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HP2DFA > TECH 04.11.90 16:06z 48 Lines 2119 Bytes #-12969 (0) @ WW
BID : 7072_HP2DFA
Subj: POCKET PICO: A RASPBERRY PI PICO TNC
Path: SR1BSZ<EA2RCF<LU9DCE<PY2BIL<W0ARP<HP2DFA
Sent: 261104/1552Z 7072@HP2DFA.#COL.PAN.CEAM BPQ6.0.24
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PACKET / AMATEUR RADIO NEWS BULLETIN
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Title : POCKET PICO: A RASPBERRY PI PICO TNC
Credits : btech (Source: n7wdz.com)
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Pocket Pico: a terminal node controller for amateur packet radio
November 2, 2026
The Pocket Pico is a terminal node controller for amateur packet
radio, a modern rebuild of the Heathkit HK-21 Pocket Packet.
Inside sits a Raspberry Pi Pico, and the firmware is the same as
the original machine's. Anyone who builds one steps into packet
radio with current hardware, yet keeps compatibility with
historic software.
A Z80 emulator inside the Raspberry Pi Pico
The trick is emulation. The Raspberry Pi Pico runs a Z80
processor emulator, and that lets it run the original Heathkit
HK-21 firmware. Instead of rewriting the TNC logic from scratch,
the project reuses code that already worked forty years ago.
The microcontroller also handles modulating and demodulating the
Bell 202 audio tones, so no dedicated modem chip is needed. The
transmission speed is 1200 baud.
Key Features:
- Raspberry Pi Pico as the only control board
- Z80 processor emulator to run the HK-21 firmware
- Bell 202 tone modulation and demodulation at 1200 baud
- APRS and AX.25 Level 2 handled by the firmware
- Built-in Personal Bulletin Board System (PBBS)
APRS, AX.25 and the built-in bulletin board
On the radio side the device handles APRS and AX.25 Level 2. It
also includes a built-in PBBS, letting other stations leave
messages. That is the feature that made the original HK-21 a real
node.
What you need to rebuild the Pocket Pico
You need a Raspberry Pi Pico, the original HK-21 firmware, the
Z80 emulator, and an audio connection to the radio. Setting the
audio levels to the transceiver remains the critical step: if
tones are too strong or weak, the 1200 baud demodulator will not
lock on.
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73 DE HP2DFA-5 / BPQ32 BULLETIN NETWORK PANAMA
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