Instructables

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.
 
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epo5 years ago
Hi! Great instructions! I was intent to getting a ricochet unit and following your instruction convert the antenna but guess what, somebody just sold a bunch with antennas already modified! I'm thinking of using the GT with a GPS unit that communicates in serial. However, the GT interface cable is usb! Is the conversion process a matter of figuring out the pinouts or something else. Any suggestions? Thanks.
Myself (author)  epo5 years ago
Both of the second-generation modems (the 128kbps, GS and GT) can run in USB or RS232 mode depending on which cable you plug in.

GT modem connector pinout is here:
http://ricochet.wikispaces.com/Hardware
I want one! Is there a cheaper place to buy them other than Ebay? Most sellers on Ebay want ~$25 shipped for the older phase I modems, and ~$30 for the phase II, most without cables. Times two.
I'm sorry, not phase two, but generation two modems. (IE the USB ones, models 21100 and 21131, which support 128Kbps)
wikityler6 years ago
What is a ricochet radio modem?
Myself (author)  wikityler6 years ago
It's just like a regular modem, but without the phone line. You dial, the other modem rings, they connect, you move data. It just happens over RF instead of twisted pair. And it happens faster, typically 100-200kbps.

I should probably make that clearer in the intro, thank you for pointing it out. There's a ModemBasics page on the Ricochet hackers' wiki, which I'm working on expanding.
Cool. You have no idea how useful that link was for a project of mine.
Myself (author)  wikityler6 years ago
Do tell! In private, if necessary. ;)
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