Electronics > RF, Microwave, Ham Radio

trouble getting class c amplifier circuit working

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drspastic:
so im building a low powered feldhell beacon using digispark, active crystal oscillator, and small solar panel. it needs a power amp stage to give a peak of maybe 1 or 2 watts at very low duty cycle.
on the bench i tried the standard textbook class c but was unable to get any gain despite the tuned circuit being spot on. i could get a little gain with a positive bias but that just makes it a heater. i tried again with a double tuned 4:1 transformer wound binocular style on a couple of tiny ferrite beads and still only managed gain in class a mode. class c just either became unstable or flipped mode to a doubler, still with no gain. at this point i should mention i am working with a maximum of 4v supply. at best settings i could get 8v pp out with a bd135 and the 4:1 transformer but that dropped to 5vpp into a 50 ohm load.
im not sure where to go from here as i think its the supply voltage being a constraint. should i use a mosfet? i dont have many rf parts on the shelf but i have some smd mosfets for fixing drones and they have a very low gate voltage: 9926a but im not familiar with design constraints using mosfets for rf. they seem to have a large capacitance on the gate which may be hard to drive.
im just fishing for thoughts here, i dont want to raise supply voltage even by dc/dc converters. the unit must be very light and small to be lifted by a small party balloon etc on its dipole wire. frequency will be between 10-29mhz in the allowed places. it may have a lipo cell or tiny ultracapacitor to give oomph on the duty cycle but mainly very thin solar.
what do lads?

kleiner Rainer:
DL2AVH designed several 1.5V powered transceivers - maybe helpful for your project:

https://dl2avh.eu/trx1v/trx1v.html

Greetings,

Rainer DG1SMD

ftg:
Class-C amplifiers have minimum drive power requirements. So you might need a small class-a driver stage in between the class-c pa and crystal oscillator.
If you don't want to add some transistor stage, a modern single gate inverter from TI/Nexperia/onsemi could potentially also be usable.

Andy Chee:
You might also want to consider a Class-E amplifier.  A good place to start would be searching for Class-E WSPR transmitters.

stretchyman:
I 2nd the class E design, so simple, why use anything else?

Do a search for 'LULU'.

J.

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