Field effect transistor voltmeter circuit principle
The FET voltmeter can replace the vacuum tube voltmeter due to its high input impedance. In addition, its sensitivity is much better than that of the vacuum tube circuit, with a full scale of 0.5V, which is difficult to achieve for most vacuum tubes. The low leakage, low noise 2N4340 is an ideal device for this circuit.
The physical structure of L. SYV is 100% polyethylene insulation; Sywv# for physical foam polyethylene insulated Cable, foaming rate of 70-80%; L. Due to the dielectric loss, the attenuation of SYV solid cable is significantly greater than that of SYWV physical foam cable; Among the commonly used engineering cables, the physical foam cable is still the best transmission performance, the lowest price of the cable, in video, radio frequency, microwave and other bands are so. The test data given by the manufacturer also shows this; L) Library coaxial cable can be used for DC, RF and microwave frequency bands. Differentiating cables by "RF"/" video "is not only insufficient, but also misleading: it seems that solid cables must or can only be selected for video transmission. ; From an engineering perspective, it is more practical to distinguish between "solid" and "foam" cable types; L The characteristic difference between high braided (128) and low braided (64) cables: Yi Aiyi laboratory experimental research shows that in the following frequency band of 200 KHZ, the "low resistance" of high braided cables plays an important role in the shielding layer, so the low frequency transmission attenuation is less than that of low braided cables. However, in the video, RF and microwave frequencies above 200-300 KHZ, the high braided cable has lost the advantage of "low resistance" due to the "high frequency skin effect", so the two high frequency attenuation cables are basically the same.
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