipe it to aplay to create virtual device
  • configure soundmodem to use the virtual sound device
  • configure aprx to use soundmodem

Just like using a radio, the SDR needs a good antenna. The antenna that comes with the RTL-SDR is basically worthless.

The Internet of Things is here

the TV wall mount holds all of the streaming media devices
the TV wall mount holds all of the streaming media devices

They say that 2014 is the year that will finally usher in “the internet of things”. I’m sure a search will find someone proclaiming 2013 or 2012 the same. I think it’s already here.

Over the past few months I’ve helped add network cable to two houses. (There is about 4,000 feet of it in the walls of the farmhouse.) The two homes are not what you would call high-tech households. So, what is driving this change? “The convenience of technology” – tablets, internet TV devices, internet bundles with telephone, etc.

The other day, my TV went all wonky. At first I was bummed and then I thought it would be a good time to get a “smart TV”. (I won’t be getting a new TV because curiosity got the better of me and I fixed the old Philips.)

While the TV was off the wall, I decided to clean up the explosion of little boxes which have reproduced like Tribbles. There is an Apple TV, a Roku, and a Raspberry Pi running XBMC. Three streaming media devices needing network connectivity so that means there is also a multi-port network switch back there too.

A soda can candle

melt old wax in a soda can
melt old wax in a soda can

I don’t know why, but it seems that candle makers today have no clue about thermodynamics. The amount of heat that a typical candle flame gives off is no where near enough to melt a 3″ diameter cylinder of wax.

Every candle I own burns down in the middle leaving a hefty hollow ring of colored, scented wax. A huge waste. Here’s my solution …

Cut the top off a soda can, place it over low heat and drop in chunks of the old candle wax. Add enough wax to fill the can. When it’s all melted, take a length of butcher’s string, tie one end to an old washer and lower it into the melted wax. Use something to hold the string centered in the can until the wax starts to harden.

Once the wax has hardened, remove your new candle from the soda can. It may require tearing the can away but the metal is so thin, it will peal away easily.