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Hellschreiber beacon - with some oomph!

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Charlie_Dont_Surf:
The efficiency is low (if the circuit is actually biased for Class C, I would expect something more like 50-60%) and I have to say that some of that is probably coming from the construction technique. Please don't be offended by this; you've constructed it in a very clean manner. Nice work. It's just that at 7 MHz, there's going to be a fair amount of loss going through all those through-hole components with relatively long leads. A PCB would allow for a more compact circuit with shorter connections between components. Going to SMD would be even better.

Radiotech:
Will try to make a board with better layout and fewer/shorter leads, but my hands are too big for the SMD stuff sadly.  :) The board is at least easy to experiment on.

I experimented some with the capacitor that goes from drain to ground on the IRF510, i tried different values, but found that i got the most power without it. Perhaps this is a sign that im operating in C-class. Also removing a few turns from the drain-vcc inductor got me some more power. Almost 3W at 13,8v is pretty ok.

I dont really have any output matching to the 50ohm load, should i try to make a PI network or transformer?


I meassured both Drain-ground(yellow) and Gate-Ground(purple). They seam to be shifted 180 degrees, but i guess that goes for both class C and E. Connecting a probe to the gate of the IRF510 affects output negative.

redhat:
Something is very wrong if all you can get is ~25% efficiency.  Even my non-optimized CMCD PA's with asymmetrical drive get north of 83% DC-RF efficiency.  Also, keep in mind that all mosfets exhibit a dramatic shift in output capacitance v. Vds.  This can cause tuning problems and a shift in efficiency over the power range, notably on the bottom where voltage excursions are closer to zero.  This can cause a host of problems, among them IPM (incidental phase modulation) which causes problems for complex modulation modes like DRM, and C-QUAM.  This is one of the reasons I try to swamp out the shift in Cds with large tank capacitances.

Per the previous comments; I've seen in my limited experience people go to the ends of the earth to try and optimize a PA, only to get less performance than circuits I tuned empirically.  Usually this is due to circuit strays that are unknown, or unaccounted for in the simulation stage.  This could also be the source of at least some of your difficulty in getting this circuit to behave.

The 180 degree shift is to be expected, as the instant the Vgs exceeds the turn on threshold, the fet will begin to conduct and pull the Vds toward zero.  I would probably explore a different driver for the fet and I imagine some of your efficiency problems will go away.

It should be also noted that measurement accuracy becomes more and more of an issue when measuring the output of these newer higher efficiency PA's.  At some point you have to figure out whose lies you believe.

+-RH

Radiotech:
I took the advice to try to make the construction a bit more compact, and reduce the leads. With the new circuit i also was able to plan a bit better when placing components.



The low output and efficiency could be due to my circuit not having a bifilar or trifilar transformer, most of the designs out there have one. I dont really understand what they doo, they could provide:

1: Voltage transformation to output more power
2: Antenna impedance matching, to provide more power.

The amplifier from QRPlabs below is one example, but there are many others aswell. I tried this with a bifilar wound 8t T50-43 but got a strange effect where the output started low as 1W and slowly over a couple of seconds rose to 2W. Its possible that i did something wrong with mine, i will try to construct a new one, i need some more materials for it though. The QRP labs amp puts out about 50% efficiency and double the output that mine does, so the bifilar/trifilar transformer is probably importent.



One thing that struck me is that the E-class amplifiers i have seen all seem to use a square wave oscillator signal, and my oscillator has a sinewave signal. Could it be that a square wave signal is needed to go quickly to saturation mode?

Stretchyman:
Yes the squarewave switching is an essential part of class E. The output device is only ever in 2 states, On or Off, a pure switch. Sinewave puts the output device in a resistive mode between the 2 states, never good..

I have, as have others, posted up schematics with circuit values, just start there, you'll get instant results.

I piddled about for years, simulating and building and testing and modifying and improving.

SMT wise 2012 are quite chunky and suggest you try that size. I too have BIG hands but use a X4 magnifier and have a decent soldering iron. I'm happy with 0805 but can use 0603 but smaller than that (0402) is too small!

I'd stick to PCBs for anything RF. So cheap from CH.

Good you're experimenting and improving....

Simple sim below;

Green is gate (non ideal, realistic slopey squarewave)
Red is output
Blue is drain.

Folk seem hung up on weird idealised circuit values, most of them dont really matter and tuning can be done using toroidal inductors (can vary inductance +/- 50%)


Drain inductor, any old value as long as its 5X or more the Z of the stage (2u is around 80R in this circuit).Any greater is just a waste of wire and more resistance.

C1 is simply adjusted to give (approx) 3.5X the voltage of the supply across the drain, this will vary with FET type as each FET has it's own build in capacitance. Again NOT critical at all.

C2/L2, you can see I've used a standard value rather than some simulated one. IT DOESNT MATTER! The 2 components form a BPF so ANY values will work as long as they are at the correct frequency and this can be adjusted (+/- 50%) by stretching and squeezing the turns to either get the most power or the best efficiency (they dont ever align btw). The BPF is NOT 'on' frequency as has to introduce some lag time wise to align the gate and drain waveforms, they should oppose.

L2 (part)/C3 these actual transform the impedance of the stage from 14R (in this case ) to 50R, it's called a (complex) conjugate match, think of it as SIMPLE match, as it is in physical terms!


That's it, simple eh! You will have to add an LPF and take into account C3 of course.

You can see why the complexity of biasing etc is a waste of time, you want a SWITCHING device NOT a LINEAR one.

Expect 10-15W from this circuit with around 0.8-1.2A of current.

DONT use the 510, USE the 520.




Str

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