Hi Marijan, > I got YU1LM DR2A RX recently receiving signals around > 1843.2 kHz. My main problem is close 300 x 1 kW AM TX > on 918 kHz which splatters around 1836 kHz. I am > anxiously waiting for your long promised Winrad notch > feature! Otherwise great programs, Alberto.
This is the second harmonic. Presumably the signal is 10 kHz wide on 918 kHz so it should be 20 kHz wide (or more) on 1836. A notch would not help at all as far as I can understand, it will be useful to remove carriers inside the desired passband, but outside it should do nothing. The stop band attenuation in the SDR should be higher than the dynamic range of your analog frontend so placing a notch outside would not help. There is another possibillity however. One can use a coherent detector to receive the AM signal at 1836 with say 30 kHz bandwidth. The output I will contain the AM modulation while the Q channel will contain the interference on the AM signal. Your desired signal will appear in the Q channel at 7.2 kHz and the splatter should be well suppressed. I could imagine one could get 60 dB or better fairly easily. The bad side is that any interference on 1828.8 that does not originate in the AM transmitter will also appear at 7.2 kHz in the Q output. You may download Linrad.exe and try it directly on your computer under Windows. The loudspeaker output can then be sent to another computer running Winrad or Linrad. Under Linux X11 it will be possible to have two instances of Linrad on the same computer with the Q signal sent over the internal network. I would be interested in playing with a wav file of this interference case. Things like listening in stereo with the normal signal in one ear (desired plus splatter) and the splatter-free signal (1843.2+1828.8) in the other ear might be extremely helpful in a case like this. Two alternatives: Place the LO at 1825 kHz for everything to be on one side of the DC and 50Hz interference or place the LO at 1833 kHz for the AM carrier to appear at 3 kHz with a second order spur at 6 kHz and a third order one at 9 kHz. The proper solution to your problem is probably to prevent the 918 kHz signal from reaching your mixer. The splatter you hear is most probably generated in the mixer where 2*LO is mixed with 918 kHz. 73 Leif / SM5BSZ _______________________________________________ Winrad mailing list [email protected] http://winrad.org/mailman/listinfo/winrad_winrad.org
