downtilt question - 900mhz

Products PMP
#1

Hello folks,

What effect will having slightly more downtilt than required have on 900MHz? I have 3 Tiltek panel antennas, I’m pretty sure they are tilted down more than needed.

Would this hurt my fringe area customers?

Just curious.

Thanks everyone. Still learning…

#2

What I really need is to get more distance from my 900 setup. Just today, I went 11 miles, and the best I could get with a M2 17 was -85dbi (noise floor at 90).

My main tower is 180’. I need to be able to service 15-20 miles.

#3

Same issue?
viewtopic.php?f=1&t=5766&p=28337&hilit=downtilt#p28337

Downtilt Angle Calculators
http://www.ratrivertech.ca/archives/too … ulator.htm
http://wisp-router.com/calculators/downtilt.php

If the AP is @ 180’ then you really don’t need any downtilt. I’d also recommend the Pac Wireless 15dBi grids when the 6’ M2 isn’t cutting it.

#4

Yes, it is the same question from me. It never really was answered that I can see. That post kind of went off on a seperate tangent.

Is the downtilt causing me not to get a good link at greater distances? As mentioned above, using an M2 17 at 11 miles, only -85 or -86dbi. That is 22 feet up in the air too.

Thank you,

Jakkwb

#5
jakkwb wrote:
Is the downtilt causing me not to get a good link at greater distances?

That all depends on the degree of downtilt. What kind of power level/jitter do you see for the customer's that are closest to the tower?
#6

This is my closest customer with an outside unit:

boot Version : CANOPYBOOT 1.0
FPGA Version : 061808 (DES, Sched, US/ETSIv1.3.1) P10
Session Timeout: 0, AirDelay 8 (approximately 0.22 miles (1176 feet))
Session Count: 2, Reg Count 1, Re-Reg Count 1, Session Uptime 1 d, 10:20:41
Jitter (Avg/Last): 8/9 Power Level (Avg/Last): -66/-66
Sustained Uplink Data Rate (SM): 128 (kbit)
Uplink Burst Allocation (SM): 400000 (kbit)
Sustained Downlink Data Rate (SM): 128 (kbit)
Downlink Burst Allocation (SM): 400000 (kbit)
Low Priority Uplink CIR (SM): 20000 (kbps) Low Priority Downlink CIR (SM): 20000 (kbps)
Rate : VC 23 Rate 2X/2X

I have this unit turned down to 10dbi. Otherwise, it would be in the -50’s.

#7

Pull all the antennas to 0deg. You don’t need any downtilt.

#8

I’m not a knowledgeable on the RF side of things by any means (and that guy’s off this week) - but wouldn’t too much downtilt (especially on 900) chop the fresnel zone and create multipath issues, thereby increasing jitter?

#9

You would be correct.

The downtilt also explains the distance problem. Antenna patterns are determined by measuring the on-axis forward gain, and then measuring the points where the gain is -3dB down.

So if the antenna is tilted down say 5 degrees, then there is only 5 degrees of vertical coverage to the horizon, and that coverage is going to be somewhere between the 9dB rated gain and -3B less or 6dB.

By aiming the centerline at the horizon, you get all 9dB to the horizon, and as the gain of the antenna lowers below the centerline, you reduce the amount of energy hitting the ground between the tower and the horizon.