Greetings all

I am planing a new coverage area for my network and would like to use a DLB AP 900, however the location I have for the AP is in a marina that uses EnGenius SN-920 high-power 900mhz phones. Alas I do not have a spectrum analyzer for the 900mhz range so I am not really sure how bad it is to be in somewhat close proximity (100m or so) to these phones. All I currently have to go on is the manual:

http://www.engeniustech.com/resources/SN-920%20Manual-0012141.PDF

That tells me that the base station is 900mw and each handset is 630mw (yikes!), but it also says "Number of Channels: 142". I have a faint hope that this means these phones will be using very narrow slices of the spectrum and that any interference they cause with the AP will be fairly short lived as they hop frequencies. I assume they are frequency hoppers as there is no way to set a specific channel I could find.

Does anyone have any experience with these phones, or anything like them, and a DLB AP 900 (or any 802.11g-in-900mhz radios for that matter)?

- Sean

I do not have experience with those exact phones or the DLB AP-900, but I do have extensive experience with 900MHz AP's and CPE's and interference. I can tell you right now that a base that puts out just under 1 WATT and a handset that puts out over 1/2 WATT you are going to experience interference. Even if the AP is mounted 100m (300+ ft) away, and even if it is up high on a tower, you will still run into interference when CPE's are close by and aiming through the marina.

I assume the marina uses 900mhz phones for communications throughout the complex? Probably a large complex?

I think your best approach here is to get a 900mhz motorola canopy subscriber module on ebay and go out and do an analysis - the Canopy radios have really nice spectrum analyzers in the software. You will be able to see the spikes from the bases and phones as they reach out for each other. Try to do it from the location you want to mount the AP. If you are seeing numbers below -50 or so, then that's really strong interference. Keep an eye out and see if the spikes are in the same frequency - if they stay around the high end of the spectrum (920 - 928) then you can always put the AP at 906 or so. We always figured 4mhz up or 4mhz down of an adjacent transmitter is enough spacing.

Or just get them to dump the 900 phones and replace with 1.9's and buy handheld radios for communications throughout the complex.

Scott

Scott

Let me clarify a bit, the AP is based at the Marina, but the CPEs will be from 7 to 9km away on an island across the water from the marina.

Also the marina staff already use handheld radios for communications, the phones are actually used as *phones.* The staff is usually out in the yard rather than in the office and need to be able to answer the landline. The marina tried quite a few varieties of phone and found none with enough range to work very far into the yard except for this model. If you take a look on their website (http://www.lionsbaymarina.com/) you can see the layout, near center is a small blue hut/office building with a black roof, this is where the phone's base is. The AP would be mounted on far end of the grey two story building at the left end of the image. CPEs would more or less be at the angle the image is taken from at a distance.

I did not know about the canopy subscriber module's spectrum analyzer - that is a good tip!

If I can find 1.9ghz phones that sufficiently cover the area I would replace 'em!

Sean -

Wow - sweet location. I looked it up on Google Maps.

Well, I have another idea. Thought about it while I was walking around town today.

Mount the AP with a directional antenna (like a 120) and make sure it is mounted H-Pol. All your subscribers would then need to be mounted H-Pol. Based on the map you are going to be dealing with mostly LOS for people living along the coasts of that small island and that large one directly west. I think a 120 sector antenna in the H-Pol alignment would be ideal for this.

The H-Pol alignment of the AP will negate the interference from the V-Pol 900 phones. You can also help yourself a little more by using a 900MHz Band Pass Filter between the AP and the antenna. This will help with other interferences that could creep up to - like cell phone.

Oh, and it really doesn't make sense to use an Omni antenna (if you were thinking of using it) due to the proximity of the Coast Mountains.

Good luck! Fun location.

Scott

Scott

H-Pol I can certainly do. As you surmise the client locations are all LOS with the occasional exception of a few tree branches on their side. I only need to aim for the large island to the west though (Gambier Island) and so planed to use something more directional then a 120 sector such as a yagi or panel. Thanks for the bandpass filter suggestion as well.

And yes, sweet/fun location indeed! The topography of Gambier Island can be a real PITA sometimes but it is a nice spot to be. My existing network covers the areas on the island where most properties are, in the three bay area on the south of Gambier and the peninsula to on south-west of the island. I have 4 stations across the island to do this including a 42ft tower on top of a 300m ridge on the larger peninsula on the south-east (called Hope Point) that can see both Lions Bay (2.4ghz backhaul PTP link for the network) and into the three bay area. Most of the island does not have power so that location is Solar and Wind power with gen backup. And most importantly I live in the center of the three main bays on the south of the island.

Thanks for the advice.

- Sean

As Scott said that is pretty rough.  Any idea what size/gain antenna they are using?

Caleb

Caleb

A 5dBi antenna on the base station, and the manual says 1.5dBi for the retractible antenna version and 3dBi for the fixed antenna version of the handsets - not sure if they have fixed or retractible.

Messy.  Marinas are also problematic with the presence of a lot of rf reflective structures. 

Caleb  

I'm pretty confident in saying that after I looked at the photo Sean provided that the height + h-pol mounting will eliminate any problems. A BPF could always be put in after the fact. But, worst case scenario is he would have to do a 900 spectrum analysis and figure out what channel to put the radio on. My guess would be that the phones run low - like 906 - 912 and putting the AP at 916+ would be the best bet.

Been tearing up the slopes the past few days and got sidetracked from the forums...

Scott

Would like to see what a spec analyzer turns up too.

Caleb

Thanks again for the helpful posts here.

DLB - Caleb:

Would like to see what a spec analyzer turns up too.

So, after a bit of a wait for an ebay purchased Canopy SM to arrive, and more wait as our boat decided to shred it's drive gears (doh!!) i was finally able to get back to Lions Bay and do a basic spectrum analysis. The results have bad news, and good news....

So for the good news first. The first time I asked about 900mhz at the marina I was speaking to the owner, and he talked about how hard it was to find a phone that worked at the ranges they need and in their env, how expensive the SN-920 was, etc. He basically said in order to not use it I would have to find something that worked equally well for the situation. This time however I talked with the staff who actually *work* at the marina. The first person I spoke to had *NEVER* used those phone in two and a half yeas, and the older employee said that he used it a bit when they got it, but that it was impractical to be answering the phone while out moving boats in the yard. In fact, when I went to do the signal testing we found that the phone line was not even plugged in to the base station and no-one had noticed! This gives me hope that this will be a non-issue entirely. Both employees remarked that the owner was one of those people with the mindset "It cost me money, I am not going to get rid of it!" - thus the unused but still present status.

The second bit of good news is that the first spectrum readings I did with the phone idle look reasonably good. You can see the results here:

• http://hoth.gambierrip.ca/~sean/pict/forum_images/lions_bay_900mhz_ambiant.png

Now on to the bad news. This is what it looks like when the phone is ringing:

• http://hoth.gambierrip.ca/~sean/pict/forum_images/lions_bay_900mhz_ringing.png

and THIS is what it looks like when a nuke goes off.... er... when the phone is in use:

• http://hoth.gambierrip.ca/~sean/pict/forum_images/lions_bay_900mhz_talking.png

I took these readings with a handset relatively close to the Canopy SM, and with the Canopy SM the same distance away from the phone's base station as the DLB AP 900 would be. All three readings are with the Canopy SM in vertical polarization, I did not have time unfortunately to try out with horizontal polarization. Though the handset was close for these tests, if you look at the max-recorded marks on the Ringing spectrum, those marks where set when the phone was briefly tested to see if it was working way back at the base-station, so the relative distance of the handsets is not going to change the picture much given the base station's power.

And on an unrelated note... for those of you who watch Battlestar Galactica, Baltar's house on Caprica is in Lions Bay just to the south of the marina, and the nuke you see in the title sequence (and original miniseries) is going off on Gambier Island where I operate.

- Sean

Sean -

What kind of antenna did you have on the Canopy 900?

This is NOT looking to promising based on those results. You cannot defeat interference as strong as -40's and -30's. It would be nice to see what you get for results in h-pol from the mounting location.

Scott

Ouch, that is nasty.  The noise floor in our office is about -40 (cell site a hundred feet away and a huge paging site just down the road that both bleed over), and I can tell you from playing in there that things don't work so hot. 

You can gain some ground by going HPOL on everything, but even if the offending phone was using a nice flat clean antenna pattern you would only get about 20db of relief.  You probably will get less than that based on the wide pattern the base station and phone are using.  Bandpass filters won't help much either as they phone walks over the whole band. 

Then again since they aren't using it, you could just accidentally unplug it and hope they don't notice the same way they didn't notice the phone line wasn't plugged in ;-)

Caleb