Your First Multi-VNA Measurement

In this tutorial, you’ll use two NanoVNA devices together to measure and compare two antennas side-by-side. By the end, you’ll understand device discovery, targeting, and software-synchronized sweeps.

What You’ll Learn

• Discover all connected VNAs
• Target specific devices
• Run synchronized sweeps
• Compare antenna performance

Prerequisites

• Two NanoVNA-H devices connected via USB
• Two antennas to compare (or one antenna with two feedlines)
• mcnanovna MCP server installed

Note

This tutorial uses Tier 1 (software) synchronization, which works with any NanoVNA firmware. No modifications needed.

Discover Your Devices

1. Connect both VNAs

   Plug both NanoVNA devices into USB ports. Each needs its own port.

2. List devices

   Say: “List all connected NanoVNA devices”

   The assistant calls list_devices() and returns something like:

   {
     "devices": [
       {"device_id": "0001234567", "port": "/dev/ttyACM0", "board": "NanoVNA-H4"},
       {"device_id": "0009876543", "port": "/dev/ttyACM1", "board": "NanoVNA-H"}
     ],
     "default": "0001234567",
     "count": 2
   }

3. Note the device IDs

   Each VNA has a unique device_id (its serial number or port path). Write these down:

   Device ID	Connected Antenna
   0001234567	Antenna A
   0009876543	Antenna B

Set Up Device Targeting

With multiple VNAs, you have two options for targeting:

Option 1: Set a Default

If you’ll mostly use one VNA:

Say: “Set device 0001234567 as the default”

Now all single-device tools (scan, analyze, etc.) will target that VNA unless you specify otherwise.

Option 2: Specify Each Time

Add device_id to any tool call:

Say: “Scan from 144 to 148 MHz on device 0009876543”

Tip

When only one VNA is connected, it becomes the default automatically. Multi-VNA targeting only matters when you have multiple devices.

Calibrate Each VNA

1. Calibrate the first VNA

   Say: “Calibrate device 0001234567 for 144 to 148 MHz”

   Follow the SOLT calibration steps: load, open, short, through.

   Say: “Save calibration to slot 1”

2. Calibrate the second VNA

   Say: “Calibrate device 0009876543 for 144 to 148 MHz”

   Repeat the same procedure with the second VNA’s calibration standards.

   Say: “Save calibration to slot 1”

Caution

Use the same frequency range for both VNAs. Calibrate each with its own cables and adapters—the ones you’ll use for measurement.

Run a Synchronized Sweep

Now connect your antennas—one to each VNA’s Port 1.

1. Run sync_sweep

   Say: “Run a synchronized sweep on both VNAs from 144 to 148 MHz”

   The assistant calls:

   sync_sweep(
     device_ids=["0001234567", "0009876543"],
     start_hz=144000000,
     stop_hz=148000000,
     points=101
   )

2. Review the results

   You’ll get S11 data from both devices, swept at the same time (within ±2-5ms).

Compare Antenna Performance

1. Run multi_antenna_compare

   Say: “Compare my two antennas on the 2m band”

   The assistant calls multi_antenna_compare() and returns a comparison table:

   Metric	Antenna A (0001234567)	Antenna B (0009876543)
   Min SWR	1.15	1.32
   Resonance	145.2 MHz	144.8 MHz
   Bandwidth (< 2:1)	4.1 MHz	3.2 MHz
   Z at resonance	48 + j2 Ω	42 - j8 Ω

2. Interpret the results

   • Min SWR: Lower is better. Antenna A has better match.
   • Resonance: Where SWR is lowest. Neither is at band center.
   • Bandwidth: Wider is more versatile. Antenna A has broader coverage.
   • Z at resonance: Closer to 50 Ω is better. Both are reasonable.

Understanding the Results

What Sync Sweep Gives You

Software synchronization (Tier 1) starts both sweeps within 2-5ms of each other. This is adequate for:

• Antenna comparison
• Signal level measurements
• SWR/impedance analysis

It’s not precise enough for:

• Phase measurements between devices
• Antenna array characterization
• MIMO testing

For those, you’ll need hardware trigger (Tier 2) or phase coherent (Tier 3).

Device Capabilities

Check what sync methods each device supports:

Say: “Check capabilities of device 0001234567”

{
  "device_id": "0001234567",
  "capabilities": {
    "hardware_trigger": false,
    "external_clock": false
  },
  "tier": 1
}

Stock firmware shows Tier 1 only. Custom firmware enables Tier 2/3.

Troubleshooting

Only one device shows up

1. Check USB connections
2. Try different USB ports (avoid hubs)
3. Run refresh_devices() to re-scan
4. Check permissions: sudo usermod -aG dialout $USER (Linux)

Device IDs keep changing

Port paths like /dev/ttyACM0 can change on reconnect. If available, use the serial number (e.g., 0001234567) instead—it’s stable across reconnects.

Timing concerns

Tier 1’s ±2-5ms is sufficient for most comparisons. If you see inconsistent results, ensure:

• Both VNAs have stable connections
• Neither is being accessed by another program
• USB host isn’t under heavy load

Next Steps

• Multi-VNA Coordination — Understand all three synchronization tiers
• Hardware Trigger Wiring — Achieve ±10-50µs precision
• Tool Reference — All coordination tools