{"id":4616,"date":"2025-01-17T22:27:02","date_gmt":"2025-01-18T03:27:02","guid":{"rendered":"https:\/\/dft.wiki\/?p=4616"},"modified":"2026-06-08T10:21:47","modified_gmt":"2026-06-08T14:21:47","slug":"sdr-tips-and-tricks","status":"publish","type":"post","link":"https:\/\/dft.wiki\/?p=4616","title":{"rendered":"Gerneral SDR Tips and Tricks"},"content":{"rendered":"<p><strong>INDEX<\/strong><\/p>\n<ul>\n<li>AM vs FM<\/li>\n<li>AM<\/li>\n<li>FM<\/li>\n<li>VHF Airband<\/li>\n<li>Marine Band<\/li>\n<li>Weather Radio<\/li>\n<li>Satellite Tracking<\/li>\n<li>Satellite Reception<\/li>\n<\/ul>\n<hr \/>\n<p><strong>AM VS FM<\/strong><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full\" src=\"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/a\/a4\/Amfm3-en-de.gif\" width=\"256\" height=\"200\" \/><\/p>\n<p>As illustrated above, AM modulates the amplitude of the carrier signal to match the transmitted waveform. FM shifts the carrier frequency back and forth around its center frequency.<\/p>\n<p>This means an AM station occupies a very narrow spectrum band, allowing many stations to be placed close together. FM requires wider bandwidth around the center frequency. In practice, up to 20 AM channels can fit within the bandwidth of a single FM channel.<\/p>\n<p>Frequency also plays an important role. AM stations transmit at lower frequencies, allowing their signals to travel farther than FM, though at the cost of audio quality. AM is better suited for voice, while FM is ideal for music.<\/p>\n<p>A loop antenna (also called a &#8220;donut&#8221; antenna) is a popular choice for AM reception. It has a variable capacitor at the center that fine-tunes to the desired frequency and filters out everything else.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4542\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-04-21-04-41.png\" alt=\"\" width=\"161\" height=\"190\" \/><\/p>\n<p>This works through magnetic coupling: when a circuit&#8217;s inductance and capacitance resonate together, energy transfer is maximized and the desired frequency is amplified while others are rejected.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4543\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-04-21-27-00.png\" alt=\"\" width=\"243\" height=\"218\" \/><\/p>\n<p>This type of antenna is very compact (well suited for low frequencies) and highly directional (resistant to interference and noise).<\/p>\n<table align=\"center\">\n<caption><strong>Sound Frequencies<\/strong><\/caption>\n<tbody>\n<tr>\n<td>CD<\/td>\n<td>10 to 20,000 Hz<\/td>\n<\/tr>\n<tr>\n<td>FM<\/td>\n<td>20 to 15,000 Hz<\/td>\n<\/tr>\n<tr>\n<td>AM<\/td>\n<td>50 to 7,000 Hz<\/td>\n<\/tr>\n<tr>\n<td>Telephone<\/td>\n<td>200 to 3,400 Hz<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<hr \/>\n<p><strong>AM (Amplitude Modulation)<\/strong><\/p>\n<p>Because AM modulation occurs in amplitude, the bandwidth is narrow and AM stations appear as distinct peaks in the FFT (Fast Fourier Transform).<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4523\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2025\/12\/Screenshot-from-2025-01-02-19-04-48.png\" alt=\"\" width=\"926\" height=\"491\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2025\/12\/Screenshot-from-2025-01-02-19-04-48.png 926w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2025\/12\/Screenshot-from-2025-01-02-19-04-48-300x159.png 300w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2025\/12\/Screenshot-from-2025-01-02-19-04-48-768x407.png 768w\" sizes=\"auto, (max-width: 926px) 100vw, 926px\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4607\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-14-20-23-16.png\" alt=\"\" width=\"761\" height=\"691\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-14-20-23-16.png 761w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-14-20-23-16-300x272.png 300w\" sizes=\"auto, (max-width: 761px) 100vw, 761px\" \/><\/p>\n<hr \/>\n<p><strong>FM (Frequency Modulation)<\/strong><\/p>\n<p>Normal Bandwidth<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-4519 size-medium\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2024-12-31-18-11-01-300x193.png\" alt=\"\" width=\"300\" height=\"193\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2024-12-31-18-11-01-300x193.png 300w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2024-12-31-18-11-01.png 766w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/p>\n<p>Wide Bandwidth<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-4517 size-medium\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2024-12-31-18-11-40-300x193.png\" alt=\"\" width=\"300\" height=\"193\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2024-12-31-18-11-40-300x193.png 300w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2024-12-31-18-11-40.png 766w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/p>\n<p>Narrow Bandwidth<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-4518 size-medium\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2024-12-31-18-11-31-300x193.png\" alt=\"\" width=\"300\" height=\"193\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2024-12-31-18-11-31-300x193.png 300w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2024-12-31-18-11-31.png 766w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/p>\n<p>Multiple stations.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4608\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-14-20-50-41.png\" alt=\"\" width=\"761\" height=\"691\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-14-20-50-41.png 761w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-14-20-50-41-300x272.png 300w\" sizes=\"auto, (max-width: 761px) 100vw, 761px\" \/><\/p>\n<p>A 57 kHz subcarrier (phase-locked to the third harmonic of the stereo pilot tone) carries a low-bandwidth Radio Data System (RDS) signal. At only 1,187.5 bits per second, it is only suitable for text.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4520\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2024-12-31-18-45-47.png\" alt=\"\" width=\"761\" height=\"485\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2024-12-31-18-45-47.png 761w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2024-12-31-18-45-47-300x191.png 300w\" sizes=\"auto, (max-width: 761px) 100vw, 761px\" \/><\/p>\n<p>See more information about what RDS can carry at [<a href=\"https:\/\/en.wikipedia.org\/wiki\/Radio_Data_System\">Link<\/a>].<\/p>\n<hr \/>\n<p><strong>VHF AIRBAND<\/strong><\/p>\n<p>Use a vertically positioned dipole antenna with each rod extended to 60 cm. Since dipole antennas are half-wave antennas, each rod represents 1\/4 of the wavelength. This matches the ~125 MHz range used for aviation communication.<\/p>\n<p>Tune with AM or SSB at a bandwidth of 5 kHz. Use squelch to cut the static noise between transmissions.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4566\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-05-21-18-01.png\" alt=\"\" width=\"751\" height=\"659\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-05-21-18-01.png 751w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-05-21-18-01-300x263.png 300w\" sizes=\"auto, (max-width: 751px) 100vw, 751px\" \/><\/p>\n<p>In one instance, I observed an aircraft transmitting silence on one carrier (<strong>#1<\/strong>), then switching to a second carrier (<strong>#2<\/strong>) when transmitting voice.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4597\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-10-21-08-41.png\" alt=\"\" width=\"758\" height=\"761\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-10-21-08-41.png 758w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-10-21-08-41-300x300.png 300w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-10-21-08-41-150x150.png 150w\" sizes=\"auto, (max-width: 758px) 100vw, 758px\" \/><\/p>\n<p>Transmissions are intermittent. Be patient and watch the waterfall for signs of activity.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4572\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-06-18-11-21.png\" alt=\"\" width=\"1550\" height=\"928\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-06-18-11-21.png 1550w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-06-18-11-21-300x180.png 300w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-06-18-11-21-1024x613.png 1024w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-06-18-11-21-768x460.png 768w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-06-18-11-21-1536x920.png 1536w\" sizes=\"auto, (max-width: 1550px) 100vw, 1550px\" \/><\/p>\n<p>Some sources may transmit on multiple channels simultaneously.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4573\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-06-18-22-25.png\" alt=\"\" width=\"1550\" height=\"928\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-06-18-22-25.png 1550w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-06-18-22-25-300x180.png 300w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-06-18-22-25-1024x613.png 1024w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-06-18-22-25-768x460.png 768w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-06-18-22-25-1536x920.png 1536w\" sizes=\"auto, (max-width: 1550px) 100vw, 1550px\" \/><\/p>\n<p>If you are within range of an airport, look up its Automatic Terminal Information Service (ATIS) frequency. ATIS is a 24\/7 automated broadcast providing airport information to pilots. It is a good way to confirm you are within range of the tower. If not, you may still pick up one-way transmissions from approaching aircraft.<\/p>\n<p>You may also notice short, high-pitched transmissions on the airband. These are <strong>ACARS<\/strong> (Aircraft Communications Addressing and Reporting System), a digital system aircraft use to send and receive short telemetry messages.<\/p>\n<p>Standard ACARS uses a global frequency of <strong>131.550 MHz<\/strong>. Some countries use additional frequencies; Canada also uses <strong>131.475<\/strong> and <strong>131.725 MHz<\/strong>. Decoding ACARS is straightforward.<\/p>\n<p>Here is a sample audio file with several ACARS occurrences [<a href=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2025\/01\/acars.wav\">Link<\/a>].<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4664\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2025\/01\/Screenshot-from-2025-01-27-20-58-12_.png\" alt=\"\" width=\"582\" height=\"618\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2025\/01\/Screenshot-from-2025-01-27-20-58-12_.png 582w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2025\/01\/Screenshot-from-2025-01-27-20-58-12_-283x300.png 283w\" sizes=\"auto, (max-width: 582px) 100vw, 582px\" \/><\/p>\n<hr \/>\n<p><strong>MARINE BAND<\/strong><\/p>\n<p>Used for ship-to-ship and ship-to-shore voice communication. Transmitter power is limited to 25 watts, giving a range of about 100 kilometers.<\/p>\n<p>Set each telescopic antenna rod to <strong>45 cm<\/strong>. Target <strong>156.8 MHz<\/strong>, set modulation to <strong>FM<\/strong>, and be patient as activity may be infrequent.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4585\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-08-22-32-37.png\" alt=\"\" width=\"1549\" height=\"878\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-08-22-32-37.png 1549w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-08-22-32-37-300x170.png 300w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-08-22-32-37-1024x580.png 1024w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-08-22-32-37-768x435.png 768w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-08-22-32-37-1536x871.png 1536w\" sizes=\"auto, (max-width: 1549px) 100vw, 1549px\" \/><\/p>\n<table>\n<caption><strong>International Marine Radio Channels<\/strong><\/caption>\n<thead>\n<tr>\n<th>CH<\/th>\n<th>Ship<br \/>\nTransmit<br \/>\n(MHz)<\/th>\n<th>Ship<br \/>\nReceive<br \/>\n(MHz)<\/th>\n<th>Use<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr align=\"center\">\n<td>1<\/td>\n<td>156.050<\/td>\n<td>160.650<\/td>\n<td align=\"left\">Public Correspondence, Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>2<\/td>\n<td>156.100<\/td>\n<td>160.700<\/td>\n<td align=\"left\">Public Correspondence, Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>3<\/td>\n<td>156.150<\/td>\n<td>160.750<\/td>\n<td align=\"left\">Public Correspondence, Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>4<\/td>\n<td>156.200<\/td>\n<td>160.800<\/td>\n<td align=\"left\">Public Correspondence, Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>5<\/td>\n<td>156.250<\/td>\n<td>160.850<\/td>\n<td align=\"left\">Public Correspondence, Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<th>16<\/th>\n<td colspan=\"2\"><b>156.800<\/b><\/td>\n<td align=\"center\"><b><span style=\"color: #cc0000;\">Distress, Safety, and Calling<\/span><\/b>.<\/p>\n<p>Ships required to carry radio, USCG, &amp; most coast<br \/>\nstations maintain a listening watch on this channel.<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>18<\/td>\n<td>156.900<\/td>\n<td>161.500<\/td>\n<td align=\"left\">Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>19<\/td>\n<td>156.950<\/td>\n<td>161.550<\/td>\n<td align=\"left\">Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>21<\/td>\n<td>156.950<\/td>\n<td>161.550<\/td>\n<td align=\"left\">Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>22<\/td>\n<td>156.950<\/td>\n<td>161.550<\/td>\n<td align=\"left\">Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>23<\/td>\n<td>157.150<\/td>\n<td>161.750<\/td>\n<td align=\"left\">Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>60<\/td>\n<td>156.025<\/td>\n<td>160.625<\/td>\n<td align=\"left\">Public Correspondence, Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>61<\/td>\n<td>156.075<\/td>\n<td>160.675<\/td>\n<td align=\"left\">Public Correspondence, Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>62<\/td>\n<td>156.125<\/td>\n<td>160.725<\/td>\n<td align=\"left\">Public Correspondence, Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>63<\/td>\n<td>156.175<\/td>\n<td>160.775<\/td>\n<td align=\"left\">Public Correspondence, Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>64<\/td>\n<td>156.225<\/td>\n<td>160.825<\/td>\n<td align=\"left\">Public Correspondence, Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>65<\/td>\n<td>156.275<\/td>\n<td>160.875<\/td>\n<td align=\"left\">Public Correspondence, Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>66<\/td>\n<td>156.325<\/td>\n<td>160.925<\/td>\n<td align=\"left\">Public Correspondence, Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>78<\/td>\n<td>156.925<\/td>\n<td>161.525<\/td>\n<td align=\"left\">Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>79<\/td>\n<td>156.975<\/td>\n<td>161.575<\/td>\n<td align=\"left\">Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>80<\/td>\n<td>157.025<\/td>\n<td>161.625<\/td>\n<td align=\"left\">Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>81<\/td>\n<td>157.075<\/td>\n<td>161.675<\/td>\n<td align=\"left\">Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>82<\/td>\n<td>157.125<\/td>\n<td>161.725<\/td>\n<td align=\"left\">Public Correspondence, Port Operation<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>83<\/td>\n<td>157.175<\/td>\n<td>161.775<\/td>\n<td align=\"left\">Public Correspondence<\/td>\n<\/tr>\n<tr align=\"center\">\n<td>83<\/td>\n<td>157.425<\/td>\n<td>162.025<\/td>\n<td align=\"left\">Public Correspondence<\/td>\n<\/tr>\n<\/tbody>\n<tfoot><\/tfoot>\n<\/table>\n<p>Check out the <strong>Full List of Channels<\/strong> [<a href=\"https:\/\/copradar.com\/marine\/channels.html\">Link<\/a>].<\/p>\n<hr \/>\n<p><strong>WEATHER RADIO<\/strong><\/p>\n<p>Tuning weather radio is similar to a regular FM broadcast station, but uses narrowband FM (NFM).<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4593\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-10-20-48-19.png\" alt=\"\" width=\"756\" height=\"566\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-10-20-48-19.png 756w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-10-20-48-19-300x225.png 300w\" sizes=\"auto, (max-width: 756px) 100vw, 756px\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4594\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-10-20-48-35.png\" alt=\"\" width=\"756\" height=\"566\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-10-20-48-35.png 756w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-10-20-48-35-300x225.png 300w\" sizes=\"auto, (max-width: 756px) 100vw, 756px\" \/><\/p>\n<p>The same information appears to be rebroadcast across multiple frequencies.<\/p>\n<hr \/>\n<p><strong>TYPES OF MODULATION<\/strong><\/p>\n<p>FSK<\/p>\n<p>This appears to be a standard 2-FSK signal. I captured the spectrum and waterfall images but was unable to decode it.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4588\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2025\/01\/Screenshot-from-2025-01-10-19-58-00.png\" alt=\"\" width=\"758\" height=\"721\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2025\/01\/Screenshot-from-2025-01-10-19-58-00.png 758w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2025\/01\/Screenshot-from-2025-01-10-19-58-00-300x285.png 300w\" sizes=\"auto, (max-width: 758px) 100vw, 758px\" \/><\/p>\n<p>The transmission is likely digital data, where the lower frequency represents 0 and the higher represents 1 (or vice versa). It appears to signal the end of transmission at the lower frequency.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4587\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2025\/01\/Screenshot-from-2025-01-10-19-58-01.png\" alt=\"\" width=\"758\" height=\"721\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2025\/01\/Screenshot-from-2025-01-10-19-58-01.png 758w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2025\/01\/Screenshot-from-2025-01-10-19-58-01-300x285.png 300w\" sizes=\"auto, (max-width: 758px) 100vw, 758px\" \/><\/p>\n<p>By comparison, 4-FSK has four distinct peaks in the FFT, each representing a digital value (0, 1, 2, or 3).<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-4591\" src=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-10-20-39-53.png\" alt=\"\" width=\"558\" height=\"247\" srcset=\"https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-10-20-39-53.png 558w, https:\/\/dft.wiki\/wp-content\/uploads\/sites\/15\/2024\/12\/Screenshot-from-2025-01-10-20-39-53-300x133.png 300w\" sizes=\"auto, (max-width: 558px) 100vw, 558px\" \/><\/p>\n<hr \/>\n<p><strong>SEE ALSO<\/strong><\/p>\n<p>SDR Reference Guide [<a href=\"https:\/\/dft.wiki\/?p=3898\">Link<\/a>]<\/p>\n<p>Linux Tools for SDR [<a href=\"https:\/\/dft.wiki\/?p=4618\">Link<\/a>]<\/p>\n","protected":false},"excerpt":{"rendered":"<p>INDEX AM vs FM AM FM VHF Airband Marine Band Weather Radio Satellite Tracking Satellite [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11],"tags":[],"class_list":["post-4616","post","type-post","status-publish","format-standard","hentry","category-software-defined-radio"],"_links":{"self":[{"href":"https:\/\/dft.wiki\/index.php?rest_route=\/wp\/v2\/posts\/4616","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/dft.wiki\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/dft.wiki\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/dft.wiki\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/dft.wiki\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=4616"}],"version-history":[{"count":10,"href":"https:\/\/dft.wiki\/index.php?rest_route=\/wp\/v2\/posts\/4616\/revisions"}],"predecessor-version":[{"id":5617,"href":"https:\/\/dft.wiki\/index.php?rest_route=\/wp\/v2\/posts\/4616\/revisions\/5617"}],"wp:attachment":[{"href":"https:\/\/dft.wiki\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4616"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/dft.wiki\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4616"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/dft.wiki\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4616"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}