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Old 14 February 2017, 22:39
Akheloce Akheloce is offline
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Anyone ever played with millimeter wave?

At work, I'm testing out a 2.5Gb 80Ghz point to point shot at 4700 meters. My math says I should have an optimum RSSI of -44dB, and the manufacturer agrees. Aligning it, I'm seeing the secondary and tertiary lobes clearly on the meter with peaks of -66 and valleys of -90. I get what I believe to be the primary lobe, and still get -56 on one end, and -65 on the other. I feel pretty confident that I'm on the center lobe on both ends based on my meter readings, but I could be fouled up.

I've aligned standard microwave and lasers plenty of times, and have not had this much trouble, primarily since the RSSI's are linear with both of those methods.

Anyone have any specific field experience with these that can offer some pointers?
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Old 15 February 2017, 07:59
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No specific experience but as a general ham licensee I'm very intrigued by what you're setting up.
I'd love to read more details as you sort through these issues.
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Old 15 February 2017, 13:33
Akheloce Akheloce is offline
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Weather is crap today, and I have other things on my plate, so I'm not going to mess with it today.

The gist of the system is 2 12" round antennas which are on an adjustable gimble attached to a 4" pole on the roof of 2 of our facilities. They are capable of 2.5Gb total, with 2 sfp inputs and 2 cat 5 inputs. It's powered via POE. My intent is to run 2x 1Gb LAG/LACP to feed a DLC in a remote area. Once I get it aligned properly, I have a pair of RFC-2544 test units on each end to flog the circuit for a few days.

The beam of the center lobe is approximately 7mm in diameter, so at 3 miles, it's quite the pain to align... in February... in Alaska. Rough geometry figures each degree of angle = 350'. To make it more interesting are the side lobes. There are at least 2 lobes on either side of the primary that I've identified so far. This makes alignment harder since as you're adjusting based on signal strength, you might find out that you're on a side lobe, and have to start all over again. AESA/SAR would be a lot easier :). Talking to the manufacturer, I asked about a doppler shift/ GUI based alignment tool in software, and he said they're working on it.
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Old 20 March 2017, 21:43
Akheloce Akheloce is offline
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So last few days, we got another piece of gear from a competitor (of the radios mentioned in the OP), and today installed it in parallel with the other one mentioned above.

The manufacturer rep was on site today to assist with the new gear, and we aligned the antennas together. We calculated a -35dB signal as optimum. We were only able to attain -44 (24" antennas) So, my difficulties in the other setup were duplicated with this new setup. However, this time, I had a factory rep on hand who validated that I've done it correctly, and we have the best signal we're going to get given the situation.

On this new setup, the throughput is 3Gb/s over a single link. An interesting thing about MM wave is that with a low signal, you do not lose speed, you lose availability. In other words, the link either works, or it doesn't. Not too happy about that as I'd rather have a 99.999% reliable 1 Gig link than a 99% 3 Gig link. Looks like 4700 Meters is a bit long for this gear.

So, my installation calculations and procedures were correct, but it looks like I'm only going to be able to use the technology in shorter range applications.

Tomorrow, I'll run both sets of circuits in parallel with 2x1Gig and 1x3Gig in the RFC-2544 suite and see how they run.
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Old 20 March 2017, 21:58
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What's the receiver sensitivity? You mentioned the main lobe is 7mm in diameter. What's angular beam width?

Also, any chance you could use helical antennas on both ends?
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Old 20 March 2017, 22:11
Akheloce Akheloce is offline
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Antenna gain is 45dB for the 12" and 50dB for the 24"
Tx is +10dB, fail point is roughly -55- -60dB
The wavelength at 80,000 Mhz is 0.00375 m, so I'm not sure it would be practical for a helix. FWIW, the waveguides look to be about 1/4" square on the outside.

Also, the radio itself bolts directly to the parabolic antenna as a package as sent from the manufacturer. We asked about modularity (separating the two) and they said that it wouldn't work, given the sensitivity to loss at the extreme high frequency.
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Last edited by Akheloce; 20 March 2017 at 22:18. Reason: calculator fail
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Old 20 March 2017, 22:29
Akheloce Akheloce is offline
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On a completely unrelated note, one of my coworkers helping me on this was an 18E. Normally, we'd give each other shit for our respective military branches, but instead, we team up on the Annapolis grad coworker.
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Old 21 March 2017, 10:14
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This is what we used on a similar project. We didn't have any major issues at about 5Km.

https://www.ubnt.com/airfiber/airfiber24/
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Old 21 March 2017, 11:32
Akheloce Akheloce is offline
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Quote:
Originally Posted by Sharky View Post
This is what we used on a similar project. We didn't have any major issues at about 5Km.

https://www.ubnt.com/airfiber/airfiber24/
The price on that seems too good to be true. What kind of availability on that are you getting? The one we installed yesterday is literally 10 times the cost of that Ubiquiti product. If the data sheet on that is correct, then Ubiquiti could be the way to go for us.
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