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Looking for a 15-20 watt amplifier (BJT or FET)

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rfc

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I am looking for a 15 to 20 watt (rf output) BJT or FET to use at 1296MHz. Gain needs to be 20db or so (greater then 18db). Any suggestions?

rfc
 

rfc

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20-30 watt amplifier

Thanks for the replies. Suggestions were good but this part needs to be operated class C. Efficiency is important. Am currently using MRF282 but it sucks to much power in class AB.

rfc
 

flatulent

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class C

Class C does not exist with transistors and at these frequencies. It is hard to get class C opeation at HF with transistors.

Another problem is that the gain goes down the drive requirements go up to the point that the overall system efficiency is very low.
 

HO_220

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Reply

hi.
plz go to:
http://rfwireless.rell.com/amplifiers.asp
in this address the various type of transistor with specification is find.
i search in this address and find the followind transistor:
SSPA1.2-1.4-200
class c amplifier
freq:1200-1400MHz
P1dB=53dBm=20W
Gain:43dB
bests.
 

dd22

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Ask a question. How would you protect yourself when you test this kind of high power PA? Do you need to wear special cloth?
 

flatulent

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test into load

Test into a dummy load and the residual radiation will be very small.

What is claimed in the above manufacturer's data link as class C is really zero bias (class B). Notice that the efficiency is 40% and the power added efficiency is 32%.
 

nandopg

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Allow me to disagree...

Allow me to disagree of my friend Flatulent. The collector current of a transistor with the base connected to ground through a RF choke is actually less than 180 deg, what means a Class C operation.
That's true also that a class C operation at the time of the vacuum tubes implied some reverse bias applied to the input of the tube, what is not used in the most of the solid-state devices.
Also should be noted that all manufacturers and all literature about RF power amplifiers refer to an amplifier with the base (or emitter) grounded as a Class C amplifier.

NandoPG
 

flatulent

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technically correct

While being technically correct that anything less than 180 degress is class C, from the old days, whenever anyone mentioned class C they were making reference to 90-120 degrees of conduction angle and efficiencies of over 70%, usually over 80% while maintaining gains of 10-20 dB per stage. Solid state devices cannot match this especially at the system level with gains of 6 dB per stage and the 32% efficiency per stage.

My belief is that the class C nomenclature is used by manufacturers to warn the user that the price for cheaper circuitry is distortion.

Prior to 20 years ago, RF transistor companies warned against trying for class C because of the limited gain, and drive power handling capability of transistors. If you look at the transistors claiming class C today they are usually for pulse application where the low duty factor would make the bias current drawn during the inner pulse times consume more power than that consumed during the RF pulse.
 

nandopg

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You are right in all you said. There are 2 or 3 manufacturer still placing Class C transistors for CW in the market. It is also true this transistors can't compete with the efficiency of the tubes. However the quality of these transistors has been improving a lot if compared with old part numbers. If you characterize in a right way these "new" class C devices, you will get a quit and repetitive PA.
I have been working with the transistors from the former GHz very successfully in applications where the DC bus lies between 25-32V. In addition to get a very well behaved PA, the voltage regulator that supplies VCC works cold, what is an advantage if you regard the overall efficiency.

NandoPG
 

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