Grid antenna question for Alltel EVDO service

technician · EVDO Newbie Joined: 08 Jul 2008 Posts: 4

Hello,

I'm working on installing a EVDO setup for a client but I'm running into speed issues. Inside the house I get intermittent EVDO signals (bounces between 1x and EVDO) but outside on the lake I get decent but sometimes intermittent EVDO speeds. I'm thinking a good antenna is a perfect candidate to stabilize my client's connection. I have line of sight to the tower about 6 miles away over a lake (can see the lights blinking, GPS says just a hair over 6 miles away as the crow flies). I'm thinking a grid antenna hooked up to my clients UM150 would be perfect.

The problem is I'm new to external antennas. Would this antenna (hyperlinktech.com/productfamily.aspx?id=295) be optimal for Alltel frequencies or would it not work at all? Obviously I don't care if I loose some dBI, I just need it to shoot pretty straight to the tower. Am I looking at possibly having to purchase an amp or should I be in luck?

n6gn · Posted: Wed Jul 09, 2008 1:47 pm Post subject:

If you are really LOS to the antennas on the tower and over water, you can probably expect to see about:

+30 dBm (approx EVDO pilot power)
-2 (WAG of cable loss)
+12 (sector antenna gain)
- 118 (pathloss at PCS)
+ 22 (24 dB grid - 2 dB cable/connector loss)

= -58 dBm

IF everything is well pointed.

However, if you are truly LOS to the sector antenna 6 miles away, you should probably see only 20-30 dB less signal on a device's built-in antenna, which would put you at -80 or -85 dBm territory. That should be plenty to get solid EVDO. Are you seeing this much signal on the internal antenna when you are located where you can see the flashing tower lights?

If you are seeing a lot less than -85 dBm, it would be good to account for the difference (no sector antenna pointed your way or ???) before you proceed too far.

I can't tell you whether Alltel is using PCS or 850 MHz where you are but roughly the same bottom line numbers hold for 850 MHz (pathloss is less but so is a given grid antenna). Of course you'll want an external antenna of the same band that the site is using.

n6gn

technician · EVDO Newbie Joined: 08 Jul 2008 Posts: 4

n6gn,

If I take the laptop with the UM150 on it down to the dock I get about three bars on the Alltel software along with EVDO connection and about 300kbps down and about 100kbps up. If I take it up to the house I get very intermittent signal and terrible speeds (very high latency, lucky if I break 100kbps down and 50kbps up). I don't know much about radios in general, but it looks as though I need to get an external antenna mounted either down by the dock or on the roof of the house. Very few trees in the way if any off the roof of the house.

Apparently the elevation of the house is about 50ft higher than the tower, however I believe it's a 300ft+ tower on the other end.

Maybe a yagi would be a better bet for me? I just want to iron this out before spending money on useless or ineffective equipment.

n6gn · Posted: Wed Jul 09, 2008 2:59 pm Post subject:

Well I'm afraid "bars" aren't a very reliable indicator of anything unless you can cross-reference them to know signal levels.
Still it sounds like you have roughly the sort of signal strength you might expect down by the lake (if 3 bars is on the order of -85 dBm, which seems possible).

If you Alltel is 1900 MHz there (PCS) then the cheapest solution offering the most gain will be one of the 24 dBi grid antennas at $50. It's likely that the best yagi you can find will be 10 dB worse than that in practice - whatever the advertisement may say.

If the roof of the house is as good a location as the dock and you can see the tower lights similarly, then it probably doesn't matter much what antenna you use. Almost anything is going to provide plenty of signal/noise ratio and things should work as well as if you were quite close to the tower. I guess this depends upon the specifics of "very few trees". At PCS, hardwoods are on the order of a quarter dB per foot loss. A single 100 foot diameter tree can cost you 25 dB!

If you don't mind doing it in stages, you might just put an antenna on the roof and run a cable down to where you want to use it to verify things. If you can come up with a piece of decent cable, LMR400 or similar, and any antenna, you should be able to verify this whole thing very cheaply. Unless you have a *very* long run of cable, I see no value in adding an amplifier. A good antenna at the dock and even a long run of coax (like 200-300 feet) with no amplifier should still work fine.

n6gn

technician · EVDO Newbie Joined: 08 Jul 2008 Posts: 4

Hmm, sounds like a plan! I don't think Alltel out here is PCS, is there any way I can verify this without calling a tech?

My phone reports this under Technology (RAZR V3m)
dual 800/1900
CDMA 1X-EVDO

n6gn · Posted: Wed Jul 09, 2008 3:43 pm Post subject:

Quickly Googling, it looks as though RAZR supports ##DEBUG. Maybe someone else here can give you details but I suspect that current band/channel/PN and other such info will be available there.
n6gn

karlyn · Posted: Wed Jul 09, 2008 4:04 pm Post subject:

I think the field settings show what the frequency is for the cell site your connecting to. With the connection active, hover the cursor over the QLM window and hit Ctrl-D. Enter diagsmsi for the password. You should get a dialog where the only option that's not grayed out is "Field Settings." Click on that and see if you see 850 or 1900. You should also see RSSI for EvDO and 1x.

I'm writing this from memory and may not have something straight. I'm going to go switch my card from the router to the laptop so I can confirm....

karlyn · Posted: Wed Jul 09, 2008 4:25 pm Post subject:

Okay, only one error in my process above -- it's Field Test instead of Field Settings.

When the field test window opens you'll be presented with all sorts of info. The numbers at the top are the basic (CDMA) info. You want to scroll down the page a bit and look for the numbers below UATI.

Entries of interest are HDR RSSI, Rx Power(dBm), and Band Class. Both HDR RSSI and Rx Power shows your signal strength but RSSI removes the minus sign. Band Class shows the cell site frequency. Band Class where I am is 800 MHz.

technician · EVDO Newbie Joined: 08 Jul 2008 Posts: 4

Which piece of software are we talking here?