Electronic schematics, circuit designs
UHF indicator - wavemeter
UHF indicator or wavemeter is some kind of device that measures frequencies and determines LC circuit frequecy resonance . This device does not need to radiate.
The oscillator is build with T1 and T2 (2 x BF494) and can be adjusted with C1 and Lx. The Lx coil is connected outsite of the metal box and has to be changeble handiest.
If Lx is inductively coupled with another LC coil wich has the same frequency as the wavemeter, then will extract energy from oscillator coil, this will result in a voltage reduction.
With Lx = 2 turns 1mm (SWG19) over 15mm, the ultra high frequency indicator - wavemeter frequency cover is 50 … 150 MHz.
BF494 transition frequency is 150Mhz, if you want to measure higher frequencies change it with BFR 91 wich has an Ft of 250MHz.
If you want to use this uhf indicator as an absobtion wavemeter or rf field measurement unplug from the battery, in this case you have to look for a minimum value on the multimeter.
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Temperature measurement circuit schematic
The multimeter is a measurement device most used by engineers and we use it in this temperature measurement circuit schematic. The temperature sensor is LM335 wich has a linear characteristic of 10mV / K . In the production process this electronic device is calibrated so can provide 2.73V at 00C. LM336 is used as a very precise 2.5V Zener diode; CA3040 amplification can be adjust between 1.08 and 1.10 times thru P1. This temperature measurement circuit can be used for Fahrenheit measurements, in this case the freezing point is adjusted at 320F. At 2120F, P2 is adjusted to obtain 0.9V at output.
So 10F correspond to 5mV. The total current consumption is 10mA.
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VHF AM converter
There are many people who want to listen whats going on in VHF 108 - 132 MHz. This vhf am converter converts a band between 106 and 150 MHz, so you can listen even 2m radio amateurs (144Mhz).
This vhf am converter is build with an vhf amplifier, one mixer and oscillator. After the input signal is amplified with T1 it is applied to a mosfet mixer and combined with the quartz oscillator output.
The tuning is between 6 and 30 MHz. The quartz frequency is fx = fi-fo where fo is output frequency and fi is input frequency.
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