Thursday, February 17, 2011

Hacking Cobra Microtalk FRS radios: Intro

Are the ubiquitous and incredibly cheap FRS radios of any use in ham radio?

I have always been really curious about that. But a Google search turns up very little in the way of hams hacking FRS radios for amateur radio uses. Well, I'm working with Dr. Cool (who prefers to remain anonymous) to do just that. We got some Cobra Microtalk FRS radios for just $2.50 after rebate. Cool opened them up to see just what's inside.

Turns out that the PLL chip is clearly marked (it's the MCD2926) and the datasheet is available. Reprogramming the PLL for different freqs is pretty simple. I even created a spreadsheet that lets you plug in a frequency and it comes up with the various command values you need to send to the chip. So theoretically, a guy should be able to push these dudes down into the ham bands by 1) retuning the VCO that's in the radio to go down about 20 MHz (from the FRS allocations, into the 430 - 450 MHz ham band) and 2) hijacking the control pins to the PLL to tell it where to go. Maybe just the first would actually get you into the ham band.

The other thing I'd like to do is to replace the VCO that's on the radio with one of the Maxim VCO parts (MAX2605/2606/2607/2608/2609, costing about $1 each). That way you'd get a nice programmable oscillator for the range of the particular VCO you select. Seems like it would be great for a small bench-top programmable oscillator or for the basis of a cheap beacon for 50/144/222/432 MHz.

We're going to keep hacking at these things, so I'll keep you posted.


[Here's the data stream being sent to the PLL chip. Won't be hard to program a little PIC processor to send that out.]

73 de W9HQ
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4 comments:

  1. AnonymousJuly 5, 2011 at 1:01 PM

    This chip can be programmed for ham bands directly. it is used in many FRS radios.
    http://www.asichip.com/ceshi/pdf-new/AS6801-DS-PR0.8%20with%20CLI%2020080717.pdf
    73s,
    Peter, KH6VP
    petervee@yahoo.com

    ReplyDelete
  2. JamesOctober 22, 2011 at 9:41 PM

    Have you done anything else with this yet? I'm sad that this is the most recent thing on the site and it was back in Feb. It's also one of the few results I find when searching for information about hacking FRS radios for the Ham band. I've been thinking about doing this myself lately, at least for some qrp fun. Modding a FRS radio down to a 440 ham frequency and replacing the antenna with a more suitable one or with a bnc connector and a nice quarter wave.

    ReplyDelete
  3. Reagan ThomasNovember 8, 2011 at 10:50 AM

    Interesting post, I'm looking forward to an update.

    In the 90's, I hacked an 8 channel desktop scanning receiver that I got on clearance from Radio Shack. I lifted the pins on the PLL and interfaced them to a PC by parallel printer port. With that arrangement and some software, I was able to have a 200 channel (about what I could fit on one page in VGA text mode) scanner. Outputs required for a proper interface were the clock and data lines on the PLL, 2 or 3 for band select. The only input from the radio was squelch logic level. This enabled me to use it to hunt down signals. I'd leave it running all day, recording the frequency whenever it saw a carrier. Then I'd review what it had found.

    Anyway, I found your post by searching "microtalk hack" only *after* I bought a pair of radios from WalMart for the express purpose of seeing if they were hackable.

    I'll let you know if/when I come up with anything

    ReplyDelete
  4. Reagan ThomasNovember 20, 2011 at 12:12 PM

    Here's my own progress so far:

    http://ratnethome.blogspot.com/2011/11/hacking-frs-walkie-talkies.html

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