uv-k1-k5v3-firmware-custom/App/apps/aprstx

APRS TX: on-radio APRS position beacon (work in progress)

Sends one APRS position frame (AX.25 UI frame, Bell 202 AFSK 1200 bauds) on the TX VFO at each press of PTT or MENU. Companion of APRS RX, which is also the test receiver.

Step	State
Frame and bit stream model (test/tx_model.py)	Done: identical to the RX app's AX.25 reference, decoded by the RX model
Radio app (aprstx_app.c)	v0.1 works on the radio (2026-09-30); v0.2 edits the position; v0.3 adds the SSID and path; v0.4 adds the corrected 20x20 bitmap and the 48-symbol selector (not built here)
On-air test: APRS RX on a second radio, FT3D	Done (2026-09-30, v0.1: frames received by a UV-K1 running APRS RX and by the FT3D, first try, default level 66 and twist 0)

Station settings (gen_assets.py, then rebuild)

Setting	Default
Source	the boot-message callsign (API boot_callsign, 1-6 letters/digits) + SSID = 7 (0-15, 0 = none): the default, until one is chosen on the radio
DEST	APZK5 (APZ = experimental software)
PATH	1 = WIDE1-1, an index in PATHS: DIRECT (no digipeater), WIDE1-1, WIDE1-1,WIDE2-1; the default, until one is chosen on the radio
LAT, LON	4850.90N, 00216.25E: the default position, until one is edited on the radio (key 3)
SYMBOL	/[ (person): the default, until one of the 48 symbols is chosen on the radio
COMMENT	UV-K5/K1 F4HWN Firmware (43 characters at most)

Frame sent: F4HWN-7>APZK5,WIDE1-1:!4850.90N/00216.25E[UV-K5/K1 F4HWN Firmware (68 bytes, ~0.79 s on the air: 50 ms of tone settle, 40 flags = 267 ms, the frame, 3 flags). If the boot message is not a plain callsign (empty, more than 6 characters once spaces are dropped, or with a /), the app shows No boot callsign and does not transmit.

In the normal view, the TX frequency is aligned left below the separator and the selected APRS symbol is shown as a 20x20 bitmap at x=108. The 48-symbol Yaesu bitmap set is stored in the app assets; the editor keeps the full width.

Keys (UV-K5 and UV-K1)

Key	Action
PTT or MENU	Send one frame
UP / DOWN (held)	Scroll the frame above the separator 1 px per 40 ms loop (UV-K1: LEFT/RIGHT, as nav_dir). In the status bar (x = 72-76), ▲ while rows are hidden above and ▼ while rows are hidden below; while F is armed its icon (x = 70-78, centred on them) takes their place, and they are not drawn while transmitting (the TRANSMIT capsule ends at x = 72). It is shown in the small font, 18 characters a row, 4 rows at a time, as in APRS RX: source in bold, >DEST,WIDE… (a row breaks after a comma), latitude, longitude, then symbol and comment
1 / F then 1	Tone level (deviation) up / down: REG_70 gain 10-127, step 4, default 66 (the firmware's tone gain)
2 / F then 2	Twist tw up / down, -4..+8: 2200 Hz gain = level × (8 + tw) / 8 (-6..+6 dB)
F	Arm the next key's down direction (1, 2), as FoxHunt's F; icon in the status bar while armed
*	Scroll view / compact view (saved): compact shows the source in bold, then the path, the position 48 50.90N 002 16.25E, the symbol and the comment in the tiny 3x5 font, 32 characters a row, without scroll
3	Edit the position, SSID, path and symbol
EXIT	Quit (level, twist, position, SSID, path, symbol and view are saved)

Editor (v0.3)

LAT  48 50.90 N
LON 002 16.25 E
SSID 7
PATH WIDE1-1
SYMB /[

0-9, * change, F+* back
UP/DN move  MENU ok  EXIT

The field under the cursor is drawn in bold: a digit or the N/S, E/W letter of the position, or the whole SSID, path or symbol value. Type the 13 digits in a row, as a frequency: 485090 then 0021625 (degrees, minutes, hundredths of a minute: the APRS format, read as is from a GPS or aprs.fi in degrees-minutes). The cursor skips the separators and N/S, and goes on from the latitude to the longitude; UP/DOWN also stop on N/S and E/W, then take it on to SSID, PATH and SYMB. When SYMB is selected, both shortened help rows remain visible and the edited 20x20 symbol is previewed at x=108, the same position as on the normal screen.

Key	Action
0-9	Digit at the cursor, then the next one (on a position digit)
*	N/S (latitude line), E/W (longitude line), next SSID 0-15 (SSID), next path (PATH), or next symbol (SYMB)
F then *	Previous SSID, path or symbol (the F icon in the status bar while F is armed, as in FoxHunt; F again disarms it)
UP / DOWN	Move the cursor: 6 digits, N/S, 7 digits, E/W, SSID, PATH, SYMB
MENU	Check (degrees ≤ 90 / 180, minutes < 60) and keep: the frame is rebuilt; Invalid position otherwise
EXIT	Cancel

Paths: DIRECT (heard only by the stations and iGates in range), WIDE1-1 (one repeat by a nearby digipeater), WIDE1-1,2-1 (WIDE1-1,WIDE2-1: the usual mobile / portable path, two repeats).

Everything is saved on exit (cfg_save, 13 bytes: magic 0xA8, level, twist, 13 digits and the hemispheres in nibbles, 0x80 | path << 4 | SSID, then the view: 14 compact, anything else scroll, then the symbol index). An older config with byte 12 erased uses the default person symbol. A v0.2 config (10 bytes: byte 10 erased) keeps its position and takes the default SSID and path; an 11-byte config (byte 11 erased) opens in the scroll view; a v0.1 config (magic 0xA7) is ignored: defaults.

How it transmits

As the Beacon app keys MCW: tx_set_params (carrier + PA on the TX VFO), REG_51 = 0 (no CTCSS/DCS under the AFSK), tx_tone(1200) (tone path on, mic ADC off, 50 ms settle). Then each bit is timed from SysTick, 40000 cycles at 48 MHz (exact), and at each NRZI transition the tone frequency REG_71 (1200 Hz = 12389, 2200 Hz = 22714, the driver's scale_freq) and gain REG_70 are rewritten: two SPI writes, a few tens of µs out of 833. tx_mute + tx_end restore RX.

Unknowns for the first on-air test (all fine with the defaults on 2026-09-30)

1. Phase continuity when REG_71 is rewritten (an NCO keeps it, probably). The RX model decodes even with a phase reset at every transition (3/3 clean, 2/3 with noise in STD); a hardware TNC such as the FT3D may be stricter.
2. Twist. The tone probably enters after the pre-emphasis, so the signal is flat and a receiver with de-emphasis sees 2200 Hz ~5 dB low. If the FT3D misses frames that APRS RX decodes, raise tw (key 2): +4 is +3.5 dB.
3. Deviation at level 66: aim for ~3 kHz; 1 up, F then 1 down.

Test plan

1. Simplex test frequency (not 144.800 for the first frames), low power.
2. Receivers: APRS RX on a second radio (its per-slicer counters s a/b/c show the twist: frames only on the space-favouring slicer = 2200 Hz low) and the FT3D (APRS on band B, same frequency).
3. PTT, check both; adjust level and twist; then 144.800.

test/tx_model.py (needs ../aprsrx/test): frame from the real assets vs ax25.build, bit stream vs ax25.hdlc_bits, bad boot callsigns refused, an edited position (south/west) vs ax25.build, every path with SSID 0, 15 and 9 and a selected symbol vs ax25.build, the config round trip (and a v0.2 config falling back to the default SSID, path and symbol), the editor rows and bold column, the editor keys (13 digits typed in a row, cursor stops, * and F then * on each field; the UP/DOWN keys through nav_dir(), with SET_NAV on and off), the position limits, then AFSK (continuous phase or reset, tw 0/+4, TX path twist 0/+5 dB) decoded by the RX model through its RAW and STD audio paths, with and without noise.