Working on the poster image for a medical documentary in development.
Recently I’ve become sort of obsessed with receiving weather data via ssb shortwave radio. I’m very interested in all the great applications that are available for Android, iPhone and iPad to accomplish this. They are great cheap little apps which replace stand alone radio equipment which are very expensive for a boater on a budget. I am very interested in receiving NAVTEX and WEATHER FAX specifically. A Furuno Fax machine costs about $2500, and a Navtex receiver with antenna costs around $500. Also these are bulky items which take up a lot of space on a boat and have to be refilled with paper. So using smartphone apps brings these services into reach for any boater, provided they already own a smartphone.
Upon discovery of these apps, I was immediately stuck with their fatal flaw. They all rely on screeching audio playing out the radio and into the smartphone microphone. When I first started playing with these apps, my wife and baby registered their annoyance with hearing that sound. Baby starts crying, wife is yelling “turn that crap off!” And who can blame her. The instructions for these apps suggest that I should hold the phone up to the radio, or use a headphone earbud and hold it up to the mic. The idea of being on a sailboat underway and decoding weather information by holding my phone up for 10 minutes, or fussing with tape and an earbud just seems crazy and full of flaws. I need to stand watch and must be able to walk away from this setup and let it quietly operate reliably. My diesel engine, a gust of wind or crying baby might cause confusion in the app. This method seems only workable for hobbyists experimentation, not for real Ocean Navigators like myself.
My first idea was to just use a double ended stereo phone jack cable to feed the audio from radio to smartphone. Luckily the phone did not even switch over to the input and protected itself from getting fried. First attempt failed. So I did some research and realized that I need to modulate the line level audio down to a mic level, which is measured in microvolts. I made this first cable with some resistors I had lying around and some guesses from online sources. This PAD kind or worked, it did bring the line level down, but it was hard for the phone to recognize and switch over to. I would plug this cable in but the APP would still receive audio from the voice mic. Second Fail.
Then it dawned on me. When I plug my mic headphones into the smartphone, it’s recognizing the impedance or resistance of the headphone mic. When I plug a line in, there is no circuit for the phone to detect, so the cable is not recognized. I used my multi-meter to measure the resistance between the various sleeves of mic headphones. It always came back the same, 2000 OHM. So in my next version, I used a 2k resistor to simulate the microphone in the circuit. The first time I plug that cable in, the apps instantly recognized this line in. And the next time too. Every time I plug it in, it switches over to my line audio in. I did this testing with a breadboard, then went about making a durable cable for real ocean going. The hardest part really is finding a 4 sleeve stereo phone jack cable that can be easily soldered. The one I found had very tiny contacts and was a challenge not to melt the surrounding plastic. All I did for the final cable was solder the rear 2 rings of the 4 pin phone jack to a 2 sleeve mono phone jack with the resistors in between covered by an inch of ballpoint pen shaft and lots of shrink wrap.
A word of caution though, don’t build the cable to be less than a foot long, when a smartphone gets close to a receiver tuned to low frequencies, the touchscreen causes terrible noise to come through the radio. An ideal location for the smartphone would be at least two feet from the radio. If I build another one, it will be longer and will include more shielding around the resistors.
If you are interested in making a DB Pad cable, it’s one of the easiest maker projects out there. 1 out of 5 in difficulty. Or if you want me to make you one, I might be compelled.
So Far I’ve tested it on an Android Phone and an iPad and it works great on both. If you need a parts list, here it is.
1x 4 Pin/Ring Mini Stereo phone Jack
1x 2 Pin/Ring Mini Stereo phone Jack or 1/4″ Phone jack. Up to you.
1x 2k Ohm Resistor
2x 500 Ohm Resistor
1 or 2 feet of 1 CM Heat shrink wrap
Also, if you want to wuss out and just buy one, here is a link.
As I count down to the beginning of the 2013 sailing season, I am collecting the gear I need to participate in maritime radio. I started off with the Grundig G3 which receives shortwave and ssb signals. Great for getting news, WEATHERFAX, NAVTEX and listening in on HAM and CB chatter. Since I mainly listen in my basement, I decided to run a long random wire onto my roof. I found that the long wire was bringing in too much signal and noise, so I built an UNUN or Balun out of some junk and an Altoids tin. The balun acts as a transformer to attenuate the signal for the Grundig. I am also using this device to ground the radio which really boosts the signal quality. If the transistors can compare the incoming radio signals to a clean grounded “nothing” and a big signal is coming in with the right impedance, you can clearly hear amateurs, broadcasts and number stations from all over the world, even down in the basement.
Next I picked up an Icom 725, a high frequency rig which can transmit from .5 to 30 MHZ, all Ham and Marine bands. The box on top of that is the palstar antenna tuner. It’s doing basically the same thing as the UNUN but for transmitter, matching the antenna’s impedance to what the radio is built to handle, 50 ohm. Curiously, the Icom is not able to pick up any NAVTEX signals which are transmitted at 518 KHZ, way down in the medium frequency band and just on the edge of it’s sensitivity range, but the Grundig picks them up no problem even in the basment. It’s internal ferrite antenna is perhaps made for MF where the ICOM is made for HF. I’ve had amazing luck using my Motorola Android phone with the “DroidNavtex” app for decoding NAVTEX signals through the Grundig G3 from as far away as Miami. For that I soldered together a PAD cable using broken iphone headphones to attenuate line level audio into mic level audio which gives me a line in on the Android or iPhone, which normally can only handle a mic in. The app developer suggest that you can just hold the smartphone up to the radio speaker to decode the signal, but that would never work during actual seagoing. I need to be at the wheel controlling the boat, not holding my phone up to a radio for 10 minutes at a time. Plus the drone of the diesel engine would likely drown it out. Also the headache inducing screaming fax sound is more than some passengers can endure. There is in fact no better way to make a baby or wife start crying than blasting fax audio. I prefer to feed that signal quietly with no interference as a hard wired line in. I guess I’m addicted to soldering now, will find any excuse to do it.
If there is interest in the UNUN and PAD cable, perhaps I should do a small production run for radio enthusiasts like myself who are looking to expand the performance of their radios and phones. With one of these PAD cables, a smartphone and $100 radio, you can get all the important maritime transmissions. Which is really great because NAVTEX and WEATHERFAX gear together costs thousands of dollars.
My next pice of kit will be a class D VHF. Probably a Standard Horizon GX 2000. I am really struggling to decide what level of AIS to use. Receive only or full Transponder. I just received my Ship station licence from the FCC, so I can legally go either way. Just can’t decide whether to spend the extra money and install another antenna just to send out my position to commercial vessels. That one transponder costs more than my whole HF rig and as much as the Zodiac which I need way more.
I take my amateur lic. exam next month and will get my callsign. Since we are in Canada it will start with VE.. then have a numeral, and with any luck it will be SH after that. If I can get VE9SH, I would be overjoyed, but it might already be taken.
I’m looking forward to using all this gear to stay in touch and informed while cruising down to the Carib next year. You can listen for me using WebSDR.org.
Been working on this spot for a Great Gulf Development with 1188. I did a test previz with a goldish building a few weeks ago, and client apparently so delighted with the goldness, they pronounced that from then on, all the marketing should show their building as a tower of gold. I am really obsessed with architecture right now, so this is right up my alley.
I recently became interested in downloading weather fax images using a handheld radio tuned to weather fax SSB radio. The weather fax is used by mariners who are far from shore wishing to read up to date weather maps to make navigation decisions.
Now that we’re used to clean digital imagery, I find it interesting to use a radio sound frequency to cary image information. The picture quality really depends on what time of day you are receiving. Shortwave or HF radio needs a freshly charged ionosphere to propagate low powered radio waves all over the world. I found the biggest improvement came with grounding the radio properly.
The fun part is that the information is coming in “bent.” The receiver has to be tuned to the right notes and skew adjusted to un-bend the image into a readable form.
I captures these faxes with HF Weather Fax for iPad. Colored them with Plastic Bullet.
I downloaded the trial version of Nuke 7 to check out it’s point cloud generation and modelling tools. pretty impressive. This scene was generated in a few minutes with the push of just a few buttons.