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!

98 thoughts on “Hackit: FRS/GMRS Portable Radios

    How about an external 6v battery pack that can maintain power longer than the AAA’s that go in the FRS units? Maybe a 4-AA or D pack. Maybe even a 12v to 6v convertor with car adapter too. Hi power units suck the AAA’s in few minutes even super-aklalines.

    Data is allowed on FRS other than Rhinos. Look up ChatNow units. ~2 mile range text messaging.

    Set up transmit GPS on PTT and either use a VOX setting to trip everytime it hears sounds from the kid or make your own tone decoder and 555 delay drop out ckt. It listens for touch-tone or single tone, fires the 555, it latches for 1-2 minutes, holding down PTT sending GPS. Will require project battery connection and an outboard project box. All parts from Radio Shack.

    Use VOX setting set to 1 or (Not recommended–>) a rubber band around PTT. With a external power source you have a powerful 2~10 mile listening device. But transmitting too long tends to piss others off. So think twice about this one. Tends to induce FCC/Ham foxhunts…

    Using the VOX feature, remote power source (solar powered?), and wall mounting fixtures you can also set up a remote 2-way intercom. Like to a vacationing friends door, a remote gate entry, an outddor event entrance (party in the woods?), etc. Ppl wouldn’t need to know how to use it just talk into it. Put it in a project box so the only thing they can do is press the CALL button to CALL you. Have a sign that says PUSH CALL THEN JUST TALK.

    Get the CES Radio (in Florida USA) Simplex Autopatch unit and build an mic/earphone/PTT/AGC (Squelch) interface unit and connect to your FRS (Not recommended. May be totally illegal!). You can make phone calls on your FRS unit. But everyone listening will know your business and record your dialed phone numbers if you don’t use the preset CES phone dialer feature. It allows passcodes and toll blocking to stop other FRS’ers from phreaking your patch. When connected it transmits continually briefly (millisecond click) opening the reciever to listen for any carrier (You pushing your PTT) every second. When it hears the carrier it drops the transmitter and you can talk until you release PTT. And it starts all over again. Its touch-tone controlled and will drop after so minutes inactivity. It also has reverse patch (incoming call too). Its designed for HAM radio and Business band NOT FRS (per se).

    Radio Shack used to sell this and you can still get them at HAM radio online stores. You can make your own with a PC, sound card, and the VOX setting. All it does is listen for any sound breaking squelch. Records it into a sound file for about 30 seconds. hen Transmits it back out to the FRS via a PTT or Vox. Imagine putting one of these on top of a building and you can talk to your friends all over the metro or county. A lot farther than with the FRS unit by itself. It takes a bit getting used to it as it is nothing but a very limited echo machine or parrot box. Ppl need to pace themselves so as not to “step” on one anothers recording phase transmissions. A guy on the other side of a mountain can’t hear your FRS recording a repeat. But he will hear the repeat. Google it for more information…


    using a pc with voice synthesizer or wave file player you can program, like in vbasic, an automated dispatcher. you would use the frs’s built-in vox (voice operated switch) feature set to mid-point. you program your pc application to check your email, your home environment, caller id, phone messages, room temp, room audio, your keyboard, or whatever.

    the application simply uses canned (pre-recorded) or text-to-voice messages to send one way messages to you from 2~10 miles away via your frs radio. To overcome the vox’s behavior of cutting off first syllable just add an audio preamble like ‘uhh’, a ‘beep’, or a noise to get the vox ptt to key before your pre-canned message starts. Remember to start audio within a 1/2 second or less later depending on your vox setting.

    All you need is an audio patch cable between your pc’s sound card’s line out or speaker jack to your frs mic jack (available at radio shack). an audio splitter would be good so you can run an external pc speaker to hear whats going on too. experiment with different audio output levels.

    one neat feature is a user interface that allows a dispatcher to make his/her responses on the frs/gmrs routine by simply pressing a number from a displayed menu, mouse clicking a button, or pressing one key on keyboard. things like ‘calling unit number’ (fill in the blank), ‘over’, ‘roger that’, ’10-4′, ‘what is your location?’, ‘repeat that’, ‘return to base’, ‘call hq by land-line’, etc. the human dispatcher would hardly ever have to actually talk. they could just push a button or click a mouse to send and reply to your frs message. this is a more efficient and standardized way of communicating when the human has problems speaking or conveying information correctly. it also makes one voice for many ppl using the system. a female voice is more attention getting.

    to send commands back to the base station some sort of dtmf touch-tone decoder might work. except mfgs don’t make tone pads any more due to drug pushers (et al) using them on pay-phones to send secret msgs to beepers. you’d have to make your own or get one on ebay. there are many dtmf decoder downloads for your sound card on the internet.

    there’s also the possibility to use voice-to-text but prolly won’t work well as most systems are speaker dependent and don’t work well in high noise environment that frs might introduce to the audio input stage. but if you said the same command 3 or more times perfectly the application could filter out false triggering from static, squelch tails, channel chatter from kids, and deliberate voice hackers trying to take control…

    ultimate pc to pc remote control via an frs unit in a high noise low-audio-bandwidth environment? psk31… google it… its the latest low-tech method to get pc data across a low-bandwidth audio channel even in poor conditions… imagine what remote control scenarios you can come up with… its even been heard in operation on noisy cb radio!!! here’s what it sounds like in the wild (scroll to bottom) http://en.wikipedia.org/wiki/PSK31 (or click on my site’s url).


  3. I am about to test using one of these radios for a remote
    paintball gun. I had made a laser tripwire paintball gun,
    but I would like to in addition be able to fire it on command.
    I already use the radios for comms during play. This
    would allow me to sucker people toward the remote guns
    position, and then paint them from afar. On my radios, when
    one is receiving, an led flashes at about 1hz. I am going to
    use the flashing led to trigger the gun using the same
    components that the laser tripwire does. All I have to do is
    add one transistor.

    I could also use the radio as a suppression signal. If non
    players enter the field (we are out of town, but we share
    with dirtbikes and mountain bikes) I can use the radio to
    kill the tripwire function.

  4. Thats true, but…

    With the radios I use, I have 22 channels with 121 ‘privacy codes’. The first privacy code is just the standard frequency for the channel. I’m not sure what they are doing to get the other 120 ‘privacy codes’. It could be a shift in frequency or even something else. It doesn’t really explain it, and I don’t have a scanner.

    If you’re not on the right ‘privacy code’, you don’t get to access the gun.

    This means there are over 2000 possible ways to run it.

    These radios have a scan function but only pick up traffic on privacy code 1, so I am safe from people with the same radios. Other radios may have a better scan function, but if it’s not strictly a frequency shift, it may not matter.

    I finished the project and it runs great. It has some quirks that make it work, and may therefore not work with other configurations (radios) without modification.

    I’ve got schematics, photos and maybe one day I’ll attach a video.

    At my website

    I am interested in something faster than psk31, as I have great plans for the mix of radios and paintball.

    I would be quite interested to see psk31 coded into a pic if you’ve got any resources?

  5. Privacy codes are actually a squelch system.

    details here:

    The code can be analog or digital (I have digital), and are used such that a radio set with a privacy code will only transmit audio when it receives the
    proper privacy code. This lets you skip anyone elses chatter on the same frequency.

    It doesn’t eliminate their chatter, so there can still be interference, but less likely.

  6. Note:

    I just tested trying to send video via FRS. IT DOES NOT WORK :[… just a black screen with lines. The modulation is not correct. I think it is because the frequency bandwith is too small.

    What do you guys think?

  7. Video is possible on this radio. But in order to do it, it would have to be digital. Not sure on the fps this would give you. Also, you can hack this to get an easy 10-20 mile converage and 20 – 40 mile from base to base. useing some high grade heliax coax and a good collinear antenna high gain base antenna(Specially digned for 460mhz) up on a good tall tower. you can buy a SWR meter for 144/440Mhz and will work for your needs. my tests with this setup and a simplex repeater as stated above, i could talk to friends around the county easy. also note that turning the squelch pod a lil to get extra range. also dont forget to use tone codes to keep people out of your way. now if i unplug the repeater from the base and use the scan feature… I hear more people talking then what i do on a CB radio. beat that. this is old news. i should have posted this 4 years ago when i was testing it. ok now within the last year. i put 2 VOX boards together. built a dipole CB antenna and mounted it in the mid section of my tower. I connected the mic of the FRS/GMRS to the CB useing VOX and the MIC of the CB to the Speaker of the FRS/GMRS and now i can goto the other side of town and show a CB buddy I can talk to him on my wrist radio. So now back to my double duplex data repeater research. peace out.

  8. one note. most new GMRS/FRS radios dont have removable antennas. you have to cut a small jumper strip the end, seperate the inside wire from the outside ground. solder the inside connector to where the antenna used to be. and the outside sheild to a close ground. that should be close or next to the antenna solder somewhere. if your not sure then ohm it out. selecting a radio that can run while being charged and a good range radio. the more watts the better.

  9. The guy a couple of comments up who was so rude (fags, gay, slurs etc.) doesn’t have very nice manners. This is a great forum with incredibly creative minds, very few here could be seen as running in the middle of a mindless herd.

    Normally, everyone knows to ignore “trolls” so as not to encourage them. Unfortunately, he was not a troll. He just was frustrated and had very bad manners. Essentially, I have to admit, he is right.

    We should be focusing our creative technical minds on extra-legal effeciencies in communicating, and perpetuating that knowledge to as many people as possible, before “the grid” goes down. No longer is this the advice of “conspiracy theorists” that I used to lampoon. It is the advice of former Reagan cabinet officials (read “Paul Craig Roberts) and Wall Street analysts who told the truth.

    Strip out what the young ruffian above said about aids, sexual preference, etc., but take the point well that the government is careful to fence the people into small legalities which forms our prison, while they offer to any company or organization that can pay, all the exceptions and access and freedom they want. This renders our lawfulness inconsequential, like a frugal wife pinching pennies while her husband is out buying the Brooklyn Bridge.

    a Patriot

  10. I was reading something else about this on another blog. Interesting. Your perspective on it is diametrically opposed to what I read earlier. I am still contemplating over the diverse points of view, but I’m inclined to a great extent toward yours. And no matter, that’s what is so super about advanced democracy and the marketplace of thoughts online.

  11. You gentle people all have really great ideas. But here is one I haven’t seen. The HCX530,HC530 and the HC520 have a repeating feature which I would like to see used. First set up a number of 110’s to send pix from my trail camera’s placed all over my hunting/veiwing area. Have a string of 520’s or 530 repeat the info until it get to my base camp. Hence real time pix of anything that pass the trail camera. You could use the same tech for home security, farm watering and so on. Programing the tone to snap pix from all cams and sending them back when needed. It would give all the gps locations with the sent pix.

  12. I have a great hack for these. I have converted one to use a magnet rip cord to ativate the alert freature found on one of the motorola brands. When a red button is pressed it freeses the recieving radios and lock open the alert radio mic for 30 seconds. So I have a handicap erson that I trained a dog to alert to an epiliptic seazure. The dog pulls the rip cord setting off the alarm and the school nurse has one of the radios in her office. This has worked great. See my blog at abetterdogkennel.com or google mark thompson dog trainer charlotte nc

  13. Mini GMRS Repeater? Take two Hand-Helds, splice mic/ear cords between each unit (mic to ear – ear to mic)- set each unit to VOX activation – Set the desired channel “in” on unit 1 and “out” on unit 2 – remote the units in weather box to a roof or tree top – Remote each unit’s ant. – can remote the power via ext. cord w/7.5 egg or solar them – your 3rd unit can now be extended via the mini repeater to other units in the “field.”

  14. Adding a useful antenna jack to the FRS radios is relatively easy… a matter of simply locating the antenna wire/cable, clipping the end, and soldering an SMA panel jack/connector onto the end. Then dill a 1/4″ hole for the SMA jack to protrude from the case. Reassemble. The hardest part is getting the FRS apart–tiny screws that are often realy torqued in place. Now simply buy an external antenna for 462-467 MHz range and screw it on (I got them from ebay). The range is extended nicely by 2-4km. There is a good youtube video on this mod also. Of course the FCC doesn’t like this. I think I see them driving around my block now…

  15. Then there are the cheap chinese VHF / UHF handheld transceivers (HT) that are available for less than $45. These have antenna connectors, speaker-mic connectors, and completely programmable frequencies in a wide range. They can also be programmed for *any frequency* in the range. You can get more information about how to hack these for FRS or GMRS at radiofreeq.wordpress.com

  16. Why don’t you all just get HAM licenses? Everything said on here has been done in HAM, and is done in HAM legally. The licensing is EASY for a tech, and super cheap. You can buy radios far more capable than your frs/gmrs radios for similar (maybe 20 dollars more) if you don’t restrict yourself to top shelf brands like yaesu and Icom, and then it’s no headache. Forget whether or not you LIKE the law or AGREE with the FCC…isn’t it simply easier? Or must you fight every rule like a child just because it’s there? Honestly, for what you’re doing, you could do the same on HAM, then you’ll know what you’re doing because you took the test (of course FRS uses FM) and you’ll know where the experimental portions of the band lie, where certain data portions lie, and you will have no problem finding people to try this stuff with. Your “pie in the sky” stuff exists. Global data (internet even) based on ground stations, satellite data comms (not so much internet…think 80s bbs and chat), email, local FM mesh based data, it’s all there. Want to try something new? Want to mod your radio? Guess what? You’re a HAM now so you know the rules and as long as you stick to them you can mod and hack to your hearts content. Don’t think of it as a limitation. Think of it as a license to do what you were doing, and then some.

  17. “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.”

    Spoken like a true idiot. The Amateur Service is the ONE SERVICE that allows hacking. It was design for and allows that. We are the only service allowed to build and modify our own radios. Every other service must use type accepted and must follow tight parameters.

    Hams have frequencies from HF to microwave and beyond. Spread spectrum and data are hot right now. So is SDR. And 7 year olds can pass the test!

    So there is no excuse.

    Mr. O’brien is clueless!

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