5 GHz vs 60 GHz Wireless Bridge

Joining two buildings without trenching usually comes down to two unlicensed bands. The 5GHz vs 60GHz wireless bridge choice is a trade between reach and robustness on one side and capacity and clean spectrum on the other, and the deciding factors are path length, local rain, how crowded 5 GHz is at both ends, and how rigid your mounts are.

5GHz vs 60GHz wireless bridge at a glance

The table compares the two bands on the points that decide most building to building links. Check each radio’s data sheet for throughput and range.

Range: why 60 GHz bridges stay short

At 60 GHz the atmosphere itself absorbs the signal. In its 2013 order on the band, the FCC says signals around 60 GHz are significantly affected by oxygen and water vapor, and that absorption and scattering limit the useful range of transmissions to a couple of kilometers.

The oxygen loss per kilometer, free space path loss and the full budget are worked in our guide on how to plan a point to point wireless link, so they are not repeated here. At 5 GHz there is no comparable oxygen peak, which is why the same budget method gives a much longer path.

In practice, a 60 GHz radio is a short range wireless bridge: rooftop to rooftop across a campus, a lot or a street. Run the full budget before you promise a longer hop.

60 GHz rain fade, worked from the ITU model

Rain is the second limit. ITU-R Recommendation P.838-3 gives specific rain attenuation in dB/km as k times the rain rate raised to the power alpha, with coefficients tabulated by frequency. For horizontal polarization at 60 GHz the table gives k = 0.8606 and alpha = 0.7656.

A worked example, with stated assumptions: a rain rate of 25 mm/h along the whole path, horizontal polarization, and the 6 GHz row (k = 0.0007056, alpha = 1.5900) as a conservative stand-in for the 5.8 GHz band.

1. 60 GHz: 0.8606 x 25^0.7656 = about 10.1 dB/km.
2. 6 GHz: 0.0007056 x 25^1.59 = about 0.12 dB/km.
3. Over a 400 m hop: about 4 dB at 60 GHz against 0.05 dB at 6 GHz.
4. At 50 mm/h the 60 GHz figure rises to about 17 dB/km.

Uniform rain along the path is a simplification that suits short hops. Size the 60 GHz fade margin for the rain rates in your region, and keep the hop short enough that the margin survives a downpour.

Interference and channel congestion at 5 GHz

The 5 GHz band’s weakness is company. Wi-Fi access points, other bridges and point to multipoint networks all use it, so a clean channel at install can be crowded a year later. Scan at both ends before choosing a channel and again after the link is up.

Part of the band adds radar rules. Under 47 CFR 15.407(h)(2), devices operating with any part of their emission bandwidth in 5.25 to 5.35 or 5.47 to 5.725 GHz must use dynamic frequency selection (DFS):

• Check a channel for radar for 60 seconds before using it.
• Stop transmitting within 10 seconds of detecting radar.
• Leave that channel alone for at least 30 minutes afterwards.

For a bridge, that means a radar detection can drop the link while the radio moves. A channel in 5.725 to 5.85 GHz avoids DFS, but it is shared like the rest of the band, so scan it first.

Alignment tolerance: narrow beams need rigid mounts

High gain means a narrow beam. The FCC’s 60 GHz order notes that point to point 60 GHz devices typically have a beamwidth of less than 5 degrees, and that they must be very accurately pointed to a very precise location to operate effectively. If the link is knocked out of alignment, it breaks and has to be realigned.

• Use a short, braced pipe mount on a solid structure; avoid long masts that twist in wind.
• Use the radio’s alignment tool or signal readout, one end at a time.
• Set polarization first; mismatch costs are covered in antenna polarization explained.

A 5 GHz bridge with a wider beam tolerates more sway, which is one reason it suits poles and lighter structures.

What FCC Part 15 allows in each band

Both bands are unlicensed under Part 15, so neither gives you protection from other users; what that trade means for a backhaul link is set out in licensed vs unlicensed backhaul.

• 60 GHz, 47 CFR 15.255: covers 57 to 71 GHz. The general limit is 40 dBm average and 43 dBm peak EIRP. Outdoor fixed point to point transmitters may run up to 82 dBm average and 85 dBm peak, each reduced by 2 dB for every dB the antenna gain falls below 51 dBi. The section has no DFS requirement.
• 5 GHz, 47 CFR 15.407: power and antenna gain limits vary by sub-band, and the DFS rules above apply in the two middle sub-bands. In 5.725 to 5.85 GHz, fixed point to point links may use high gain antennas without reducing conducted power.

Hybrid links: 60 GHz with a 5 GHz backup

A hybrid link pairs a 60 GHz primary with a 5 GHz path between the same two points, either inside one dual band radio or as two radios joined by failover on the switch or router. When rain or misalignment drops the 60 GHz link, traffic moves to 5 GHz, which the rain figures above barely touch.

• Expect lower capacity on backup. The 5 GHz path carries traffic at its own rate, so decide which traffic must keep running.
• Budget both paths. Each needs its own fade margin and its own clear line of sight.
• Choose the backup channel carefully. On a DFS channel, a radar event can take the backup down for at least the 60 second check.
• Use active and backup, not both at once, unless your equipment is designed to combine them.

Where to find radios for a short range wireless bridge

The 60 GHz point to point radio and 5 GHz radio category lists bridge radios, and the wireless network antenna category and wireless mounts category list the antennas and brackets that go with them. All sit in the broadband and WiFi division.

For pricing and availability on a link, contact your sales representative through the Bursma contact page, or open a Bursma dealer account.

Frequently asked questions