I recently designed and put together a mobile setup for measuring field
strength. (More on this later -- it is really slick!) My initial setup was on
HF, to measure power-line noise. I noted something interesting, though. In
some intersections, I am hearing a "tick tick" sound that sounds just like
ignition noise from an engine at idle. It happened at intersections where
there were no other cars, though, and it didn't vary with my engine speed. I
also noted that at one intersection, one and only one of the LED lights was
noisy, with about an S7 noise whenever it was on.
I will see what I can learn about all this as soon as the weather warms up. ;-)
73,
Ed Hare, W1RFI
ARRL Lab
225 Main St
Newington, CT 06111
Tel: 860-594-0318
Internet: w1rfi@arrl.org
Web: http://www.arrl.org/tis
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enjoy.
> -----Original Message-----
> From: Ed - K0iL [mailto:k0il@arrl.net]
> Sent: Friday, December 20, 2002 8:23 AM
> To: 'RFI Reflector'
> Subject: FW: [RFI] RR crossing lights
>
>
> As promised. My connection in the RR business had some info
> on the RR
> crossing lights. Looks like the LED displays are the future
> not only for
> traffic lights, but the RR business as well.
>
> 73,
> de ed -K0iL
>
> -----Original Message-----
> Subject: Re: [RFI] RR crossing lights
>
> Ed,
>
> We have been installing red LED lamp units in our crossing
> warning systems
> for several years. We would like to have LED lamp units at all of our
> crossings, but with approximately 13,000 active warning
> systems it will be
> a
> few more years before all of the old incandescent lamp units
> are replaced.
> The LED lights will operate on AC or DC as most existing
> crossing warning
> systems on our railroad and across the country use AC for
> normal operation
> and DC as a backup when the commercial power is off. Unlike traffic
> signals, crossing warning systems must continue to operate when the
> commercial power has failed. AC operation doesn't
> necessarily indicate the
> presence of a switching power supply, a bridge rectifier on
> the input will
> provide for AC/DC operation. Most crossing warning systems
> use 10 volt
> lamps
> operated by a 12 volt power system. Some LED lamp units use a current
> regulator and a low voltage stack of LEDs to allow operation
> directly from
> 12 volts. Switching power supplies are used in some brands
> of LED lamp
> units because the manufacturer has chosen to stack more LED's
> in series
> than
> 12 volts can drive directly. One popular model uses a 70
> volt stack of
> LEDs
> operated from a switching power supply. The switching power supply
> versions
> are more efficient as no wattage in wasted in current
> regulating circuitry.
>
> Power systems for railway signaling and crossing warning
> systems are never
> grounded. This is done to maintain the integrity of the low
> voltage DC
> circuits which we use to control our wayside (train) signals
> and crossing
> warning systems. One byproduct of our "balanced" power
> systems is that any
> RF hash we produce is not in reference to a ground plane,
> which reduces our
> incidental radiation. Likewise, any external RF that our systems are
> exposed to ends up in common mode on both polarities of our
> power systems,
> limiting the RF voltage appearing at the input terminals of
> our equipment.
> When grounded equipment must be used, such as a VHF or UHF
> radio with a
> grounded negative, we isolate the grounded equipment from our
> main power
> system with a DC to DC converter.
>
> Red LEDs were the first to be cost effective. The
> development of yellow
> and
> green LEDs has reached the point that we plan to start using them for
> wayside signals next year. Burned out signal lamps are one
> of our largest
> (and most frustrating) causes of train delay.
>
> Here are some links to manufacturers of railroad LED lamp units:
>
> http://www.gelcore.com/products/led_signals/r_t/
>
> http://www.safetran.com/
>
> https://www.getransportation.com/general/apps/global_signaling
/GlobalSig
nalingHomePage.asp
> -----Original Message-----
> From: Rob Atkinson, K5UJ
> I'm not yet calling this a problem, but in keeping with the earlier
thread
> on traffic signals, I noticed on the way home last night, when stopped at
a
> railroad crossing, that the big red flashing lights were big red LED
> lights.
>
> Rob Atkinson
> K5UJ
> k5uj@hotmail.com
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