by Ken W2KB
RedLantern wrote:Just a quick extra mention, I've seen railfans with external speakers on their scanners with the volume cranked up to the point that when a train was passing by and the conductor keyed the mic, I could hear feedback. I've only seen this once first hand, but I've heard the feedback a bunch of times on my scanner from other parts of the system. That part on the back of your scanner where it says "This device must not cause harmful interference" doesn't just mean transmitting. Even if you only have a scanner, if it's up loud enough that the microphones on the crew members' radios can pick it up, that's as bad as broadcasting, since it essentially is.I wholeheartedly agree that railfans should be careful to not cause audio feedback, though please note that the FCC Part 15 Regulation quoted in part on the labels of many electronic devices including scanners applies only to "unintentional radiators" which means devices that emit radio frequency energy incidental to operation other than an intentional radio transmitter. (The local oscillator circuits in receivers such as scanners are actually very low power transmitters used in the reception of signals, but are not intentional radio transmitters.)So the warning on the back of the scanner does not apply to audio feedback. (Intentionally causing feedback may run afoul of other laws or regulations proscribing certain activities delaying or obstructing railroad operations, but that is outside the scope of the scanner warning label.)
When a 2-way radio (any 2-way radio, not just railroad issued ones) picks up the sound of itself while the microphone key is down, it will produce feedback, which is kind of a loud annoying whistling sound. EVERY receiver on that frequency within range (or over a repeater) will receive that sound, including other train crews in the area, and even the dispatcher. When the crew member is keying the mic, they won't hear it because they are broadcasting (assuming they don't notice it blasting from your car audio system or they assume it's something else like a flange on a curve), their message won't get through, and they won't know that it didn't get through. So keep your scanners at a reasonable volume, or point the speakers away from the tracks.
See: http://www.fcc.gov/oet/info/rules/part1 ... -10-08.pdf for a copy of the regulation.
~Ken :: Fairmont ex-UP/MP C436 MT-14M1 ::
Black River Railroad Historical Trust :: [/url]
Black River Railroad Historical Trust :: [/url]