5.4Ghz OFDM Backhauls & 5.8

Does anyone use these? I’ve heard you need to worry about radar from airports interfering. We have a link we’re looking at where there is an airport 7 miles away.
Should we be worried about it?

The short answer is “it depends”.

is this airport a small municipal airport or is it chicago o’hare?
small airports and even a lot of large ones don’t use the band for radar, but some do.

your best bet is to do a spectrum analysis.

We have used the 5.4 OFDM backhauls with great success, but we are in a very rural mountainous location.

from my experience i will tell you that occasionally they will have a “false positive” and the link will shutdown for 1 min. while it looks for a clean channel. This happened to us a lot because we had 5 of them co-located at our main POP. after a lot of channel planning and locking down some of the frequencies this no longer happens.

As always your mileage will vary…also be sure you run everything thru the link planner (or have your VAR do it for you). If you plan accordingly and do a spectrum analysis beforehand these radios are awesome.

Well it’s definitely not O’hare, but it’s not tiny. It’s Grand Rapids, MI airport which I would say is medium sized.

The problem is we don’t have any way to do a 5.4Ghz spectrum analysis without buying the backhauls first.
And if we buy the backhauls, we’re going to use them. :slight_smile:

as a “cheep” spectrum analyzer you could buy a 5.4SM from e-bay or your VAR and use the built in Canopy spectrum analyzer.

There are also companies that will rent an analyzer.

For the amount of money and time that it costs to put in one of these links it is worth your due diligence on the front end to make sure that you’ve checked everything out and planned accordingly.

my “guess” would be that you’re probably ok especially since there is a lot of spectrum available in the 5.4 band…but that is only a guess.

Ok, that’s what I was kind of thinking too but I wanted to make sure.
Thanks seano.

Ok, lets say we go ahead and use 5.8Ghz. We know of another company that has Motorola 5.8Ghz OFDM on the same tower pointing south.

Ours will be pointed north for the most part.

We figure on being 80-100 feet higher than their antenna. Should this be enough vertical separation?

the vertical separation should be fine. (honestly we have 3 of the 5.4 OFDM radios mounted almost back to back at our main POP and we just locked down their channels to be far enough apart so they don’t step on each other)

again i’d check the spectrum just to be sure there is nothing else there.

if you can use 5.8 then i would pick that band because of the higher power and the radios don’t go down for a minute if they have a DFS hop.

we use 5.8 AP’s and SM’s so we didn’t have enough spectrum for all the AP’s and BH’s to use the same band.

That’s probably plenty of vertical spacing. You have the advantage of being 180* opposite as well which will allow you to take full advantage of the front-to-back isolation on the antenna. If you want to ensure even further separation between the two systems (which I would do if I were in your case), I would advise you to use a high-performance antenna which has a shroud around the feed which will provide even higher front-to-back ratios (as much as another 20dB).

Be sure to allow as much frequency separation as well between the two systems. It will probably be best if you lock the frequencies down and not allow the unit to use iDFS.

Yeah we’re looking at 3 or 4 foot dishes right now. What kind of “shroud” do you mean exactly?

Both bands use the same antenna, and are type certified for both in the FCC region.

Manufacturer: Radiowaves

3-foot Parabolic: HPD3-5.2NS

4-Foot Parabolic: HPD4-5.2NS

These antennas look similar to the “drum” style antennas you find on licensed microwave systems. I’m sure you’ve seen them before as they are very common.


So the shroud is what actually goes over the dish then?

We’re looking at purchasing some Andrews antennas.

That is correct. It is factory installed.

Again, the primary purpose of a high-performance antenna is to further reduce colocated interference at hub sites such as the one you are looking at.

I don’t know if Andrew has one, but I do know Andrew will be more expensive than Radiowaves. I think you’d be pleased with any of Radiowaves products. I know we are.

Ok, so the shroud actually has a radio meaning. Does it protect the radio in anyway for weather purposes or anything like that or is it solely for front-to-back ratio?

Nope. Shrouded antennas are solely designed that way to reduce off-axis interference at high-density sites. I just did a quick comparison between the SP4 and the HP4 for the dual-pol antennas. The SP4 (non-shrouded) has a FB ratio of 42dB. The HP4 has a FB ratio of 49dB. Keep in mind when you take 3dB off or added you are around ~2.5 times less powerful, or ~2.5 times more powerful. 7dB gives extra separation between you and the noise, both coming and going. 7dB less of your signal will reach the other antennas on the tower, basically and vise versa. To clarify, the higher the dB level in the front to back radio the lower the amount of radiation there is behind the specific antenna system. All antenna systems have a backlobe, which can and does cause interference to other devices BEHIND said antenna. The less “junk” you send behind you, the more you can reuse frequencies, or have less colocated interference. The same holds true to sidelobe suppresion. The better your antenna is at focusing the energy OUT away from the antenna, the less “junk” goes off the sides.

The most important part really is the feed design. Poorly designed feeds do not illuminate the antenna efficiently and thus splatter RF all over the place.

Radomes however are used to protect against weather, namely ice buildup on the feed. It also protects the feed from being torn off the antenna should the antenna be hit from falling ice. Then again, if you are in this situation you should install an ice guard above the antenna to begin with.

Has anyone installed a BridgeWave AR80X (80 GHz), or any other BridgeWave unit, along with a Motorola PTP600 in 5.4 GHz or 5.8 GHz on the same tower or similar? How close can you install the two units to one another or how much vertical separation is recommended between the BridgeWave and the Motorola? With the narrow beamwidth on the BridgeWave and different freqs, I would think you would not need a lot of vertical separation.

Being that Bridgewave is Millimeter Wave gear, you could install it next to it.

I’d put 5 to 10 feet verticle though.

Thanks for the input 411!