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Frequency Allocation

TARPN links operate on simplex frequencies in VHF and UHF amateur bands. Each link between two nodes uses a dedicated frequency.

Frequency Bands

2 Meter (VHF) - 144-148 MHz

Primary band for most TARPN links due to good propagation and available surplus equipment.

Frequency Range Use
144.91 - 145.09 Packet/data (weak signal adjacent)
145.50 - 145.80 Misc/experimental
146.40 - 146.58 Simplex
147.42 - 147.57 Simplex

70 Centimeter (UHF) - 420-450 MHz

Good for shorter links with less interference.

Frequency Range Use
420.00 - 426.00 Digital/packet modes
430.00 - 432.00 Digital/mixed
440.00 - 445.00 Shared simplex
445.00 - 447.00 Shared simplex

1.25 Meter (222 MHz)

Less common but excellent for packet with minimal interference.

Frequency Range Use
222.10 - 223.38 Weak signal/digital
223.52 - 223.64 Simplex digital

NC Packet Coordination

The NC Packet network (ncpacket.net) maintains a frequency coordination database. Check with your regional coordinator before selecting frequencies.

Typical NC Packet Allocations

Band Common Frequencies
2m 145.01, 145.03, 145.05, 145.07, 145.09
70cm 441.025, 441.050, 441.075, 445.925, 445.950

Selecting a Frequency

Guidelines

  1. Check coordination database - See if frequency is already in use nearby
  2. Avoid repeater inputs/outputs - Don't interfere with voice repeaters
  3. Use designated packet segments - Prefer frequencies allocated for data
  4. Coordinate with neighbor - Both nodes must use same frequency
  5. Consider propagation - Higher frequencies = shorter range

Frequency Separation

For multiple links at the same site:

Band Minimum Separation
2m 20 kHz between channels
70cm 25 kHz between channels

Example 4-Port Node

Port 1 (Link to Node A): 145.01 MHz
Port 2 (Link to Node B): 145.03 MHz
Port 3 (Link to Node C): 441.025 MHz
Port 4 (Link to Node D): 441.050 MHz

Baud Rate vs Bandwidth

Baud Rate Bandwidth Notes
1200 12.5 kHz Standard AFSK, most compatible
9600 25 kHz G3RUH FSK, recommended
19200 25 kHz High speed G3RUH

9600 Baud Recommended

Use 9600 baud for best throughput while maintaining reliable links. 1200 baud only if distance requires it.

Programming Your Radio

Most radios need to be programmed with:

  • Receive frequency - Same as transmit for simplex
  • Transmit frequency - Same as receive for simplex
  • Squelch - Set to open or carrier squelch
  • Power - Usually low/medium (5-25W)
  • CTCSS/DCS - Not used (disable)
  • Narrow/Wide - Wide for 9600 baud

Avoiding Interference

Don't Use

  • Repeater input/output pairs
  • Calling frequencies (146.52, 446.00, etc.)
  • Satellite frequencies
  • Emergency/ARES frequencies
  • Active simplex channels in your area

Monitoring

Before going live:

# Listen for activity on your planned frequency
tarpn listen 1

Frequency Plan Template

Port Direction Frequency Band Baud Neighbor
1 East 145.01 2m 9600 N0CALL-2
2 West 145.03 2m 9600 K0ABC-2
3 North 441.025 70cm 9600 W0XYZ-2
4 South 441.050 70cm 9600 K0QRS-2

Coordination Resources