Ubnt Calculator

Professional Wireless Link Budget & Fresnel Zone Planner

Signal Strength Reference for UBNT Equipment

Signal (dBm)	Quality	Recommended Action
-45 to -55	Perfect	Ideal for maximum modulation rates (MCS).
-55 to -65	Great	Very stable, good for high throughput.
-65 to -75	Good	Functional, but throughput might drop in rain.
-75 to -85	Poor	Unstable, high packet loss, low MCS.
< -90	No Link	Receiver cannot decode the signal.

What is a UBNT Calculator?

A ubnt calculator is a specialized radio frequency (RF) planning tool used primarily by network engineers and wireless ISPs (WISPs) to simulate the performance of Ubiquiti Networks (UBNT) hardware. Whether you are deploying AirMax AC, LTU, or AirFiber equipment, understanding the math behind the link is critical for a successful installation.

By using a ubnt calculator, you can predict the signal strength (RSSI) at the receiving end before ever climbing a tower. This helps in selecting the right antenna gain, choosing the appropriate transmit power, and ensuring that there is enough “fade margin” to withstand atmospheric changes like heavy rain or fog. The ubnt calculator also calculates the Fresnel zone, which is the elliptical area around the direct line-of-sight path that must remain clear of obstacles to prevent signal diffraction.

UBNT Calculator Formula and Mathematical Explanation

The core logic of any ubnt calculator relies on the Link Budget Equation and the Free Space Path Loss (FSPL) formula. To get an accurate reading, we calculate how much power is lost as the radio waves spread out over distance.

1. Link Budget Equation

The received signal strength is calculated as follows:

RSSI = Ptx + Gtx - Ltx - FSPL + Grx - Lrx

2. Free Space Path Loss (FSPL)

This is the loss in signal strength of an electromagnetic wave that would result from a line-of-sight path through free space. In a ubnt calculator, it is expressed as:

FSPL (dB) = 20 log10(d) + 20 log10(f) + 32.44

Where d is distance in kilometers and f is frequency in Megahertz (MHz).

Variables Table

Variable	Meaning	Unit	Typical Range
Ptx	Transmit Power	dBm	0 to 30 dBm
Gtx / Grx	Antenna Gain	dBi	5 to 34 dBi
f	Frequency	MHz	900 to 60,000 MHz
d	Distance	km	0.1 to 100 km
FSPL	Path Loss	dB	80 to 160 dB

Practical Examples (Real-World Use Cases)

Example 1: Short-Range 5GHz Bridge

Suppose you are setting up a 2km bridge using two LiteBeam 5AC Gen2 radios. The litebeam has an antenna gain of 23dBi and you set the transmit power to 20dBm at 5800MHz.

• Inputs: 5800 MHz, 2km, 20dBm TX, 23dBi TX Gain, 23dBi RX Gain, 1dB Cable loss.
• Calculation: FSPL = 113.7 dB. RSSI = 20 + 23 – 1 – 113.7 + 23 = -48.7 dBm.
• Interpretation: This is a “perfect” link signal level, allowing for the highest possible throughput (MCS8/9).

Example 2: Long-Distance AirFiber Link

Using an AirFiber 5XHD with 34dBi dishes over 25km at 5200MHz.

• Inputs: 5200 MHz, 25km, 24dBm TX, 34dBi TX Gain, 34dBi RX Gain, 2dB Cable loss.
• Calculation: FSPL = 134.7 dB. RSSI = 24 + 34 – 2 – 134.7 + 34 = -44.7 dBm.
• Interpretation: Despite the long distance, the high-gain dishes result in an incredible signal level.

How to Use This UBNT Calculator

1. Select Frequency: Enter the center frequency in MHz. Use 5800 for standard 5GHz links or 2400 for 2.4GHz.
2. Enter Distance: Measure the distance using GPS or Google Earth and input it in kilometers.
3. Configure Hardware: Look at your UBNT device datasheet. Enter the Transmit Power (dBm) and the Antenna Gain (dBi).
4. Account for Losses: Add up losses from any RF cables or connectors. For integrated radios (like NanoStation), this is often 0 or 1.
5. Analyze Results: The ubnt calculator will instantly show your expected signal. Compare this to your receiver sensitivity to find your fade margin.

Key Factors That Affect UBNT Calculator Results

• Thermal Noise Floor: Even with a great signal, if the noise floor is -80dBm due to local interference, your Signal-to-Noise Ratio (SNR) will be poor.
• Fresnel Zone Obstruction: If a building or tree encroaches on the Fresnel zone, your actual signal will be much lower than what the ubnt calculator predicts.
• Weather Conditions: Rain fade is significant at higher frequencies (above 10GHz). A link that works perfectly in the sun might drop in a storm.
• Antenna Alignment: The ubnt calculator assumes perfect alignment. If your dishes are off by just a few degrees, you could lose 10-20dB of gain.
• Earth Curvature: On very long links (over 15km), the curvature of the earth can actually block the line of sight.
• Cable Quality: Using poor-quality LMR-200 or long pigtails can introduce losses that the ubnt calculator reminds you to include.

Frequently Asked Questions (FAQ)

Why is my real signal lower than the ubnt calculator result?

Usually, this is due to misalignment, cable loss, or Fresnel zone encroachment. Always check for a clear Line of Sight (LoS).

What is a good fade margin for UBNT gear?

A fade margin of 20dB or more is recommended for high reliability, especially in areas with variable weather.

Can I use this for non-UBNT equipment?

Yes, the math behind the ubnt calculator (FSPL and Link Budget) is universal for all RF equipment like Mikrotik or Mimosa.

What frequency should I use for 5GHz?

Most outdoor UBNT links operate between 5150 MHz and 5875 MHz depending on local regulations.

How does rain affect my UBNT link?

At 5GHz, rain has a negligible effect. At 24GHz or 60GHz, heavy rain can completely drop a link that shows high signal in the ubnt calculator.

Is the Fresnel zone the same as Line of Sight?

No. You can have visual Line of Sight but still have an obstructed Fresnel zone, which causes signal reflection and phase cancellation.

Does TX power improve throughput?

Up to a point. However, running UBNT radios at maximum TX power can sometimes distort the signal (EVM), actually reducing throughput.

What is dBi vs dBm?

dBm is an absolute power level (1 milliwatt reference), while dBi is the gain of an antenna relative to an isotropic radiator.