HF GENERATOR using a 68HCx11

  
The GHF1 is a small generator covering the HF and LF band from 30 Hz to 30 MHz in 6 ranges. The sinusoidal signal obtained can be amplitude modulated (AM) or frequency (FM). The GHF1 also has a sweep function. An LCD display 2 x 16 characters allows the frequency, mode and selected for each, the modulation rate, the value of the trip sweep. GHF1 claims to replace the generators of the past, (often called at that time `heterodyne`) with significantly better performance. Unlike these old generators which were type LC, switched coils and lines for variable capacitor for adjusting the frequency, GHF1 is of the type RC, which allows excellent MAX038 from MAXIM.
HF GENERATOR using a 68HCx11 - schematic

HF GENERATOR using a 68HCx11 - img1

HF GENERATOR using a 68HCx11 - img2

At the heart of the scheme the MAXO38. This circuit delivers on its pin 19 a perfectly constant amplitude signal of 2 Vpp. The sinusoidal shape is selected by A1 (pin 4) to +5 V and A0 (Pin 3) to 0. The frequency is determined by the capacitor connected to pin 5. Either C11 or C15 Caj selected from 6 by the switch Sw1 ranges. In each range, the frequency is determined by the current injected into the stud 10 (Iin). This current is equal to U P1 / R3. It is therefore determined by the multi-P1 and voltage follower iC3b. The coverage ratio is around 10. Vernier frequency is added. This is obtained by varying the voltage applied to the pin 8 (FADJI). This voltage is determined by a second multi-P2 and the voltage applied to the + input of iC3b. This entry serves us for FM and sweep. In the first case, we inject a sinusoidal voltage from 400 to 1000 Hz, amplitude 100 mVpp about. In the second case, a sawtooth downward approximately 1.75 VDC. The exact levels of these tensions will be resolved in finalizing by AJ2 (VOBU) or AJ3 (FM) The modulation signals are generated by XR2206 , which is perfect for this mission. They are obtained on the pin 2. The level is adjustable from 0 to max, for P3a. A switching Sw2 skips the sine to sawtooth. The frequency of the sine wave is adjustable from 400 to 1000 Hz, by P4. This ramp is 8 to 50 Hz approximately, P5. The output level of these signals is calibrated by AJ1 The XR2206...



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