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100w wave generator at 5-7 Mhz without an amplifier?

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ful babu

ful babu

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100w wave generator

I am looking for a 100V 50-100W sine wave generator at 5-7 Mhz, any suggestions? Btw I don't want to use an amplifier.
 

Re: 100w wave generator

If you don't want to use an amplifier you are asking for a VERY high powered oscillator that can drive a 100V sine wave into 100Ω over more than 25% of it's tuning range.

Good luck with your search, please don't switch it on in Europe, it would be too close to me.

Brian.
 

Re: 100w wave generator

betwixt said:
If you don't want to use an amplifier you are asking for a VERY high powered oscillator that can drive a 100V sine wave into 100Ω over more than 25% of it's tuning range.

Good luck with your search, please don't switch it on in Europe, it would be too close to me.

Brian.
Click to expand...

would you mind explaing that, why it us not realistic?
 

Re: 100w wave generator

You can use a simple oscillator followed by a driver and a power amplifier made with ADF440/441, which is a very cheap transistor.
For 100W out and 50V supply needs just 1W at the input.
You can try also using 100V supply, where the gain is higher and needs even lower input power.

https://www.farnell.com/datasheets/29731.pdf

or other options:
https://www.microsemi.com/catalog/parmlist.asp?P0_RFMKTID=31&APT=1&RF=1&P1_TYPE=RFMOS

Finlay this will be a high power RF transmitter, and not anymore a signal generator.
 

    ful babu

    ful babu

    Points: 2
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Re: 100w wave generator

Ful babu want's to do it without an amplifier.

The reason I don't think it is realistic is that without an amplifier, you are relying only on the oscillator to provide that much power. Oscillators are normally more stable at low power levels than high ones.

You might be able to do it with a vacuum tube oscillator, I'm thinking along the lines of type 813 which has a graphite anode and could be made to oscillate but you need lots of supply voltage and current to run it and it would be horribly unstable.

I don't think you could achieve 100V / 100W from a single transistor oscillator.

Brian.

813 - I'm showing my age again!
 

Re: 100w wave generator

I don't think you could achieve 100V / 100W from a single transistor oscillator.
Click to expand...

A "single transistor" oscillator would be required to use class A or AB and in so far have a limited efficiency. But one of those
MegaHertz switching Power MOSFETs, that can achieve kW in class F should be still good for 100 W in class A.
 

Re: 100w wave generator

Ok ... Given that I do not have any restriction of using an amplifier what do you guys think is the best way to generate such a signal is a very concise circuit design
 

Re: 100w wave generator

With an amplifier it should be fairly easy but we need more information:

1. You mention 5-7MHz, do you mean it has to be tunable in that range, it is at a fixed frequency in that range or it will have a 2MHz bandwidth?

2. How stable does the frequency have to be? Does it need quartz crystal control, PLL control or doesn't it matter?

3. Does the signal have to be 'clean' (as in broadcast radio station) or 'dirty' as in an induction welding machine?

4. What power source do you have available?

5. Is the 100Ω load resistive or reactive and if the circuit is tunable, do the load characteristics vary with frequency?

6. Is it modulated and if so, is it AM, FM, PM or something else?

Brian.
 

Re: 100w wave generator


1. You mention 5-7MHz, do you mean it has to be tunable in that range, it is at a fixed frequency in that range or it will have a 2MHz bandwidth?
It will be better to have a tunable range of signal from 1 to 10 Mhz

2. How stable does the frequency have to be? Does it need quartz crystal control, PLL control or doesn't it matter?
I need it moderately stable and concise how it is done is not so important

3. Does the signal have to be 'clean' (as in broadcast radio station) or 'dirty' as in an induction welding machine?
it has to be clean

4. What power source do you have available?
Li-poly rechargeable cells

5. Is the 100Ω load resistive or reactive and if the circuit is tunable, do the load characteristics vary with frequency?
it a 2.2nF(+/- 0.5) capacitive load and it is a Piezoelectric transducer, i would say that the load characteristics is pretty much constant

6. Is it modulated and if so, is it AM, FM, PM or something else?
as i said in point 1 i need to vary the frequency so my guess is it would be a FM and i need to vary the output amplitude so AM as well.

Thank You.
 

Re: 100w wave generator

It might help if you told us what the application is.

To drive 100V across a 2.2nF capacitive load at 10MHz requires nearly 1.4KW of power and I don't know of any rechargeable cells that can cope with that kind of load for long.

I'm puzzled at why such a high frequency and power are needed for a piezo transducer, what exactly is it doing?

Brian.
 

Re: 100w wave generator

To drive 100V across a 2.2nF capacitive load at 10MHz requires nearly 1.4KW of power
Click to expand...
It's reactive power only, and it would be usually compensated. However, the design of the impedance matching is
probably more difficult than of the power stage itself.

P.S.: At it's resonance frequency, a piezo transducer doesn't act as a capacitive load.
 

Re: 100w wave generator

betwixt said:
It might help if you told us what the application is.

To drive 100V across a 2.2nF capacitive load at 10MHz requires nearly 1.4KW of power and I don't know of any rechargeable cells that can cope with that kind of load for long.

I'm puzzled at why such a high frequency and power are needed for a piezo transducer, what exactly is it doing?

Brian.
Click to expand...

ok... what i am doing might sound weird to you ... i know its not a good way to do this ... but what I am trying to do is get a water jet stream out of the transducer when it is submerged (something like the attached image, sorry for the image quality).

currently I am using a 100W RF amplifier and a signal generator to resonate the piezo and I can get a small jet up to my satisfaction so now I want to make it as compact as possible and portable.
 

Re: 100w wave generator

It makes more sense now.

It the same principle used to eject tiny ink drops from a printer cartridge but on a much bigger scale.

As FvM says, generating the power (WITH an amplifier) isn't difficult but matching it to the piezo transducer, especially over such a wide frequency range would be a nightmare. I'm no expert in these devices but I assume they have a natural resonant frequency due to their construction.

In view of the resonant effects, I would downgrade your requirement to 'dirty' RF as the matching and piezo device will tend to clean the signal. That makes design a lot simpler as you can change from class A/AB amplification to something more efficient and electrically simpler to build.

A question for you: Bear in mind I'm no expert in this field, given the density and viscosity of water restrict it's natural flow rate, why is such a high frequency needed? I would have thought it more efficient to use a much lower frequency, not more than a few KHz to do the job.

Brian.
 

Re: 100w wave generator

betwixt said:
It makes more sense now.

It the same principle used to eject tiny ink drops from a printer cartridge but on a much bigger scale.

As FvM says, generating the power (WITH an amplifier) isn't difficult but matching it to the piezo transducer, especially over such a wide frequency range would be a nightmare. I'm no expert in these devices but I assume they have a natural resonant frequency due to their construction.

In view of the resonant effects, I would downgrade your requirement to 'dirty' RF as the matching and piezo device will tend to clean the signal. That makes design a lot simpler as you can change from class A/AB amplification to something more efficient and electrically simpler to build.

A question for you: Bear in mind I'm no expert in this field, given the density and viscosity of water restrict it's natural flow rate, why is such a high frequency needed? I would have thought it more efficient to use a much lower frequency, not more than a few KHz to do the job.

Brian.
Click to expand...

well this particular piezo resonate at 7.3Mhz the point I get the strongest stream for fresh water ... I have different type of piezos and different water (fresh/salt)

so you are saying it will be lot easier to build a single point frequency generator with a impedance matching circuit? then I have to build diffrent with different configuration ??
 

The load impedance will be high at resonance (7.3MHz for example) but very low at other frequencies. If you try to change the frequency the way you have to match the power to the transducer will be completely different as you pass through the resonant point.

For example, at 7.3MHz you might be able to directly drive the transducer but at 7.1 or 7.2MHz you might need complex transformers and impedance matching circuits.
Tuning it across a wide frequency range would need widely different component values so it might not be practical to do.

As I stated, this isn't really my field of expertize but I if I was to design something like this my first idea would be to use a bridge amplifier to get maximum voltage and either drive it with a square wave at resonant frequency from an oscillator or *possibly* use the transducer itself as the resonant element by wrapping a feedback circuit around it.

Perhaps others with more experience would like to comment.

Brian.
 

    ful babu

    ful babu

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