The 3G Project – Update!

24May09

Today was Recon day.  That’s short for reconnaissance for those unfamiliar with the term.  It’s a military term that means to explore with the objective of gaining information.  And gain information we did!

I’m happy to report that I was wrong about the distance to 3G coverage.  I took my son with me this morning, and after arming ourselves with my Blackjack II mobile phone, the Compass 885 modem, and a laptop (with an AC inverter to keep the battery from running dry) we headed off in search of Mr. 3G and his family of high-bandwidth.

After placing the Blackjack into field test mode I set it to reject signals unless they were carrying WCDMA traffic in the 1900 MHZ band.  I could have chosen 850 MHZ, but I figured 1900 would be in use.  This filtering kept the phone from automtically locking onto what it judged was the best signal (there are several combinations for AT&T – the Blackjack II is a quad-band handset), and I was able to get a more accurate picture of where the 3G coverage umbrella ends.

When in field test mode, the Blackjack rewards the user with a heads up display of all pertinent connection information, including RSSI (Recieved Signal Strength Indicator), transmit and recieve channels (this number can be used to determine the frequency – more on that later), neighboring cell sites standing by to take over if we stray too far, and power output levels.

With all of that information at our fingertips, we (my son and I) hightailed it north looking for signal.  Rejecting all unwanted signals, we were able to find, and hold,  3G coverage at only 9.5 miles from the house.  At that fringe area of reception we placed the Compass 885 into service and were surprised to find out that the service is actually HSPA, not plain-jane 3G.

HSPA is an enhancement over the original 3G standard, and it is the combination of two separate improvements that were made to address upstream (HSUPA) and downstream performance (HSDPA) limits.   That must be why I recorded speeds of up to 2.2 MB today from a SpeakEasy test at DSLreports.com!

The best speeds were actually obtained at the extreme fringe of coverage while the Blackjack was reporting an RSSI of only -102.  The signal is displayed in dBm; lower-powered applications (such as wireless networks) function with signal levels in the negatives.  The closer the reading is to a zero, the better the signal quality. 

The EDGE service I use at home (with no antenna) fluctuates around -74 to 78 dBm, which is a very usable signal.  -102 dBm is basically right at the cusp of “have it” and “don’t have it”.  At -108 the Blackjack was still able to see the signal (on the drive back home) but I would have likely been unable to pass any traffic across the Compass 885.

So we learned today that quality HSPA 3G coverage is only about 9.5 miles away as the crow flies, and we were able to hold it with no special equipment.  I’m encouraged that with the right directional antenna on a high enough mast, it can be caught at my house.  Oh yeah, I said I’d mention more about how the channel number can be used to determine the frequency.

The basic rule of thumb is (thanks to Jim in Virginia over at EVDO Tips and Tweaks)  if the channel number is evenly divisible by 25, you’re getting a 1900 MHZ signal.  But with the Blackjack in field test mode I get to cheat- it lets me lock out all other frequencies, so I knew the coverage I found was on 1900 MHZ.  Now I know enough to plan my antenna setup so it’s optimized for that frequency spectrum.

To be continued (in a couple of weeks…after I get brave enough to try hoisting a 40 foot mast onto the roof)…

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