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Field strength meter(reviewed)

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crusoe

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FSM for Bands II and III.
Band II 87.5-108MHz
Band III 174-230MHz

the resistor under the inductor is a variable,just forgot to correct it.the varactor is to provide the variable capacitance.
by varying the voltage across the variable resistance,we vary that across the varactor and hence the capacitance of the varactor.
i wish to display the output voltage on a dc voltmeter.
can anyone help me analyse the circuit and compare it with my other post
 

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1) The voltage that tunes the varactor will be amplified by the transistor because there is no coupling capacitor beween the varactor and the diode.
2) The circuit cannot measure signal levels below the forward voltage of the diode.
3) The resistor in series with the coil ruins the tuned circuit.
4) The diode and 10nF filter capacitor will short the tuned circuit for half-cycles because there isn't a high input impedance buffer amplifier between the tuned circuit and the diode.
5) The output voltage will be about +2.5V without a signal and will be +0.92V with a strong signal.
6) Most BC558 transistors have no gain at 150MHz and above. Some don't have gain at 100MHz and above.

Why didn't you continue on your other post?
 
to audioguru
i'm still working on the previous post,i've noted the corrections.i'm just trying to find a suitable transistor to replace the other one.what software did u use to analyse/simulate the previous project? if u did it manually can u send me a copy,i have to campare it with mine.
also for the fsm should the output voltage without a signal be high or low?
 
If you want to talk about your other circuit then talk on your other post, not here. The other circuit had too many transistors so forget about it.

Use an RF transistor instead of an audio transistor.

I simply calculated the voltage divider of the base resistors, subtracted the base-emitter voltage then calculated the emitter and collector currents and voltages.

A Field Strength Meter should read 0V without a signal and a positive-going voltage with increasing signal strength. If the output voltage changes logarithmically then the meter will show a wide range of levels.
 
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