The Motorola Radius SM50 is an old business band radio that has been converted by many to serve as repeaters. There is plenty of documentation over on Repeater Builder about this radio including service manuals. I decided to pick one of these up to use with APRS. Specifically I planned on setting it up with a weather station.
Since I've had the auto radiosonde running for the last few months I thought I'd do another update. For the most part there is nothing but good to report, with a little bit of not so good as well as a little bit of ugly.
A dummy load is a piece of test equipment that can be used in place of an antenna when testing out a transmitter. They consist of either a single or multiple resistors that absorb the RF power out of the transmitter. Cooling is provided either through fins on the dummy load acting as a heat sink, or through the use of a dielectric oil bath. The amount of RF that can be put into a dummy load is dependent on the wattage of the resistors being used. Likewise the amount of resistance value needs to be properly calculated in order to achieve 50Ω.
This is just a short little update to my post about tracking weather balloons. Last night I had an email from auto_rx about discovering a new balloon. No big deal nothing unusual here, I normally get anywhere from 3-5 of these a day between the 0Z and 12Z launches. When I looked at the details though, something caught my interest. The distance to this particular sonde was 467 km or 290 miles away! This surprises me seeing as my antenna is only about 9 feet or so off the ground. I'm planning an upgrade of sorts to this setup in the not to distant future. I'm hoping to set up a 10m mast and I plan to stick it at the top. Getting higher up in the air should let me detect the sondes when they're a little closer to the ground.
Somewhere around the second or third wind of being a ham I learned about the illustrious J-Pole antenna. It has been around for a while but has been touted as having somewhere around 6 dB of gain. While this seems like an impressive amount of gain for such a simple antenna, it seems that it's really closer to 2-3 dB of gain. Still not bad for an antenna built from the plumbing section.
Just like every other band in ham radio, the 70 centimeter band also has it's own band plan. Similar to 2 m, 70 cm sections of the band allocated to things such as EME, weak signal, satellites, repeaters and simplex. The FCC has allocated 420 MHz to 450 MHz for amateur radio. Unlike 2 m, there is no section of the 70 cm band set aside for only CW.
