Spotwave's Cellular Signal Booster: Two Days, Two Locations, Two Results, One Happy Ending
July 3 , 2007
By BRIAN DIPERT
EDN Senior Technical Editor
A few years back, I decided to get a personal cellular account to supplement my work-provided mobile phone. My wife already had an account with a CDMA provider (Sprint; she just recently migrated to Verizon). So, to maximize our probability of getting a cellular dialtone no matter where we were, I went with a GSM provider, T-Mobile.
Overall, I've been quite pleased with my T-Mobile service; notably, since GSM is SIM card-based, I can easily migrate my account to newer phones as well as test GSM-based phones that companies send me for review in EDN . Quite pleased....albeit with one 'gotcha'. GSM reception is lousy here at the home office. Punch my location into AT&T or T-Mobile's coverage map sites and you'll find that I'm in a coverage null in-between two cellular sites; a T-Mobile base station to the east and an AT&T tower to the west.
AT&T's site claims that my reception should be 'moderate', while T-Mobile rates it as '2 bars'. Both evaluations are, in a word, charitable , and they're only valid for outside usage. Within the house, coverage ranges from non-existent to '1 bar', depending on time of day, what room I'm in, how I orient both the phone and myself, and how still I hold myself throughout the duration of a conversation or cellular data session. You can probably understand, then, why I was glad to stumble across Spotwave's booth at January's Consumer Electronics Show.
The company's Z1900 Cell Phone Signal Booster, which I recently had the opportunity to test-drive, amplifies cellular signals only in the PCS (Personal Communications Service 1850-1990 MHz, aka '1900 MHz') band. If you punch your zip code into the coverage calculator in the upper left corner of the company's website home page, it'll tell you which cellular providers and services the Z1900 supports. In my case, the list includes:
But it doesn't include either Nextel or Verizon. Before continuing, I'd recommend a visit to Spotwave's Learning Center; specifically, I think you'll find the document 'The Adaptive Difference – Intelligent Technology' (PDF) to be of interest.
The company's FAQ claims that "Spotwave's Z1900 can take a relatively weak outdoor signal (eg 2 Bars or -100dBm) then boost it and retransmit it inside the home at a full 4-5 bars on your cell phone (-85 to -80dBm)." Elsewhere, that same document also states "If you can place a call outside your home or small office, the Z1900 cell phone signal booster unit will help you by boosting the signal inside the building. Usually this can be done with one or two bars displayed on your cell phone." The reviewer's guide I received, however, was more definitive: "When considering your review location, I also wanted to note that you must have at least 2 bars of signal on the device outside the location in order to effectively enhance coverage indoors."
Given my earlier-described location's reception attributes (or, perhaps more accurately stated, idiosyncrasies) I knew there'd be no guarantee that the Z1900 could help me here. Nonetheless, I plunged ahead, assisted by my friend Denis and his Danger/T-Mobile Sidekick 3, which reports more precise reception statistics. The table below details the initial signal strength we measured in various rooms of my home, both in dBm and in ASU:
| My Office | Wife's Office | Kitchen |
| 9 ASU (-95 dBm) | 6 ASU (-101 dBm) | 6 ASU (-101 dBm) |
| Bedroom | Living Room | Dining Room |
| 3 ASU (-107 dBm) | 9 ASU (-95 dBm) | 9 ASU (-95 dBm) |
We placed the Z1900's directional reception antenna (Network Access Unit) in the dining room, against the east-facing wall, and connected coax cabling between it and the omni repeater antenna (Coverage Unit) in the southwest corner of the living room. After powering up the Coverage Unit and confirming that we were getting valid status indicator LEDs on both units, we re-measured signal strength and got the following numbers:
| My Office | Wife's Office | Kitchen |
| 6 ASU (-101 dBm) | No Coverage | 5 ASU (-103 dBm) |
| Bedroom | Living Room | Dining Room |
| 5 ASU (-103 dBm) | 12 ASU (-89 dBm) | 5 ASU (-103 dBm) |
One possible interpretation of these results is that the Z1900 boosted reception in the immediate vicinity of the Coverage Unit, but degraded it elsewhere. I have a different interpretation; while the Z1900 may have had a minor positive effect in the kitchen, bedroom and living room, I'm more inclined to explain the before-and-after differences as being the result of the earlier-described usual moment-to-moment and orientation-to-orientation reception variability. The source signal strength was just too weak for the Z1900 to discern and amplify amidst the ambient noise, I suspect. And, to its credit, the Z1900 didn't subsequently try to boost the signal anyway, a move which would have not only further degraded the cellular reception but might have also caused other wireless interference problems.
The reception at our other abode isn't great either, so I thought I'd take the Z1900 up there last weekend to give it another opportunity to shine. Normally, indoors I get between 1-2 bars of GSM reception on my iMate SP5m, along with 1-2 bars of Sprint CDMA coverage on my Samsung SPH -A660. If you punch zip code '96161' into AT&T , Sprint or T-Mobile's coverage map sites , you'll find that the CDMA and GSM signals are strongest along the I80 corridor and, specifically, in Truckee.
We're several miles away from Truckee, but we're also several thousand feet above Truckee, so I placed the Z1900's Network Access Unit in a window, oriented down and towards town. Much better results this time; I now consistently get 4 bars' worth of both Sprint and GSM reception throughout the entire interior of the home. Consider me a pleased consumer, and an impressed engineer, with Spotwave's product performance.
