jitter and site survey help - 900 canopy support please help

ran into a very unusual circimstance tonight. firstly, let me say we’re using the new canopy 900 mhz equipment, we’re mounted about 110 feet up on a paging tower using a maxrad antenna from a trial kit. we’re using the 911 frequency, and we are 2.72 miles out according to the registration page. here’s the deal. we tried several different spots on this property near the house (inside the house), on the roof, beside the roof, front of the house, back of the house…everytime when we were actually able to get the signal, the RSSI was real good (900-1450), but the jitter was ALWAYS 7 or higher. Most of the time it was between 10 and 15…and this was everywhere on this house we tried [with one exception!]. Here are those exceptions. Finally, we went up above the eve of the roof and went to an upper section of the roof (above the second floor windows) and, amazingly, there was NO SIGNAL there. We came back down 10 feet or so to the eve of the roof again, and we got the same higher signal with jitter values of 10-15. We never did successfully register with the access point here…but as you saw from my distance reading earlier…we did actually register…but it was…get this…on the GROUND…facing DOWN towards the EARTH with the antenna…and the jitter finally dropped to 4-5. It was very difficult to keep this steady…but when we did finally register, we ran a bandwidth test @ toast.net and pulled down 800k (on a 1.5 mbit connection…this is acceptable). Latency was higher than I would have expected (by this time, jitter seemed to have returned to 10-12 value) and I never would have guessed we would clear up the jitter value by aiming DOWN. It is my understanding from reading the documentation that jitter is how…intact…the 900 mhz wave is once it is received. If the jitter is higher (as these were), the waves were badly damaged, and therefore, that is why we have unsuccessful registrations. My questions are this: a site survey…is that what we need to be doing on a site survey, or are we way off in left field? What typically happens when you guys do a site survey? Also…is there some secret to getting a low, acceptable jitter in an environment like this? In other environments where we had a higher jitter, re-elevating the antenna (higher or lower) seemed to always fix it. Not here. We are still very new at this game and frankly, we’re all scratching out heads tonight. Help…and please, Canopy_Support, don’t hesitate to throw out your suggestions here…we’ll sleep better at night with them. Thanks…from alabama!

We are also new at this 900mhz game. Have you used the Spectrum Analyzer on the SM to see if there is excessive noise? I put one of the units at my house and found that a video extension unit that I had in my house was running 900mhz also and was causing interference. I also seem to remember that the flat panel had a 30 degree beam pattern top to bottom on vertical polorization. Could the elevatio of the location be higher that the beam at your location? Have you tried horizontal polorization just in case there is interference. It also seems that the 900mhz phones might cause interference and extra height might get you past that. Hope this helps.

There is noise…but nothing too odd. I can tell you with the antenna pointing at the ground (a concrete patio), hes surfing with a jitter of 4-7. However, if he trys to mount on his house, his jitter is still much higher. He has a video extension unit but it’ s in the 2.4 range. So is his cordless phones. :slight_smile: I think it’s a beam of 60 x 60 each way [horozontal or vertical]. We’ve already played the polarization game…we’re horozontal all the way. :wink: We are looking at moving the access point up another 30 feet or so on the tower (the tower is in a hole…granted…we’ve seen that), but we get a great signal a mile and a half away (further out), 100 feet in the air on another tower we’re planning to use [an old fire tower!] RSSI values terrific up there… It’s difficult to understand.
I had hoped we could focus more on eliminating jitter…but I would imagine the issues you describe would be closer related to RSSI than jitter…please correct me if i’m wrong? Still new at this too… thanks; )

we’re getting the same thing- lots of re-registers and high jitter on our 900 sites- one of which has 900 paging at 929. We’re using 906. I have a filter comning from txrx they made with a 10meg bandpass at 906. We’ll see if that changes anything. It should be here next week. The other site with a smilar problem is not co located with paging but there are 3 929-931 transmitters about 2 miles away.
the rssi from the spectrum analyzer looks like a noise floor is high (around 700-800) at both places. I haven’t taken the service monitor out there yet to look at a real spectrum analyzer. On the bench though, the 900 sm analyzer screen showed about 20 db higher than I was putting into it with the signal gen. Also, what I don’t know is how selective the front ends are on the 900 receivers. Will a signal over 20 meg away desens it? Maybe the cavity will tell the tale. I’ll post my results as soon as I know something. I would have hoped Motorola may have worked out some of these issues before dumping this stuff on the market and we’re $30K into it.

very interesting you should mention that…we switched from 911 to 905 (or was it 907?) today temporarily to see if another frequency would help and , sure enough, it wouldn’t even register there. We switched back to 911 and it registered, but jitter values were still higher. I’m almost willing to bet paging is interfering with the signal at this point…jitter is a measure of interference in the signal , true? Thanks for your reply… :slight_smile:

I would also be willing to bet that your jitter and interference issues are being caused by that paging transmitter. Paging transmitters ALWAYS seem to cause interference. Jitter is a measure of the multipath your antenna is receiving. In other words, it is receiving multiple instances of the same signal, at different times. This is not good obviously.

A good example of multipath would be shooting a 5.7 link through trees, and having a high jitter if it actually registered. The high jitter would most likely be caused by reflections from the leaves on the trees, therefore delivering multiple instances of the 5.7 signal to the SM at different times.

I would definitely recommend moving your 900 AP gear far far away from any paging transmitter.

assuming this is the case, we should expect to see high jitter on each receiving SM, correct? If we don’t, that’s proof the problem is at the subscriber location and not at the tower. Not making bets yet, but frankly, we haven’t even paid attention to the jitter values until now. Boy…we’re learning. BTW, we’re brand new into the WISP game…still in testing stages but have deployed our first “test dummies” - we have no proir experience in any other band.