
Maine County Deploys Wide-Area Emergency Public Radio Service - wglb
https://www.rrmediagroup.com/News/NewsDetails/NewsID/18899
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frandroid
Now if only cellphones included an AM receiver. And if only modern radios
didn't often strip the AM band out of their devices anyway...

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pkaye
How big an antenna would a cellphone with an AM receiver need?

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AWildC182
AM is around 1Mhz so that's a 300 meter wavelength. For a half wave dipole
(basic high efficiency antenna) that's 150 meters of wire. A vertical antenna
(like on your car) using a ground plane as the other end of the dipole would
be 1/4 wave so 75 meters.

All this said, AM @ 1Mhz propagates very efficiently regionally and they
broadcast at insane power levels so efficiency on your end isn't that big a
concern if you're within a couple hundred miles of the transmitter. You can
get away with a meter long antenna just fine.

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floatingatoll
The press release indicates that they're using RadioSAFE:

[http://www.theradiosource.com/products/radiosafe.htm](http://www.theradiosource.com/products/radiosafe.htm)

> _RadioSAFE Broadcast Systems have the capability of staging hundreds of
> preplanned safety messages that can be selected locally or remotely at a
> moment’s notice and updated minute by minute. Programming can be performed
> at the station or remotely via telco or UHF /VHF transceiver or by LAN/WAN
> if optioned. Redundant levels of message control are provided in the
> RadioSAFE design._

An antenna upgrade is offered:

[http://www.theradiosource.com/products/antenna-
hpr0990.htm](http://www.theradiosource.com/products/antenna-hpr0990.htm)

> _300 Watts, 470-1800 kHz, 20+ Mile Radius Range_

Various warnings are noted about requiring an FCC license beyond certain
transmission power thresholds.

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AWildC182
That's one hell of an inefficient antenna. At a ~1MHz center frequency it's
basically just a dummy load (resistor) that happens to radiate a little. 300
Watts at those frequencies on a long run of speaker wire with a matching
transformer/unun at one end could get you 100s of miles during the day and
1000s of miles at night.

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floatingatoll
Speaker wire generally degrades in sunlight, so that might not be a valid
comparison for the "disaster-resistant permanent installation" market.

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mrguyorama
Weird, I wonder why they chose to build this? Is this sort of an "end of the
world" style system, where it's assumed cell phones, internet, and other forms
of communication are already failing?

Here in Maine we already use AM radio (I think 1600 or so?) to broadcast short
range info about situations that occur on the interstate, using the mentioned
Travelers Information System. Next time I'm in my car I should verify I can
receive AM radio signals

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wglb
There are non-end-of-the-world scenarios in which this is useful. For example,
during the California wildfires, landline and cell service was down. During
the Chicago Marathon, the crowding was so great that cellular service in
downtown was very spotty, and they needed Ham Radio to carry on medical
emergency communications.

