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Messages - Charlie_Dont_Surf

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766
The RF Workbench / Re: Simplest Tx
« on: April 19, 2020, 0950 UTC »
Quote
And oh look: I just noticed that the Cree SiC device has an internal 26 Ohm gate resistance already. Gate resistance that high is not inherent in SiC technology; they added some resistance to the device inside the package. I'll give you one guess as to why they did that. This reinforces my point. Adding more externally would help protect (given the caveats above) but obviously the need is reduced in this case. I still don't like the idea of blowing up the internal gate resistor and wrecking the whole device when I could have done something about it.

I don't think this is quite true.  The gate resistance is usually caused by the lossy-ness of the semiconductor material and the very fine binding wires used to connect the die to the outside world.  You'll notice on most datasheets this is derived by measuring the AC resistance of the junction at a known frequency and amplitude.  The larger the die and its gate structure, the larger the parasitic gate capacity, and the higher the gate AC resistance.  This is dependent on which silicon technology and topology is being used, obviously.

I can't speak with any authority on other technologies, but the metalization of the gate structure in SiC is one of the reasons for the higher gate resistance than comparable Si devices.

+-RH

Hmmm. Yes, it is measured at 1 MHz but they indicate "resistance", not "reactance" or "impedance". Though 1 MHz is probably more application-specific for most users than just a DC resistance.

26 Ohms at 1 MHz works out to 4.14 uH (assuming it's purely reactive). A product like this can get away with that much gate inductance. If this were a microwave transistor, the thing wouldn't work at all.  :D

767
The RF Workbench / Re: Simplest Tx
« on: April 19, 2020, 0929 UTC »
Hopefully that's the end of my thread getting hijacked as did the other.

If you have a simpler design or one as good and not too tricky to build then post up otherwise, please, don't bother.


To the moderator: does anyone, other than a moderator, have "ownership" over threads?


Also please don't post up any useless theoretical simulations, Yes we've all got a cracked copy of ADS or whatever but barely worth the time and effort for such simplistic design/build, may as well go straight to PCB.

You don't get it, do you? I wanted to see what the response at the harmonics were. I wanted to see what you were doing, whether you were seeking to minimize 2fo or something else because it wasn't clear to me. What better way to get the answer since you couldn't be bothered than to simulate it? And the result validated exactly what your schematic indicated, that the response peak is at around 45 meters and also that 2fo and 3fo were attenuated  So, what's the problem again?

(Shaking my head.)

If ADS is so "useless" then why do you have a copy of it?

Since you are so sure that sims are "useless", you had better tell the Qualcomms, the TIs, Huaweis, the Ericssons (and for that matter the General Motors, the Toyotas and the Whirlpools) of the  of the world. They'd be very surprised to know that all that money they have invested in design simulation is a waste.

Keep in mind that every time you use Ohm's Law, every time you calculate your expected power output, every time you determine the expected inductance on an Amidon core, you are using a mathematical formula that describes a physical phenomena. That's all simulations are, math models. So Ohm's Law is useless too, huh?


If you have a better design, built it, market it and tell us about it otherwise don't bother.

I've got something better. I've got one of your 40 W TXs that I bought secondhand that blew up on me about 20 seconds after I turned it on. I could literally see flames through the air vents on the enclosure. You really know how to leave a great first impression with your "superior" hardware.

I'll start a whole thread on my investigation into that explosion, so that you get to come in and "hijack" it.

768
The RF Workbench / Re: Simplest Tx
« on: April 11, 2020, 2137 UTC »
...there's no need for a gate Res as it just slows down the drive waveform. I use SiC in this design.

That's akin to saying, "I removed the brakes from my automobile. They only served to slow me down." or, more particular to the subject at hand, "I bypassed the fuse. It was limiting my transmit power."

There is a time, place and purpose for everything.

Gate resistors regulate the rate at which the gate and output circuitry can add or drain charge from the parasitic capacitance of Cgs, Cds, etc. This is why power MOSFET datasheets include specs like Qgs, Qgd and Qg. Because Q=CV and i= dQ/dt.

The rate of discharge of those parasitic capacitors is, ultimately, the slew rate - the rise and fall time. And we know that faster rise and fall times often go along with more overshoot and ringing.

So somewhere there is probably a happy sweet spot of gate resistance that doesn't make the edge rates so slow to be unusable at the desired frequency, while also limiting overshoot and ringing and offering some protection to the gates and the gate driver.

And oh look: I just noticed that the Cree SiC device has an internal 26 Ohm gate resistance already. Gate resistance that high is not inherent in SiC technology; they added some resistance to the device inside the package. I'll give you one guess as to why they did that. This reinforces my point. Adding more externally would help protect (given the caveats above) but obviously the need is reduced in this case. I still don't like the idea of blowing up the internal gate resistor and wrecking the whole device when I could have done something about it.

You can leave out the external gate resistors. That's your choice, not mine.


769
The RF Workbench / Re: Simplest Tx
« on: April 11, 2020, 1207 UTC »
You can't pass and reject at the same freq!

That should have been "Do you mean to tune the LPF to optimize rejection of 2fo and pass fo or do you mean tune the filter to optimize passing 2fo and rejection of fo (which is not really a textbook Class-E amplifier)?"

Never mind. I figured it out myself.




The LPF had nothing to do with class E but ...

Uhhh, no. Class E has to have a filter to reject harmonics, by definition.

I don't bother with 'Simulation' as I use a network analyser to make sure it Really works!

OK, dude. So you start every project with no prior knowledge to work from by walking into the lab and randomly grabbing any old parts off the shelf, put them together and arrive at a solution by complete trial and error. For everything. And you stumble through life that way. So happy for you!

Obviously everything gets checked out and tuned on a VNA, spec an, etc. in the end, regardless of whether you simulate it or not.

770
Microphone audio is tough to understand with the static crashes. Using an SDR in Indiana.

0218 CW ID sounds like "WRXI" through the static crashes. Good idea to do the CW ID tonight with all the interference.
0229 Clear ID and email address. Acknowledging HFU reports.
0255 Slowly fading down.
0259 More announcements. (I switched to Rochester, NY.)
0310 Black Sabbath
0319 Bad Company
0443 I checked back and appears to be gone.


771
The RF Workbench / Re: Simplest Tx
« on: April 10, 2020, 2159 UTC »
I've made hundreds of these and they work fine. Voltages and drive come up in sequence and there's no need for a gate Res as it just slows down the drive waveform. I use SiC in this design.

Regards.

Stretchy.

OK.

Your write up calls this a Class-E design but your schematic indicates to "tune the LPF to the second harmonic". I have not simulated your LPF to check the impedances so forgive the question:

Do you mean to tune the LPF to optimize rejection of 2fo and pass 2fo or do you mean tune the filter to optimize passing 2fo and rejection of fo (which is not really a textbook Class-E amplifier)?

772
Amateur Radio / Re: Chirp download --- Windows 7?
« on: April 06, 2020, 0408 UTC »
Sounds like something to tweet about.

Or at least chirp about.

773
Equipment / Re: Loop or Longwire?
« on: April 06, 2020, 0024 UTC »
there doesn't seem to be anything above 20 K.

Yes, for now. In about 4 or 5 years from now, it should be pretty good though. There will be periods between now and then when that area may show flashes of brilliance but you've got plenty of time to prepare for that.

774
Thing I note abt this thread is there's a shtload of people who used to post here and don't anymore.

It must be my bad B.O. driving them away.

775
The RF Workbench / Re: Simplest Tx
« on: April 05, 2020, 2338 UTC »
I realize that the title is "Simplest TX", however, this is a bit too simple for me. Here are a few things that concern me upon initial inspection.

No gate resistors in the circuit

Widely agreed upon switch-mode principles would say that small-value resistors in series with the gate are recommended. This is for two main reasons:

   a) To de-Q (reduce the Q) of the gate circuit and reduce the severity of any ringing.
   b) Protect the transistor gates and the gate driver IC in the event of a fault.

Transform, the maker of the GaN device in the schematic, strongly recommend gate resistors in their datasheet and application notes. According to the datasheet of the FET driver in this schematic, the On Semi NCP81074A, the series resistance of its outputs is ~0.5 Ohms. This is insufficient. Consider adding 10 to 30 Ohms in series.

You may consider adding ferrite beads in series with the gates as well to reduce transients and keep RF out of the FET driver. Transform recommends these.

While I am mentioning protection, this has nothing to do with the gates but it's also worth saying that fuses and MOVs are not shown in this schematic and are a very good idea too.

https://www.transphormusa.com/en/document/datasheet-tp90h180ps-900v-gan-fet/
https://www.transphormusa.com/en/document/recommended-external-circuitry-transphorm-gan-fets/


Power supply sequencing is important for GaN

I don't know about the SiC device shown in the schematic but if you are using the GaN device, you must pay attention to power supply sequencing at turn on and turn off. If you do not follow the correct steps, the transistor may work initially but there is a very good chance that it will fail (destruct) soon enough. That time period between first use and destruction will vary with the drain to source voltage, the gate to source voltage, the temperature, etc. It could be microseconds later or it could be hours later, based upon my experience.

The basic turn-on sequence for GaN is as follows:
   - Apply a gate voltage well below threshold (even a negative voltage is a good idea) to bias the GaN device.
   - Apply the desired drain-to-source voltage.
   - Increase the gate voltage to bring to the desired operating point.
   - Turn on the RF.
   
The basic turn-off sequence is exactly the reverse order. The sequencing can be implemented manually or with one of the many bias sequencing semiconductors on the market. In case you think I am pulling your leg and think that this procedure is unnecessary, here's the same information from Qorvo:

https://www.qorvo.com/design-hub/blog/how-to-bias-gan-transistors-without-damaging-the-device-video-tutorial


EDIT 4/6 - I looked at this a bit more. This is not a typical GaN device, rather, a hybrid of a typical enhancement-mode GaN and a traditional enhancement-mode MOSFET. This means that turn-on and turn-off sequencing are not like regular GaN. I communicated with Transform and they recommend first applying gate voltage then drain voltage, so not completely unlike what I wrote above. Thus, regardless of composition, the concern over sequencing remains.


The circuit in the schematic does (says) nothing about proper sequencing. It is either left to chance or to the user to implement. 

Things to consider:
   - How fast does the +5 V regulator and the Cardinal CPP oscillator come up to full voltage? It might be faster than the modulated drain voltage. If so, that is undesirable.
   - Of note here, the NCP81074A datasheet lists a UVLO period of 10 microseconds. Then what happens to its output if the Cardinal isn't ready with its output when the UVLO period has expired? It depends upon what the Cardinal does.
   - If the Cardinal and the NCP81074A are delivering a voltage well above the FET threshold voltage while Vds is still coming up to final value, that is also undesirable.
   - How fast do all the supply voltages come to final value and do they do so at their same individual rates under all conditions?

If you plan on making one of these, I recommend checking things out with a storage oscilloscope so that you can capture the turn-on and turn off effects, make sure that the sequencing is correct and check for ringing without having to do a repetitive waveform. Turning things on from "cold" is not always the same as from "hot".


Schematic.


776
General Radio Discussion / Re: COVID Watch Net
« on: April 01, 2020, 0007 UTC »
Does anyone know if this is actually happening?

777
10/11 meters / Re: Sporadic "E" on 11M / 10M Sunday evening.
« on: April 01, 2020, 0006 UTC »
Yes, hearing a lot of north-south 11-meter activity today.

778
Amateur Radio / Re: Kevin J Bess, KK4BFN on coronavirus
« on: March 31, 2020, 2005 UTC »
Were amateur radio operators involved during the swine flu epidemic?

Of course. Where do you think the SWINE FLU came from but HAMS?

779
In the case of W6WBJ, I think we have a common sociopath. Nothing more, nothing less.

Good point.

As for the others you're probably right, but I don't know if they've reconvened as I haven't found them all at one place - not that I'm really looking

I've been checking a bit more often since I posted about this earlier. WA7BZI and some of the others seem to show up a lot but mostly it's people playing editing recordings of the other former regulars, including the bootleggers. Most of the regulars are still listening though and you can hear them drop a comment in here and there.

[Side note: one of the main retorts to the bootleggers has been, "Do you have a callsign?" However, it's not like the regulars, who are acting all high and mighty by asking that question, adhere to the rules about identification either. They dip in and dip out without identifying. You can listen for hours on that frequency and not hear them identify.]

A year ago or more, the other regulars got sick of the frequency and ended up on the extra-class portion of 80 meters (until the jammers found them there too) but also sometimes 160 meters. They don't seem to be doing that anymore, at least recently anyway.


780
There's even a 440 repeater in socal that carries much the same bunch with the same repertoire. Can't recall the freq but they're famous for having fcc investigations and so on.

K6MWT: 147.435 (output), 146.400 MHz (input), 103.5 PL tone.

https://your435.com/about/

Whoops. I was looking at the thread again just now and realized that I replied to a 440 repeater inquiry with a 2 meter answer. DUH.

In any case, on the same peak (Santiago Peak in southern Orange County), there is a 446.64 ( - offset, 77.0 PL tone) repeater that has, let's say, similar clientele. Not nearly as out of control as K6MWT - not even in the same universe - but similar.

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