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Messages - Charlie_Dont_Surf

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The RF Workbench / Re: Someone had Corsair II AM TX experience?
« on: March 15, 2021, 2120 UTC »
How wrong you are...

Well, you do try to lord all over a lot of people here so...

Just ignore...

There you go. Keep your head in the sand and keep thinking that your shit don't stink. At least you are on brand.


My thought was that since these chips put out a PWM signal but at a voltage and drive current level that isn't going to modulate a transmitter well, simply add a follower/level-shifter after the PWM chip which will do the heavy switching and let that modulate the transmitter thought appropriate LPF filtering. As a simple feasibility check, I obtained an Adafruit PAM8302 module and put that output into the gate of a IRL510 which I had in my supply and chosen because of the low threshold voltage. It worked well enough that I am going to put together a test board with the PAM8302 driving a real FET driver and then a good FET and some filtering to drive a TX B+ input.

An update on this.

When I first looked into this, I put a follower on the PAM8302 many months ago, I spent most of my brief time looking at it (5 minutes?) more concerned with assuring that the follower was "following" than anything else. I hooked it up again recently to look at some more things and realized that I should have spent more time examining the nature of the smoosh on the oscilloscope screen that the PAM8302 puts out when I looked at it the first time.

It's advertised as Class-D, which I assume is true, but it's for sure not PWM. It looks more like Pulse Code Modulation (PCM) to me. I can't find the USB stick that has the scope image right now but from memory: the output consists of very narrow (im)pulses at something like single-digit microsecond regularity (so hundreds of Kilohertz) and the height of the pulses follows the envelope of the audio input. So it is not a constant amplitude output and not PWM. I assume that they do envelope restoration on the Class-D output (what is probably more commonly known in hobbyist circles as "drain modulation") to get it to follow the envelope of the input signal.

In any case, this changes what I was going to do with the PAM8302; a variable amplitude signal isn't going to get through a FET driver and also isn't going to take advantage of the efficiency of a switching modulator. There may be a time when I decide to make a series modulator with it (PAM8302 + follower + perhaps a level-shifter) but that time is not now so I have set that aside.

Instead, I have a PWM board in progress using the LTC6992 PWM chip and TI UCC5304 isolated FET driver and some other bits. It basically worked the first time I turned it on but there are some issues to work on before I'd be happy using it outside the lab bench.

Often these same users hook up a coat hanger as an antenna and also hope for the best  :)

Yeah, I've noticed.

The RF Workbench / Re: Stretchyman 40 W TX Reliability Modifications
« on: February 14, 2021, 0040 UTC »

The very first ever design I made was an unashamed copy of the venerable LuLu design. Fat better than any other design to date and I must emphasise not my design. All I ever did was make a PCB to make replication a simple matter.

It uses a Xtal which I had to get made at considerable cost (£14 ea.) and managed to get quite a few units made (100 approx).

That was five years ago and all designs since 2016/17 have an AD9833 DDS.

...So as I must say again it's not my design, however  there are other designs out there that are and Yes you've slagged those off as well....

Your name and email address are on the PCB silkscreen. You probably put your "STRETCHYMAN PIRATE RADIO" stickers (a ripoff of Breaking Bad) on the case too. But now you are claiming because the original design came from someone else that's it's not your fault?

I'm sorry, but you own that problem.

The rate of occurrence of this weird drifty oscillator issue is more than some sort of random, chance occurrence. You shipped "several" of these units but apparently never put them through sufficient validation and or any sort of burn-in to confirm that they stay stable over time.  If you had, then you would have found this issue. Just like you would have found the famous high-voltage snap that takes out either the drain filter cap or the FET or both (and caught on fire in front of me), but you didn't, because you don't know what you are doing and can't be bothered.

Designs get shared and tweaked all the time. There's a fellow named Paul Brokaw, whose Brokaw Bandgap Cell (https://en.wikipedia.org/wiki/Brokaw_bandgap_reference) is used as a reference in nearly every IC from all manufacturers since the 1970s. There are billions of these things around the world now. By your logic, if someone makes a Brokaw Bandgap and fucks it up, then we should complain to Brokaw and not the person who fucked it up? Riiiiiiighhhhhhht.

You want all the accolades and none of the responsibility.

I still suspect most 'simple' Xtal controlled designs to exhibit some form of FM that's visible on an SDR.

Cool, except that a sudden drift of 1 KHz that Chris showed is not FMing.

I look forward to seeing any design from particularly yourself or anyone else for that matter that you mass market and build 100+ units.

I doubt (know) that this will ever happen.

I look forward to your reply.

So very nice of you to invite me to play the "my balls are bigger than yours" game. Explain to me how many you've shipped has anything to do with your ability to solve problems before they are created? Apparently none. And shipping lots of defective product is the hill you've chosen to die on? And the barrier to entry for whether something is "worthy" or not is not whether it's good, it's just that you've shipped many of them, warts and all?

Also, what good would it be for me to put a schematic out when most of my problem with you is that you are absolute crap at validating and testing? You aren't going to learn those skills from a schematic.

(Shaking my head)

My professional life is in the design, validation and manufacturing and post-sale support of electronics that sells in somewhat higher orders of magnitude than what you are talking about, but please do tell me more about the the 100 you made over the course of a many years. It's amusing to me in a very haughty sort of way.

Since I have been doing this for decades, I've give you a couple of lessons for success:

1) If you don't know something, don't pull some bullshit text off the internet and use it to justify your preconceived notions. Look into yourself. Figure it out. If you don't have the answer, say, "I don't know but I'm looking into it." The smart people I know admit when they don't know something and don't make shit up.

2) Test your shit out extensively. Build 10 and put them through their paces. Leave them on for a long time. Examine design marginalities. Push and pull the design before you ever ship any product.

3) Despite your best efforts (which you have not made, see above), there will be post-sale problems with your products. Don't sweep them under the rug. Fix it or make it up to the customer.

I'll say it again: You want all the accolades and none of the responsibility. You don't know what you are doing, and don't care to know how to do things better.

As for my designs, my employment is somewhat engrossing and I'm not interested in becoming a BIG TIME PIRATE SUPPLIER MOGUL like you apparently are. I get my jollies by shipping good product that doesn't catch on fire right in front of customers.

The RF Workbench / Re: Someone had Corsair II AM TX experience?
« on: February 13, 2021, 2301 UTC »
The reason why it gets some much attention is that many have been built and used in the past. I've found out so much about the designs asking the right people. The parts are easy to get hold of and if your into home construction it can cost under 20 UK pounds to build depending on the version.

I've built Corsette (LM386), Corsair (LM386) and Commando (Transformer) that's on Dave's website and in my opinion they all work well.

Shhh. Quiet. You're destroying Stretchy's bullshit narrative that everyone MUST.THINK.LIKE.HE.DOES and no one could be happy and content without doing what he wants. There's probably been more Corsette, Corsairs (I&II) and Commandos built than he has ever sold and that gets under his skin.

The RF Workbench / Re: Someone had Corsair II AM TX experience?
« on: February 13, 2021, 2248 UTC »
Just depends on how you drive it, squarewave = class E, sine =C, sure there's more to it as the o/p has to be bandpass but still the quicker the switching the greater the eff% pure and simples.


Umm yeah, there is more to it.

Like, amplifier class is not defined by how it is driven. It is defined by the shape of  the drain/collector waveforms.

Also sinewave drive can also be Class A or B, in addition to C, it depends upon the associated drain waveform. Squarewave drive can associated with class D,E,F, S or J.

Propagation / Re: 49m good this evening....
« on: February 12, 2021, 1043 UTC »
Sorry, I was referring to the extended period above 7 MHz the day before, so the red trace on the right side of the graph.  The circa 0620 UTC blip is certainly just bad data.

Oh. OK. I misunderstood.

I suppose if you're on such a KiwiSDR, you could tune in CHU or WWV, see what the frequency error is, then compute the ppm error and apply that to the frequency of the station you're listening to. Note you need to treat it that way, it's not just a constant frequency offset error.

That's exactly what I have done a few times to confirm my suspicions that some receivers were a bit off frequency.

I also suspected that the offset would increase with frequency and one time I went through the trouble of confirming this at 2.5, 5 and 10 MHz. It was incrementally worse at higher frequencies (by a few Hertz, but still..). (Could not hear 15, 20 or 25 MHz at the time.)

So there is no manual trim on the frequency with the Kiwi? I guess that would have to be some sort of override to the GPS, which, in my limited understanding, seems problematic

The RF Workbench / Re: Someone had Corsair II AM TX experience?
« on: February 12, 2021, 1014 UTC »
Sorry, I was confusing my memory of this with something else when I wrote the above and in my case the load was probably around 3-4 Ohms but the peaks probably presented the difficulty for my Class-D amp. (My guess.) Either that or the amplifier was not what the manufacturer claimed.

In your case, 12 V/9 Ohms = 1.33 A. (12 Volts ^2)/9 Ohms = 16 Watts (average). (24 V ^2)/9 Ohms = 64 Watts (peak).
Your power was/is probably close to that of the Corsair.

Propagation / Re: 49m good this evening....
« on: February 11, 2021, 0620 UTC »
foF2 was up above 7 MHz for a while, this often happen just as a geomagnetic storm is starting, the K index was 4.

When I see a blip like that at ~0620 UT, my first inclination is to think that it is not authentic (i.e., bad data) and some quirk of reception happened or the algorithm that determines FoF2 from the ionosonde data was "fooled" somehow. That data point is too weirdly out of place, even though FoF2 did appear to be slightly elevated that day compared to other recent days.


1)  ...  Is GPS antenna really needed or can I forego that for now?

The GPS antenna is not required, but highly encouraged, that's how the KiwiSDR corrects for errors in the ADC clock sampling frequency.

Does GPS also serve as a frequency/time reference? Can you also manually trim the reference or clock to WWV/CHU/whatever in absence of (or in addition to) that?

I notice that Kiwis can be anywhere from <10 Hz to as much as 60 Hertz (maybe more?) off from a standard. While that's not a life-or-death offset in a hobby listening scenario, it would be nice to be kind of on frequency when listening to SSB, where I notice being >10 Hz offset there.

The RF Workbench / Re: Stretchyman 40 W TX Reliability Modifications
« on: February 11, 2021, 0546 UTC »
Chris - I think that the answer lies in the power dissipation of the crystal.

This makes sense to me because:
a) Where there is power dissipation, there is heat.
b) Where there is heat, there is a temperature change and drifting oscillators.
c) A crystal is pretty simple. What the heck else could it be?
d) I found references that say so. Here is one:


On page eleven, in the third full paragraph in the left column:

The permissible maximum power dissipation of crystals in the 1 to 20 MHz range, operating in the fundamental mode, is about 200 microwatts and is  similar for overtone operation. ... Operating a crystal above or near this level degrades its stability, and the circuits chosen here avoid this problem by limiting the dissipation.

Further down:

The main point to remember is  that crystal  oscillators are meant to provide a stable frequency source, not power output. Frequency stability, both short and long term, and crystal life are compromised when an oscillator is operated at an excessive power level.

I have no idea whether Stretchy's circuit goes beyond tolerable limits. I'm just putting this out there for thought.

The RF Workbench / Re: Stretchyman 40 W TX Reliability Modifications
« on: February 11, 2021, 0524 UTC »
Why being so negative about comments?

               Keep the Peace!  8)  -  It's almost Xmas!

CoolAM Radio - Shortwave
the Netherlands


Hi André - I am sorry that you feel that way because on the other 364 days of the year people might come to this thread for answers, without the "burden" of being in the "Christmas spirit", and find nothing. It's now nearly 2 months later and we have no answer.

The RF Workbench / Re: Someone had Corsair II AM TX experience?
« on: February 11, 2021, 0518 UTC »
You could also replace the series modulator with a $11 class d audio amp board from amazon.  Efficiency would be MUCH higher, and it makes more sense to go this route since you already have a 24V supply at your disposal.


Not disagreeing with you (you're absolutely right about the efficiency) but some day I should write up my experiences trying to use a cheap Class-D amp as a series modulator, requiring the cheap amp to supply all the bias for the RF stage.

The cheap class-D amps that I am aware of don't like to drive loads below 1-2 Ohms, which is exactly what you would be asking it to do by becoming a series modulator. It gets "unhappy" when you do this and I damaged more than one by asking it to deliver x Amps continuously as DC bias for the RF final, in addition to modulated bias. Sometimes the damage was not catastrophic, sometimes it was catastrophic. (It's a good thing that the amplifiers are "cheap".) My proposed solution (which I never got around to trying) is to add 2 Ohms in series between the class-D amp and the RF amp. That way the Class-D amp is never seeing less than 2 Ohms and is less likely to be "unhappy". Of course, this is wasteful and might eliminate the efficiency gains you made by using a Class-D amp.  :(

Well, I guess I have now written up my experiences on this, so today is "some day".

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