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--- hambasics:sections:wavemodulation [2024/11/24 12:43] – va7fi
+++ hambasics:sections:wavemodulation [2026/07/10 10:00] (current) – va7fi
@@ Line 7: / Line 7: @@
 ===== Amplitude, Wavelength, Frequency, and Period =====
-Here's a good introductory video for this section:((Dave Castler makes his videos for American Licences, which don't completely match the Canadian licences, but the concepts are the same.))
-{{ youtube>lrfLk2kjwMc }}
 Here are two moving waves (press the play {{/play.png}} button on the bottom left corner of the picture).  What's different about them?  What's the same?
@@ Line 41: / Line 37: @@
 </WRAP>
-Note that the reason we're using just 300, instead of 300,000,000 is that we've cancelled 6 of the zeros so that the frequency is in MHz instead of in Hz.
+Note that the reason we're using just 300, instead of 300,000,000 is that we've cancelled six of the zeros so that the frequency is in MHz instead of in Hz.
 Now, here's a related question: how long does it take for each wave to complete one cycle?
@@ Line 73: / Line 69: @@
 Modulation is the process of "encoding" a message (be it voice or digital) onto a radio wave.
-{{ youtube>D9Oa6jaHwtA }}
+===== Activity =====
+If you have access to an HF radio:
+  - Tune in to an AM signal and notice what happens as you slowly move off frequency:
+    - How does the quality of the audio change?
+    - How far can you go before you can't understand the audio anymore?
+  - Tune in to an SSB signal and notice what happens as you slowly move off frequency:
+    - How does the quality of the audio change?
+    - How far can you go before you can't understand the audio anymore?
+FIXME:  Add videos
 ===== AM =====
@@ Line 140: / Line 143: @@
 There are three things to notice here:
-  * The two side bands are 10 kHz on each side of the carrier (same as the <fc #ff0000>baseband</fc> signal!).  It is that distance away from the carrier that represents the audio signal we want to recover.
+  * The two side bands are 10 kHz on each side of the carrier (<wrap hi>same as the <fc #ff0000>baseband</fc> signal!</wrap>).  It is that distance away from the carrier that represents the audio signal we want to recover.
   * Most of the power is going into transmitting the carrier, which in itself doesn't carry any information, so that's a bit of a waste of energy.
   * More fundamentally: even though we say that the signal is transmitted at 200 kHz, in this example, it is really contained between 190 kHz and 210 kHz.  That is, it has a bandwidth of 20 kHz (210 kHz - 190 kHz).  This bandwidth is regulated and depends on the [[intro#full_frequency_list| band used]].
@@ Line 192: / Line 195: @@
 ^Bandwidth |About 2.7 kHz on the low side of 3.875 MHz |About 6 kHz (2.7 kHz on each side of 3.885 MHz, with two gaps near the carrier) |
 ^Pauses |During pauses, no radio signal is transmitted. |During pauses, the carrier is still transmitted. |
+^^^
 ^Relationship |An AM signal can be understood in LSB mode because it contains the lower side band required.  But an LSB signal can't be understood in AM mode because both sidebands and the carrier are needed to process the signal.    ||
@@ Line 207: / Line 211: @@
 {{  fm02.png  }}
-Here, the math is a bit more involved and requires at least 1<sup>st</sup> year calculus to understand but in a nutshell, if the carrier is \$$ c(t) = \cos(2 \pi f_c t) \$$ and the baseband signal is \$$s(t)\$$, then the FM signal will be:
+Here, the math is a bit more involved and requires at least 1<sup>st</sup> year calculus to understand but in a nutshell, if the carrier is \$ c(t) = \cos(2 \pi f_c t) \$ and the baseband signal is \$s(t)\$, then the FM signal will be:
 <WRAP centeralign>