How Can I Design a 13MHz Sine Wave Signal Generator with 30-40V Output?

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Discussion Overview

The discussion revolves around designing a signal generator capable of producing a 30-40V peak-to-peak sine wave output at a frequency of 13MHz. Participants explore various circuit design options, including oscillators and amplifiers, while addressing load characteristics and potential issues related to impedance matching.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • The original poster (OP) seeks assistance in designing a signal generator or amplifier that can achieve the specified output voltage and frequency.
  • Some participants inquire about the specific requirements of the signal generator, including whether 13MHz is the only frequency needed and the nature of the load (resistive, capacitive, or inductive).
  • The OP expresses flexibility regarding frequency if it allows for achieving the desired output voltage, while also indicating a preference for minimizing current.
  • One participant emphasizes the importance of knowing the load's impedance and warns about potential issues with coaxial cable mismatches affecting output.
  • Another participant suggests that fabricating such a generator may be more complex and costly than purchasing a commercially available one, citing power requirements for amplifiers to achieve the desired output.
  • A suggestion is made to use MOSFETs to generate a square wave, which could then be filtered to produce a sine wave, raising a question about acceptable harmonic content.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best approach to design the signal generator, with multiple competing views on circuit design, load considerations, and the feasibility of fabrication versus purchase.

Contextual Notes

Participants highlight the significance of load impedance and matching, as well as potential regulatory concerns regarding signal radiation at certain frequencies. The discussion reflects uncertainty regarding specific load characteristics and the implications for circuit design.

Who May Find This Useful

Individuals interested in circuit design, signal generation, and those exploring high-frequency applications may find this discussion relevant.

TeeBeeBee
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I am very new to circuit design so any help is much appreciated. I need to design a signal generator that will output about 30V-40V peak to peak at 13MHz (sine wave) If the signal generator is not able to, then I need some kind of amplifier. So far I have looked into Hartley and Colpitts oscilators and am not having any luck reaching my desired output. Any help or suggestions would really help. Thanks in advance
 
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Is 13 MHz the only frequency the signal generator needs to produce?
What will the load be on the signal generator (how much current)?
Is the load strictly resistive or can it be capacitive or inductive?
Will the load be constant or variable and if variable by how much?
 
I would like to keep the frequency around 13MHz but if the output can be reached at lower/higher frequencies then the output takes priority. The load can be resistive, capacitive or inductive. The load is constant and I am not too sure about the current, but like to keep the current at a minimum though
 
Knowing how much current or better yet the impedance of the load is very important. If your load is connected by coax and the coax is more than about a meter and the load doesn't have the same impedance of the coax or the coax isn't the same as your signal generator, your output will be reduced. A VSWR meter can tell you if you are matched or not. If you aren't you can make of buy a matching network which you can adjust until you get a minimum reading on the VSWR meter.

Without seeing your circuit or knowing what your load is, I can't help you any more.

Will your signal be radiated? There are broadcast stations in the 12MHz frequencies, marine mobile around 13 MHz and radio astronomy above 13 MHz. A mismatch between generator and load as well as an improper ground can cause it to radiate. Recently two ham operators near Cleveland were fined $30,000 collectively for abusive radio transmissions.
 
Someone unskilled in the art is unlikely to fabricate such a generator cheaper than one can be purchased. Common signal generators reach 20 MHz, but are limited to about 20Vp-p when terminated into 50 ohms. It would require a 16 watt amplifier to barely achieve 40Vp-p into 50 ohms resistive, 32 watts for 25 ohms, and 8 watts into 100 ohms. So, knowing the load and being able to match to it is very important (see transmatch).
13.56 MHz is an ISM frequency reserved for equipment that might inadvertently radiate, so there is a convenient frequency nearby.

All of this is a bit much for a hobbyist to fabricate, but readily available to purchase.
 
A pair of mosfets, (as used in a switching power supply), would generate a square wave, that could then have a resonant tank circuit to remove the harmonics.
The OP specifies a sine wave. What level of harmonic content is acceptable?
 

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