I declair a fix point as a reference point in the middle of a midsize hall (40m x 10m). On both ends there are the two access-points. Fist access-point works on channel 1 with power setting 3 Second access point on channel 6 with power setting 3.
I place the first 7921 phone, start the function SiteSurvey and stop it after 1,5 minutes. After that I read the sitesurvey result from the phone over IE. (The delta between min. RX and max. RX is ~8dBi)
I do this 5 times ( prevent for a temporary outbrake) and calculate the results (add up and divide it with 5)
And here is my problem. Like Raul told, I think too, that a different of 5-10dBi (realy*) is OK between phones on same typ (7921).
But, which is the delta between phones where I can say "it's not ok , the phone is faulty"??????
* Think Cisco told for Voip: do sitesurvey with the phone. If you have a good phone you mark your cell border with -67dBi. With the next phone you have -77dBi on the same border, only (10dBi delta between phones)
We have over 2000 7921 / 7925 phones. If they get dropped a few times the antenna connector disconnects inside the phone. In fact, we just went though an entire hospital replacing bad phones ... Out of 300 phones 50 were replaced...
Check for little chips or cracks on the antenna of the phone with the bad signal...
"Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin