A very useful feature of an operating GUI is the ability to program Preset Frequencies without editing the basic frequency selection menu of the overall DSP. Preset Frequency capability is one approach to implement frequency memory into a GNU Radio DSP. Frequency changes with the GNU Radio sliders and knob style tuning widgets can be tedious and not always 100% satisfying. I include the Preset Frequency memory into all of my DSP’s, whether HF or microwave. Any frequency can be quickly programmed into memory, to allow frequency changes easy and less fraught.
Examples are easy to imagine. Here are a few examples from my station. The 2 meter weak signal calling frequency in our area is 144.2 MHz. Sometimes we meet on the calling frequency and agree to QSY to another frequency for rag chews, say 144.240 MHz. It is easy to enter the 144.240 MHz rag chew frequency into the Preset Frequency Variable field and QSY simply by selecting the Preset Frequency from the Operating GUI. As a result there is no ‘tuning’ up to 144.240 MHz. It is easy to toggle back and forth from the Preset Frequency to the calling frequency and check for friends who might not be aware of the rag chew QSY. And, for rover operation, an aid to confirm that the rig is working while listening on an otherwise quiet band, is to set the frequency of a local beacon signal as a Preset Frequency. How do you set up a Preset Frequency?
To implement the Preset Frequency capability add 2 DSP blocks into your flow graph: a Variable block in which the desired preset frequency is entered, and a Static Text block which will display the preset frequency in the Operating GUI. The choice ‘Preset Frequency’ links the Static Text block to the GUI Chooser frequency selection block. The strategy is to identify a Variable block with a preset frequency in the Value field and a block ID of ‘pre_set_freq’, link that Variable block to the Static Text block with the ‘pre_set_freq’ ID, and link the Static Text block to the GUI Chooser block with the ‘PRESET FREQUENCY’ label. Let me illustrate with a flow graph the Preset Frequency function for an HF SDR DSP.
Let’s look at the Parameters for each flow graph block to implement a Preset Frequency of 3.818 MHz
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