Radio Tuner for WaveCap-SDR

This skill provides tools to adjust SDR radio settings including frequency, gain, squelch, bandwidth, filters, and AGC parameters.

When to Use This Skill

Use this skill when:

• Changing the tuned frequency
• Adjusting gain for optimal signal level
• Setting squelch threshold to eliminate noise
• Configuring channel bandwidth
• Enabling/disabling filters (deemphasis, notch, etc.)
• Adjusting AGC parameters
• Changing demodulation mode

Available Settings

Capture Settings (SDR-level)

Setting	Description	Range
centerHz	Center frequency	1 MHz - 6 GHz
sampleRate	Sample rate	Device-dependent
gain	RF gain	-100 to 100 dB
bandwidth	IF bandwidth	0 to sample_rate
ppm	Frequency correction	-1000 to 1000
antenna	Antenna port	Device-dependent

Channel Settings (Demodulator-level)

Setting	Description	Range
mode	Demodulation mode	wbfm, nbfm, am, ssb, raw, p25, dmr
offsetHz	Offset from capture center	-50 MHz to +50 MHz
squelchDb	Squelch threshold	-120 to 0 dB
audioRate	Output audio rate	8000 to 192000 Hz

Filter Settings

Setting	Description	Default
enableDeemphasis	FM de-emphasis filter	true (WBFM)
deemphasisTauUs	De-emphasis time constant	75 µs (US), 50 µs (EU)
enableAgc	Automatic gain control	true
agcTargetDb	AGC target level	-20 dB
agcAttackMs	AGC attack time	10 ms
agcReleaseMs	AGC release time	500 ms
notchFrequencies	Notch filter frequencies	[]

Usage Instructions

Step 1: List Current Settings

Get current capture and channel settings:

# Get capture settings
curl http://127.0.0.1:8087/api/v1/captures/c1 | jq

# Get channel settings
curl http://127.0.0.1:8087/api/v1/channels/ch1 | jq

Or use the helper script:

PYTHONPATH=backend backend/.venv/bin/python .claude/skills/radio-tuner/adjust_settings.py \
  --capture c1 --show

Step 2: Adjust Capture Settings

Change frequency:

curl -X PATCH http://127.0.0.1:8087/api/v1/captures/c1 \
  -H "Content-Type: application/json" \
  -d '{"centerHz": 90300000}'

Change gain:

curl -X PATCH http://127.0.0.1:8087/api/v1/captures/c1 \
  -H "Content-Type: application/json" \
  -d '{"gain": 35.0}'

Or use the helper script:

PYTHONPATH=backend backend/.venv/bin/python .claude/skills/radio-tuner/adjust_settings.py \
  --capture c1 \
  --frequency 90.3 \
  --gain 35

Step 3: Adjust Channel Settings

Change squelch:

curl -X PATCH http://127.0.0.1:8087/api/v1/channels/ch1 \
  -H "Content-Type: application/json" \
  -d '{"squelchDb": -50}'

Change mode:

curl -X PATCH http://127.0.0.1:8087/api/v1/channels/ch1 \
  -H "Content-Type: application/json" \
  -d '{"mode": "nbfm"}'

Enable/disable AGC:

curl -X PATCH http://127.0.0.1:8087/api/v1/channels/ch1 \
  -H "Content-Type: application/json" \
  -d '{"enableAgc": true, "agcTargetDb": -20, "agcAttackMs": 10, "agcReleaseMs": 500}'

Step 4: Add Notch Filters

Remove interference at specific frequencies:

curl -X PATCH http://127.0.0.1:8087/api/v1/channels/ch1 \
  -H "Content-Type: application/json" \
  -d '{"notchFrequencies": [1000, 2000, 3000]}'

Helper Script Reference

# Show current settings
python adjust_settings.py --capture c1 --show

# Change frequency (MHz)
python adjust_settings.py --capture c1 --frequency 90.3

# Change gain (dB)
python adjust_settings.py --capture c1 --gain 35

# Change bandwidth (Hz)
python adjust_settings.py --capture c1 --bandwidth 200000

# Change squelch (dB)
python adjust_settings.py --channel ch1 --squelch -50

# Change mode
python adjust_settings.py --channel ch1 --mode nbfm

# Multiple settings at once
python adjust_settings.py --capture c1 --frequency 90.3 --gain 35 --bandwidth 200000

Demodulation Modes

Mode	Description	Typical Use
wbfm	Wide-band FM (200 kHz)	FM broadcast radio
nbfm	Narrow-band FM (12.5-25 kHz)	Two-way radio, amateur
am	Amplitude modulation	Aviation, AM broadcast
ssb	Single sideband	Amateur radio, marine
raw	No demodulation	Digital modes, ISM
p25	Project 25 digital	Public safety
dmr	Digital Mobile Radio	Commercial two-way

Optimal Settings by Application

FM Broadcast Radio

{
  "sampleRate": 1024000,
  "bandwidth": 200000,
  "mode": "wbfm",
  "enableDeemphasis": true,
  "deemphasisTauUs": 75,
  "squelchDb": -60
}

VHF Marine / Aviation

{
  "sampleRate": 2000000,
  "bandwidth": 25000,
  "mode": "nbfm",
  "squelchDb": -50,
  "enableAgc": true
}

Amateur Radio SSB

{
  "mode": "ssb",
  "ssbMode": "usb",
  "enableSsbBandpass": true,
  "ssbBandpassLowHz": 300,
  "ssbBandpassHighHz": 3000,
  "squelchDb": -60
}

Configuration Warnings

WaveCap-SDR automatically detects problematic configurations and displays warnings in the UI. Check configWarnings in capture API responses to see current warnings.

Check Current Warnings

curl -s http://127.0.0.1:8087/api/v1/captures/c1 | jq '.configWarnings'

Warning Types

Code	Severity	Description	Resolution
rtl_unstable_sample_rate	warning	RTL-SDR sample rate <900kHz causes IQ overflows	Use 1.024 MHz, 2.048 MHz, or 2.4 MHz
bandwidth_exceeds_sample_rate	warning	Bandwidth > sample rate violates Nyquist	Reduce bandwidth or increase sample rate
bandwidth_near_sample_rate	info	Bandwidth >90% of sample rate causes edge aliasing	Use bandwidth ≤80% of sample rate
sdrplay_high_sample_rate	info	SDRplay >8 MHz may cause USB issues	Lower sample rate if experiencing dropouts
zero_gain	info	Gain set to 0 dB	Increase gain if signals are weak

Best Practices to Avoid Warnings

1. RTL-SDR Sample Rates: Use 1.024 MHz, 2.048 MHz, or 2.4 MHz

   curl -X PATCH http://127.0.0.1:8087/api/v1/captures/c1 \
     -H "Content-Type: application/json" \
     -d '{"sampleRate": 1024000}'
   

2. Bandwidth/Sample Rate Ratio: Keep bandwidth ≤80% of sample rate

   # For 2 MHz sample rate, use ≤1.6 MHz bandwidth
   curl -X PATCH http://127.0.0.1:8087/api/v1/captures/c1 \
     -H "Content-Type: application/json" \
     -d '{"sampleRate": 2000000, "bandwidth": 1600000}'
   

3. SDRplay Sample Rates: Stay ≤8 MHz for reliable USB throughput

   curl -X PATCH http://127.0.0.1:8087/api/v1/captures/c1 \
     -H "Content-Type: application/json" \
     -d '{"sampleRate": 6000000}'
   

Common Issues

Issue: Audio Too Quiet

Solutions:

• Increase gain on capture
• Increase agcTargetDb (e.g., -15 instead of -20)
• Check antenna connection

Issue: Audio Distorted

Solutions:

• Reduce gain on capture
• Lower agcTargetDb (e.g., -25 instead of -20)
• Enable de-emphasis for FM

Issue: Too Much Background Noise

Solutions:

• Increase squelchDb (less negative, e.g., -40 instead of -60)
• Add notch filters for specific interference
• Enable noise blanker

Issue: Signal Cutting In/Out

Solutions:

• Lower squelchDb (more negative)
• Adjust AGC attack/release times
• Check if frequency offset is correct

Issue: IQ Overflows (RTL-SDR)

Solutions:

• Use stable sample rate (1.024 MHz, 2.048 MHz, or 2.4 MHz)
• Avoid sample rates below 900 kHz
• Check USB connection quality

Issue: Aliasing at Spectrum Edges

Solutions:

• Reduce bandwidth to ≤80% of sample rate
• Increase sample rate if wider bandwidth needed
• Use appropriate IF filter settings

Files in This Skill

• SKILL.md: This file - instructions for using the skill
• adjust_settings.py: Helper script for adjusting radio settings