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New Member
Posts: 33
Registered: ‎05-18-2017
Solutions: 1

Dumb questions regarding GPS

I have spent quite a while searching the forum for the answer to thses questions but all I seem to get is conficting information much of which is almost a decade old.

 

Config:

4 devices. 2x Prism G2, one AC400 ISO 1 AC500 ISO

1 prism has an omni antenna and is about 15m from the other three which are all on the same pole.

The top dish is a prism G2 with a 31db light. It is at 6m above roof and is a 1.5km link 80Mhz wide 5.8 Ghz PtP

Middle dish is a AC500 at 2,5m, 80Mhz wide 2.1km link 5.5Ghz PtP

Bottom Dish is a AC400 at 1m. 80Mhz wide, 200m link 5.3Ghz PtP

Omni is Prism G2 10db 40Mhz wide PtMP. 5.7Ghz

For the three point to point links bothe ends are the same equipment.

 

I am having problems with the AC400 link doing strange things with VOIP and almost every time I log onto it there is a "crash report" so I am replacing it. I have no VOIP issues at all on any other link.

 

I was thinking of making them all prisms so they sync up and don't fight but I am not sure that is what the prisms are designed to do.
I can't seem to find anywhere to turn on or off GPS sync on the existing Prism PtP.

 

So where am I going wrong and is there a better way to do this?

Emerging Member
Posts: 89
Registered: ‎12-11-2014
Kudos: 20
Solutions: 4

Re: Dumb questions regarding GPS

I'll take a stab at it. As far as I know, 80MHz isn't supported yet, but 20/40 is. Also, I believe you need it on PtMP mode along with fixed frame to get the GPS on/off option. The only other thing I can think of is firmware since this GPS sync stuff is pretty new with these units.

Established Member
Posts: 1,170
Registered: ‎02-04-2015
Kudos: 666
Solutions: 51

Re: Dumb questions regarding GPS

For those crash reports, try upgrading the firmware, I was getting a lot of them around 8.1.3 to 8.3.0, and then from 8.3.2 to 8.5.0 they slowly got better (the last one I had was in December).

 

TCILarry is right, for GPS Sync you need to use a 20 or 40 MHz channel, and set your radios to PtMP mode.  I have 3 PtP links that I run in PtMP mode with GPS Sync and it works well.

 

GPS Sync has two main benefits

1. Synchronize timing to GPS clocks in order to re-use frequencies / eliminate interference.  This requires AP radios with a GPS antenna.  I don't think you need this.  If I'm reading your post right you have zero frequency overlap:

top dish 5760 - 5840 80MHz

guard band 5720 - 5760 40MHz

omni 5680 - 5720 40MHz

guard band 5540 - 5680 140MHz

middle 5460 - 5540 80MHz

guard band 5340 - 5460 120MHz

bottom 5260 - 5340 80MHz

 

The guard band between the top dish and omni is a little small, I think the average of the two channel widths is recommended ((40 + 80) / 2 = 60) but it's still pretty good.

 

2. Fixed framing which provides dedicated upload and download slots and more consistent performance.  This can be enabled on any airMAX AC radio and even some M radios (as Stations), no GPS antenna required.  I think this is the benefit you're looking for.  You should be able to try it out with your existing gear by upgrading to at least 8.3.0 although I would upgrade to 8.5.0

New Member
Posts: 33
Registered: ‎05-18-2017
Solutions: 1

Re: Dumb questions regarding GPS

Thanks for the repiles.

 

All of the firmware is 8.5. I need 80Mhz for the bandwidth. 

I have considered using AirFibre but in Australia the costs are very high e.g. AF5 is almost $2000 per  end AF24 almost $3000 per end and the AF24HD is $5000 per end.

 

This is way above budget. I could buy a new car for the cost of the links.....

 

The one that is the headache crashing is a AC400. If there really is no advantage in using GPS I will replace both ends with IS5-AC and see if that improves the situation.

The primary issue in this link is VOIP dropping out and I reaslly need to fix that one first

 

 

Established Member
Posts: 1,170
Registered: ‎02-04-2015
Kudos: 666
Solutions: 51

Re: Dumb questions regarding GPS

I wouldn't say GPS has no benefit, I use it even though I don't get the synchronization benefit, just because it makes things more consistent.  I think that consistency would help with your VOIP problems.

 

But if you really need 80MHz then you can't use GPS Sync.  Have you tried 40MHz?  Sometimes 40MHz is a lot more efficient per MHz so the difference in total capacity isn't actually that much.

 

If you replace the PBE-5AC-400 with an IS-5AC keep in mind you are going from a 25dBi antenna to 14dBi.  The antenna amplifies the receive and send signal so you will be losing 22dB of signal strength without turning up your power. 

New Member
Posts: 33
Registered: ‎05-18-2017
Solutions: 1

Re: Dumb questions regarding GPS

I have the AC400s turned down to 10dBm already as that is more than enough to cover the short link.

 

I lashed out and bought two prism stations so I will just have to see how they go.

 

I need the 80Mhz because the link is used for offsite backup between 7pm and 5am. At the moment it makes out at about 220Mb/s with the CPUs sitting on 100%. I hope the prism ones are a bit quicker.

SuperUser
Posts: 5,748
Registered: ‎08-26-2009
Kudos: 1757
Solutions: 55

Re: Dumb questions regarding GPS

The CPU on the prism is faster. However, 100% CPU doesn't actually mean there isn't more headroom for packet forwarding, it may not be totally accurate...

Ubiquiti Employee
Posts: 7,648
Registered: ‎04-14-2017
Kudos: 1492
Solutions: 212

Re: Dumb questions regarding GPS

@ttecs 220 Mbps aggregate throughput? You shouldn't be CPU limited in this case, but we'd have to see your full configuration to verify that.
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