sdr: update gnuradio am post

1 files changed, 36 insertions, 0 deletions

diff --git a/md/notes/sdr/gnu_radio_receive_am.md b/md/notes/sdr/gnu_radio_receive_am.md
index e193e1a..5a29214 100644
--- a/md/notes/sdr/gnu_radio_receive_am.md
+++ b/md/notes/sdr/gnu_radio_receive_am.md
@@ -3,3 +3,39 @@ keywords:sdr,am,demodulation,gnuradio
 
 #
 
+Lets listen to AM radio stations with AirSpyHF
+
+## Frequencies
+
+For frequencies search at http://websdr.org/ find the nearset receiver
+on the map that support AM broadcast frequencies as it will give a clue
+if propogation of time of the day is ok around your location.
+
+In this example I found only few AM station in 17Mhz range at day time
+to test receiver. 
+
+## GNU Radio blocks
+
+Base blocks for the AM receiver. This blocks have 2 channels and those 
+are to test switch between two radio stations.
+
+![AM receiver blocks](/img/sdr/airspyhf_am_receiver_blocks.png)
+
+| Name | Value | Note |
+| --- | --- | --- |
+| band | 192000 | AirSpy samplerate, closely follows the bandwidth |
+| freq | 1749000 | The channel0 stations frequency |
+| f_channel0 | 0 | If the stations is there, no need to change main frequency |
+| f_channel1 | 10000 | offset from the channel1 find offset from waterfall |
+| fir_dec | 4 | nicely match 48kHz for audio |
+| fir_bw | band/(2*fir_dec) | auto filter calculations for Xlate FIR blocks |
+
+![AM receiver block params](/img/sdr/airspyhf_am_receiver_params.png)
+
+Example when the blocks are running, with arranged GUI's
+
+![AM receiver block params](/img/sdr/airspyhf_am_receiver_gui_.png)
+
+## Links
+
+1. [http://websdr.org/](http://websdr.org/)
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