Is it possible to find such a VCO?

[tony_lth]

I need a VCO:
1st option:
Freq: 300~500MHz
Phase Noise: <-120dBc/Hz@1KHz
2nd option:
Freq: 90~140MHz
Phase Noise: <-120dBc/Hz@1KHz
I need VCO, not DDS, because of the DDS spurs.
Who know such a part number?

 

[vfone]

It is very hard to get a commercial VCO with those specs. Synergy have some, very close in spec, but not exactly.

Synergy Microwave Corporation - Design and Manufacture of high performance RF and Microwave signal sources and signal processors.

On the other hand you can try building your own custom made VCO, following all the low-phase noise requirements (using JFET working at low current, feedback noise circuit, high-Q LC components, etc). Sometimes tuning a feedback noise circuit in a VCO you can get lower phase noise just at a specific offset from the carrier, which actually is your target.

 

[tony_lth]

Hi, vfone, thank you very much.

 

[Dr.Drew]

I need a VCO:
1st option:
Freq: 300~500MHz
Phase Noise: <-120dBc/Hz@1KHz
2nd option:
Freq: 90~140MHz
Phase Noise: <-120dBc/Hz@1KHz
I need VCO, not DDS, because of the DDS spurs.
Who know such a part number?

I think, it's impossible. Simple calculation gives Ql=1500 or greater for 300-500 MHz VCO. If you have -120 at 1 kHz, then at 100 kHz will be approx. -170...-160. In most cases noise floor of oscillators is -170...-160. Then f0/2Ql=100 kHz and Ql=1500...2500. Only YIG can give such Q in octave tuning. Or you can use swiched VCO's. For 90-140 MHZ Ql=450...700.

 

[tsvetelin_velkov]

Fast search on eBay showed :

Z-COMM VCO, 150MHZ to 230MHZ, Part Number: V150S015

General Spec:

Frequency Range: 150MHz to 230MHz;
Phase Noise: -102dBc/HZ at 10KHz offset;
Tuning Voltage: 0V to 11V;
Tuning Sensitivity: 8MHz (avg);
Output Power: 11dBm;
Load Impedance: 50 Ohms;

Fast search on Z-COMM webside showed this :

Part No. V440MC01-LF
Frequency Range (MHz) 370 - 515
Phase Noise @ 1kHz (dBc/Hz)(typ) -78
Phase Noise @ 10kHz (dBc/Hz)(typ) -107
Harmonic Suppression (2nd, typ) (dBc) -5
Tuning Voltage (Vdc) 0 - 8
Tuning Sensitivity (MHz/V) 40
Power (dBm)(typ) 9.5
Input Capacitance (pF)(max) 200

link :

V440MC01-LF

The phase noise that you require is really low, I do know some oscillators, usually crystal, with such level of phase noise, but these are high quality crystal oscillators ( fixed frequency, not VCO ) build with high quality crystals. And I am not really sure that trying to build such is an easy task, especially if you don't have the equipment to measure the phase noise.

Hope this helps!

 

[vfone]

Loaded Q is one of the factors that affect the phase noise, but is not the first. At this offset the biggest contributor is 1/f flicker noise.
The list of VCO's that I posted in the link above, made by Synergy Microwave, use the feedback noise patent of Ulrich Rohde who is the Chairman of the company. Check the technical articles of the company.

The VCO in the link below have -128dBc/Hz @ 10kHz and about -106dB/Hz @ 1kHz.
**broken link removed**

If the feedback noise network is tuned only to achieve best phase noise @ 1kHz offset, better results can get (of course at greater offsets the phase noise it will degrade somehow).
100 MHz is relative low frequency, and if you have room for bigger inductors (with higher Q), and trying different discrete JFET's at various bias currents, it is possible to get good results, maybe better than above.

 

[tony_lth]

Thanks all of you.

 

[tsvetelin_velkov]

Maybe you want to share what is your application. Why do you need such high quality VCO? This might be interesting for others too.

 

[tony_lth]

I want to design a sweep freq source for our weather radar, that's the object.

 

[biff44]

do you really need the vco to have that low phase noise, or can you use a stepped frequency synthesizer.

There are plenty of ways to make a synthesizer do that, only a very few to make a vco do that and they are more than just a simple VCO.

 

[tony_lth]

HI, biff44,
Can you give some papers or schematics on stepped frequency synthesizer? Is there some products on stepped frequency synthesizer? Any frequency band is OK.
Thank you very much.

 

[liletian]

I would think the phase noise requirement is too high, the tuning range is too high as well to make

I need a VCO:
1st option:
Freq: 300~500MHz
Phase Noise: <-120dBc/Hz@1KHz
2nd option:
Freq: 90~140MHz
Phase Noise: <-120dBc/Hz@1KHz
I need VCO, not DDS, because of the DDS spurs.
Who know such a part number?

 

[Dr.Drew]

Loaded Q is one of the factors that affect the phase noise, but is not the first. At this offset the biggest contributor is 1/f flicker noise.
The list of VCO's that I posted in the link above, made by Synergy Microwave, use the feedback noise patent of Ulrich Rohde who is the Chairman of the company. Check the technical articles of the company.

The VCO in the link below have -128dBc/Hz @ 10kHz and about -106dB/Hz @ 1kHz.
**broken link removed**

If the feedback noise network is tuned only to achieve best phase noise @ 1kHz offset, better results can get (of course at greater offsets the phase noise it will degrade somehow).
100 MHz is relative low frequency, and if you have room for bigger inductors (with higher Q), and trying different discrete JFET's at various bias currents, it is possible to get good results, maybe better than above.

I don't think so. Using low noise Si bjt's one can achieve 100-1000 Hz flicker corner. So phase noise at 1 kHz is determined by Ql.

 

[biff44]

I don't think so. Using low noise Si bjt's one can achieve 100-1000 Hz flicker corner. So phase noise at 1 kHz is determined by Ql.

And oscillating power!

 

[vfone]

Always, JFETs have lower flicker noise than BJTs which is sitting on the second place.

Using Leeson equation to estimate the phase noise, can be found that at low corner offset double of loaded-Q will give about 6dB variation in phase noise.
Double of loaded-Q in real life means a lot, when starting from an initial design.

So, to achieve the best performance in phase noise at low offset should bet (in the same time) on each approach, component, or phenomenon.

 

[tsvetelin_velkov]

why not this one :

Crystek Microwave

when I need a really good quality components, with known performance, I try to buy them from somewhere, price is not the most important factor.

or maybe this one :

Crystek Microwave

And I want to share this diagram also, I know that it is not something new, but gives reference components and manufacturers, so could be of some use.

 

[tsvetelin_velkov]

this advertisement just came to me and I want to share it because I think it might help you

**broken link removed**

 

[Dr.Drew]

And oscillating power!

I mean, that power in resonator is constant.