On Mon, 19 Sep 2011 12:48:09 -0500, dave wrote:

On Sun, 11 Sep 2011 16:05:44 -0700, Jeff Liebermann wrote:

On 10 Sep 2011 18:27:58 GMT, dave wrote:

Cell sites are a different animal . We were talking about 2-way,
point-to-point, VHF/UHF broadcast type sites.

Perhaps you didn't notice but several of the examples of PIM and rotten
coax induced intermod were for non-cellular systems. The problems are
much the same with any service type. If you have moderate TX power,
magnetic materials in the connectors, and sensitive receivers, PIM might
be a concern.

It's still a math problem. You can predict intermod products from known
frequencies whether the non-linear device is active or passive.

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.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558