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How ham radio endures

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161 points CrankyBear | 1 comments | 14 Oct 24 17:26 UTC | HN request time: 0.217s | source
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Animats ◴[16 Oct 24 08:16 UTC] No.41856761[source]▶
Homeland Security tries to get local first responders to join the SHARES emergency radio network.[1] This is 5 HF channels at 5 MHz, and some more around 15 MHz. They test on Wednesdays around noon. Transmission is voice or PACTOR. It's ham-type technology for government emergency response.

Although many local first responders are not on this net, the USCG, military, and Homeland Security monitor it. So it's a way to reach U.S. Government resources in emergencies. This isn't something you access with a handheld, since it requires at least a long-wire antenna. You can get hundreds or thousands of miles of range. The idea is to have something that can get through from a large disaster area.

[1] https://www.cisa.gov/resources-tools/programs/shared-resourc...

[2] https://ema.arrl.org/wp-content/uploads/files/SHARES_Spectru...

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kermatt ◴[16 Oct 24 16:09 UTC] No.41860780[source]▶
Do you have a link that describes the equipment, for those of us who don't yet understand what a long wire antenna is?

Having been in the WNC hurricane area, I have a newfound interest in this stuff.

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1. gabesk ◴[16 Oct 24 17:22 UTC] No.41861499[source]▶
In the simplest analogy, it's just the TV rabbit ears with two wires in opposite directions, except much longer wires, because the frequencies are lower and therefore the wavelength is larger. Those classic rabbit ears are effectively a dipole antenna, which is basically: "stretch a wire out in a line so it's half the wavelength of the frequency you want to receive or transmit on, cut it in half, and send the signal from the middle, out both ends of the cut wire".

https://www.aa5tb.com/dipole.html

Picking that length of wire results in the lowest impedance (kind of analogous to friction) at the radio for pushing signal out to the antenna, but various lengths work with more or less efficiency, and you don't have to send the signal from the middle either if you have appropriate inductors and capacitors to adjust the impedance (it's just the simplest way).

As with most things on the internet these days, it seems the best content is in the form of YouTube videos, so amusingly, this is the best written information I came across after some quick searching:

https://apps.dtic.mil/sti/tr/pdf/AD0684938.pdf