[IRCA] The Increase of AM Noise

["Rene Tetro" <rtetro@xxxxxxxxx>]

Fellow Hams and DXers,

The following is the text of a message that I sent to our company's engineering email list concerning the increase of electrical noise on the AM band.  I thought you might find it interesting.  We hams and dxers are not the only ones who are concerned about the trend of increased electrical noise.  Broadcasters are, as well, and have a lot at stake in doing something to see the situation is improved.

73,
Rene'
W2FIL,
Lansdale, PA

---------------------------------------


There's been a lot of discussion recently on various engineering sites and publications, and among radio dxers, about the deteriorating state of AM coverage.  I would obviously concur with this (who couldn't?).  The situation is evident to anyone who listens to AM radio, and it seems to be getting worse as time goes by.

Laying IBOC and BPL aside for a moment, which have their own set of interfering dynamics, there are other issues that are becoming more predominant on the AM band.  Most notably there has been a dramatic increase in electrical noise on the band in recent years.  This is getting worse and is having the effect of dramatically reducing coverage in many cases.  All of the latest electronic gadgetry seems to be the major cause of "dirty power lines" and other noise.  Among the devices that seem to be most culpable are medical devices, computers, light dimmers, and - one of the biggest offenders - newly designed electronic, SCR controlled, traffic signals.  There are so many other devices, they become too numerous to mention.

What concerns me as an engineer is the effect this is having on listenership, as well as the practicality of continuing to use the 0.5 mV/m contour as an indication of normal daytime coverage.  From listening to our stations and many others, it appears that a more realistic figure would be 2.0 mV/m or even higher in extremely bad situations - as much as 5 or more millivolts.  

I have had discussions with our general manager and many others over the past few years, including sales people, listeners, and others concerning this phenomenon.  I get calls regularly from listeners who complain that they have great difficulty in hearing the stations because of "static."  Be they managers, sales people, listeners, or others, they all say the same thing:  "The station's coverage just isn't what it use to be!"  And I have to agree with them.  WNTP, for instance, does not have nearly the daytime coverage it had when I worked here in the early 80s...even with one less tower and an loosened directional pattern.

As far management and sales are concerned, and therefore from the standpoint of those who are largely non-technical, the first thing to come under suspicion is a change in the transmission system (either transmitter, or antenna, or both).  When one performs a quickie proof on the antenna system, and checks the power/impedance/etc, all is found to be normal.  On WNTP, for instance, our Inverse Distance Fields on all radials are pretty much exactly what they were in 1986 when the system was built; but, electrical noise has reduced usable coverage by at least 1/3.  

I know that we are not the only stations who are experiencing such problems.  And it is not just broadcasters.  The problem also exists for hams and other users of the radio spectrum.  It is evident across the nation.  In a large market such as Philadelphia, the electrical noise can be incredible.  For instance, attempting to listen anywhere near the electrified 25,000 Volt, 25 Hz powered commuter rail lines is next to impossible.  This is especially evident on the Amtrak Pennsylvania main line near Downingtown and Thorndale, along which Business Route 30 runs for several miles.  When such lines extend for great distances along heavily used roads, it becomes a major issue.  Another example is a traffic light located about a mile from both our transmitter site and the site of KYW.  Since new circuitry was installed a while ago, it is impossible to listen to either WNTP or KYW (both of which are 50kw) or WFIL (which is 5kw).  The buzz from the light circuit creates a loud hum that overpowers the audio of these and other stations.  "Buzzes" from other traffic lights are just as bad.

I fear that all of this does not bode well for the future of AM radio.  Electrical noise is reaching a point of being such a concern that IBOC and BPL, as issues, pale by comparison.

I say all of this to ask a simple question:  is there some way broadcasters can combat the encroachment of noise on AM?  I the answer to that question.  We, as a society, are too dependent on these new technologies to expect a turn-about.  Will greater regulation on electrical devices solve the problem?  Perhaps as a long-term solution; but in the short term I only see the situation getting worse.  It seems to me that broadcasters, either through the NAB, SBE, or other organizations, (perhaps in cooperation with ARRL and other interested parties) need to band together to put a stop to the construction and deployment of electrical devices that pollute the airwaves.  The FCC and other regulatory agencies must place more stringent requirements on devices so as to greatly reduce or eliminate unwanted electrical noise.  If something is not done soon, we will have reached the point of no return, and broadcast AM will become a medium whose practical applications are forever relegated to history.  Likewise, amateur radio and other users of the LW-MW-HF spectrums face a similar fate.  For broadcasters, there is too much at stake from a business perspective to allow that to happen.  As AM broadcasters, it is our duty not to go down without a fight.  

Rene'

Rene F. Tetro
Chief Engineer
Salem Communications - Philadelphia
WNTP-AM / WFIL-AM
117 Ridge Pike
Lafayette Hill, PA  19444
Phone:  610- 828-6965  Extension 41
Fax:  610-828-6725
Email:  rtetro@xxxxxxxxx

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