Help me with making a 14 Mhz oscillator that outputs more than 500 Watt

[ahmed osama]

Dear All

i need your help & tips in the following project ,

i need to make a 14 Mhz Osc. with output power more than 500watt and to be able to guide such RF in a certain direction ...

how can i start ?? and how to deliver such huge power ??


thanks

bye

 

[khouly]

High Power .......??

u need a power amplifier with high power transistor , even u need to use a combiner to combine the output of 2 or 4 PA

khouly

 

[shg]

High Power .......??

Try a MOSFET-based design, such as this:
https://www.microsemi.com/micnotes/APT9903.pdf
It's for different frequency, but the whole idea behind stays the same.
Of course, an amplifier should be driven by oscillator. It is, however, possible to design an oscillator with 500W output power, but its generally a bad idea. There would be some issues, mainly with stability.

What do You mean by guiding a power in certain direction?
You want to transmit it as electrical signal, or as electromagnetic wave?

In the former case, a coaxial cable should be enough, however a care should be taken when choosing one. Find attenuation per unit length of a particular cable and calculate amount of power, which that cable will dissipate as heat.
Also, You should match amplifier's output impedance to cable's impedance, the same goes on load's side. The load should either have the same impedance as cable and amplifier, or be equipped with impedance-matching circuit.

In the case of transmitting a signal as electromagnetic wave, all You need is a directional antenna, which will be huuuuuge at this frequency.

 

[byteptr]

Re: High Power .......??

Good choice in the class E amplifier.

"In the case of transmitting a signal as electromagnetic wave, all You need is a directional antenna, which will be huuuuuge at this frequency.
"

Yes, the wavelength in a free space is ≈ 20m for 14 MHz, but you can try a small Loop antenna, It's a good start, it has a form of "∞" radiation pattern (if is correctly balanced into a feed point, it needs a balun) and you can easily modify into a cardioid pattern for more directivity.

**broken link removed**

Best regards.

 

[flatulent]

Re: High Power .......??

There are legal problems. You cannot intentionally radiate signals without a license and only in frequency ranges that the license covers.

 

[ahmed osama]

Re: High Power .......??

There are legal problems. You cannot intentionally radiate signals without a license and only in frequency ranges that the license covers.

kindly check that

https://en.wikipedia.org/wiki/ISM_band

i will try to use

The ISM bands defined by the ITU-R are 13.553–13.567 MHz (centre frequency 13.560 MHz)

and i will use it for a vey short distance may be less than 20 cm , there will be kind of absorber after 20 cm from the Tx



thx

 

[FvM]

Re: High Power .......??

E. g. inductive heating or medical applications at 13.56 MHz are generally possible, that's what the ISM bands are reserved for. It's also usual, that some RF power is radiated if it can't be avoided with appropriate effort. I'm not currently aware of the regulations for industrial or medical RF power applications. For communications purposes, e. g. RFID, there are rather strict requirements for residual far field strength.

I'm also wondering what you mean with guide such RF in a certain direction. Because of the 20 m wavelength, you are effectively using near field. You can also regard your antenna basically as either a capacitive or inductive coupler and consider electrical or magnetical field only. An electromagnetical field description comes into play, when the (typical very small) radiated part of power has to be calculated. Thus guiding the RF in a direction practically means utilizing a coil or electrodes.

For the said ISM regulations, the generator must obviously have a crystal oscillator. For the power stage, a solid state solution would be the smarter variant, fast standard MOSFET should be sufficient, I think, although RF FET allow an easier design. Or use a traditional valve power stage.

 

[flatulent]

Re: High Power .......??

You will be best off by using inductive coupling. Especially if everything is in a large metal box.

In the EU there are rules on unintentional radiation in the HF ISM bands. You can exceed these with just tens of watts of power.

 

[Siniša]

Re: High Power .......??

14MHz is assigned for radio amateur use. For emmiting 500W on that frequency you will need licence and only for purpose of amateur communication under allowed modes of operation.
If you attempt to do this illegaly, it won't be long before someone knocks on your door. If you have problem with radio amateur in your neighborhood, you should try to resolve problem with him or communication authorities. Most electromagnetic interference problems can be resolved with some good will and knowledge. ( I am guessing this might be the motivation)

If this transmitter is to be used in industrial use, it has to be enclosed to prevent leakage outside of process that needs to be radiated with this RF power.

 

[byteptr]

Re: High Power .......??

"There are legal problems. You cannot intentionally radiate signals without a license and only in frequency ranges that the license covers.
"

Yes, It's true, 14-14.350 is an amateur 20m band. I guess he knows.


73, EA2CTK
EA2RKG Radio club member.

 

[zirtapoz]

Re: High Power .......??

There are legal problems. You cannot intentionally radiate signals without a license and only in frequency ranges that the license covers.

kindly check that

https://en.wikipedia.org/wiki/ISM_band

i will try to use

The ISM bands defined by the ITU-R are 13.553–13.567 MHz (centre frequency 13.560 MHz)

and i will use it for a vey short distance may be less than 20 cm , there will be kind of absorber after 20 cm from the Tx



thx

if you need mostly 20cm. why are you looking for such a high power?
i think you r working on ISO 14443 (mifare or NFC) you dont need such high power. and if you dont use such power your design ll be legal

 

[RF-OM]

Re: High Power .......??

To ahmed osama,

14 MHz is impossible to use. Ham radio operators will find you immediately. 13.56 MHz is the closest ISM band where you may try your project "without license". But ISM is actually licensed for certain activity. If your application is not in FCC list you are in trouble. By the way, FCC usually limits not the power, but electrical field strange at certain distance. This is smart solution and works well for inspection. However, for you it is not so easy to check this parameter. ISM band is also used for RFID and medical applications. It is well controlled by NTIA and FCC. Therefore, be very careful if you are in US. Actually for this frequency 500 W signal can go to any place in the Earth if some conditions are met.

To byteptr,

It is nice to meet ham operator here, you may understand two last letters in my nick. Your location is France, call sign is Spanish, but this is not so important.

73! RF-OM