Picking up second harmonic of local broadcast station!

Long back I used to listen to the second harmonic of the local broadcast station in my Philips Prestige vacuum tube radio. Today I thought of listening to it with my RTL-SDR. This recording shows the fundamental frequency of 684 kHz.

Here is the second harmonic on 1368 kHz. Actually I was searching for broadcast stations from neighbouring districts which I used hear with my Philips Prestige radio earlier. But I could not hear any of them with the RTL-SDR and 80m antenna at a height of about 5m from the ground. My 40-10m dipole is currently having high SWR. I am unable to check the feed point due fairly incessant rains. Shall try to listen to broadcast stations from other districts after getting that antenna ready, as it is at 10m from the ground. I expect better reception with that antenna, though none of these are medium wave antennas. I also checked the 160m amateur radio band which can be seen labelled on the waterfall display. I could not hear anything on that band either.