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I'm trying to avoid blogging about the flooding here in Indiana.. It sends me into an emotional fog after seeing firsthand people's houses, just miles from my house, flooded up to the rooftops. I can tell you that there are a lot of heros in our area. You can be one too by helping out with donations to the Red Cross of Indiana.

Automatic backup power

We lose power quite a bit, and when bad weather comes I need it more than ever for radio gear. I have a 13.8v power supply and a 12v battery for backup power. I wanted a simple circuit that would automatically fail over to the backup power if the primary power supply goes out. So here is what I came up with, a simple OR gate built with a couple of diodes:

From Ham Radio

Here I have 2 40v 35amp schottky diodes mounted on a heat sink. The ground (black) from each power source is tied together with the ground out, and the positive (red) from each power supply goes to one of the two diodes. The output of the diodes is tied together to make the positive on the output line. Currently this does not handle charging, but I can leave a smart charger on the battery as long as the charging voltage does not get near 13.8v (the higher voltage will always be the one to draw from in this circuit). I believe there should be a way to charge the battery from the permanent power supply, I'm thinking a resistor and a reversed diode into the positive side of the battery, but I'm not quite sure if that will work right. For now this fits my needs just fine.

The APRS Portadigi

We use APRS in a lot of events here in the Monroe county area. Given the terrain there are a lot of difficult places to transmit from (most of the trackers being low powered) so this box is put together to temporarily place in a dead spot and act as a fill-in digipeater. The box was already used as such a project before I bought it at Dayton. I've got some more work to do on it, and the antenna in the picture is not one that I plan to use permanently (I'll be using a 2m collinear).

From Ham Radio

This is from the first real field test of the "portadigi" outside of my house. It digipeated my packets from a .5w tracker transmission I had as I mowed the grass (yeah, laugh it up). I don't have a good idea of battery life yet since it performed for 16 hours without failing during the first test (with the radio putting out 50watts). I will be taking it to our local field day operations in a few weeks and we will see if it lasts the entire weekend.

I imagine that this could have been useful in SAR efforts last weekend during the initial flooding. However, there needs to be a lot of education and experience in APRS in this area before it can be feasible. We've passed the point in time where amateur radio is useful in providing voice communications during localized emergencies, now let's move towards providing a "situational awareness" with APRS.

Cheers!