On Tue, 20 Sep 2011 00:16:29 -0700, Jeff Liebermann wrote:


Yep. And after I've done the math, I still have to get rid of the
intermod. The problem is not the math. That's well known and easy to
do. The problems a
1. Finding which of the hundreds of signals found on a typical mountain
top is causing the problem.
2. Finding where the likely culprits are located (i.e. which building).
3. Finding any and all sources of non-linearity that are producing the
mixes. That could be anything from a gold on nickel connector to
insufficient reverse power protection on a broadband power amp. 4. Site
management and politics.

It's no longer single "known frequencies" causing the intermod. In
these days of broadband everything, it's fairly wide swaths of digital
noise that's causing the intermod. For example, CDMA phone is 1.25Mhz
wide, WCDMA is 5Mhz, and CDMA2000 is up to 25Mhz wide. The worst part
is that most of the culprits can't be decoded on my service monitor, so
I can't tell for sure if they're causing the intermod.

Cellular phones are a different animal. I worked on fixed and mobile,
mostly analog, mostly FM radios. Theory and practice are quite different.

The tower owner should have an inventory of every transmit and every
receive frequency, plus all the standard I.F., plus nearby external high
powered sources. The owner should have cleared each frequency before it
went on the air, and should not add a tenant if doing so would create a
harmful spur to existing users. This is site management 101.

I don't care how the WL people run their data streams. Cellular folks
don't like high mountains (except for backhaul). I know they use very
advanced techniques to hear signals below the noise floor; keeping that
noise floor as low as possible is of paramount importance when you are
looking at 100 mW devices in people's pockets 5 miles away.

FWIW, Tek has a real nice analyzer that will reverse engineer TDMA spurs.
make time-lapse spectrum analysis, and can even write on a map for you.