Hams should seldom have to suffer harmonics or spurious emissions from AM
broadcast stations.
Every AM broadcast station is required to perform annual measurements,
searching for these types of problems. I contract to perform spectral
measurements for most of the AM stations within a 100 mile radius of my home.
I have the necessary equipment and travel to within approximately 1 kilometer
of each transmitter site. I measure each station’s occupied bandwidth, measure
harmonics, up through and including the 6th and search for spurious signals,
below, in and above the broadcast band. Each station receives a written
report, including data and graphs. The station is required to retain these
reports for a period of two years. Measurements must be performed annually,
with no more than 14 months elapsed between successive ones. See 73.44 and
73.1590.
My experience indicates that it is rare for an undesired emission to suddenly
appear. These types of errant signals, almost always, occur gradually. I keep
copies of my reports and always compare any new report with the previous one.
I have notified stations that their spectral purity is gradually deteriorating.
This may be a sign of failing electrolytic capacitors. Notification of an
impending problem allows the station to make corrections, before falling out of
compliance with FCC regulations.
If you encounter a problem with an AM station, you might ask if you could see
their last two NRSC 2 measurements. If there’s a problem, it is possible that
these measurements have not been done for several years. If you are being
stonewalled, file a complaint with the FCC. Don’t hold your breath for a
response, however. The field enforcement division was almost eliminated,
several years ago.
I agree with Rob, in that many AM stations have acquired translators on the FM
broadcast band. Regulations, with some exceptions, require that the parent AM
station remain on the air, in order for the FM translator to exist. In many
instances, management and programming have determined that the FM signal is the
only one that is marketed or valued. I am aware of AM stations that are only
mentioned in the required, top hour ID. Otherwise, all one hears is the FM
frequency being promoted. This is a strong indicator that the AM transmitter
plant may be the victim of benign neglect. Many of these stations do not have
anyone on staff with technical competence. In a crisis, a contract engineer
will be called in to put out the fire. However, this is no excuse for
violating the rules and regulations.
Gary Peterson
KzeroCX
Rapid City, SD
...stations should budget for maintenance like
this. It's a management problem. A lot of what's really going on
with an AM like this is revealed here:
WNTS-AM also broadcasts its primary channel from this additional transmitter
W280FR 103.9 FM Beech Grove, IN (99 watts)
In other words, the AM has a LPFM and nowadays, that's the signal that
matters to management. In a lot of cases like this, the AM is only on
because it justifies the license for the FM. A lot of licensees with
LPFMs simulcasting, let the AM go because they think no one listens to
it; in this case the class D FM covers most of metropolitan
Indianapolis. That's where the license value is, plus the AM DA real
estate. I'm not criticising the station engineer, but years ago,
this would have been caught a lot sooner without a ham having to
complain about it.
Rob K5UJ
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