Hackit: FRS/GMRS portable radios

FRS and GMRS radios have the performance that we wished walkie talkies had when we were kids. I find them interesting because they aren’t quite as tied down as amateur radio bands. (They’re freaking cheap and you can give them to unlicensed users.) I’ve been surprised by the lack of hacks for these little guys. Garmin married them with a GPS unit to create a sort of hand held APRS device called the Rhino. Since I’ve got a couple of kids, I’m thinking that smacking a GPS into one of these little wrist radios with a modified opentracker (PIC based APRS encoder) would be great for tracking the family on hikes and ski/snowboard trips.

The response to Hackit has been fantastic! Each week I’m going to bring up some hardware. You guys get to pick your brains and suggest new, interesting projects. Look for a round-up and bounty post in the next week or so.

So, got a better idea? Let’s hear it!


  1. jaded says:

    Just a correction, transmitting on GMRS radio frequencies does require a license. It’s not a “proof of competence” license like a ham license; the only test is whether or not the FCC can cash your check.

    There are interesting things you’ll learn once you get your license, though. For example, it’s illegal to use GMRS channels 19 and 21 north of the 49th parallel from Washington to Minnesota, and other points sufficiently near the Canadian border (apparently they conflict with some Canadian military frequencies.) The thing that always puzzled me was why Garmin didn’t encode that line in the internal map, and shut off those two channels in the “forbidden zone”.

  2. Max says:

    How about making it into a cheap wireless modem. You could run the audio out from a modem into the microphone jack. You could have another running into a phone line or another computer.

  3. Blind says:

    I am not sure that I like this idea the more I think of it, but I’m going to mention it anyhow… Make a “gaydar”-style social networking thing. Have a server elsewhere that maintains a list of your interests, what you are looking for, etc. As you travel around it tracks you and it’s other users and when one that it feels is an appropriate match is in the immediate vicinity, it notifies the two of you so that you might meet face to face.

  4. a says:

    you do realize that gmrs radios require a license, don’t you? also they must be fcc type accepted to operate on the frs/gmrs bands, therefore no ‘hacks’. the rhino also was a rare exception and granted special permission to transmit data within the band.

    • Eric says:

      Nobody cares about the license requirement. Good luck finding someone at the FCC who wants to track down a FMS/GMRS violation out in the middle of the boonies

  5. Blind says:

    this is what i get for posting when it’s late and I should be sleeping.

    Assuming that it isn’t obvious, I’m expecting there to be gps tracking on all of the units (like the original post) in addition to the required connection to the server.

    Probably an easier way to do this though.

  6. i have a bunch of these. i’d love to be able to harness their power and use them as an R/C control, or at least figure out how to boost the tx power or change the frequency :)

  7. i also noticed that the frs band has a greater frequency than whats required by an analog NTSC video signal. perhaps its possible to transmit video signals with a slight modification or two.

  8. josh says:

    After the obligatory comments about modifying this equipment being against FCC rules, I have a pair of Bellsouth FRS model 1050 radios that have actually have internal 10k pots for more high end radio features like squelch and microphone gain that can be broke out relatively easily. Adding external BNC connectors to the antenna and hooking the radio to some 70cm ham radio antennas will exponentially increase the range on the radios.

  9. josh says:


    Yes, GMRS is licensed. Barely. You pay a fee, fill out a form and you’re licensed – no test whatsoever. And that’s if you’re hyper-honest. I don’t think most people bother with even that small formality.

  10. wikityler says:

    @4, @7:
    Not in canada, Here they are bound only by RSS-210, as is FRS. Refer to Annex 6 of RSS-210 for details.

  11. TJhooker says:

    Here in NC the police use GMRS somehow. I think it’s on there belt mounted radios. They use EDGE or something on there computers.

  12. TJ says:

    The freq can be readjusted pretty easily with a handheld freq meter and a pot tool on most model’s.

    You can’t go far only .5 mhz but it’s enough to get all the channels to be in between the regular channel’s so that anyone without a adjusted radio only gets garble junk that doesnt even sound like a voice.

    Aka poormans scrambler.

    Ive done it dozen’s of times

  13. Brat says:

    Funny all the licensing crap. I like the idea of having the GPS attached to one of the radios. It is not cost effect to have it on all of them. Nor would young kids like this.

    Maybe to use the main radios (FRS with GPS) TX a homing signal to the child FRSs) This way the child Radios can track the parent when the parent is on the move. What and how the protocal would be, I do not how to handle this.

  14. Brat says:

    I like the idea of sending video. You have a lot of channels can you make you of that as added bandwith. But how does that make use of the GPS? Maybe to encode the remote users location?

  15. lwr says:

    You could connect a radio to your PC and using Voice over IP magic, have conversations with people on the other side of the world!

    e.g.: http://www.446user.co.uk/article_12.html

  16. Static says:

    Man, I would love to see some hacks for these things. I’ve got a ton of these radios, a couple of them hacked apart.
    Canada used to have the same legislation regarding GMRS. Commercial and private pressure got them to remove the licensing requirements. There is a substantial amount of pressure in the US to follow suit.

    I’m not an electronics guru. I’ve tried to send video (NTSC) over a short range FRS link, simply by playing with the plugs. No dice.

    However, if someone could come up with a method to do this, we have struck gold. A decent, hackable radio interface that performs well at range, with no need for tuning. Come up with a method to use it as a short haul wireless modem, and you’ve got a dream system.

    I’ve seen some of the most innovative people on this board do some amazing things. I can’t believe someone hasn’t come up with something along these lines.

  17. Skyler Orlando says:

    Hmm, this is tough. You could modify them for a wall-mounted intercom system. I’m not sure, but you may be able to modify a radio to act as a scanner. I know you can do it with an AM receiver, but I don’t know whether FRS/GMRS radios use AM or what.

  18. aefaradien says:

    simple idea: how about a hack to make a 2-way system? that way it could be used hands-free.

    if only 2 people are using the link, then a separate channel could be used in each direction. now you have a poor-man’s radio-telephone.

    the only way i can think to do this is strap a pair together – making it quite heavy. however since it is hands-free, and if you take the skiing example, the “box” could go in a back-pack or deep-inside pocket or something.

  19. aefaradien says:

    another idea (sorry for double post):
    2 gps/radio units that always point at the other?

  20. Jeff says:

    FCC rules on FRS and GMRS say “No unmodified radios” (sigh) , and also say only an approved radio can be used… which annoys me, since if I were to freeband my Ham HT and set it for low power (both software changes), I could emulate FRS and GMRS except for the “no mods/approved hardware only” rule. Would be nice to have just one radio to talk to Hams and non-Hams alike just by turning the knob.

    You’re also not supposed to push data over them, unless you have an FCC exemption.

    That said, what kind of _legal_ fun?

    I believe an FRS with Vox plugged into the soundport of a computer would be legal. Load up one of the voice recognition packages, add text-to-speech and build an FRS/eMail gateway. Have a pre-defined “Heinlein/Number of the Beast/Gay Deciever” syntax to control it, and you’d be all set.

    Having it tied to an RSS feed accumulator of some sort would rock too – being able to be out on the far side of the farm and say,”Computer, weather report, execute” would rock.

    Tie it into one of the cheap USB X-10 controllers, and you’ve got the house lights and outside light. “Computer, Front lights, fifty percent, execute”

    The VOIP one has been done with EchoLink, but that’s a Ham-only set up. Should be able to use off-the-shelf software for the rest.

    If you can track down one of those old “dialers” you hold to the telephone, or use your PDA headphone jack plugged into the FRS, you could send DTMF from an unmodified radio…. Might be useful to control various things.

    One option for an unmodified radio being used more efficently with a vehicle would be a plastic box with a magnet in it. Use long earphone/mic cords through the car window, put the radio up on the roof so the car doesn’t block 90-odd% of the RF. You won’t be able to change channels, but it should substantially improve the range while on the road.

    • k7zgq says:

      Buy a cheap 70cm ham HT and transmit wherever! Its not legal to use on FRS but they kill on that band with 5 watts and a good antenna! I don’t condone its use but I won’t tell if you do it!

      • jeff wylie says:

        i have a couple of 22 channel hand held gmrs/frs radios but they work in the city only two miles or so. sure would like a extra mile or two in the car. the antennas are not removable. I see midland (18258) makes an window antenna that uses no cable. do you think that could help at all?. an extra mile or two would really be nice if possible!. Any ideas appreciated.

  21. @10 – You win. That’s the best information on FRS I’ve ever read. I have 5 of these units. Ideally, when we have soccer tournaments that mean my wife and I are trying to keep track of multiple games and kids at different events within a mile or so of each other we can use them. Unfortunately, the band is so crowded with kids being stupid on them that it doesn’t work out. They’re a little better for road trips between cars in a caravan (a convoy if you’re old enough to remember the 70’s film).

    Anyway, I’m going to look into that 1/2 step freq change you mentioned. That would rock.

  22. jason Winningham says:

    the garmin rinos only TX a position report when you key up, so they’re not much good for finding someone who isn’t actively wanting to be found.

    data transmission on FRS/GMRS is strictly forbidden; garmiin was granted an exception for the rinos, and that exception has limits (no automatic position beacons – they must be requeted by a human operator).

    there are some tools that go with xastir (unix APRS application) to import the rino data into xastir alongside APRS data. pretty cool.

    and a minor nit, the opentracker is based on an MC68Hxx controller, not a PIC. I think the original TinyTrack was a PIC, but he’s switched to Atmel micros.

  23. Gary Weber says:

    I’m looking for batteries for the watch-style radio in left of picture. Got mine from Marlboro. Can’t find battery XB-10 anywhere.Help.

  24. strider_mt2k says:

    I use an FRS link for a DTMF controller on board my ROV.

    please google “probe II sg” as I don’t have photos up of this project anymore.

    Aside from repositioning the antenna to the outside of the ROV and wiring the external speaker output of the first FRS radio to the DTMF controller on the receive side, all I did was parallel the audio from the speaker of an old radio shack portable autodialer device and wire a momentary switch from that into the mic input of the other FRS radio on the transmit side.
    (I tried to use VOX, but it’s cumbersome with DTMF.)

    It works flawlessly, although I don’t get the additional dtmf a,b,c,or d buttons using the rad shack autodialer for the DTMF tones.

    The DTMF system on the ROV controls a homebrew video camera switcher to select any one of three onboard video cameras, control the zoom focus and iris of the color camera and to trigger a little speaking thermometer to inform me of the internal temps of the two vehicle sections over the existing video link audio.
    (My ROV was designed for outdoor operations and I was concerned about overheating.)

    “probe ii sg” is currently mothballed intact, along with all of it’s support gear and spares in my den closet.

  25. Keelan says:

    I did a bunch of research into this very idea a year or so ago. I even got to the point of building a 300 baud audio FSK modem (based on an Exar XR2211) to test with my idea.

    Part of what I discovered is that prior to the Rhino, there was no provision in the FCC regulations to allow for data transmission in the FRS and GMRS bands. It looks like Garmin lobbied to have the regulations tweaked just enough to make their product work. The rules are not specific to Garmin. It makes a number of stipulations, the most important being:

    “Digital data transmissions shall not exceed one second, and shall be limited to no more than one digital transmission within a thirty-second period, except that an FRS unit may automatically respond to more than one interrogation request received within a thirty-second period.”

    The regulation can be found here:


    If you live in Canada (as I do), the exact same rules apply. The Canadian section of the GMRS/FRS regulations look like a copy-and-paste of the relevant US section.

  26. Keelan says:

    Regarding comments 10 and 19, the rules do not simply specify the bottom and top frequency of the band; the rules specify the exact frequency of individual channels. Modifying a radio to transmit and receive 500kHz off-frequency is a violation of the law. As well 500kHz is way too much; the GMRS/FRS channels are spaced 25KHz apart.

    When it comes to something that is globally shared (radio spectrum), play by the same rules that everyone else does; the alternative is chaos.

  27. Sean says:

    The FCC Restrictions are also why there are no trucker-CB-style units available. The entire thing has to be self contained – there are no base stations with an external antenna, microphone, and speakers. Probably to keep them from being tampered with. I would love to see some modem hacks for these too… The range would be awesome!

  28. chris says:

    If you could transmit data easily, pair them up with a 3-axis magnetometer, GPS unit and microcontroller, and play “real-life” scorched earth or something similar

  29. Rustybadger says:

    Here in Canada, we get to use GMRS without licensing restrictions, which is nice. I doubt it’s legal to send data over the frequencies (packet data in store-forward mode is expressly forbidden). That being said, there are a lot of hacks I’d like to see done with this gear- in rural areas like I live in, nobody ever checks up on illegal transmitters, so it’d be easy to get away with.

    1) Video transmission, like others have mentioned.
    2) Packet radio modem, for sending still frame-captures and weather data from a weather station.
    3) Autopatch system- base station connects to PSTN line and you use a portable DTMF generator to dial out from the gmrs handheld.

    Someone mentioned pairing 2 radios into a duplex system- the problem with that is that you’re going to be TX’ing constantly with one radio, which will a) drain the batteries in no time and b) overheat the unit’s tx board. Bad on both counts, but would still be a fun hack.

  30. James says:

    This is kind of pie-in-the-sky, but you could use this for home automation or similar. Just set up voice commands on your “hub” PC and pipe the output from your “home base” GMRS into your mic input. You could even establish 2-way communications if the radio unit has a line-in (if it’s PTT, that might be tricky).

    Going further down that path, you could leverage all sorts of voice-based PC interfaces, not just home automation. “Computer, Google ‘chinese restaurant 21050′” and it reads you a list of names and phone numbers. “Computer, playlist White Stripes” — I’m sure that would sound terrible in mono over this kind of radio link, but it’s still a neat hack. “Computer, email Jane, subject: ‘Lunch today’, body: ‘I’m going to be in town starting at 11:30…'”. Lots of possibilities here, and you probably don’t even have to write any code or solder anything yourself. Ehh??

    Bonus: it’s not a violation of the FCC ban on data transmission if you’re doing everything by voice. Right?

  31. Crypto77 says:

    Is there any way that the results of Hack-it could be displayed in a blog post so that people who browse the blog, but don’t have time to dig through 100 comments still get to hear the ideas of the winning contestant? If so that would be great.

  32. RK says:

    Re: linking with voice recognition software… voice quality and interference is terrible on these puppies, so I don’t think that will work. However, DTMF (or your own equivalent) would seem pretty basic, and probably falls within the law. Furthermore, since you’re leaving the radio portion intact, it would not really be considered “modified”. What would be suitably hackish is to embed a custom tone generator with keypad physically into one unit (rather than taping an old DTMF generator to the mic) and a recognition circuit built into the other one, which could then send the “codes” sent over the link to a USB/serial connection for consumption by a computer or other device.

  33. TheOneTrueStickman says:

    @ #14 (Skyler Orlando) & #15 (aefaradien): Some radios have channel and privacy code scanning built in, such as my Cobra 950s. I believe regular radio scanners should be able to pick up FRS/GMRS frequencies without trouble, it’s just an FM signal. For the intercom thing, hands-free is easy, if not always reliable, if your radio has VOX features.

    And just to reiterate what others have said, there’s a reason there haven’t been hacks for these radios – almost all modifications and data transmission are illegal. For FRS, that means no internal modifications (or antenna mods), and keelan (#30) summed up the data issue nicely. FCC Part 95.191-194, for reference. GMRS is expressly forbidden from transmitting data. (Part 95.631(f))

    There’s also a reason the rules exist – these bands are basically designated for family communications on trips. If you want to do data, Ham or MURS (http://wireless.fcc.gov/services/index.htm?job=operations&id=multi_use) are the legal options.

  34. Almost There says:

    >I’ve been surprised by the lack of
    >hacks for these little guys.

    I hacked one, see http://www.GeoCities.com/Almost_There_Weather_Balloon/

    Good Luck!

  35. tony says:

    MURS, Multi-Use Radio Service, allows voice and data with much fewer restrictions than FRS.

    151.820 MHz
    151.880 MHz
    151.940 MHz
    154.570 MHz
    154.600 MHz


  36. Bob says:

    Modifiying this type of radio to send video is not practical and would put out energy on frequency’s used by other services.

    The FRS channels are 25KHz apart. An NTSC video transmission using AM or FM is at least 8.4MHz wide. (You can’t practically turn an FM walkie talkie into a vestigal sideband video transmission to get the bandwidth down to 6MHz)

    There are lots of other radio services using the 3MHz either side of the FRS channels.

    Even if you wanted to anyway, changing the receiver filters and building add on video modulator and demodulator circuits is not practical.

  37. Miguel says:

    My wish is mating a GPS receiver module of about $50 to a gmrs and a timer to burst transmit its position every minute.

    Would install it permanently hidden in my car to be able to find it if stolen.
    No. I do not want Lo-Jack monthly payments.

  38. PT says:

    Got this idea at lunch today, when a motorcycle set off someones sound based car alarm. Your own lojack system, would require I guess a Rino. Just hack the buttons (or you could build devise a mechanical actuator to keep the Rino unmodified.) You would want some sort of sensor in the car, that would activate the ptt button. It would leave it on for say 30 seconds so you can listen in, after which it activates 15 seconds every minute. If the gps doesn’t show movement, you could use a DTMF tone to shutdown the broadcast and rearm the system. Even if the car manages to go out of range, a grid search could be done to try to locate it. Probably less than $40 dollars for parts if you already have the Rinos.

  39. Brent says:

    Some of them can probably be hacked to work on the 70cm ham band.

    Really, if you want to experiment with radios, get your ham license and do it on the ham bands. It’s not only the legal way, it’s also where most of the people who know what they’re doing are.

  40. M4CGYV3R says:

    How about instead of that little ‘Roger’ beep thing that it does when you finish talking, that could actually be serial(UART?) GPS data from one of the smaller modules, so they would be transmitting their location whether or not they know it…? It would probably require some rather larger or more expensive equipment to receive and plot the position (a-la a laptop with some custom hardware) but I could see it being useful in a military setting(paintball anyone?).

  41. A_Blind_man says:

    a Bomb – just fill the case with some mouldable explosive and set the talk switch to send enough current into the explosive to detonate it… just need some batts and A capacitor…

    or a metal detector,
    using the antenna as the reciever, and program it to send out a pulse every second when you hold the talk button and if it hits something and recieves it have it send another immidately and so the closer you get the faster it beeps
    Granted you would have to attach it to a stick or something and possibly replace the talk button with an On/OFF switch but whatever

  42. javaworm says:

    You can boost the reception on these things with just a little soldering and a scrap of wire. Pop the case open and find where the antenna solders to the board. Make a rough measurement of the antenna and find a scrap of small wire that is approx. the same length. Solder it onto the same spot the stock antenna attaches and route it in the case so it points roughly 180 degrees away from the factory antenna. Instant boost in reception for most of these. The basis of this hack is that most of these radios contain 1/8 wave antennas, not very efficient. by doubling the antenna length you make it into a 1/4 wave antenna which is infinitely more efficient in propagating the radio signal.


  43. doug says:

    What about taking the insides out of the radio and fashioning a case for a cell phone that also contains the frs/grms radio guts in it. along with that add a plug to use the speaker of the radio as a speaker phone for the cell phone.

    this would give you short range communication with your frs radio along with cell usage without taking it out of the case.

  44. M says:

    I would love to see a software program that could take a live feed of the screen (or at least the tracks of other identified rinos) and put it on the web, into GMaps, etc.

    Would hacking the screen data feed be the same thing as hacking the radio (wrt fcc regs)?

    One excellent thing that differentiates Rino from Opentracker is that the Rino is already tracking peers.

    With the right setup, I imagine OpenTracker could be set up to track larger events with multiple GPSs.

  45. beakpy says:

    anyone ever heard of PSK31? (http://en.wikipedia.org/wiki/PSK31)

    its great, text chat over half-duplex radio link. That would be nice, maybe using just a PIC, a couple of DAC and a couple of ADC and two FRS.
    I’ve read that in open spaces some guys got 10 Km (6.21 miles) of working range for a talkabout.

  46. n0qbh says:

    The GPS and FRS technologies married together are much more capable and less expensive than the Project Lifesaver http://www.projectlifesaver.org/site/ system being touted by many law enforcement agencies. My county just spent $15k for two receivers and some training – for 50 year old Ham radio fox hunt technology!
    Hey Garmin, do you smell business possibility?

  47. static says:

    UH.. The Garmin Rhino out of the box transmits and receives GPS position data. As I read the rhino manual, you can send a position beacon every 30 seconds by cycling the PTT. Shouldn’t be a problem to hack in circuitry to automate that. No license is needed if you stick with using the FRS channels. The only drawback with the rhino is, that it the packaging of the data for RF transmission is proprietary to Garmin . That may hamper gatewaying Rhino position beacons.

    Jeff; RS used to sell and FRS radio where the antenna and basic xceiver mag mounted to the roof connected to a speakermic with a long cord, as you subscribed.

    Steve D.; Are you proposing to use the entire FRS allocation to send ONE video signal? That may be a good way to attract attention ;)

    aefaradien; Yes radio-telephone is a simple idea but implementing it in single radio service band generally isn’t.

    To close; obtaining a technician class amatuer radio license isn’t that difficult or costly. Even with the limitations Amateur Radio has to be the best way to play with RF.

  48. J.R VanHoek says:

    What a really fantasic idea! I’m pretty sure that you’d better patten and market befor I DO! “COUNTDOWN!”

  49. KW7DSP says:

    GMRS licensing is a “must do” requirement. Licensing is not a formality, but the law. A license is not a request, but a requirement. Breaking the law because it is an inconvenience, or you don’t think it should apply to you, leads to anarchy. It is everyone’s responsibility to see that laws are first JUST, and second ENFORCED. Failing to do so is Anti-American. What kind of a citizen do you choose to be?

    • John Doe says:

      Nothing is a “must do” requirement when it comes from the illegitimate United States government. Their repeated treason and global murder is just the beginning of why your contract with them has been broken.
      Ok, let’s apply your test. Part one, Is GMRS licensing just? Being how it’s just a revenue generating scam for the aforementioned criminals with no skill requirement at all except can you write a check, then obviously no.
      Breaking the law of an illegal government leads to freedom, following illegal socialist laws IS anti-american and treasonous.
      I could go on about how some laws (even ham licensing) could be justifiable, but doing such wouldn’t get me any brownie points anyway, and you have demonstrated you are not using any logic anyway with supporting pointless GMRS licensing (you’d have an argument if they actually required more than your money), so why bother.
      Also it’s stupid to us your license/call sign as a handle on here since any idiot can look up your home address with it.

  50. GMRS Licensee says:

    GMRS requires a license. All these hacks mentioned are either in violation of FRS regs, GMRS regs, or both.

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