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uhf tunable oscillator - RF Cafe Forums
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| fede-rfcafe
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Post subject: uhf tunable oscillator
Posted: Fri Aug 19, 2011 8:17 am
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Joined: Mon Aug 15, 2011
6:41 pm
Posts: 2 |
Hello I can´t understand something about
this oscillator.
from
http://www.seekic.com/circuit_diagram/Power_Supply_Circuit/TUNABLE_UHF_OSCILLATOR.html
It says that f0 can vary from 350 to 500 MHz.
Wavelength at those frequencies goes from 86cm to
60cm. The planar inductance is much smaller than
the wavelength so why the feed point is at 15% from
ground as it says? There is no impedance variation
along the inductance length, isn´t there?
Thanks
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nubbage |
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Post subject: Re: uhf tunable oscillator
Posted: Sat Apr 14, 2012 8:17 am
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| General |
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Joined: Fri Feb 17, 2006
12:07 pm
Posts: 218
Location: London UK
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Hi
The resonator is based on a quarter wave-length
line. The line length is shorter than a quarter
wavelength because of the tuning capacitor and the
active device output capacitance.
The impedance
along a transmission line does change: it is proportional
to the tangent of (2 * PI * length/ wavelength).
That is why the 50 ohm output tap needs to be near
the ground end.
_________________
At bottom, life is all
about
Sucking in and blowing out.
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Posted 11/12/2012
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