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Measuring the DC volts fed to varicaps in this circuit

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aj_silverthunder

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when 9V is supplied through 56K ohm resistor then how much would be the output volts!how to calculate it!please help me guys!
 

Re: resistance doubt!

it depends on ur Load resistance that u r connecting to it

Added after 11 minutes:


voltage_across_load = (load_Resistance) / (56k + load_Resistance) x 9v
Click to expand...

don't 4get to press helped me
 

Re: resistance doubt!

aj_silverthunder said:
when 9V is supplied through 56K ohm resistor then how much would be the output volts!how to calculate it!please help me guys!
Click to expand...
It doesnt matter what resistance isconnected to the supply untill a load is connected. Mean if you measure the voltage after connecting 56K or 100K to 9volts, the out put will be 9 volts. Cheers
 

Re: resistance doubt!

pranam77 said:
aj_silverthunder said:
when 9V is supplied through 56K ohm resistor then how much would be the output volts!how to calculate it!please help me guys!
Click to expand...
It doesnt matter what resistance isconnected to the supply untill a load is connected. Mean if you measure the voltage after connecting 56K or 100K to 9volts, the out put will be 9 volts. Cheers
Click to expand...
how can it be 9V,for example in this circuit,there u can see a 10k pot and the its output connected to 56K,the 10k varies the voltage to the varicap in order to change the capacitance,my doubt is how can i know the voltage supplied to BB139 when i change the 10K pot,thats my actual doubt!
42_1260207612.jpg
 

Re: resistance doubt!

Why didn't you post the question like your last post in the first place?

The 9V is not supplied to the 56k resistor. The 9V is connected to a 10k pot, then there is a 56k resistor connected to the slider. Looks totally different to me.

If we consider the other side of the 56k resistor (NOT the potentiometer side) as a high impedance for DC. Then there is no load on the potentiometer slider to ground (very high resistor + 56k = very high resistor). the DC-level is blocked on one side by the varicaps, on the other side by the 220nF capacitor.

So what is the voltage on the slider of a potentiometer when you connect the fixed resistor between 9V and GND?

stefaan
 

resistance doubt!

When you turn the pot, its output voltage varies from 0V to 9V.
When the voltage fed to the varicaps changes from 0V to 9V then their capacitance changes that changes the tuned frequency.
 

Re: resistance doubt!

aj_silverthunder said:
how can it be 9V,for example in this circuit,there u can see a 10k pot and the its output connected to 56K,the 10k varies the voltage to the varicap in order to change the capacitance,my doubt is how can i know the voltage supplied to BB139 when i change the 10K pot,thats my actual doubt!
Click to expand...
Yes...its exactly my answer given by Stefen..Cheers
 

Re: resistance doubt!

Audioguru said:
When you turn the pot, its output voltage varies from 0V to 9V.
When the voltage fed to the varicaps changes from 0V to 9V then their capacitance changes that changes the tuned frequency.
Click to expand...
u said when the pot is turned around slowly, voltage to the wiper changes from 0V to 9V,but how can i know how much volt is passing through the pot!
with the help of voltmeter.......!please help me !
 

Re: resistance doubt!

aj_silverthunder said:
u said when the pot is turned around slowly, voltage to the wiper changes from 0V to 9V,but how can i know how much volt is passing through the pot!
with the help of voltmeter.......!please help me !
Click to expand...

connect one probe of meter with ground & the other with the wiper
 

resistance doubt!

so then measuring the volts passing to the varicaps can be done by voltmeter.
 

Re: resistance doubt!

aj_silverthunder said:
so then measuring the volts passing to the varicaps can be done by voltmeter.
Click to expand...
I think you mean to say..."so then measuring the volts passing to the varicaps can be measured by voltmeter" Yes...but the meter should have a high impedeance input or it will affect the readings. Mean as you connect the meter, the frequency will drift....Cheers
 

resistance doubt!

If you want to measure the DC volts fed to the vari-caps then since they don't load down the pot, measure the voltage at the pot.
 

resistance doubt!

is analog voltmeter is good or the digital !
 

Re: resistance doubt!

Digital meter is more accurate , easy to read + high impedeance
 

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