[BC] 9th FM harmonic causing interference

[Warren Shulz]

To insure compliance you need a calibrated line probe and compensation
chart for the 9 octave frequency change.  Dielectric products makes a
directional probe that can be calibrated from FM band to 9th harmonic.
You cannot connect an analyzer to a random probe and get usable results.
Best would be with a tracking generator  establish the sensitivity curve
for the directional probe.  This is not a trivial measurement to get
accurate results.  Its one thing to get an estimate and a whole other
matter to 
Obtain FCC qualified - 80 dBc results.

Warren Shulz
WLS CGO

-----Original Message-----

 From: Phil Alexander

The harmonic emission limit requirement is spelled 
out for FM's in 73.317(d) which covers all frequencies 
removed from the carrier by => 600 kHz. If you meet 
this requirement you are compliant with the Rules WRT 
your 9th harmonic. 

Thus, the first recommendation is having an occupied
bandwidth (OB/W) scan of your emissions on a calibrated
spectrum analyzer measuring by sampling your TPO on
the coax to the antenna by someone who knows the
correct methods. (NOTE: If IBOC was recently installed
the rules required a scan which should be in your files
because the Rules require 2 year retention.)

If you are compliant (essentially -80 dBc or lower) 
then the problem may belong to the cellular operator. 
For example, an overload or rectification in their 
system could **generate** harmonics from your fundamental
**internally** from something as simple as a poor 
connection.

Most measuring services will do an OB/W scan and 
engineering report for a few hundred dollars enabling 
you to inform the cell company that your signal is 
leaving clean and compliant, or, if that is not the 
case, the report will give you a starting point for 
a discussion with your transmitter manufacturer.

IOW, make sure your own house is clean first, and
if it is, lay the problem where it belongs, at the
feet of the cellular operator.

Phil Alexander, CSRE, AMD

-----Original Message-----
>From: Ron Cole <rondcole at gmail.com>
>
>Has anyone one had an issue with 9th harmonic interference
>with Cellular networks?
>
>It looks like it may be more common with with stations that
>are running low-level combining for IBOC.
>that operate on 92.1 - 94.3 Mhz.