Intro: Mod a Ricochet Radio Modem to Take an External Antenna
The product of a before-its-time business model, Ricochet modems are great technology with a surprisingly low price tag. They act just like regular modems, but with an RF layer instead of a phone line. Build your own dial-in access server, control a microcontroller project, or do other serial tricks from thousands of feet away!
Transmitting one watt at 900 MHz, the modems pack quite a punch, but the stock rubber-duck antennae suck. What's worse, the internal antenna connector is nonstandard, and we've been as yet unsuccessful at identifying it. Adding better antennae makes it easy to surpass the maybe-a-mile distances achievable on the stock omnis, but first, we need a way to connect those antennae.
(Note: This Instructable originally identified the stock connector as a Hirose H.FL, but we've now confirmed that this is not the case. It's very similar, but not quite identical! If better information comes down about the connector itself, it will be posted here.)
Fortunately, it's relatively easy to replace the H.FL with the much more common (and much smaller) U.FL connector, which is found on MiniPCI wireless cards, among other places. Thus modified, the modem is easy to equip with the new antenna of your choice. The operation is straightforward, and this instructable is as much about good soldering technique as it is about the specific task at hand.
Because the radio modem was certified to meet FCC Part 15 requirements with its built-in antenna, changing that antenna breaks the certification, just like changing the antenna on an 802.11 device. This may fall under part 15.23 but I'm not a lawyer and can't say for certain whether a user-modified device counts as a home-built device. Refrain from pissing people off, and the feds should have no reason to bother you.
Or, if you're an amateur radio operator, you can operate under Part 97. Either way, if half-mile links were typical on the rubber ducks, just imagine what you'll achieve with some decently directional antennae!
This is my first instructable. Please be unsparing with your constructive criticism.
Step 1: Materials, Tools, and Work Space.
You'll need a Ricochet modem, obviously. They work better in pairs, so get at least two. They come up on eBay occasionally, and you can expect to pay ten or twenty bucks including shipping. The pictures in this instructable were taken with a GT modem, but the GS and SX also use H.FL connectors internally, and the procedure is generic. (The SX is first-generation, though, so skip it unless you have a good reason.)
Some U.FL connectors would be nice, obviously. I got mine from Digi-Key, where they're $1.39 each as of this writing. You can also scavenge them from dead Mini-PCI wireless cards, if you have any sitting around, but removing them intact is tricky.
And of course, you'll need new antennae and cables, since the stock ones won't fit anymore. The easy availability of U.FL pigtails from a number of sources was the reason behind this instructable.
For the GT modem, you'll need a 1/16" hex (Allen) key or driver. For the GS, it's a T6 Torx.
A set of really fine needle-nose pliers is essential. I like box-joint pliers, which have less lateral play than the cheaper pin joint. Tweezers are a fine idea, too.
Get a good soldering iron, or temperature-controlled station. Get the finest tip they offer, in the neighborhood of 3/64" if it's available. I use a refurbished Edsyn 951SX "Loner" station that I got at a ham swap from EAE Sales. It's changed the way I think about solder, and is easily the best tool purchase I ever made. If you do a lot of electronics work (and you're on this site, you should!), consider it money well spent.
Paste flux is the most overlooked part of any soldering setup. Get good flux and use it every time the iron touches something. Soldering should be called "soldering and fluxing", but I guess that doesn't roll off the tongue so easily. I can't emphasize this enough, use flux! It dissolves oxides, it conducts heat, and it solves all the surface-tension problems that make soldering awkward. If you've had a bad experience with solder, I bet this is why. (If you're getting a solder station from EAE, Bruce will set you up with the right flux and solder, too.)
Oh yes, solder! For most electronics work, finer solder is better. If it's stiff enough not to droop when you extend it five or six inches, throw it back in the plumbing toolbox and get some real electronics solder. Rosin core is nice but not essential if you're using external flux.
Some desoldering braid is nice to have, too. It's cheap and it lasts a long time, so throw some on your Digi-Key order. (I do a LOT of soldering, and I can't remember the last time I reached the end of a spool of braid.)
A vise really helps. Your workbench deserves a Panavise350 or something similar. They're made in the USA and lifetime warranted, so shell out the bucks and rest assured that your great grandkids will marvel at your foresight in buying such a useful, timeless tool.
Safety glasses. Solder and flux can spatter, and small parts can go flying. You only get one set of eyes, so please treat them well! I've been extremely pleased with the MSA SafetyWorks glasses, which I get at Home Depot. They're absurdly clear, and the lenses are very flat so they don't shift the image like other glasses I've tried. If you feel like you're underwater or on another planet when wearing safety glasses, you're wearing the wrong safety glasses. They're cheap, so keep trying new ones until you find a style you like. Then keep the old ones around for guests to use.
Step 2: Open the Victim.
Open the modem, remove the internal screw securing the board to the chassis, and disconnect the battery and antenna from the board.
Step 3: Some Perspective.
Just so you understand what we're getting into, here are some pictures of the old H.FL next to the new U.FL. The size difference really is as dramatic as the datasheet makes it look!
Step 4: Remove the Old Jack.
Secure the board in a vise. Use the ultra-fine desoldering braid, along with the ultra-fine soldering iron tip, to remove as much solder as possible from the signal pin. Then heat the ground pins and pry on the jack. Eventually move back to the signal pin.
With constant leverage on the jack, every time you melt one pad, it should move just a little. Just hop around from pad to pad, and eventually it should pop free.
The text in this step is mostly extraneous, all the goodies are in the photos.
Step 5: Prep the Board for the New Jack.
Clean up all that nasty solder residue by "mopping" the area with some absorbent braid. It works just like a towel, but for molten metal. Isn't that a fun concept to contemplate?
Use flux, and hold the braid far enough back that you don't burn your fingers. Copper is a very good heat conductor!
Step 6: Line Up the New Jack.
Here's where having a sturdy, stable vise really pays off! If you bump the board during this process, the jack will skitter out of alignment. A bit of flux might help "lick it and stick it" in place.
Flip between images 2 and 3 in this step to see how the jack lines up on the pads.
Step 7: Solder the New Jack Into Place.
Clean the iron tip by wiping it on the sponge. Get a bit of flux on the end of the solder, then touch it to the iron so a tiny droplet of solder clings to the iron.
Hold the jack in place with a toothpick, popsicle stick, or whatever. Touch the molten solder to the intersection of the jack and one ground pad. If there was flux on the pad, the solder should flow and make the connection. Remove the iron and check your work.
Repeat the process for the other ground pad, then for the signal pad. The rearmost ground pad, which was used for the H.FL connector, doesn't need to be used for the U.FL connector but I soldered it anyway.
Step 8: Finish Up!
Attach the pigtail, close the modem, and perform some form of strain-relief to keep stress off that flimsy little U.FL connector.
Build or buy a spiffy 900MHz antenna, and connect it. Fire the modem up in the presence of another one, and watch them start blinking when they find each other. Pat self on back.
Since these modems will go 2000 feet or farther on the stock antennae, you should have no trouble getting several miles out of them, given a couple dB of gain and some decent mountings. Use them like any other modems, running a dial-in server or even a Ricochet BBS for your friends.