HFU HF Underground
Technical Topics => The RF Workbench => Topic started by: Radiotech on February 10, 2022, 1735 UTC
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I decided to try to use the El Pititico transmitter as an oscillator for a project with some more power than the 750mW i got from the last one. QRP-Labs has a nice HF-amp with an IRF510 that i would like to try.
To get more stability from the oscillator i powered it down to 8v, about 400mW. The voltage will be higher for the PA, to get more RF output. Does anyone know if i should keep the low-pass filter after the oscillator? Or is it enough with the one after the power amplifier?
Also i am redesigning the enclosure, there will be some more heat to dissipate with this alteration, and i need space for more components.
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Keep the LPF after the oscillator. No need to amplify the oscillator's harmonics and create other byproducts in the PA stage.
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The circuit is now ready for bias adjustment, and then to do some testing on RF-output vs voltage. There are two voltage regulators on board, 5v for mosfet-bias and the micro controller, and 8v for the oscillator. I got a 0-30v 3Amp power supply, that makes things a lot easier when testing these transmitters.
Im using a T50-43 10T bifilar transformer to the RF-output, it is supposed to impedance match the IRF510 to the 50ohm antenna.
The 400mW drive should be enough, according to the author of the document above, about 500mW is needed to fully drive the IRF510.
I found this http://www.iw3sgt.it/IW3SGT_PRJ/IW3SGT_AMP_LF/ClassDEF1.pdf (http://www.iw3sgt.it/IW3SGT_PRJ/IW3SGT_AMP_LF/ClassDEF1.pdf) that describes the different amplifiers in a very easy and understandable way. Its written by NA5N, it made me understand amps better.
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The IRF510 amplifier works, i get sort off a wave form ;D
Running the oscillator at 8V gives an output of 81vpp. The oscillator puts 16vpp into the gate of the IRF510, and i adjusted the gate bias to just where it starts to draw power.
At first i got no power out from the amp, after a while i discovered that i had wound the T50-43 bifilar 10T the wrong way, once that was solved it worked better!
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I made a 5.th order chebyshev low-pass filter to filter the output, it made the signal look a lot better, but its still not very good looking. Should i use a filter with more components?
I did expect a bit more output power, with 30v of supply i get approx 5,5Watts of output after the low pass filter.
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I changed the filter to a Buttersworth of the 7.th order, and it made the wave form look a bit nicer. Found the calculator for it here https://rf-tools.com/lc-filter/ (https://rf-tools.com/lc-filter/)
At 13,8v i get approx 2W of RF out, and its farly stable. At 24v however, it starts at approx 4 watts, and during about 3 seconds it increases to 10,5W where the supply goes into current limitation and power stabalises. Is this some kind of thermal run away?
The oscillator drive voltage doesnt increase, its stable. I am driving the IRF510 with a high VPP, so the bias doesnt really do anything, it doesnt affect RF output at least.
Edit: I read that the IRF510 should never have more than 8vpp on the gate, and i have double that. This might be the problem, i will try to power down the oscillator.
Edit 2: Problem percists, even at 7vpp on the gate, power is surprisingly low and unstable at higher voltages. Too high bias and the power increases until current limitation cuts in. Too low, and it doesnt give any output. 1w at 13.8v is a bit low, it should be able to prove higher output.
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The ripples on your O/P waveform are due to the lengthy earth lead of your 'scope probe.
Please use the class E amp from the same article, far better efficiency and no need for bias either.
So why use class C I wonder?
I'd forget the IRF510. I've never found any good ones, far better devices around now. Try the 520 if your happy with old devices, usually works well.
Oh the filter is overkill, no harm in that but a single inductor and a pair of caps is fine for this power level at attn is approx 100 times (20dB).
Str.
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I have played around some with the cuircuit and discovered that it was the bifilar transformer that made the output power non-stable. Once it was removed(I put a T80-2 with 19 turns) the circuit was very stable, no increasing/decreasing over time. Also made the filter simpler with only one inductor and two capacitors, output waveform still looks nice.
I now get the following power:
30v supply = 4,50W RF output(400mA), efficiency = 38%
25v supply = 3,25W RF output(360mA), efficiency = 36%
20v supply = 2,25W RF output(300mA), efficiency = 37%
15v supply = 1,45W RF output(270mA), efficiency = 35%
12v supply = 0,85W RF output(250mA), efficiency = 28%
After removing some components, there is more room on the board. 4,5W is nice, but it can be a bit tricky to supply when you havent got a variable powersupply at hand.
I will have a look at alternatives to IRF510, that doesnt require as high voltage, it seams to be the most common HF amp on diy projects, cant find many examples with other ones.
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I found a couple of usefull pages on how to build an E-class amplifier, and gave it a try. With 12v i get about 1.5W out, so its usefull, but not as high output as i expected.
http://www.wa0itp.com/class%20e%20design.html (http://www.wa0itp.com/class%20e%20design.html)
Edit:
Also tried this circuit from https://www.researchgate.net/publication/320623200_Notes_on_designing_Class-E_RF_power_amplifiers (https://www.researchgate.net/publication/320623200_Notes_on_designing_Class-E_RF_power_amplifiers) But i got no usable power from it.
This Class-E stuff is clearly more complex than i expected.
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Also tried this circuit from https://www.researchgate.net/publication/320623200_Notes_on_designing_Class-E_RF_power_amplifiers (https://www.researchgate.net/publication/320623200_Notes_on_designing_Class-E_RF_power_amplifiers) But i got no usable power from it.
(https://i.postimg.cc/TPRJw1Zr/image.png)
My biggest problem with this paper and this circuit is that to specify a Class-E output network as he has without specifying a transistor is somewhat misleading; it fools the user into thinking that they can plug any old transistor (even a MOSFET) into it and expect it to work. Maybe this would work at 50 KHz with old power MOSFET transistors (which tend to have humongous output capacitance that swamps any other performance differences between models of transistors) but not at 6.9 MHz (as in the paper). The reality is more complicated and the component values of a Class-E network absolutely have to be tuned and optimized for each transistor at each frequency.
Also, it is humorous to me that this author does mention that he performed SPICE simulation but again without specifying what transistor was used and without providing any actual measured results to go with it. Had he substituted another transistor into his SPICE model, he would have seen exactly what I wrote above - the matching network has to be tuned and optimized for a particular model of transistor, which would make it obvious that specifying a network needs to be accompanied by naming the actual transistor used.
This paper is one of these garbage undergrad papers that people put out to pad their resume/CV; there's nothing new in there and it's lacking aspects that would make it useful to others. He references Sokol's book on Class E but then goes through a bunch of derivations that Sokol already did in his QEX article from 6 years before the book. I don't see the point.
I'm sorry that you wasted your time expecting this kid's navel-gazing project to work. That's a few hours of your life that you won't get back.
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The ripples on your O/P waveform are due to the lengthy earth lead of your 'scope probe.
Yes, certainly good practice but also I was going to say that attention has to be paid to stray inductance in the circuit in general. It's hard to say where the problems lies since he's provided 'scope images of what appears to be different locations in the circuit and I'm not sure which is which.
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My biggest problem with this paper and this circuit is that to specify a Class-E output network as he has without specifying a transistor is somewhat misleading; it fools the user into thinking that they can plug any old transistor (even a MOSFET) into it and expect it to work. Maybe this would work at 50 KHz with old power MOSFET transistors (which tend to have humongous output capacitance that swamps any other performance differences between models of transistors) but not at 6.9 MHz (as in the paper). The reality is more complicated and the component values of a Class-E network absolutely have to be tuned and optimized for each transistor at each frequency.
This is the primary reason I'm sticking with CMCD. The design process is as simple as tuning the tank to resonance and going about your day. In theory you could precisely calculate the tank values taking into account the Cds and so forth, but I found it much easier to spitball it.
+-RH
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The design process is as simple as tuning the tank to resonance and going about your day. In theory you could precisely calculate the tank values taking into account the Cds and so forth, but I found it much easier to spitball it.
OK, I'll take your word for it.
For what it is worth, I haven't built any yet but I have done some simulations with a few different power transistors in CMCD configurations for 43 meters and the optimized results have ended up with very different tank circuits; the same network (parallel RLC between the drains) but with very different component values depending upon the transistor.
Now, to be clear, my design process in the simulator is to do a bunch of sweeps of the RLC values to pick values that basically work then I put the optimizer to work to peak up the output power and efficiency, minimize power dissipation, etc. From there I usually end up tweaking it for one reason or another. The reason I mention this is because the optimizer can spend minutes trying to squeeze out every last milliwatt and that can move the design to a very different place. (I'm not watching everything that goes on at this stage - I'm usually asleep or doing something else while it does the drudgery for me.)
The end effect of this is that if you don't care about the difference between 120 and 125 Watts (picking numbers out of the air) then, yeah, it's probably fine to just swag at it. For better or worse and potentially overdoing it, the optimizer sweats the small details for me and that may be why I end up with very different tank circuits for different transistors at the same frequency.
What I do find interesting about CMCD is it doesn't have the high voltage peak on the drain at resonance like Class E; it's a current-operated mode (duh) and that seemingly permits the use of a lot of dirt cheap power MOSFETs with 100 V or lower BVdss that are plentiful with power inverters, switching supplies and motor control everywhere now.
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Finaly, i made some progress. I get approx 2W at 12v and 8W at 24v.
The oscillator puts 17Vpp into the IRF510, and the bias is adjusted to 2,1Volts. The DC bias at 2,1v is a sweetspot, output quickly drops of both before and after. The drive voltage is 17VPP, Efficiency is about 27-28%
One design i found online had a capacitor from the drain to ground. I just merged the two together, i have no idea what i am doing. My guess is that its operating in class C mode, due to the low efficiency.
Chanel 1(yellow) is voltage into 50ohm dummy load, Chanel 2(purple) is Gate voltage on IRF510.
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For the original circuit, with an IRF510 and 7V gate drive, you could modify the existing circuit in the paper to get a bit more out of it. Since you said you got nothing before, maybe you can get something now.
(https://i.postimg.cc/TPRJw1Zr/image.png)
Change the 139 pF to 124 pF (the exact value matters quite a lot here - a few pF either way makes a large difference.)
Change the 652 pF to 740 pF.
The RFC must be 1 uH or more, I would use 2 uH.
I continued with the 4.81 uH for the above simply because modifying it is more of a pain than changing a capacitor. If we pick better inductor and capacitor combination, the other two capacitors may have to change to suit.
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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.
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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.
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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
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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?
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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.
(https://i.imgur.com/iNt0Ekl.png)
Str
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I found an error in my datasheet, the efficiency wasnt as bad as i thought ::)
It turns out that the inductor(8T FT50-43) between drain and VCC impacts the power and efficiency quite a lot! The monofilar had the highest efficiency at 61%, but the trifillar had the highest output in RF-power.
After some tweeking i got nice values
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Finally i have completed the smaller circuit, and tested it. I lost a bit off efficiency compared to the "test circuit"(2-3% less), but the output power is very nice. At 13,8v i get allmost 10W of output power after the LP-filter. The amplifier maxed out at 21 watt at 24v :)
Edit: I managed to increase efficiency to just above 50% by adjusting the bias
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It turns out that the inductor(8T FT50-43) between drain and VCC impacts the power and efficiency quite a lot! The monofilar had the highest efficiency at 61%, but the trifillar had the highest output in RF-power.
It does, but only if it is too small.
If it is large enough that XL is sufficiently high then any inductance beyond that has little effect. What is "sufficiently high" you ask? I think that Stretchy's Rule Of Thumb (ROT) of 5x the drain impedance makes sense to me, but I've learned after doing enough of this that at 43 meters for low and moderate power transistors that 2 uH is the minimum sufficient value to avoid any possible issues and get well beyond the range of values where there is a strong effect of L upon the output. I came to this conclusion via simulation and experimentation with real circuits. It is a very clear to see in simulation.
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Finally i have completed the smaller circuit, and tested it. I lost a bit off efficiency compared to the "test circuit"(2-3% less), but the output power is very nice. At 13,8v i get allmost 10W of output power after the LP-filter. The amplifier maxed out at 21 watt at 24v :)
Edit: I managed to increase efficiency to just above 50% by adjusting the bias
Nice. You have probably reached the point where further time invested will have little effect upon the output power. The simulation that I did yesterday to arrive at my suggested changes to your Class-E circuit (which is very idealized since it does not include parasitic L, C and R) suggests that you will struggle to achieve more than 10 Watts output in Class E (at 12 Volts on the drain), not to mention Class C or whatever it is your circuit is in. Consider 10 Watts (at 12 Volts) to be the "ceiling" of what is possible without some sort of stroke of luck or gift from the parasitic gods.
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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.
In my world, we call this "AM to PM" (amplitude modulation to phase modulation), where AM (drain modulation) drives a change in phase.
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Today i started up the beacon for a test drive, and it worked nicely! I got a clear signal from a web SDR almost 700km away, only using a random wire antenna. I tested it with 10W RF output on 40m(14v supply), TX once a minute, but no issues with temperature. The Arduino controller is mounted on its belly, and i printed out some nice feet for it.
This build was interesting, and i learned a lot about how amplifiers work, and what powers to expect. I also got used to keeping the legs on the components short, and planing the layout better. Thanx for the help and tips i got during the build!
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Congrats! Are you going to put this beacon on the air 24/7 ?
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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.
I don't think that this was completely aimed at me but let me be clear.
In the professional world, we can simulate the the PCB, encompassing all the parasitic RLC it presents, and perform full-up EM simulations in software called HFSS or Momentum. It takes time to set up and run but it can be a huge time saver in the long run where it makes sense to do. These models can be crazy accurate up into the GHz range. At the internal chip level, full-up parasitic extraction is employed, taking into account all the layers and all the parasitics they generate, then they do an EM model of the package around the die and roll it all up to get the complete story of how a chip is going to perform. This is invaluable.
As a hobbyist, I'm not going to do an HFSS model for my dumb little FR4 PCB used at 7 MHz. :D I spend some time getting things to work well in simulation but, because I am an experienced user, I don't spend a lot of time on it because I know enough to realize that I can't encompass all the parasitic activity. The way I deal with it is what I call the "driving (a car) in deep snow method": target a frequency in simulation above the intended operating frequency, understanding that parasitic activity tends to bring the resonances down in frequency. When you build the actual circuit, it never operates at the the frequency the simulation said it would because of the parasitics. Rather than trying to figure out every little parasitic that causes that, I just offset by how far off from intended the resonance is, make a correction for that offset and then get it to operate close to where I want. Usually this just takes one course correction but sometimes a couple tweaks. I call this "driving in deep snow" because, unless you are traveling in a straight line, you have to pretty much aim the car sort of where you want to go and do course corrections along the way. There won't be precise steering. (Especially in an old rear-wheel drive car with bad tires. :) ) For the folks that live in more temperate locations, the analogy would be steering a small boat in choppy water. You aim the boat in a direction and manage through course corrections to get basically where you want to go.
So, if you end up having to tweak the simulated result anyway, the question is, "why bother with simulation at all then?" "Why not just go straight to 'build it and tweak it?' "
Because:
1) Rather than guess, you need a starting point, especially on new circuits. Simulation gives you that starting point and it is a huge time saver to explore possibilities. Knowing that you have a simple method to correct for the inevitable imperfect model gives confidence to explore further.
2) I find that never simulating usually means a hell of a lot more iterations and tweaks to get to where I want.
3) It is worth spending time figuring out some fudge factor frequency offset you need because you may want to use that output network on another board, at another frequency or with a different transistor, etc. Understanding how to reuse that network, the associated PCB layout and what to expect from it saves time in the long run. If you never bother to simulate, you never find out how far off you are and you will make the same mistake again and again.
4) I grew up just building and tweaking stuff until I got it to sort of work the way I wanted. Once I started working professionally in the field, I realized the power of doing a sim first and, for better or worse, now I am totally accustomed to it and can't imagine operating any other way.
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Maybe so, and I'll be the first to admit that I can be a stick in the mud. Its kinda like the old addage, stick with what works. I've gotten to a level of satisfaction with my current rigs that simulation for me is uneccessary. It may be true that it would have saved some design time in the beginning getting things to behave, but my methodology seems to work for me most of the time.
I've also seen my share of EE's that couldn't design a hole in the ground. They would get all wrapped up in modeling something, yet their builds never worked. You need a good balance of intuition and experience to make things play nice on the first try.
+-RH
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You beat me to it, mind you it was yours to do..
I'll + my 10p(c)'s worth.
I started by simulating in LTSpice whilst working for a 3G base station design company in 2005. I had the best engineers in the world to help, scientists too!
Initially started with 160m as the low frequencies mean you can use virtually any FET and wow couldn't believe how simple LTSpice was to use (still free!) and then when construction of the circuit was complete how close the simulation was to the real world.
Of course such a simple program has its shortfalls but you can see waveforms change shape when adjusting circuit values and hence get a 'feel' for what's going on.
Designing a PCB is a piece of cake with even online programs and super cheap manufacturing, highly recommend learning to do this as it's good fun and gives a tidy finish.
Like RH I've done all the simulations I need to do and actually know that the 'idealised' values don't matter at all. The circuit values are published and the circuit works well with off the shelf (not junk box!) modern components.
So you carry on with your simulations mate, we've been there and have done it and are actually doing it whilst you are.....?
Well, what are you doing exactly??
Str.
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Congrats! Are you going to put this beacon on the air 24/7 ?
I am thinking bout the applicaitons of this beacon, i will keep you posted :)
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I gave the thread a quick read through but will comment on one thing for now. If a good IRF510 is needed, don't buy it on ebay. I paid 82 cents each for the parts from Mouser and all were good so who cares if they cost more than the really cheap/crappy ones from other sources?
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Buying semi's from ebay is extremely risky, particularly with suppliers from overseas, China specifically. You never know what your going to get. Always go with a mainline distributors where possible (Mouser, Digikey, Newark, etc). Whatever you think you will save in money will surely be lost in time and frustration. These are jellybean parts, buy the proper ones from the start.
+-RH
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I got rid of the Arduino Micro and got a Attiny45 to do the same job, programmed it with the Tiny AVR Programmer(using Arduino language). It lowered the standby current from 40mA to 12mA.
The Attiny45-10pu draws 2,4mA at 5v, probably the oscillator that has a standby current of 10mA.
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Maybe so, and I'll be the first to admit that I can be a stick in the mud. Its kinda like the old addage, stick with what works. I've gotten to a level of satisfaction with my current rigs that simulation for me is uneccessary. It may be true that it would have saved some design time in the beginning getting things to behave, but my methodology seems to work for me most of the time.
That's fine. I don't think that I said that it's mandatory.
I've also seen my share of EE's that couldn't design a hole in the ground. They would get all wrapped up in modeling something, yet their builds never worked. You need a good balance of intuition and experience to make things play nice on the first try.
All of these statements are true. But it's only through learning why things didn't work that you acquire that intuition.
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I started by simulating in LTSpice whilst working for a 3G base station design company in 2005. I had the best engineers in the world to help, scientists too!
Initially started with 160m as the low frequencies mean you can use virtually any FET and wow couldn't believe how simple LTSpice was to use (still free!) and then when construction of the circuit was complete how close the simulation was to the real world.
Of course such a simple program has its shortfalls but you can see waveforms change shape when adjusting circuit values and hence get a 'feel' for what's going on.
Of course, the above is you agreeing with me without realizing it, as is usual. ::)
And you know, earlier in this thread, while poo-pooing simulation, you just had to go drag out a simulation (at the wrong frequency, BTW) to "demonstrate" a point. (https://www.hfunderground.com/board/index.php/topic,92791.msg297415.html#msg297415 (https://www.hfunderground.com/board/index.php/topic,92791.msg297415.html#msg297415)) You know, because simulation doesn't matter, right? ::)
Like RH I've done all the simulations I need to do and actually know that the 'idealised' values don't matter at all. The circuit values are published and the circuit works well with off the shelf (not junk box!) modern components.
Disagree that they don't matter. That you can't figure out that the idealized values do matter - especially based upon what you wrote in the paragraph quoted above - tells us everything we need to know.
Think about what you are saying before posting. If the idealized values had no bearing then the circuit would be dominated by, or entirely composed of, parasitics. Does that seem right to you? You would be tuning your LC networks by "feeling your way in the dark", stumbling around, with no predictability. I don't know about you but mine aren't that bad.
I'm done with you on this topic. There's no logic coming from you at all, with contradictions up the wazoo. As is typical, you are trying to pretend to be relevant and knowledgeable and you just end up making yourself look foolish to anyone paying attention.
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I got rid of the Arduino Micro and got a Attiny45 to do the same job, programmed it with the Tiny AVR Programmer(using Arduino language).
I assume that this is for the outgoing message, correct?
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I got rid of the Arduino Micro and got a Attiny45 to do the same job, programmed it with the Tiny AVR Programmer(using Arduino language).
I assume that this is for the outgoing message, correct?
Yes, the Attiny45 carries the code for keying the transmitter and sending the Hellschreiber message. The Attiny works well, despite beeing in close proximity with the 10W transmitter.
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I gave the LULU rf a try, the square wave output from the 74HC240 worked very well, but the output was behaving the same way as before. Output slowly rising for 1-2s and after that it looked like a mess on the oscilloscope. This was the same problem i had with my E class experiments last time.
Perhaps its my 50v ceramic capacitors that doesnt hold upp?
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Hi. I have a few things to say.
I assume that the first o-scope image is the gate drive. That's actually pretty good. The remaining ringing is possibly from your o-scope ground but also the 74HC240 package (DIP or SMD) was not designed to be a low inductance package and not designed to operate well at ~7 MHz. (Short version of the story: the limitation is chip internal layout and the wirebonding inside the DIP package. They were not designed for 7 MHz and not designed to be a massive-parallel FET driver.) The frequency indication in the upper right is 6 MHz. I thought you were trying to use 7 MHz? This frequency indication should be very accurate if the trigger is working well.
The drift with time is undoubtedly due to self-heating thermal drift. While you have a nice heatsink on what I assume is the final transistor, there will always be some thermal drift regardless. Do you have heatsink grease or a thermal pad between the back of the transistor and the heatsink?
You should also understand that the HC240 is being asked to deliver (what is for it) a lot of current at high frequency. The Icc/Idd will increase quite a lot just simply because of the frequency involved then to deliver the drive current to the transistor will also create a lot of heat. Most of the heat in this particular internal chip layout will come out of the bottom (because that is where the leadframe, which is what the wirebonds attach to inside, is located) but you have the bottom of the chip pointed up in the air ("dead bug"). (Yes, heat rises but the plastic-to-air thermal interface is never very good at transmitting heat.) You might be able to slightly improve things by trying to put some sort of heat sink or heat spreader on the bottom of the HC240.
There may also be other sources of thermal drift that I am not thinking of right now.
The other thing to note is that the messy o-scope image (the second one) probably has a lot to do with the trigger level you have set. Try moving it lower and experiment to find what gives the clearest result. If that is the output into a 50 Ohm load, it should be a reasonably nice sinewave, once the trigger level is adjusted correctly. Also, check the grounding of your probe. If that is the drain of the transistor, it should not look like that at all.
If you want to know more about the limitations of the LULU, you might want to see this: https://www.hfunderground.com/board/index.php/topic,89881.msg288345.html#msg288345 (https://www.hfunderground.com/board/index.php/topic,89881.msg288345.html#msg288345)
(I did see some thermal drift on my circuit as well. I just did not write about it.)
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IF the first waveform is the drive to the fet, the duty cycle is WAY too high. It should be closer to 40-50%. This has a large effect on your efficiency, and thus heat load on the final device. This is one of the reasons I use purpose built fet drivers in PA applications, better control over drive.
+-RH
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All good advice and here's some more.
Throw away those ceramic caps, they never were any good. Fine for random 'Sprinkle brothers' decoupling but utterly useless for anything else.
Hopefully, eventually you'll go SMT and see the light!
Please stick with modern NPO or COG caps and use 630V ones across the FET and in the output and filter circuits.
Waveform wise your looking for a half sine on the drain at 3.5 X VCC, the classic class E shape.
Get yourself a 2x365pF (or whatever) variable capacitor from an old A.M. radio, you can use it when tuning the output. Must show a video on that as it's very easy to see the different shapes of the drain voltage.
Str.
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(https://i.postimg.cc/vT2C7PBV/image.png)
I really don't understand how the duty cycle of the FET drive could be that far off from 50 %, but my first guess is that the feedback resistor (Rf below) that bias the input and output of the inverter is too low. It's usually something like 1 Meg Ohm. Either that or the load capacitors for the crystal (C1 and C2 below) are grossly mismatched. For the crystal you are employing (HC-6?) something like 18-27 pF is probably appropriate and their values should match.
(https://i.imgur.com/AXzmYYm.png)
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Yes, the Attiny45 carries the code for keying the transmitter and sending the Hellschreiber message. The Attiny works well, despite beeing in close proximity with the 10W transmitter.
The ATtinys are perfect for this. You can easily get the standby current down to a mA or less by putting it to sleep for 8 seconds at a time ...of course you can loop the sleep statement to sleep it for longer times as needed. Code is cheap and you can really minimize burning mAh's by sleeping the micro whenever possible.
I've not played with the 45 , but I've spent a lot of time with the ATtiny85. Great little chips.
I'm getting ready to build another beacon with mine, and you can do neat stuff like lowering your transmit duty cycle based on battery voltage, etc in order to put some hysteresis in the charge time. That's a powerful little chip for short money.
You've got a lot done with your project. Very cool!
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You boys are losing your edge. Three pages to get to the fights. You used to be going at it after three posts. Pitiful.
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You boys are losing your edge. Three pages to get to the fights. You used to be going at it after three posts. Pitiful.
I've turned over a new leaf.