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Re: [RFI] LED traffic signals .. AM Broadcast - bell has tolled

To: "Donald Chester" <k4kyv@hotmail.com>, <rfi@contesting.com>
Subject: Re: [RFI] LED traffic signals .. AM Broadcast - bell has tolled
From: "Jim P" <jvpoll@dallas.net>
Date: Sat, 15 Dec 2007 00:49:22 -0600
List-post: <mailto:rfi@contesting.com>
Re: AM Radio, death knell.

I think they are busy putting nails in their own coffins,
with the insistence of producing copious interference
(so I am not too far off topic on this reflector!) in
their own band via IBOC transmissions.

What with limiting the upper audio BW to 4.5 kHz
(yes, there are wider bandwidth receivers that actually
sound GOOD when tuning in a reasonable BW AM
Broadcast source) and the subtle but detectable audio
processing that 'wears' on one after a period of time
(one TIRES after awhile of the just over telephone-
quality BW audio - that it is refreshing to switch over
to 'standard' analog FM for relief!)

We have one broadcaster, because of RF BW of their
multi-tower array and the 'change' in directivity that
occurs out in the IBOC sideband area produces
noticable amounts of clock-noise in their program
audio at normal listenting levels in the areas of the
metroplex I frequent  ... this is, at best, insanity in
practice for a 'band' that is constantly fighting for any
kind of audience.

And I haven't mentioned yet that non-synthesized
AM receivers that drift just enough to require constant
touch-up so as to keep that IBOC  'clock' whine to
a minimum.

Did I mention also that AM is useless in the single-story
building we lease for operations? FM gets through, but
AM is covered by a barrage of noise from a variety of
sources that IT is render unusable.

So, my own personal opinion,  let AM sink under the
weight of the mis-directed focus group 'driven'
corporate mandates such as the kind that designed
the 'ever-popular' Edsel automobile and now has
chosen IBOC for the AM band.


Jim P // WB5WPA //

----- Original Message -----
From: "Donald Chester" <k4kyv@hotmail.com>
To: <rfi@contesting.com>; <w1rfi@arrl.org>
Sent: Friday, December 14, 2007 2:43 PM
Subject: [RFI] LED traffic signals

> I  live in the country with no traffic lights nearby, so this isn't a
problem with me, but I keep hearing about RFI generated by the new l.e.d.
traffic signals.  Apparently, the noise is due to a switching power supply
used to feed the lights, and the power line leading to the unit acting as an
> Someone I know has one of those LED stoplights about 100 yards from his
house.  It wipes out the AM BC Band when you are in the car sitting at the
light, and he says he can hear it up and down the band and  weaker signals
on 75 and 160 at night are GONE.  He figures there isn't anything he can do
about it at all, except move.
> I wonder if anyone has checked to see if those led traffic lights have
been certified to meet Part 15 standards.  Since they are becoming
ubiquitous in almost every city and town and there are traffic lights
literally everywhere, this could grow into a major rfi problem that rivals
or surpasses BPL.
> Perhaps the AM broadcast industry would get involved, since this stands to
hurt them severely.  Over 90% of the prime time radio audience during
morning and evening hours is made up of commuters, and most listeners will
simply switch over to FM if they start getting interference at every traffic
light.  This could become the death knell for AM broadcast radio, with its
odds for survival already marginal at best. Those switching power supplies
could easily be fixed with a little filtering.  I'm not even sure that
shielding would be required.
> This is a problem that needs to be addressed NOW before the overwhelming
majority of traffic signals nationwide are replaced with noisy l.e.d. ones
and the problem becomes impossible to remedy.
> Don k4kyv

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