APRS IGate with DireWolf and MC3362P receiver

Currently under testing, a APRS iGate with Raspberry under DireWolf, and a good sound card SoundBlaster3 USB, didn’t want to use a dedicated VHF receiver for that so i have take a old good MC3362P from my first 2 meters receiver, old board from F5RDH project, i have removed the local LO (L/C), and replaced it by a ADF4351 (integrated voltage controlled oscillator), in Europe APRS QRG is 144.800Mhz, so i need 144.800 – 10.7 = 134.100Mhz, some lines of code with a Arduino can easly program ADF4351 to generate this frequency, the ADF’ board come from ebay for some $$, Mc3362P need around 80~100mv of level. The LO give around -5db output, that just enough for the mixer.

MC3362P Low-Power Narrowband FM Receiver
Rx144 part list
Rx144 board and pcb
Modified schematic

RED areas need to be removed:
-frequency control P1 and component around,
-P2 squelch control, tie R12 to Vcc,
-remove audio amplifier U2, no needed
-remove local oscillator L/C, L2, C9, and R4, put 100nf on pin 21, connect pin 22 to your LO (134.100) with 100nf.

MC3362P is a « obsolete » part since around 2005′ year, but still available on market, some sellers on ebay, or Futurlec (1.90$)

Go to github and install DireWolf on your Raspberry

Dire Wolf is a software « soundcard » AX.25 packet modem/TNC and APRS encoder/decoder. It can be used stand-alone to observe APRS traffic, as a tracker, digipeater, APRStt gateway, or Internet Gateway (IGate). For more information, look at the bottom 1/4 of this page and in https://github.com/wb2osz/direwolf/blob/dev/doc/README.md

All part are inside a 1U rack, recycled from old switch

Rf Input on  BNC connector, RJ 45 to connect the Raspberry, external USB port, and power.

Power part

The MC3362P receiver with the LO on 134.100Mhz.

On top, the hard drive on the usb hub, at bottom, the Raspberry Pi with the USB Sound Card.

TO-DO: Connect the RJ45 socket to Rpi, & install a properly safety shut down power system for Rpi.

Small, cheap UPS for Raspberry

As you know, if you use Raspberry, the operating system on SdCard is very fragile, that the reason you need to power off properly the system to avoid corrupt files system. This small circuit can help you.

There is no PCB, all component was recycling, coming from old stuff, 10000uf capacitor, 3A diode from computer power supply, the battery from cell phone or old wearable device, except the StepUP converter and the battery charger are from ebay, for 1$ (shipping included).

The main power supply feed the relay coil and the Raspberry through D3, big capacitor is here to avoid voltage drop out, and D3 is here to avoid voltage feedback and latch delay for the relay.
Vcc 5.5v is converted to 6.5v. During this time the TP4056 li-po charge the battery. If main power fail, the relay RL1 turn to initial state, 3.7v from battery can feed MT3608, and keep supply the Raspberry, in my test i can still have Rpi under good power condition during around 10min, so it’s work fine with « short » power failure.

I plan to implement a power management system to power off properly the Raspberry (through GPIO), 10 minutes or more is just enought, may be with a Arduino Nano, or with a simple timer with capacitor and transistor.

My testing conditions was with a Rpi B1, and wifi dongle, with LCD touch screen, the power was +5.5v 2A.