Behavior of different protocol signals in a single system - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues - primarily having to spend time purging garbage posts from the board. At some point I might start the RF Cafe Forums again if the phpBB software gets better at filtering spam.

Below are the old forum threads, including responses to the original posts.

-- Amateur Radio
-- Anecdotes, Gripes & Humor
-- Antennas
-- CAE, CAD, & Software
-- Circuits & Components
-- Employment & Interviews

-- Miscellany
-- Swap Shop
-- Systems
-- Test & Measurement
-- Webmaster

daverali

Post subject: Behavior of different protocol signals in a single system

Posted: Sun Apr 15, 2007 12:48 pm

Lieutenant

Joined: Sat Sep 18, 2004 7:27 pm
Posts: 4
Location: Texas

I have a in-building antenna system where I have threee different Wireless Providers. Two of the providers are GSM based and the third is a CDMA provider. The system is designed to provide a ubiquitous -85 dBm or better coverage in the coverage area. The power per carrier levels for each of the three providers is +4 dBm for each RF carrier. When the two GSM Providers came on the system at the said power levels for eac of their RF carriers, the RSSI measurements matched the design predictions. However, for the CDMA Provider the RSSI levels in the coverage area are atleast 10 dB or more lower than the GSM levels. And note that all are coming into my antenna system at the same power level per RF carrier. Also, all operate in the same vicinity of the spectrum (1900 MHz). With this strange behavior, while the two GSM Providers are satisfied with the coverage provided, I am unable to provide the same level of coverage to the third provider.
Any thoughts?

Thanks,
Daver

_________________
Daver Malik
RF/Wireless Engineer

nubbage

Post subject:

Posted: Mon Apr 16, 2007 5:33 am

General

Joined: Fri Feb 17, 2006 12:07 pm
Posts: 304
Location: London UK

I guess you have done all the obvious things to eliminate strange component behaviour, like frequency sweep the combining/splitting system, the feeders and the antenna with a VNA for S11 and S21 over the entire band?
Also you need to check the vertical pattern of the antenna and see if, at the CDMA frequency, there is an excess up-tilt or down-tilt due to element phasing. On the other hand, perhaps you are using multiple distributed antennas around the building?
If nothing unusual comes from those investigations, then my first thought is this problem is due to unfortunate vector cancellation. If the average level across many parts of the building is consistently 10dB below expectation, however, this is unlikely to be the explanation. It would only present itself in certain areas but not in others.

Posted 11/12/2012

Webmaster:

Kirt Blattenberger,

BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website: AirplanesAndRockets.com

My Daughter's Website: EquineKingdom