New Power meters
The Easter holiday was spent in Luleå together with SM2WMV to construct the new power meters for openASC. The system is designed by Mike, and is using two AD8307 Log Amps together with an ATMega32A Microprocessor. The board will measure both forward and reflected power, do some calculations and send the data out on the openASC bus to be monitored at the operating positions. At SK3W we will use six power meters, one for each band. After the amplifier for each band, two directional couplers are connected to measure forward and reflected power. The directional couples are surplus, made for 2-3GHz, and the coupling is much lower on the HF bands. Since the coupling is different for each band and very low on 160m, we decided to calibrate each power meter individually.
Since we are running Multi transmitters, there is a risk that RF from other bands is entering into the couplers measuring Reflected power and indicating VSWR. The difference in coupling between 10 and 160m is about 30dB, meaning that the Reflected meter for 10m will be about 30dB more sensitive than on 160m. If a signal with 0,1 watt of power from the 10 meter transmitter is entering the 160m antenna, the reflected power on 160m will indicate 100 watt reflected power. This was solved by building small bandpass filters to put in front of the reflected port for each power meter. Mike WMV made a quick design in Elsie, and a couple of hours later they were built, tested and installed!
