Coherent arrays

An array processes samples from several antennas together. Direction finding and beamforming need stable phase relationships; passive radar needs aligned sample timing. The hardware’s shared clocks determine which operations are available.

Tier	Shared hardware	Supported measurements
`phase_coherent`	Reference clock and synthesizer	Bearings, beamforming, combining, and passive radar
`time_sync`	Reference clock	Passive radar; phase-dependent operations also need a calibration reference
`none`	No shared reference	Independent reception only

Retuning a time_sync array changes the relative tuner phases. Use an injected noise source or a known pilot carrier to calibrate them. Without that reference, the direction finder reports phase unknown and produces no bearings. Receivers without a shared clock drift apart and cannot form a coherent array.

Radios that are already an array

For a multi-lane receiver such as a Dragon Labs CR-8, an RSPduo in dual-tuner mode, or a multi-channel SoapySDR device, add one Device node. Connect its iq, iq2, iq3… outputs to the processing nodes. The driver reports the receiver’s coherence tier.

Radios you wired together yourself

Use an Array node for separate receivers connected to a shared clock.

Add a Device node for each radio and select its receiver.
Set the radios to the same sample rate. For shared tuning, their centre frequencies must match.
Add an Array node and connect each Device’s iq output to an array input. A spare input appears as you add members.
Set Wired as to match the physical connections: shared clock, or shared clock and LO.

Input order determines antenna element numbering. Move the wires if that order is wrong. Connect the Array’s output lanes to a direction finder, combiner, channel, or recorder.

Tuning and membership

Once connected, change frequency and sample rate through the Array node to keep its members consistent. Independently tuned arrays have a frequency control for each lane. Disconnect the array before scanning or hunting.

Each Device node retains its radio and existing channels, scopes, and recordings. Removing the Array leaves those running. Removing a member removes the dependent array. If a member disconnects, the array reports a fault and reconnects its streams when all members recover.

Use fixed gain on each element. AGC changes the amplitude relationship and invalidates calibration. Fixed gains may differ: calibration measures and corrects each lane’s amplitude and phase.

Calibration

Press Calibrate on the coherent node. Calibration measures a delay and complex weight for each lane, then applies those corrections before processing.

Cal source	When to use it
Signal	A strong signal received by every element
Noise	A noise burst injected through a splitter for bench calibration

A time_sync array needs injected noise or a specified pilot frequency to solve relative phase. On phase_coherent hardware, calibration corrects the additional differences from cabling.

The readout shows solved, still solving, or phase unknown. Phase unknown means the hardware tier and calibration source do not provide enough information for a bearing.

Combining antennas

A Combiner sums the lanes of one coherent source and sends the result to a beam lane. Connect an ordinary channel to that lane to decode the combined signal.

Mode	Effect
Combine	Aligns and sums antenna signals. Two antennas can improve SNR by about 3 dB under suitable conditions.
Cancel	Uses the other antennas as noise references and subtracts their contribution from the first.

For cancellation, use the first antenna for the wanted signal and the others to receive the local noise source. Both modes calculate weights from the covariance between lanes and require known relative phase. A time_sync array therefore needs a pilot or noise reference.