Yesterday I built the first complete PecanPico3 Tracker with a Si4464 transceiver chip. This is Serial #2. Serial #1 was only partially populated because I was hesitating to put an expensive GPS chip on the PCB without knowing if it works.I’ve had problems with PecanPico2 to couple the oscillator signal into the Si4464 and it turned out that I needed to attach the signal to the XOUT pin instead of the XIN pin. More experimenting showed that a 22 pF coupling capacitor is optimal for a stable operation of the Si4464. The theoretical value of 4 pF was too small and the PLL didn’t always lock to the correct frequency. However, this version of PecanPico3 seems to work fine just out of the box


Here are some example packets that can be seen on

2013-05-13 20:17:17 CDT: KT5TK-2>APECAN,WIDE2-1,qAR,KT5TK-6:T#224,072,000,000,000,019,00000000
2013-05-13 20:17:30 CDT: KT5TK-2>APECAN,WIDE2-1,qAR,KT5TK-6:/011506h2943.53N/09530.47WO000/000/A=-00179  3.8V 28C 101987Pa
2013-05-13 20:19:45 CDT: KT5TK-2>APECAN,WIDE2-1,qAR,KT5TK-6:T#225,072,000,000,000,019,00000000
2013-05-13 20:19:58 CDT: KT5TK-2>APECAN,WIDE2-1,qAR,KT5TK-6:/011732h2943.53N/09530.48WO000/000/A=-00179  3.8V 28C 101987Pa
2013-05-13 20:22:13 CDT: KT5TK-2>APECAN,WIDE2-1,qAR,KT5TK-6:T#226,071,001,000,000,019,00000000
2013-05-13 20:22:26 CDT: KT5TK-2>APECAN,WIDE2-1,qAR,KT5TK-6:/012001h2943.53N/09530.47WO000/000/A=-00181  3.8V 28C 101993Pa
2013-05-13 20:24:41 CDT: KT5TK-2>APECAN,WIDE2-1,qAR,KT5TK-6:T#227,071,000,000,000,019,00000000
2013-05-13 20:24:54 CDT: KT5TK-2>APECAN,WIDE2-1,qAR,KT5TK-6:/012232h2943.54N/09530.46WO046/016/A=-00181  3.8V 28C 101993Pa
2013-05-13 20:27:09 CDT: KT5TK-2>APECAN,WIDE2-1,qAR,KT5TK-6:T#228,073,001,000,000,019,00000000

The tracker is up on air for nearly 6 hours on a 400 mAh NiCd battery and still going. This made my decision easy for next Saturday where we’ll launch a 300 g balloon from our Fishfest QTH (Lake Livingston TX).  Pecan3 will fly!

Schematic: PecanPico3

Arduino Code:

Here is my parts list:

The uBlox MAX6Q GPS is available from HAB Supplies



6 thoughts on “PecanPico3

    • It’s on 2 meters (APRS). With slight modification on the output filters I have also used it on 70cm already. It should work on 222 MHz and 902 MHz likewise.

  1. Hiya, What modulation are you using? I’m intrigued by the SI4464 chip, but it doesn’t do AFSK modulation, so far as I can tell. I want to build a balloon sending APRS and hit IGates with it, but I’m figuring AFSK modulation would be the most common. I looked over your source code, briefly, but wasn’t quite figuring out what modulation scheme it was using. Can you give me a few hints?

    Mike / KD2EAT

    • Hi Mike,

      Pecan Pico 4 actually does AFSK 1200 bd and I always use it for APRS. The modulation is not done in the Si4464 chip, but the VCXO that drives the transmitter chip is modulated by a PWM audio voltage generated by the Arduino.

      I hope this helps,


      • It helps a great deal, thanks. 🙂 I read some stuff about doing that, but wasn’t clear that’s what I was seeing in the modep.cpp code.

        Thanks for this great resource! I’m going to but some bit and build a crude version of your pico4 for testing. I don’t (yet) have mad soldering skilz! Hehe


  2. Mike,

    Any chance you have a schematic for pico that used the ADF7012? I’m trying to do a version for a pro mini that uses the ADF7012 and I can’t locate a schematic, just references to that chip.

    I’ve also got an SI version in the works, but right now, just looking for the ADF version?

    Thanks any help appreciated,

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