our CMM Micro gps elevation is constantly changing the range is anywhere within a 50 foot spread.
We are installed low outdoors surrounded by metal grain elevators with about 30% total clear sky.
We used RG58 with appropriate cable ends, same ohmage as the suggested lmr200, about 20’ long.
My question is does it matter? all the cmmmicro gps is for is the one second timing pulse, correct? as long as we get that and the APs show they are in synch, is there a problem?
The only thing that matters is the clock.
so, the way i understand it is that the synchronization doesnt really do us alot of good here with only one AP cluster? is that correct?
No.
If your cluster consists of more than one AP you need synchronization. See pages 95-96 from the user guide.
“For example, in Figure 27, AP4
◦ is not synchronized with any of the other APs.
◦ is transmitting nearby the other APs while they are expecting to receive SM transmissions from a maximum distance.
The result is self-interference. In this scenario, the self-interference can be avoided only by synchronizing the TDD transmit cycles of all APs that operate in the same frequency band. An AP that is isolated by at least 5 miles (8 km) from any other Canopy equipment, or a BHM in an isolated standalone BH link can generate and pass sync pulse without GPS timing and not risk that interference will result from the generated sync. In any other type of Canopy link, sync should be derived from GPS timing.”
We are installed low outdoors surrounded by metal grain elevators with about 30% total clear sky.
This may be an issue. Reflections from the metal on the elevators may cause a problem. And only a 30% view of the sky may also cause issues.
We used RG58 with appropriate cable ends, same ohmage as the suggested lmr200, about 20' long.
The type of cable used could definitely cause issues, but again you are only using 20 feet. I would try LMR400. Find a loss calculator on the Internet (I think Times Microwave has one on their web site) and see how much loss you are realizing @ 20' with RG58. I have seen the cable used for the GPS antenna make or break installations.
Using LMR-195:;
GPS frequency 1225MHz you’ll see average 3.2dB plus connector loss
GPS Frequency 1575 you’ll see 2.9dB plus connector loss
Using quality connectors and building them properly you should expect to see around .32dB of loss, add that into 3.2dB of cable loss and you get around 3.52dB of loss in the transmission line system or 3.22dB.
I cannot recall which frequency it is running on so, sorry on that one.
Using LMR-400:
GPS Frequency 1225MHz you’ll see average 1dB plus connector loss
GPS Frequency 1575 you’ll see average 1.053dB plus connector loss
Again, .32 dB and you are around 1.32dB of transmission line losses or 1.37dB on the higher frequency.
Remember: 3dB of loss effectively cuts your receive power in half. 1W in, 3dB of t-line loss and you have .5W out of the cable and into the receiver.
Here is the calculator that I use:
http://www.vk1od.net/tl/tllc.php