Jim, KC7FG- (1) Most light rail lines, whether subway, surface, or
elevated, operate 750 volts DC, whether from third rail or overhead
catenary. I am not aware of any specific HF communication interference
problems caused in proximity of such systems. Of course there may be some
popping noise when sparking occurs, such as when the pantograph (overhead)
or the shoe (3rd rail) occasionally bounces. Electrified heavy rail lines,
like Amtrak's northeast corridor, run 16 KV feeders on their catenary, at
25 hertz AC. These can produce noise under certain conditions, as you
might imagine. You need to find out on what power supply your system
operates. Contact that transit authority's engineering office. Above all,
go to the area with someone's mobile HF station, and do some operating.
(2) All cellular systems operate in the 800 MHz band. The tower you
describe is either 800 MHz cellular, or 1900 MHz PCS. The filtering on
cellular systems is extremely tight, so it is extremely unlikely that there
will be any interference either to or from any cellular tower, given any HF
mode, or cellular mode. This is particularly true if the system on the
tower is using CDMA (spread spectrum) mode, for obvious reasons.
Regards,
Alan Dixon, N3HOE
Cellular Network Engineer
(WMATA, MTA, Amtrak, certified contractor)
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Original Text
From: C=US/A=INTERNET/DDA=ID/kc7fg(a)juno.com, on 3/2/98 22:31:
My radio club has to move to a new location due to a property sale. One
site we were offered is in a two story building and seems great except
for two issues:
1. In 1999 a new light rail train is being installed next to the
building. This system has overhead wires and will be maybe 150 to 200
feet from the antenna. Would this be likely to generate AC hash on the
HF bands?
The light rail system is currently running in the San Jose area and this
is an extension. We intend to try to see what the noise looks like on
mobile rig in the San Jose area where it currently is operating. It
occurs to us that not only is sparking a common event, but if the trolley
is a mile or two away, any sparking might be radiated through the
overhead conductors. Do I worry too much?
I should add that the club station primarily is used on HF and is a
contest grade station.
2. On the roof of the large building is a 40 foot Rohn tower that is
unused! But about 100 feet away, also on the roof, is a new 1900 MHz
digital cellular antenna, about 30 feet above the roof. I suspect that
the filtering on the cellular equipment is pretty tight but would this be
a problem of us (receiving interference) or would our 1500 watt HF
station get into the cellular equipment?
The roof is about 35 to 40 feet high so this would seem like a good site
if the two issues above are manageable.
Thanks very much for your assistance.
Jim Woods, KC7FG
Lockheed Martin Employees' Recreation Association Amateur Radio Club
Sunnyvale, CA
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