Good Antenna for 900 AP

I had posted about this problem neighborhood that we have. It’s a tightly clustered neighborhood served by a 900 AP which sits on a hill overlooking this neighborhood from about 1 mile away. this is a very rural area. No other neighborhoods for miles around. Many of the customers do not have clear LOS, but since they are so close to the AP, most have very good signal.

We have about 23 clients in this neighborhood and 20 of them have no problem hardly ever, and the other 3 just seem to freak out from time to time. Jitter goes all over the place, and they can get dropped. Often times the problem goes away by itself, and other times I can often get them back by playing around with the frequencies. And they are up and running which can last anywhere from 1/2 a day to a month and then suddenly more freak outs. And not all 3 freak out at the same time. I have done many spectrum analysis remotely, but have not been able to find any obvious issues. At this point I am thinking we are looking at local interference from baby monitors perhaps. This has been going on for a year now, and we just can not see any kind of consistent pattern that would explain why it is happening.

The AP is using the standard panel antenna that used to ship with Motorola 900 units a few years ago, which I believe is the Maxrad MP9026CPRXFPTNF which provides 6.4 dBd gain.

We are wanting to try and install a larger antenna with the hopes that we can drown out any local interference that may be causing this.

So 2 questions:

1. What if any thoughts on this issue? Could we really drown out other signals?
2. Does onyone have recommendations for a replacement antenna?

Thank you.

we went with the MTI omni, its huge and expensive, but man is it awesome, we engineered for a single mile coverage, but are getting ten, we could go further, but we arent pushing our luck. We even have some competition playing games, going to the same channel and color code, but thus far we are winning the battle for the subs

Both MTI and Til-Tek get very high marks for their antennas. I can attest personally that we’ve gone 20 miles with an MTI omni (low noise environment).

Thanks. Going with an omni really does not make sense for us in this situation and could actually cause other problems, as we would not want to transmit behind the current AP. Would you give good marks to panel antennas from same manufacturers?

I would consider the sector antennas from MTI or TilTek. MTI has a 90, 120, and 180 degree sector, and TilTek has a 60, 90 and 120 degree sector (even though there website doesn’t show the 60 or 90). The MTI’s typically have slighly bettern gain compared to the TilTek and are lighter in weight, but of course are more expensive.


This brings me to a related question:
Is there a need for any additional signal amplification when using something like the MTI 120? I ask this because we are actually using one of these in another location with very disappointing results. The antenna is located on a tower which is the highest point in our area (probably about 3000’ above everything else) and can see 360 with no problems. We installed this antenna with the hopes of being able to service clients who are in the next town which is about 20 miles away. Well most clients there are seeing just enough signal to be able to stay on. The best we have out there is a client with LOS and we had to use a 4’ yagi for him and he has a -75db RSSI and jitter of 2-3 which is fine. We had certainly expected that using the MTI 120 we would have no problem reaching people with standard integrated SM’s.

We have another integrated 900 AP on the same tower pointing at another sector and we have pretty much the same results as we do with the MTI. So where is the additional 6-7 db in gain as compared to the integrated antenna on the other 900 AP?

So, do we need to boost the signal from the connectorized AP to the MTI? Or does the antenna have some sort of amplification built-in? I mean sure, it is a larger antenna, but don’t you at some point need to boost the signal coming out of the AP? How big an antenna can an AP run?

The gain on both the MTI 120 degree sector antenna (P/N: MT-263004/NH) and on the Integrated AP (P/N: 9000AP) are both 12.5 dBi, so this would be why you see the same results. If you use a RF Link Budget Calculator for that 20 mile distance and use the receive gain for both the AP (w/ 12.5 dBi Antenna) and SM (14 dBi 4 Ft. Yagi) you get a Rcv Signal Strength -70.1 dBm which is about 5dB off from what you are currently getting at this customer’s site. This may be due to other environmental variables, obstructions etc. or if the AP is that high up, you may want to try and tilt the antenna down slightly.

There are amplifiers that you can purchase as the antenna doesn’t do any type of amplification and this would only work with your connectorized AP as the amplifier is placed between AP and antenna. However, using a amplifier will put you outside the FCC/IC specification of 4W (36 dBm) in the 900 MHz frequency.

To increase performance, I would:
1. Tilt the antenna at the AP down slighly and see if RSSI improves.
2. Use higher gain antennas at the SM site (17 dBi Yagi or 18 dBi grids.)

Hmmm… I am not sure why I was under the impression that the integrated AP had only 6db gain. I guess is because the Maxrad that Motorola was shipping with the original connectorized set is rated at 6db. I think back then we thought they were both the same, and that it made sense to go with the connectorized so that we could increase the strength by using a larger antenna.

Forgive my ignorance, but jus os I understand this better, what you are saying is that in my above scenario with the problem neighborhood (original post topic), where I am using a connectorized AP with an external Maxrad antenna that is rated at 6db gain, my actual total power is 6db? So, other than price, and coverage, is there an advantage to going with a 12db MTI vs. and integrated AP which has the same gain?

As to the existing MTI, it is already tilted down, and there is not much obstruction, but based on your calculation we are not that far off in terms of our signal strength.

And am I missng something: How does Moto cliam the typical LOS range of the integrated 900AP to be 40 miles? Am I just stupid to be buying their marketing BS, or am I misunderstanding something here? We are barely getting 16 miles out of it, and even then we have to use a 4’ yagi at the other end.

The Maxrad panels actually have 9 dBi gain and they are a subscriber antenna. Base station antennas will typically have better F/B Ratio etc. which is why you would use one of these at the AP. If you only need 60 degree coverage, than the Integrated AP will work just fine.

EIRP is calculated by adding the transmitter power (in dBm) to the antenna gain (in dBi) and subtracting the cable loss (in dB).

e.g. TX Power 25 dBm + 12 dBi Antenna - 1.0 dB Cable Loss = 36 dBm (4 Watts)

If you currently have your AP set at TX 26 dBm and you are using a 12.5 MTI Antenna. You cable loss from the connectorized AP pigtail is 0.5 dB.
26 dBm + 12.5 dBi - 0.5 dB = 38 dBm (6.3 Watts). You actually should drop the TX power on the AP to 24 dBm to stay withing FCC/IC.

You should be able to get 40 miles LoS out of the link as long as there is absolutely no other 900 MHz in the area and you have perfect LoS. The equipment does support it and it can range that far, but I wouldn’t say it is typical. The farthest shot we have ever accomplished is 28 miles.

Under IDEAL circumstances you could achieve 40 miles, but you’ll need high gain antennas on BOTH ends. 900MHz carries a long ways.

I would say if you only need the small area of coverage, there may not be much of a benefit over using an integrated AP instead of the connectorized AP + sector antenna. It would only be nice if you could foresee in the future needing to extend your coverage to 360* or something. I personally always deploy connectorized units because we start off with an omni antenna and as we grow we add additional APs and sectorize things - it allows me to reuse my APs more effectively.

900MHz is a complicated animal. Sometimes it works absolutely as expected, sometimes it exceeds your expectations and other times it under performs terribly. It all depends on your RF environment.

Thanks. Don’t recall Moto telling us that the Maxrad was a subscriber site antenna. That’s what they shipped to us in our 900 starter kit.

Also looks like I was looking at the wrong Maxrad model. They have a Right Hand Circular version (MP9026CPRXFPTNF) that is rated at 6db.

Well I think I will go ahead and order the MTI 90 (that’s all the coverage we need), and perhaps relocate the Maxrad to one of the problem sites and see what that does for them.

Thanks for all the advice and knowledge.

I’ve had wonderful success with stingers from Wireless Beehive vs panel antennas. We used to use panels from Mars antennas - the stingers are so much easier to work with and give us just as much gain. We also use M2 yagis with great success.

I agree with wifiguy, the wbh stingers are great and easy to install. Probably because of the distance of most of your subs, you will have to use M2’s 14 and 17 dBi antenna for most of your installations.

etech wrote:
Thanks. Don't recall Moto telling us .......

Thats a Moto Trademark
mbsi wrote:
I agree with wifiguy, the wbh stingers are great and easy to install. Probably because of the distance of most of your subs, you will have to use M2's 14 and 17 dBi antenna for most of your installations.

Why not try a yagi or panel antenna from ZDA Communications, The sample antenna is free, and with two year warranty. Performs as good as M2 Yagi, but with robust mounting braket, light and strong, cost much less.

Last Mile Gear has a 17db yagi that gets good reviews too.

For the record- M2 finally fixed their mounting hardware. We use them exclusively for our yagi antennas.

Robert29229 wrote:
Why not try a yagi or panel antenna from ZDA Communications, The sample antenna is free, and with two year warranty. Performs as good as M2 Yagi, but with robust mounting braket, light and strong, cost much less.

We use both Stingers and Yagis. The 17db yagis from ZDA are great deal. Superb to deal with and great price/performance. Never had an issue with them.

If I wanted to cover a town 20 miles away I would suggest you use a Kathrein-Scala 900 Mhz 18dbi Grid and point it at that town. IIRC this antenna provides about 9db at the 120deg mark as well.