Oscillator Measrement

Hi all,

Can someone please explain this statement to me, "Oscillator is ruuning at 6 dB pad (attenuator) to avoid frequency pulling".

https://www.youtube.com/watch?v=7jyCchLAu1o

I know about frequency pulling but I didn't understand the above statement.

Thank you very much.

Ghurki said:

"Oscillator is ruuning at 6 dB pad (attenuator) to avoid frequency pulling".

Click to expand...

We can assure -12dB return loss even if load is open or short.
So we can avoid or alleviate load pulling.

a 6dB pad is another way of saying the the oscillator goes in to a attenuator that attenuates the signal by 6dB.
To add attenuators between different RF stages is a classic way of isolating them so they can't influence each other, in this case so that the load the oscillator sees wont affect it's frequency.

This works because as the signal from the oscillator travels out from the oscillator thru the attenuator the signal get dampened 6dB, if there is a miss match of the impedance at this stage you will get a reflected wave back to the oscillator.
This wave has to travel back thru the attenuator and will therefore get attenuated by 6dB as well.
So if there was a sever miss-match like a complete short or open circuit the most energy that could travel back to the oscillator is -12dB, that corresponds to a SWR of 1.67 with is a well matched circuit.
So the Oscillator always sees a perfect match regardless of what the load is after the attenuator.

Harry Zachrisson said:

a 6dB pad is another way of saying the the oscillator goes in to a attenuator that attenuates the signal by 6dB.
To add attenuators between different RF stages is a classic way of isolating them so they can't influence each other, in this case so that the load the oscillator sees wont affect it's frequency.

Click to expand...

What do you want to say as conclusion ?
I can't find out any useful thing in your append at all.

you are all right. The oscillator runs at one frequency depending on what frequency the resonator is tuned to. But the resonator is also coupled to the outside world. So outside load impedances other than 50 ohms can change slightly the resonant frequency of the resonator. By adding a 6 dB attenuator, whatever the load impedance is, its load return loss gets 12 dB better thru that 6 dB pad, and looks more like 50 ohms.

People like Kurokawa wrote load pull effect papers you could study