Friday, June 01, 2007
Measuring RF-noise by SDR-RX (sdr-14)
Summer is time to check the antennas etc up here in the North when sun shines and low-band dxing at least to East & West is not possible. Two years ago I discoved the rise of noise below 1 MHz on most antennas at my rural-QTH like KAZ and long wires. A bit better with the BOG directed away from the cottage. Soon I noted that the house 500 meters away had started using the ADSL and the connection is via a old-type cable going only a few meters from my cottage´s roof! I used my miniwhip mounted on the fishing rod at about 8 m height (look at the picture) and measured a very big rise of QRM at around 700 kHz. The reception is almost impossible between 200 and 700 kHz. Above 1 MHz the situation is better and above 1200 kHz almost OK with "bottom level" around -130 ... - 110 dB (SDR-14 scale) depending on the antenna. But below 700 kHz the level rises up to - 45 dB when measured only 2 meters from the wire and yeat at about -60 dB at about 30 meters from the wire! The miniwhip itself is quite good for measurements as it really picks up noise easily (though it is a quite active antenna but really needs to be placed away from RF-noise).
Maybe I have to consult the local telephone company ?