Hi,
Found this forum while searching for diversity information and would appreciate any comments/thoughts.
Have a number of PTP600’s on short range data links however 1 has been giving us trouble for over a year now.
A PTP54600Lite that is installed on a 2.2Km link across tidal water. Calculated link loss is -114dB and on a good day actual is aprox -112dB. Master 12.5m above water and slave 37.5m both effectively within a few meters of shore. Need about 10Mbps at the Master location, and around 30Mbps to the slave for current system.
Unfortunately while the fresnel is well above the water level there is about 400m of reflection area.
On an average day we have a slow fade of around -130dB and quite often it reaches as much as -140dB for 1-3hrs a day, sometimes twice in a 24hr period.
I have tried shifting the current ODU’s as much as possible up/down at current sites.
Spectrum is clear with no detected interference/radar.
I have tried tilting the ODU’s up slightly and it made it worse if anything.
Changing to a conectorized version is not a major issue as there is a 2nd analogue link that needs upgrading.
There are space issues at current slave end so I am thinking of shifting to an almost identical location on the other side of the channel and picking up some cameras there. Then using the current PTP54600 to replace existing analogue link there and hop to the final destination. Distance increases to 2.3Km but same heights for the problem link.
Master end is a break back pole.
So local supplier couldn’t help me and passed the problem on to Motorola. After hitting my head against a brick wall multiple times I finally was given a solution.
Two x 27.8dBi antennas master end, integrated antenna slave end. Does this make sense to you?
From what I can tell in link planner it only provides a marginal improvement to the master which is the direction we need the least data rate.
Last thing I want is to spend a fortune on cranes, new antennas etc and have it still fail.
Given the size fade we have been getting do you think it will work?
why not use 5.7ghz ptp600 since the maximum tx power (52db vs. 30db)
is much higher than the 5.4 band it would give you much more fade allowance. (assuming you are in the U.S.) usually we use radiowaves dual-pol dishes and a connectorized unit. with dishes it would give you a smaller beamwidth and hopefully less relfection.
Should have mentioned I’m in Australia region 13. 5.4 and 5.8Ghz are my options and the 5.4 does lose some channels due to radar band lockout.
I should also mention the fade is almost perfectly symmetrical on the Vertical/Horizontal screen.
I can get the Radiowaves antennas but can get Andrews ones also listed in their link planner cheaper/easier.
Going to connectorized is not an issue I can shift the current equipment to replace the analogue link I mentioned.
But is going from 23dBi integrated to a 27dBi diversity with the dual antenna at the end I need least data rate likely to work with such high fade?
Is going to say 33.4dBi, still below max eirp, antenna better or does it introduce other issue?
The link planer shows I should start with 0.7m diversity at master or 2.4 at slave. Given that I want the highest data rate to the slave is there an end that on average is better for the diversity?
Edit;
Sorry for all the questions, not an wireless expert only got lumped with this stuff as the senior tech. Primary job is CCTV/Alarms.
Understand that some of the answers I am asking for are rule of thumb/best guess.
i show, at least on moto’s website, that 5.4 is a max eirp of 30db and 5.7 is a max eirp of 36db (for Australia), with every 3db jump in power it effectively doubles wattage output so for 30db is 1 watt for 33db is almost 2 watts. so if you went with 5.7 and connectorized with 29db dual-pol dish and real low noise floor my guess would be that it would help quite a bit with fade and would give you a larger fade margin. just my 2 cents.
being that you are using the 600 lite what width of channels are you using and what modulation do you have it set at? becuase with the lites at max width and modulation you should get 150mbps link.
also what is your receive power level?
I can change to that frequency when I buy the conectorized units. We were supplied with the 5.4Ghz version as there is a 5.801V/5.725H link in the general area of the slave end. Turning the other link off does not stop the fade. New slave location will give plenty of separation.
-59dBm is normal receive value with it dropping as far as -90dBm. Both ends equal give or take a few dBm.
Was on 30Mhz channel bandwith, have trialled 15Mhz to try giving more channels at the lower data rate.
It just gets into the 256QUAM/150Mbps but more often at 64QUAM/126Mbps.
Did you try to use Motorolas Link Planner software to see what the spacing needs to be for the spatial diversity arrangement? The software does have the ability to do some limited reflection analysis so that you can take advantage of the units design.
If you do not have the ability to do this I would be happy to run the profile for you and make a few comments. I would need the following information either in a PM or posted here on the forums:
GPS Coordinates of each site
GPS Datum
Maximum antenna height on the towers
Tower type
Desired operational frequency
Desired throughput
Desired reliability (% uptime)
Maximum channel size desired
dB level of local interference if you know it
The link planer shows I should start with 0.7m diversity at master or 2.4 at slave.
I have the profiles setup but am not at work currently, will post them when I can so you can load it into your copy.
.7 meters?
That doesn’t sound right just knowing how SD systems work. Usually at the frequencies we are talking you are needing to place the diversity antenna at 6 to 7 meters, but it all depends on the reflection point.
Path profile.
As said before with the current link I was told to install diversity option with 27dBi antenna at Master end as a solution to current 30dB fade.
The second one is just me playing around with idea for relocated location.
Spectrum page on current link for background noise levels.
http://www.geocities.com/privatteer/Spectrum.jpg
Random pick of master RX power so you can see the fluctuations its having.
http://www.geocities.com/privatteer/MasterRxPower.jpg
Thanks. I will look into it today and comment back. As I said, somethin is odd with the diversity spacing.
On the diversity systems I have looked at I manually adjusted spacing until I reached the desired result. Link planner is very simplified in that it does not show the extra Fresnel zones that one would normally look at while planning diversity systems. I suspect it is just not shown and only calculated in the back end.
What is the maximum antenna size you can use?
The alternate path looks much better.
I’d like to see 3 foot dual polarity antennas personally.
The master end just fits the integrated unit on the current mounting above a camera. Could with some work add something lower but then ships might start blocking. Wind loading is an issue too due to jetty strength already had cracks recently around pole. I would be thinking of a grid antenna if I have to go any larger than the integrated unit.
Slave end wind loading not a problem on the alternative link location and Ive got up to 4meters of pole to play with. Over 4ft/1.2m antenna might give me issues but 3ft is definatly possible.
3foot both ends or just one?
Thanks for the heads up on the diversity spacing, I’ve just been using whatever it told me in the reflection screen. I’ll have a play with the spacing as well.
Hi
All of this puzzles me a bit. This link should be a walk in the park. I have a fair amount of experience with this gear.
5.4 looks like the wrong choice when attempting an over the water link.
I can grantee you that a 5.8 GHZ PTP 500 Integrated will get 50 MBPS full duplex on this link no matter what the water is doing. I’m sure it will co exist quite happily with whatever that 5.8 thing is you mentioned. Looks like you are in a low noise environment from the Google earth image.
You could do a link test with PTP 500 5.8 integrated to prove the point.
I have a 13.8 KM link over water using the much cheaper Airmux product which should perform worse then the Motorola this is an 18MBPS full duplex link with integrated antennas that sits on about 12 MBPS full duplex and I don’t think it’s dropped a packet since it went up five years ago.
Feel free to contact me to discuss we may be able to help.
Email sam@jettech.com.au
Should be yes, but either multipath or refraction are playing havoc with it.
Before the PTP600 was installed there was a original link that was 5.8Ghz. While it was not multi-frequency like the Motorola unit it had the same issues with fading out for 6hrs or more at a time. It may help due to higher eirp but I doubt just changing the frequency to 5.8Ghz is going to be enough.
I’ve gone with a conectorised 5.8Ghz with 3foot dual dish at the slave end and are just waiting on budgets/approvals for the work to commence.
At this stage don’t care if its overkill, long as it gives us a stable link.
Can you increase distance above water?
receive power is fluctuating too much…
try(just to see what hapens) generate region 8 full power licence key.
Im a big fan of the PTP product.
However the exalt boys came to show us their new product.
5.2 - 5.8 GHZ conectorised or intergrated. Single polarised. Does 108 MBPS in 16 QAM. I think 32 MHZ. Conectorised unit they showed me looked well built almost as nice as the PTP conectorised slightly smaller.