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diff --git a/md/notes/sdr/gnu_radio_receive_cw.md b/md/notes/sdr/gnu_radio_receive_cw.md
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--- a/md/notes/sdr/gnu_radio_receive_cw.md
+++ b/md/notes/sdr/gnu_radio_receive_cw.md
@@ -3,3 +3,41 @@ keywords:sdr,airspy,gnuradio
#
+Lets listen to CW/morse on HAM bands
+
+## Frequencies
+
+The easiest frequencies where CW tranmissions can be spotted are on
+HAM bands. There is option to search for military related ones but those
+are dependent on schedule.
+
+| Bands, KHz Lower Limit| Upper Limit |
+| --- | --- |
+| 3500 | 3560 |
+| 5258.5 | 5264.0 |
+| 7000 | 7040 |
+| 10100 | 10130 |
+| 28000 | 28070 |
+
+## GNU radio blocks
+
+Here is the blocks that monitors the CW on few HAM bands
+
+![AirSpyHF](/img/sdr/airspyhf_cw_receiver_part1.png)
+
+![AirSpyHF](/img/sdr/airspyhf_cw_receiver_part2.png)
+
+This creates tunes to central frequency as channel0 and channel1
+is offset from central frequency. To catch few CW transmissions if there is any
+and allowe to switch between 2 of those with slider.
+
+## Links
+
+https://en.wikipedia.org/wiki/Morse_code
+https://rsgb.org/main/operating/band-plans/hf/
+https://rsgb.org/main/operating/band-plans/hf/3-5mhz/
+https://rsgb.org/main/operating/band-plans/hf/5mhz/
+https://rsgb.org/main/operating/band-plans/hf/7mhz/
+https://rsgb.org/main/operating/band-plans/hf/10mhz/
+https://rsgb.org/main/operating/band-plans/hf/28mhz/
+