What frequency should I use for a long-distance PtP link?

Lower frequencies (900 MHz, 2.4 GHz) have less free space path loss and better obstacle penetration, making them suitable for long distances and non-line-of-sight. Higher frequencies (5 GHz, 11 GHz, 24 GHz) allow more bandwidth and spectrum availability but require strict line of sight and have higher path loss.

Point-to-Point Wireless Link Calculator

Q: What is free space path loss (FSPL)?

Free space path loss is the reduction in signal strength as a radio wave spreads out over distance in open air with no obstacles. It is calculated as FSPL (dB) = 32.44 + 20×log10(distance in km) + 20×log10(frequency in MHz). The signal level at the receiver is then TX power + antenna gains − cable losses − FSPL.

Q: What is a good link margin for a PtP link?

A link margin of 20 dB or more is considered strong and resilient to rain fade and obstructions. 10–20 dB is acceptable for most fixed links. Below 10 dB is marginal and below 0 dB means the link will not work.

Calculate free space path loss (FSPL), estimated received signal strength, and link margin for any point-to-point wireless link. Enter the link parameters to verify viability before installation.

Link Budget Calculator

Distance

Distance Unit

Frequency (MHz)

TX Power (dBm)

TX Antenna Gain (dBi)

RX Antenna Gain (dBi)

TX Cable Loss (dB)

RX Cable Loss (dB)

RX Sensitivity (dBm, negative number)

Link Budget Results

—

Free Space Path Loss

—

Received Signal

—

Link Margin

—

Link Status

Formulas

Free Space Path Loss (Friis formula):

FSPL (dB) = 32.44 + 20 × log₁₀(distance in km) + 20 × log₁₀(frequency in MHz)

Received Signal Level (RSL):

RSL (dBm) = TX Power + TX Antenna Gain − TX Cable Loss − FSPL − RX Cable Loss + RX Antenna Gain

Link Margin:

Link Margin (dB) = RSL − RX Sensitivity

Link Margin Guidelines

≥ 20 dB: Strong — resilient to rain fade, vegetation movement, and Fresnel zone obstructions.
10–20 dB: Acceptable — suitable for fixed links in most climates with clear line of sight.
0–10 dB: Marginal — will experience occasional dropouts in rain, fog, or high winds.
< 0 dB: Insufficient — the link will not operate reliably or may not connect at all.

Practical Example

A 5 km 5.8 GHz link with 23 dBm TX power, 23 dBi antennas on both ends, 1 dB cable loss each side, and −80 dBm receiver sensitivity:

FSPL = 32.44 + 20×log10(5) + 20×log10(5800) = 32.44 + 14.0 + 75.3 = 121.7 dB RSL = 23 + 23 − 1 − 121.7 − 1 + 23 = −54.7 dBm Margin = −54.7 − (−80) = 25.3 dB → Strong link

Frequently Asked Questions

What is free space path loss (FSPL)?

FSPL is the attenuation of a signal as it spreads in open space with no obstructions. It increases with both distance and frequency — doubling the distance adds 6 dB of loss, and doubling the frequency also adds 6 dB. FSPL does not account for vegetation, rain, or buildings.

What is a good link margin for a PtP link?

A minimum of 10 dB is required for reliable operation. 15–25 dB is recommended for outdoor links that experience rain and seasonal foliage changes. In microwave designs, 25–30 dB fade margin is standard for highly available links (99.999% uptime).

What frequency should I use for a long-distance link?

Lower frequencies (900 MHz, 2.4 GHz) have less path loss and better non-LOS performance, ideal for links longer than 10 km. Higher frequencies (5.8 GHz, 11 GHz, 24 GHz, 60 GHz) offer more bandwidth and less interference but require strict line of sight and have more path loss. Always check Fresnel zone clearance for links over 1 km.