Dear LF,

 

the "big buzzer" is on again today... it's most certainly the EFR transmitter at Budapest-Lakihegy, 135.6 kHz:
http://maps.google.com/maps?f=q&hl�amp;qG+22+17+N,+19+00+22+E&ie=UTF8&z&llG.373866,19.004492&spn=0.003426,0.005488&t=k&om=1

 

Several times I could hear relatively weak sweep signals, probably generated by a network analyzer used for antenna testing. Most of the high power tests were apparently applying a continuous 010101 sequence at 202.55 baud FSK, causing the hum-like sidebands. Reducing the receiver gain by 7 dB cleared up the severe overloading effects on the LF grabber. This left a set of thin red lines spaced at 101 Hz, reaching up to about 136.7 kHz. However with real data, the sidebands will smear out and clutter the lower half of the band during the telegrams.

 

Spectrum taken 06-09-11 6:41, 135.600 kHz at 1100 Hz.

Assuming that we will have to live with this beast, I wonder if there is a way to extract its teeth. A signal processing software could decode the data, model the filter transfer function and estimate the FSK transition times. Then one could generate a local replica of the signal, and use that to cancel it. Seems related to a key-click filter algorithm ( http://www.dxatlas.com/Rocky/ ) - has anyone in the group tried to implement something similar?

 

Kind regards

Markus, DF6NM