strategy for designing a locking component in PLL

[yefj]

Hello,there is a circuit shown below taken from the attached article, where we put a YIG signal to a cavity resonator(from A to B) .
Then for feedback we lock on the point of the dip.
this dip is supposed to be a resonance of a cavity.

resonance is when the magnetic energy equals the electric energy maximal energ is stored in the cavity.
So why for feedback we lock on the cavity at this point?
Thanks.

 

[biff44]

Hello biff44,i have some question to better understand your explanantion:
1.the main oscillator gets a signal from the YIG .The oscillator sends back a signal with an amplitude depending on the oscillator resonance.
regarding what you say about the "angle" below.by angle i understand that the phase also changes when we move away from the resonant frequency?
Why do you say that the phase of the reflected signal will change?
" the reflection coefficient angle of the Q=59000 resonator is ZERO degrees."

2.So what is the logic of putting this carrier nulling section if need to compare the YIG RF signal with the main oscillator RF signal?
"carrier nulling section that removes the carrier and only lets the noise sidebands come out of the mixer output So it will not be so simple to tune the yig oscillator until the mixer output is Zero Volts DC, since there is no carrier to generate the null!



3.regarding the servo amplifier how do you propose me to check in my lab the my servo amplifier will succeed in doing the locking.
i can record the signal coming out of each device. also i can create a transfer function
how do you propose me to convert this recorded data into a simulation?

View attachment 187136

reflection phase shift off of a simple resonator looks like this:

Note that at the exact resonant frequency, the reflection phase is zero.
You can get a different phase curve if the resonator is undercoupled or overcoupled, but they all pass thru zero phase at resonance

--- Updated Dec 29, 2023 ---

Carrier nulling section is not necessary. it is typically only used with high power oscillators, where they would blow out a mixer used as a phase detector

 

[FvM]

Carrier nulling section is not necessary. it is typically only used with high power oscillators, where they would blow out a mixer used as a phase detector

Sure about this? The point isn't discussed in original paper but I think it's necessary to zero carrier leakage in circulator which is typically higher than -36 dB minimal reflection from resonator.

 

[yefj]

Hello Biff44,I understand the logic and its a real eye opening.and i agree with you.
In the diagram below they did do carrier supression with A1 and phi1 but then they amplified the whole signal.
What is the purpose of first nulling the carrier and them to amplify it?
it seems to me like the mixer will compare the YIG signal to amplified white noise and i dont see any logic in that.

 

[D.A.(Tony)Stewart]

The Circulator b reflection is mixed with phi1 to modulate phi2 to change the YIG differential flux shown as Varicap and thus frequency.

Degrading the suppressed carrier reduces the dynamic range or SNR of the control for the VCO. (perhaps)


That plot looks like the voltage attenuation of a dielectric resonator.

Note that the mixer output when positive feedback accelerates the loop, it spends less time in that half cycle. But since integrated f = phase adds apole, the f capture range total depends on the bandwidth of the loop filter near unity gain and its phase margin. Iff VCO gain is reduced at offset f or this reason the BW
must be greater in loop filter than max error f. So calibration of s parms of each unit is critical.

Remember. the DBM is a phase mixer , not a frequency mixer, the considering only the negative FB half cycle, it will attenuate the further away from center.

 

[yefj]

Hello, i have made a system to test the YIG. The tune is constant while the the FM coil is powered by the driver circuit we talked about before.
The tone goes from left to right.The big problem is as you can see below ,while its scanning sometimes i see relatively good signal some times i see the signal with two tones near the main,as shown below.
As i see it i have a problem with my YIG .
Could you please say what could cause such bad outputs from the YIG?
Thanks.

 

[biff44]

it could be a LOT of things. but you are "Tuning" with the FM coil, and keeping a constant current in the TUNE coil?
Maybe you are overdriving the FM coil's current limit, and it is causing weird effects, like yig sphere heating?
I would typically drive the TUNE coild with a low noise D/A converter, and tune for each center frequency i wanted with that.
Then at each desired channel center, i would only try to move the YIG frequency a little, perhaps +/- 3 MHz (just enough for your noise cancelling loop filter to do its job). This will mean a much smaller +/- current is needed in the FM coil.

 

[yefj]

Hello Biff44 , I am driving the FM coil using simple copper lines as shown below.
I am using breadboard and LM350 regulators(i cant see anywhere that its switching),regarding what you said:
1.As you can see the YIG moves at 12MHz from side to side,i will try to move it 3Mhz width.
2.regarding boat load of capacitors, could you please recommend me a capacitors configurations that could do the job?
3.maybe there is also an option to put FERRITE BEADS to make the signal cleaner, if you could recommend me something?

 

[D.A.(Tony)Stewart]

Your pix are unreadable and test conditions unknown. Over-excitation may cause resonant sidebands

 

[yefj]

Hello Mr.Stewart,what is "over excitation" for a YIG.how this phenomena happens?
Also Biff44 said i should use capacitors,what capacitors do you reccomend?
do you reccomend to use ferrite beads?
Thanks.

 

[D.A.(Tony)Stewart]

Hello Mr.Stewart,what is "over excitation" for a YIG.how this phenomena happens?
Also Biff44 said i should use capacitors,what capacitors do you reccomend?
do you reccomend to use ferrite beads?
Thanks.

CC excitation

 

[FvM]

Could you please say what could cause such bad outputs from the YIG?

There's obviously an unwanted modulation. Presentation of results suggests that you are not familiar with systematic debugging of this kind of problems. Test setup isn't shown clear enough to see all possible causes. Generally you should consider:
- unstable oscillator power supply
- faulty oscillator module
- unstable main tuning source
- unstable fm coil driver
First step would be to disconnect the fm coil driver and test if it's a possible source of disturbance

 

[biff44]

a little off topic, but i just learned that Zvi Galani, who pioneered a number of ultra low phase noise sythensizer designs, including this class of YIG Resonator frequency-discriminator phase noise reduction circuits, has just passed away peacefully. He holds a number of patents in this area from when he was at Raytheon Missile Systems Division in Massachusetts, USA

He showed us the way to do it all!

He will be missed!

It is good to see there is STILL interest in these techniques, some 40+ years later

 

[D.A.(Tony)Stewart]

Galani was famous at Raytheon, although I never knew him. I have worked with similar designs 40? yrs ago (I forget) using the PD he used in the 90's patents with YIGs.

I was lucky to work with brilliant engineers in Canada from Bell & Northern Telecom at a small company in Winnipeg doing a broadband FDX DS1 network with a VHF dual channel converters mounted outdoors in -40 to + 40 deg ambient. So I appreciated and learned the skills they possessed to create world-first 2-way RF & Data networks.

--- Updated Jan 14, 2024 ---

Hello, i have made a system to test the YIG. The tune is constant while the the FM coil is powered by the driver circuit we talked about before.
The tone goes from left to right.The big problem is as you can see below ,while its scanning sometimes i see relatively good signal some times i see the signal with two tones near the main,as shown below.
As i see it i have a problem with my YIG .
Could you please say what could cause such bad outputs from the YIG?
Thanks.

View attachment 187542
View attachment 187543
View attachment 187544

View attachment 187545

I believe this is your hysteresis from the I in YIG. ( although I have never tessted any myself) It should be present when the modulation crosses thecenter of the hysteresis loop. Iron has hysteresis but much smaller in the YIG crystal but large compared to your PLL loop BW. The fourier spectrum with phase can be interpretted mentally or the time domain signal can see it in zero span mode in a time sweep if it is AM or on the edge of the IF filter if it is PM or FM.

I predict it is AM.
The amplitude of the sidetone will vary with the offset from centre. This deviation boundary is defined as Hysteresis, but I'm not sure the precise parameters for its metric.

Record this data with delta f vs -dB from fo.
Also the centre will drift with T so it needs to be ovenized with other components.

- please learn to take better photo's with hood to block ceiling lights.
- when you describe a sideband or sidetone or ("birdie") describe the offset frequency that is hard to read on your pix.

Next excite the table with an impulse and measure the response. Then for more accurate measurements mount an accelerometer on it and determine the sensitivity of amplitude vs excitation g (f) which may be nonlinear with amplitude. The same exists even for ovenized SC cut crystals in OCXO's used for Statum-1 clocks used for telephony fiber channels and laser repeaters for the internet.

 

[biff44]

Galani was famous at Raytheon, although I never knew him. I have worked with similar designs 40? yrs ago (I forget) using the PD he used in the 90's patents with YIGs.

He was one of those rare genius type engineers, who thought it was their duty to bring along the next crop of engineers to take his place. a great guy, easy to get to know.

the genius of those noise degeneration synthesizers was, instead of finding the worlds highest Q resonators and somehow making them tunable, you instead took a resonator with a good Q, and virtually amplified its "effective Q" it by ~25 dB using cheap op amps in the control loop. It also fixed a lot of vibration issues

 

[D.A.(Tony)Stewart]

He was one of those rare genius type engineers, who thought it was their duty to bring along the next crop of engineers to take his place. a great guy, easy to get to know.

the genius of those noise degeneration synthesizers was, instead of finding the worlds highest Q resonators and somehow making them tunable, you instead took a resonator with a good Q, and virtually amplified its "effective Q" it by ~25 dB using cheap op amps in the control loop. It also fixed a lot of vibration issues

Was that called "Active Q" where loaded-Q is normally lower than Qu (unloaded) from damping.

My 1st office computer was the HP9825 which could talk to a few RF, TIA and power instruments in a rack with HPIB in the lab in 1977. I learnt how make a SCADA system for remote testing all the instruments in a rocket. But then a SW radio caused burps on the RS485 LTDS datasets a mile apart between my HP9825's
Thgat was when I did 2 week stints up in Churchill NRC Rocket range. I was blown away by a hundred racks of 19" instruments for telemetry and a bunch of quad helix servo trackers etc. , literally wall to wall racks on 19" floor to ceiling.


Yes I think HP invented those methods on Saphire Oscillators for wide tuneability and OCXO's for low phase noise., I read he figured out to do that with lower Q YIGs .
Then HP also developed those too. I loved using the earlier versions of the HP9674A in the late 70's.

https://www.keysight.com/ca/en/assets/9018-05514/service-manuals/9018-05514.pdf I think this service manual will be of great interest to @yefj (600 pages with YTO)
Now Ebay sells them for $650 hah. I loved the roller dial with inertia. We would double the frequency output with a diode adapter when needed.

I wish I had met Galani but I never interacted with Raytheon. ( no security clearance for non-residents)

 

[biff44]

Was that called "Active Q" where loaded-Q is normally lower than Qu (unloaded) from damping.

My 1st office computer was the HP9825 which could talk to a few RF, TIA and power instruments in a rack with HPIB in the lab in 1977. I learnt how make a SCADA system for remote testing all the instruments in a rocket. But then a SW radio caused burps on the RS485 LTDS datasets a mile apart between my HP9825's
Thgat was when I did 2 week stints up in Churchill NRC Rocket range. I was blown away by a hundred racks of 19" instruments for telemetry and a bunch of quad helix servo trackers etc. , literally wall to wall racks on 19" floor to ceiling.


Yes I think HP invented those methods on Saphire Oscillators for wide tuneability and OCXO's for low phase noise., I read he figured out to do that with lower Q YIGs .
Then HP also developed those too. I loved using the earlier versions of the HP9674A in the late 70's.

https://www.keysight.com/ca/en/assets/9018-05514/service-manuals/9018-05514.pdf I think this service manual will be of great interest to @yefj (600 pages with YTO)
Now Ebay sells them for $650 hah. I loved the roller dial with inertia. We would double the frequency output with a diode adapter when needed.
View attachment 187891

I wish I had met Galani but I never interacted with Raytheon. ( no security clearance for non-residents)

yes i have a couple of those HP8662/3s still. Fractional N synthesizers before you could BUY a fractional N chip! HP was a great innovator!

Yes, the whispering gallery mode saphire resonators were the pinnacle, some smart australian company patented their use.

 

[D.A.(Tony)Stewart]

yes i have a couple of those HP8662/3s still. Fractional N synthesizers before you could BUY a fractional N chip! HP was a great innovator!

Yes, the whispering gallery mode saphire resonators were the pinnacle, some smart australian company patented their use.

yes !
"HP 8662 gives you all of them, from 10 kHz to 1.28Ghz, with an astounding 0.1 Hz frequency resolution. It accomplishes this by an intricate arrangement of PLL loops within PLL loops and remarkable RF engineering quality, down to triple gold shielded cabling."