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Author Topic: Hellschreiber beacon - with some oomph!  (Read 2501 times)

Offline Radiotech

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Re: Hellschreiber beacon - with some oomph!
« Reply #30 on: February 23, 2022, 1736 UTC »
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  :)

Offline Teotwaki

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Re: Hellschreiber beacon - with some oomph!
« Reply #31 on: February 24, 2022, 0720 UTC »
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?
Jim
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Offline redhat

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Re: Hellschreiber beacon - with some oomph!
« Reply #32 on: February 24, 2022, 2151 UTC »
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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Offline Radiotech

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Re: Hellschreiber beacon - with some oomph!
« Reply #33 on: February 26, 2022, 1058 UTC »
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.

« Last Edit: February 26, 2022, 1113 UTC by Radiotech »

Offline Charlie_Dont_Surf

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Re: Hellschreiber beacon - with some oomph!
« Reply #34 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.
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline Charlie_Dont_Surf

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Re: Hellschreiber beacon - with some oomph!
« Reply #35 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.
« Last Edit: February 27, 2022, 2237 UTC by Charlie_Dont_Surf »
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline Charlie_Dont_Surf

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Re: Hellschreiber beacon - with some oomph!
« Reply #36 on: February 27, 2022, 0034 UTC »
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?
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline Radiotech

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Re: Hellschreiber beacon - with some oomph!
« Reply #37 on: February 27, 2022, 0751 UTC »
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.

Offline Radiotech

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Re: Hellschreiber beacon - with some oomph!
« Reply #38 on: February 27, 2022, 1810 UTC »
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?






Offline Charlie_Dont_Surf

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Re: Hellschreiber beacon - with some oomph!
« Reply #39 on: February 27, 2022, 2317 UTC »
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
(I did see some thermal drift on my circuit as well. I just did not write about it.)
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline redhat

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Re: Hellschreiber beacon - with some oomph!
« Reply #40 on: February 28, 2022, 0144 UTC »
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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Please send QSL's and reception reports to xfmshortwave [at] gmail [d0t] com

Offline Stretchyman

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Re: Hellschreiber beacon - with some oomph!
« Reply #41 on: February 28, 2022, 1057 UTC »
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.
« Last Edit: February 28, 2022, 1113 UTC by Stretchyman »
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Offline Charlie_Dont_Surf

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Re: Hellschreiber beacon - with some oomph!
« Reply #42 on: February 28, 2022, 2347 UTC »
Quote

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.

I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

 

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