Looking at the DSL spectrum of the new V ... / 2014-03-29

2014-03-29 Looking at the DSL spectrum of the new V ...
Looking at the DSL spectrum of the new VDSL modem I noticed the used frequencies overlap with spectrum used by AM broadcast stations. With a few stations in the area that transmit at reasonable amounts of power, I thought this might be a source of interference. Someone who lives close to the AM transmitter near IJsselstein has noticed the carrier containing 675 kHz isn't used, the frequency of the nearby AM transmitter. Found at HF-dichte modem/router gezocht - zendamateur.com forum in Dutch

When I searched whether someone had looked into this matter before me I found A VDSL tutorial by Frank Sjöberg which notes:
The main source of RFI is believed to be amateur radio (HAM) transmitters. This is because they can be located just a few meters from a telephone line and the transmitting power can be relatively high - up to 400 W in the UK and 1.5 kW in the USA. Even though AM broadcast transmitters use much higher transmit power, they are usually not located so close to the telephone wires. The number of active AM transmitters is also quite small compared to the number of amateur radio users, especially in Europe. Furthermore, AM-broadcast transmitters always transmit the carrier wave, which makes them more stationary and easier to deal with, compared to amateur radio users that can change frequency often and mostly transmit single side-band (SSB) modulated signals.
From a DSL viewpoint amateur radio is indeed unpredictable and a strong source of interference. Time for fiber.

I don't transmit on HF yet, so I don't have any personal experience yet. Looking at the signal/noise ratio graph from the modem there may indeed be a small dip in signal/noise ratio around 675 kHz.

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