G8JCFSDR Instructions for Use

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Power Start/Stop Receiving, and close down the SDR software
Display Set display size - See below for other display modes
AF Out The AF output level is set as follows
  • Mute - Click the Mute checkbox on to mute the AF output
  • Slider left to attenuate the output; slider right to amplify the output
  • Volume knob counter-clockwise to decrease AF output level; clockwise to increase AF output level
  • Mouse scrollwheel over the dB digits to decrease/increase the AF output level
Noise Reducer The experimental noise reducer is a level sensitive frequency filter. The spectrum of the received signal is analysed, and any frequency whose amplitude is below the threshold set, is zeroed - when switched on the NR does generate artifacts but I have found that the brain is good at learning to ignore the "twinkling" and pick out signals.

The SDR may be tuned using several mechanisms.

  • Mouse Scroll Wheel

Move the mouse pointer over the digit you want to tune, eg if you want to tune in steps of 100Hz then move the mouse pointer over the 100' Hz digit. When you tune a digit, eg 100Hz, all digits to the right of that digit are set to zero. If you want to lock the tuning rate, then RIGHT Click over the digit you want to lock the rate at, OR LEFT click over the tuning rate indicator, ie the one showing x N KHz etc. 

If you click on the words MHz, KHz, or Hz, just under the main frequency display, then the appropriate part of the frequency is set to ZERO, ie click on KHz, and the KiloHertz portion is zeroed.

Presets 1)    Presets are SET by holding down the SHIFT key, and simultaneously clicking the RIGHT mouse button for a QUICK preset set.
2)    Select a preset by  LEFT mouse click.
3)    You can edit a Preset by RIGHT clicking over the preset you want to edit. (I will be extending this capability to editing the band selectors soon).
4)    Pressing the Ctrl key whilst over a preset will toggle on/off the preset detail display panel

The Bandplans/presets are held in *.BPL files in the same directory as the program. If you add another .BPL the SDR will automatically find it the next time it starts up and add it to the list if available Bandplans.

  • AM selects Amplitude Demodulation
  • BC selects an alternative AM demodulation mechanism which sometimes sounds better for MW music stations
  • USB selects Upper Sideband demodulation
  • LSB selects Lower Sideband demodulation
  • FM selects Narrow Band Frequency demodulation
  • DRM tells the SDR to release the soundcard, & mute the output, so as to enable the use of external s/w such as dream.exe to demodulate the DRM signal - The tuning part of the G8JCFSDR is still fully functional
  • Select the filter bandwidth appropriate for the demodulation mode desired. 400Hz is good for CW, 2.0KHz is good for SSB, 3,4,5 kHz are good for AM broadcasts. 
  • Click Music On for extended Bass response which is good for AM Broadcasts
  • Click IF On for improved selectivity. 
  • Dyn is special kind of filter which automatically tracks the greatest amplitude peak frequency of the received signal, and sets the filter's centre to that peak in real-time.
  • The G8JCFSDR provides fully adjustable filters. The adjustment precision is 10 Hz. To adjust the High frequency cut-off, place the mouse over upper Hz figures; use the mouse scrollwheel to roll the HF cutoff frequency up or down. To adjust the Low frequency cut-off, place the mouse over the lower Hz figures; use the mouse scrollwheel to roll the LF cutoff frequency up or down.
  • To reset the filters to their preprogrammed default pass-bands, Right mouse-click over the cut-off adjust figures.
Notch The Notch facility allows you to notch out,  over -60dB suppression, an interfering signal. The notch facility is particularly useful when two broadcast stations interfere and produce that annoying heterodyne whistle. The Notch facility is implemented by a band-stop filter.
  • Off - Switch off the Notch filter
  • Man - Switch on Notch filter in Manual mode
    In Manual notch mode, the operator adjusts the notch centre frequency using upper Hz figures (mouse scrollwheel), and the width of the notch using the lower Hz figures (mouse scrollwheel). if the Spectrum display is enabled, the notch frequency will be shown as a red line, and if you select AFOut on the spectrum display, you will see the affect of the width adjustment
  • Auto - Switch on Notch filter in Automatic mode
    In Automatic notch mode, the G8JCFSDR continuously and automatically adjusts the notch centre frequency in real-time to notch out the strongest frequency.
AGC The AGC, Automatic Gain Frequency, keeps the output level of the G8JCFSDR at a uniform level - preset to a an output count of 16384. The amount of Gain being applied by the AGC function is shown in the lowest pane when Full display mode is selected. AGC is NOT a good thing, but it is very convenient !  Try to adjust the DRT1's gain level rather than relying on the AGC function if possible
  • AGC is turned On/Off by clicking on the AGC Check Box
  • N - Normal AGC time constants
  • F - Fast AGC time constants
  • S - Slow AGC time constants - Best for SSB reception
  • You can adjust the AGC Attack and Decay time constants using the upper and lower figure displays in the AGC box using the mouse scrollwheel.
The CONFIGURE button lets you configure the SDR
A)    Select audio devices
B)    Set IF Frequency
D)    Calibrate DDS CLKIN
E)    Select Parallel or Serial I/F to the h/w, Default is Parallel - so uncheck it if you haven't got a parallel cable
F)    Select the COM port for Serial mode
G)    Select if you want to use the Intel SPL instead of the G8JCF SPL (If you can find a copy of the iSPL to install)
Scope The G8JCFSDR has a built-in Oscilloscope, Spectrum Analyser and Phase Angle display. Probably the most useful is the Spectrum Analyser since it allows you to see the shape of the received signal, and also activity around the received frequency.
  • Freq - Select Spectrum Analyser mode
  • Time - Select Oscilloscope mode
  • Phase - Display Lissajous figures of Y1 and Y2, ie Y2 is used as the X sweep
  • Filter - Display the filter passband as an overlay onto the received signals (only applicable in Freq Mode)

Display Modes

Comp - Compact
Std - Standard
Ext - Extended