First transmission through a real radio path in the project. A 4756-byte
JPEG went from transmitter to receiver over two antennas 60 cm apart at
225 MHz and reassembled byte-identical, reproduced across three runs.
The cable loopback still needs an SMA male-to-male adapter that has not
arrived, so this air run is a track verification, not the controlled
measurement: room levels are not held the way a cable holds them. Its
purpose was to exercise the device wrapper the models cannot cover.
Four defects the software model passed but the hardware exposed, each
reproduced and fixed:
- a 566 528-sample frame did not fit the 262 144 receive buffer, and the
sample stream is not continuous across separate reads, so a frame on the
seam was destroyed. Reception now uses one buffer sized to the frame
- carrier correction was always applied, but with a shared reference the
true offset is near zero and the 80-symbol marker estimate is noise;
correcting by it rotated phase along the whole frame, 65% bit errors
measured. Ported should_apply_cfo_correction from Lab023
- receiver gain of 20 dB left the signal at 0.0003 of full scale. Levels
set by measurement: RX 50 dB, TX -10 dB give zero bit errors with margin
- the error-vector metric returned zero on a failed receive, reporting a
perfect signal where there was none, the same class of defect as the
written-in figures of Lab041. Replaced with an explicit not-computed value
The air TX gain ceiling is now derived from the link budget by antenna
distance rather than a constant. Three loopback modes: software, cable,
air. PROJECT_LOG entry 019 records the run and the defects.
Software and cable results stay reproducible; 125 tests pass, gate passes.
The gate now runs pytest as well, so one command answers whether the code
base is broken: syntax, protocol imports, the 125 core tests, then the lab
functional suites. It fails when a test fails, verified by feeding it a
deliberately broken test.
Two leftovers from moving the labs into experiments/ are fixed: the lab
command still pointed at tests/, and the hook only watched protocol and
tests, so edits under experiments/ and tools/ triggered nothing.
Profiling the 3.6 s gate: 0.24 s syntax, 0.12 s imports, 0.61 s pytest,
2.7 s lab functional suites, of which Lab042's software loopback is 1.14 s
because it pushes a whole image through the chain. The pytest addition is
the small part. prepare_jpeg is now cached, since six checks call it and
each call re-encoded the image at several qualities.
README described the gate without the tests it now runs.
First lab in the project that switches the transmitter on. Lab001-Lab041
built the whole chain but never called into an SDR to send anything.
Two modes. Software closes the channel in memory and needs no hardware;
it is the reference the hardware run is measured against, so the
difference between them is what the radio path contributes. Hardware
drives one PlutoSDR with its transmit output looped back through a 30 dB
attenuator into its own receive input.
Everything outside the device wrapper is reused from protocol/ unchanged:
image_fragments, packet and the primitives in bpsk_radio.
Software run: a 4756-byte JPEG in 10 fragments, 5 272 064 samples, 2.059 s
of signal, 10 of 10 fragments recovered, image byte-identical, repeatable
across runs. Channel rate 18.475 kbit/s, below the 20 kbit/s symbol rate
because of framing and guards.
Three defects found by the verifier and fixed:
- the guard interval was only appended after the frame. Lab018 puts one on
both sides, and the leading one is the one that matters: the first
samples of a transmission are unreliable, so the preamble would have
landed exactly on the transient. Invisible in software mode, which has
no converter and no transient
- transmission was started before reception, contradicting section 8 of
the specification and its own trap 3. The receiver now runs first and
the first buffer is discarded, as in Lab024a
- packet and frame size were reported from the first frame only, while
the tenth is 172 bytes against 536. Sizes are now per frame in the CSV
and the report gives the honest range
Also fixed before verification: the JPEG did not fit its own 5000-byte
limit, so quality is now lowered until it does and reported as a result;
and the wall-clock rate was presented as a channel rate, which in software
mode measures computation, not a channel.
Artifacts are left out deliberately. data/processed/lab042 currently holds
the software reference; the committed results should be the real
experiment, which needs the cable.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
