how to use a vco for radio

[nanoman]

hello
i am New in this forum, excuse my inglish it's very bad, i need help for one idea
i want to use the vco of an analog satelite receiver for tune fm radio and i want to give anathor life for this receiver and use it for build fm preset radio be cause i am find a variable voltage in to the tuner of the satelite receiver it's change between 1v and 17v when i change the frequency
now my questions is
can i tune any fm radio with two varicap diodes , when yes, do you have schématics or nother ideas.....?
or i must use a vco fm tuner like the tuners of a car radios ?
thanks for your help :idea:

 

[tony_lth]

I really don't understand your queation. The VCO can only be tuned by voltage, you can't directly use the varactors to tune VCO. The VCO generally is based on varactors, so you can use varactor diode to build your own oscillators.
FM is laways about 100M, but satellite receiver use VCO about several GHz, so the satellite receiver VCO can't be used for FM.

 

[davenn]

hello
i am New in this forum, excuse my inglish it's very bad, i need help for one idea
i want to use the vco of an analog satelite receiver for tune fm radio and i want to give anathor life for this receiver and use it for build fm preset radio be cause i am find a variable voltage in to the tuner of the satelite receiver it's change between 1v and 17v when i change the frequency
now my questions is
can i tune any fm radio with two varicap diodes , when yes, do you have schématics or nother ideas.....?
or i must use a vco fm tuner like the tuners of a car radios ?
thanks for your help :idea:

An analog, or digital for that matter, satellite receiver DOES NOT cover the FM broadcast radio bands (88 - 108MHz)
Satellite receiver tuners cover ~ 900 to 2200MHz. Us amateur operators use them on the 1200 MHz area for receivers on our ATV systems on 1250 and 1280MHz.

cheers
Dave

 

[nanoman]

hello
thank you for the responces
i just want to use the variable voltage of the satelite tuner to tune or (drive) fm coil like this example, see the atachement
i now, it's not easy but is it possible to do?
but when you have another suggestions i'l take it.
thank you.

 

[betwixt]

If all you want is a tuning voltage why not use a potentiometer? If you disconnect the tuning voltage from the oscillator inside a satellite receiver, in almost all cases it will nor work as you expect. The voltage comes from a PLL which in turn is fed from the original satellite receiver's local oscillator. If you break the signal or DC link the voltage will probably go to zero or to as high as it can as it attempts to regain control again.

Just connect a potentiometer between ground and a stable voltage and connect it's wiper to the resistor in your schematic.

 

[nanoman]

i want to use the satelite receiver because i want to build fm preset stations and when i change the chanels of the receiver with the remote control i tune
the fm radio , and i want to give another live for the satelite receiver because the analog systems will stop and replace with the digital technologie. :idea:
i hope my inglish is easy to anderstand.
for bitwixt thank you i am finding the idea of the potenciometre in the, web but it's not what i want.

 

[betwixt]

It will not work.
You must understand how a PLL works. It samples the local oscillator frequency, divides it by a fixed number then compares it to a reference frequency to produce an error voltage which in turn goes back to tune the local oscillator. By changing the division ratio you produce different frequencies while still maintaining the stability of the reference oscillator.

What you propose is to monitor a different and unconnected local oscillator, the one in the satellite front end, and use it to lock the FM receiver. The PLL would not be able to lock to an FM station without being able to sense its own local oscillator frequency.

You can still use the satellite receivers tuning voltage but it would not lock to the FM station, in other words you could equally well use a potentiometer to set the tuning.

 

[nanoman]

ok, thank you bitwixt i am anderstand now, i can't modifi or cut the original osillator because the vco must work with it, maybe i can use interface with a servomotor to drive a potenciometer, it's just idea.:idea:
i shall say to you when i have new.