Low Bandwidth Connections

Low Bandwidth Connections

Reduce network traffic when connecting over metered, congested, or bandwidth-limited links such as LTE, satellite, or VPN tunnels (ZeroTier, WireGuard, Tailscale).

The Problem

A normal AetherSDR connection generates significant UDP traffic:

Stream	Format	Approx. Bandwidth
RX Audio	float32 stereo, 24 kHz	~1.5 Mbit/s
FFT Spectrum	uint16 bins, ~15 FPS	~0.5-1.0 Mbit/s
Waterfall Tiles	uint16 bins	~0.3-0.5 Mbit/s
Meters	uint16 pairs	negligible

On a home LAN this is fine, but over a cellular or VPN link the combined ~2-3 Mbit/s can cause dropouts, latency, and data charges.

AetherSDR provides two independent controls to reduce bandwidth. Use one or both depending on your link quality.

Option 1: Audio Compression (Opus)

Location: Settings > Radio Setup > Audio > Audio Compression

Setting	Behavior
Auto (default)	Opus on SmartLink, uncompressed on LAN
Uncompressed	Force uncompressed on all connections
Opus	Force Opus compression on all connections

Selecting Opus reduces the audio stream from ~1.5 Mbit/s to ~64-128 kbit/s -- a 10-20x reduction. Audio quality is excellent for SSB/CW monitoring.

This setting can be changed while connected -- it takes effect immediately by recreating the audio stream with the new compression parameter.

When to use: Always enable Opus when on a metered or limited link. There is minimal audio quality impact for voice modes.

Option 2: Low Bandwidth Connect

Location: Connection Panel > "Low Bandwidth" checkbox (above the Connect button)

When checked, AetherSDR sends client low_bw_connect to the radio before establishing the session. The radio acknowledges this and reduces the volume of FFT, waterfall, and meter data it sends.

This is a radio-side optimization -- the radio decides how to reduce data rates. Observed effects include reduced FFT bin counts and lower waterfall tile rates.

Important: This setting takes effect on connect. If you change it while connected, you must disconnect and reconnect for it to apply.

The checkbox state persists across restarts.

How this differs from SmartSDR

SmartSDR sends client low_bw_connect automatically and only for SmartLink (WAN) connections. There is no user-facing toggle. AetherSDR exposes it as a manual option because overlay networks like ZeroTier, WireGuard, and Tailscale place the radio and client on the same Layer 2 subnet -- the radio sees it as a "local" connection even though the actual link may be cellular or satellite.

Recommended Settings by Connection Type

Connection	Audio Compression	Low Bandwidth
Home LAN (Ethernet/WiFi)	Auto	Unchecked
SmartLink (WAN)	Auto (Opus applied automatically)	N/A (automatic)
VPN over broadband	Opus	Optional
VPN over LTE/cellular	Opus	Checked
VPN over satellite	Opus	Checked
Manual IP over LAN	Auto	Unchecked
Manual IP over WAN	Opus	Checked

Option 3: Network MTU

Location: Settings > Radio Setup > Network > Advanced > Network MTU

The radio's Network MTU setting controls the maximum size of VITA-49 UDP packets. The default in AetherSDR is 1450 bytes (reduced from the radio default of 1500), which is compatible with most VPN and SD-WAN tunnels.

Why this matters

VITA-49 FFT and waterfall packets are ~1436 bytes at MTU 1500. Most VPN tunnels add encapsulation overhead that reduces the effective MTU:

Tunnel Type	Typical Effective MTU
WireGuard	1420 bytes
OpenVPN (UDP)	1400 bytes
Cisco SD-WAN	1400-1450 bytes
ZeroTier	~1400 bytes
Tailscale	1280-1420 bytes

When a 1436-byte packet exceeds the tunnel MTU, it is either fragmented (adding latency) or silently dropped (causing missing spectrum/waterfall). Audio packets are smaller (~1052 bytes) and usually pass through — this is why you might hear audio but see no spectrum over a VPN.

Recommended MTU Settings

Connection	MTU Setting
Home LAN	1500 (or leave at 1450)
VPN / SD-WAN	1450 (default)
Satellite / high-overhead tunnels	1300-1400

AetherSDR sends client set enforce_network_mtu=1 network_mtu=<value> to the radio on each connect. This is a per-session client-side setting — it does not permanently change the radio's configuration or affect other clients.

Additional Tips for Low Bandwidth

Beyond the two settings above, you can further reduce traffic client-side:

• Reduce waterfall FPS -- Display applet > FPS slider (try 5-10 instead of 15)
• Reduce panadapter bandwidth -- Zoom in to show less spectrum (fewer FFT bins transmitted)
• Increase waterfall line duration -- Display applet > slower waterfall scroll
• Disable waterfall entirely -- If you only need the FFT spectrum trace, collapsing the waterfall to minimum height reduces tile traffic