Messages

601

The RF Workbench / Re: Hellschreiber beacon - with some oomph!

« on: February 26, 2022, 2033 UTC »

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)  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.

602

The RF Workbench / Re: Stretchyman 40 W TX Reliability Modifications

« on: February 26, 2022, 2020 UTC »

Quite easy to reprogram them to a higher (offset) frequency to negate the error.

Someone asked me privately last year if there was a way to fix the offset. I was very bored over Xmas and finally got around to reverse engineering several of your .hex file codes for 43 meters to figure out corrections and get them a lot closer to the intended target (~ +/-20 Hz off, instead of -100 Hz).

The other thing to note is that there are multiple sources of drift or frequency shifts. Most of them are pretty small and not worth worrying about. The largest one is that the synth takes a big jump of ~ -70 Hertz when the final transistor is turned on. That could be due to many reasons but I'm guessing it's due to supply voltage shift. My corrections take this into account but because of self-heating and temperature drift with time, it can't be better than ~ +/- 20 Hertz over the long term, which I feel is acceptable.

603

The RF Workbench / Re: Some words about parts off ebay and other non-oem distributors

« on: February 26, 2022, 1958 UTC »

The only things I have purchased from Amazon or Ebay (general Ebay, not a dedicated Ebay store for some manufacturer) are wire, test clips, etc. and even with the simplest things there is risk.

I bought some 2 foot long coax cables with BNC connectors on both ends from Ebay and they are absolute shit. I tossed them out.

604

The RF Workbench / Re: Hellschreiber beacon - with some oomph!

« on: February 26, 2022, 1952 UTC »

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.

605

The RF Workbench / Re: Stretchyman 40 W TX Reliability Modifications

« on: February 21, 2022, 2147 UTC »

I don't know how many versions of your synths you have gone through but the ones that I have used have always ended up a bit lower in frequency than I would like - usually about ~100 Hertz low. We're not expecting WWV accuracy here and the consequences of this are not the end of the world but I think that we can agree that they could be closer to target.

I suspect that a number of the loggings on this website indicated as "xxxx.9 KHz" (more or less) come from your synths, but I can't prove that. Perhaps this is yet another way to identify one of your transmitters on the air. 

606

The RF Workbench / Re: Hellschreiber beacon - with some oomph!

« on: February 21, 2022, 2045 UTC »

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.     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.

607

General Radio Discussion / Re: Interesting Amateur Radio Connection in this 60 Minutes Australia Story

« on: February 21, 2022, 1834 UTC »

Mr Godfrey is using what has been coined "GDTAAA" (Global Detection & Tracking any Aircraft Anywhere Anytime) and (as far as I can tell) it relies on disturbances in the SNR of WSPR transmissions to "follow" the aircraft path. I have not had time to read all the stuff on this but as I understand it, his GDTAAA tracking lines up with the satellite tracking to some or a complete extent.

Here is his blog: https://www.mh370search.com/2021/12/31/mh370-flight-path/

Here is the first part of a report that he wrote on this: https://www.dropbox.com/s/k4fn8eec4z9np0z/GDTAAA%20WSPRnet%20MH370%20Analysis%20Flight%20Path%20Report.pdf?dl=0

608

The RF Workbench / Re: Stretchyman 40 W TX Reliability Modifications

« on: February 20, 2022, 1813 UTC »

No crystals or complex synthesizer needed. A simple Arduino code sets the TX frequency!!

No disrespect to you personally intended but I consider myself to be comfortable enough with microcontrollers and synthesizers to be "dangerous" with them and I don't feel this to be a terribly simple solution. You need a microcontroller, you have had to write software for it, then the output is pretty weak and it will need a decent linear amplifier (which you have not discussed here) to boost the output to be heard farther than 10 meters away. Also, I don't consider the AD9850 to be a particularly simple synthesizer. Perhaps it appears that way if you treat it like a black box and don't know what's going on inside but I don't recommend doing that. (I actually don't feel that any synthesizer is "simple".)

To be clear, there is a need and a place for synthesizers and I don't know how you do a AD9850 (and the like)-based synth without something providing the digital words to them (here, it's a microcontroller) but let's not pretend that this is a simple solution.

So not my cup of tea, but to each his or her own I suppose.

Finally, I'm not quite sure why this ended up here in this thread. It's completely unrelated to the original topic.

609

The RF Workbench / Re: Hellschreiber beacon - with some oomph!

« on: February 20, 2022, 0306 UTC »

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.

610

The RF Workbench / Re: Hellschreiber beacon - with some oomph!

« on: February 20, 2022, 0248 UTC »

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.

611

The RF Workbench / Re: Hellschreiber beacon - with some oomph!

« on: February 20, 2022, 0215 UTC »

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.

612

The RF Workbench / Re: Hellschreiber beacon - with some oomph!

« on: February 17, 2022, 1809 UTC »

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.

613

The RF Workbench / Re: Hellschreiber beacon - with some oomph!

« on: February 17, 2022, 1734 UTC »

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.



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.

614

The RF Workbench / Re: Hellschreiber beacon - with some oomph!

« on: February 17, 2022, 1643 UTC »

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.





 

615

The RF Workbench / Re: Hellschreiber beacon - with some oomph!

« on: February 17, 2022, 0303 UTC »

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.