Ramp: Versatile ramp generator
2008/8/18
experiment of the Hartley sweep generator need one 'full functional ramp', i.e, set the sweep center, adjust the sweep width(how far from the center voltage level), and more easily adjust the ramp time, Scope output width(0 to 5v ramp get full screen on scope when use 0.5V/Div) . "The simple man's Spectrum Analyser" have an wonderful ramp generator, see Fig1. Simple man's Ramp generator have all the facility i want and plus use single supply. detail information goto http://www.hanssummers.com/spectruma...asweepgen.html
Fig.1
My Version built with LM358, a most popular OP amp, Final project panel show in following Fig.(pretty?!)
The left Image shown a Crystal response in testing. there is a gap near the top(left 1.5Div). that's should cause by ramp, the saw tooth waveform's pitfall, in fig.4. there is a broken on both raising and falling edge.
Fig. 4
left shown the sync relationship between the ramp and the sweeper
the OP output to Scope X and VCO have same problem. if disconnect the log 10kpot from 6V reference, disconnect the 82k resistor also. that broken is gone. adding decouple caps to 6V reference does not help much. Fig4 left picture proven the scan pitfall cause by the ramp circuit. [i realised this is should be the OP amp's crossover distortion, 1/29 2012]
as the saw tooth generated by charge from OP output, that's constant voltage source, linearity is not perfect. Alan's Lab had a 555 SA project that's just amazing, http://www.vk2zay.net/article/256 , as a bonus, a constant current 555 ramp generator is available, replace IC5a with this circuit,Fig.5. at same time, use the IC5a as the buffer for Fig5, we will get much performance and linearity.
