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--- guides:chipcon_cc1020_software_define_radio [2010/12/30 19:33] – [CC1020 SDR] laurenceb
+++ guides:chipcon_cc1020_software_define_radio [2010/12/30 19:43] (current) – active ant laurenceb
@@ Line 19: / Line 19: @@
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+===== Active antenna support =====
+ An "active antenna" with built in low noise amplifier can be used with 3.3v supply down the coax through an RF choke and decoupling capacitors. If a pull up resistor is put between portc pin 2 and 3.3v, sufficient to give around 2 volts on the pin with the pin floating, then the presence of the amplifier can be detected (and closed or open circuit ruled out). Power will then be applied at bootup. Note that avr pins cannot supply more than 20ma. The led on port c pin 0 will flash twice at bootup to indicate a detected amplifier (one 100ms flash and a short 33ms flash as opposed to the normal single 100ms flash).
 ===== Usage instructions =====
@@ Line 27: / Line 30: @@
  With dump.c compiled and the hardware connected to the machine, fire up dump (./dump /dev/tty<port> e.g. ./dump /dev/ttyUSB0 ) and it should say "waiting for the stream to be opened". Then in fldigi/dl-fldigi go to file-audio-stream and locate stream.wav in the same directory as dump. Entering positive or negative numbers between -1 and +1 into dump retunes the cc1020 in steps of 225Hz. Alternatively a frequency in integer Hz can be entered, between 400e6 and 470e6. Always shut down by first stopping playback in fldigi before closing dump, or fldigi may hang. On bootup the cc1020 will be tuned to 434.075MHz.
 ==== Using with AFC ====
- Compile dump.c as before. You will also need python installed. Run autotune.py /dev/tty<port> <squelch 0|1> then open fldigi/dl-fidigi as in the instructions above, but also setting rig control to use xmlrpc. You can now set the SDR frequency using the rig control entry box in fldigi. Any frequency between 400 and 470MHz is possible. The AFC built into the fldigi modem can control the PLL on the SDR to keep the audio frequency around the region of 2.5KHz, and it is also possible to manually retune by moving the red bars on the waterfall display to the transmitter frequency. The squelch option ('0' to enable) allows the SDR to make a somewhat crude attempt to avoid retuning in the middle of a telemetry packet by checking for a squelched signal. Unfortunately at low signal to noise the squelch usually has to be turned off, and at present it is not possible to determine if squelch is enabled over xmlrpc (hopefully this problem can be addressed in a future build of dl-fldigi). Thus there is a 30 second timeout - if there are no squelched periods for 30 seconds the retuning functionality will be re-enabled until there is a squelched signal period. Also, if the squelch slider in fldigi is taken to the bottom of the scale then retune will be allowed at any time.
+ Compile dump.c as before. You will also need python installed. Run autotune.py /dev/tty<port> <squelch 0|1> then open fldigi/dl-fidigi as in the instructions above, but also setting rig control to use xmlrpc. You can now set the SDR frequency using the rig control entry box in fldigi. Any frequency between 400 and 470MHz is possible. The AFC built into the fldigi modem can control the PLL on the SDR to keep the audio frequency around the region of 2.5KHz, and it is also possible to manually retune by moving the red bars on the waterfall display to the transmitter frequency. The squelch option ('0' to enable) allows the SDR to make a somewhat crude attempt to avoid retuning in the middle of a telemetry packet by checking for a squelched signal. Unfortunately at low signal to noise the squelch usually has to be turned off, so under these circumstances a retune will take place whenever the frequency deviation becomes sufficiently large.