Keyboard Shortcuts
ctrl + shift + ? :
Show all keyboard shortcuts
ctrl + g :
Navigate to a group
ctrl + shift + f :
Find
ctrl + / :
Quick actions
esc to dismiss
Likes
Search
QDX Success story
开云体育Without.? My plan is to get good data
without, then add them and see what the difference is.
This is Science isn't it?
On 25/08/2023 20:11, Daniel Walter via
groups.io wrote:
Chris, is this with or w/o Zeners?
|
开云体育I've started playing with a spectrum analyser, this is what I have so far. There's a bit of scruff round the signal and the second and third
harmonics are about -60 dB which seems pretty good, better than my
Pixie. And at this stage L513 had 9 turns instead of 10. At present I'm using a crude 38 dB attenuator and was running about 1W.? I've a 10W 20dB attenuator coming and that should allow me to run my QMX at full power. Not used a spectrum analyser before so a bit of a learning
experience, there must be a way of getting a screen shot onto a SD
card. ?And I have some Zeners, 1N4756A.? Hans, I could send you a couple if it helps. I'm taking my time over this, not applied more than 10V to my 12V
QMX, that gives 2 to 2.5W, astonishing how far that gets. Chris, G5CTH
|
|
An addition that I should have included in the prior post:
In my estimation, simulation is good to help work out issues with a design.? Actual measuring should be done for an individual radio.? If you rely on measurements only, you can get into a parts variation problem.? Is your measurement sample large enough to verify the outliers in a production run? The above is from experience in taking processes from R&D to production.? The results are not always as expected.? This is from food industry experience, but I believe the concept applies. 73 Evan AC9TU |
|
Willie and John,
I believe that the simulation works for the QDX version of the amp.? I'm unsure about the EER/power addition of the QMX.? That may be more of an issue when Hans offers the SSB upgrade for the QMX.? Zener protection has been put on CW and Digital mode radios.? I have not seen it for SSB, though that does not mean it is not a common practice.? I do not have an extensive history with higher-power SSB construction.? Most have been at QRP? or under 20 watt levels. Regardless, actual measuring is always better for an individual rig. 73 Evan AC9TU |
|
Hans!
toggle quoted message
Show quoted text
I am 20+ years your senior. It should be me grumbling with skepticism about your simulations and not vice versa! :-) Smiling anyway, JZ On Fri, Aug 25, 2023 at 11:59?AM Hans Summers <hans.summers@...> wrote:
|
|
Hi Willie ?
Yes, spot on. That, and whether the diode and/or zeners add anything to the receive noise floor. Probably not.? But I need to measure, simulation isn't good enough for me :-D?? I tried to order some 47V zeners but got BZY47. Which is 9.1V. Sent back, and got BZY47 **again**. I should put in a large Digikey order in the next couple of weeks and will add some to it. Here Digikey orders take 10 days and incur a significant expense so you can't do it for a sub $1 order like you can in US.? 73 Hans G0UPL |
|
Willie,
toggle quoted message
Show quoted text
Simulation FFT says that the commutating diode does no damage to spectral purity. This makes sense for two reasons: 1) The current flowing through the diode is small and capacitive until commutation takes place at the end of a transmission. That is where a large diode current will flow, but only briefly. 2) The diode current never flows through the primary or the secondary of the output transformer, and so it never makes it to the LPF. If you are greatly concerned about spectral purity, consider that sloppy winding of the output transformer, or parameter imbalances between the two banks of PA transistors, will do more damage to second harmonic cancellation and content than the diode can ever do. JZ KJ4A On Fri, Aug 25, 2023 at 10:53?AM William Smith <w_smith@...> wrote:
|
开云体育And, of course, the third question is if adding the commutating diode and/or the zemers will affect the output characteristics (spectral purity, spurs, harmonics), in such a way as to render transceiver illegal to operate.? 73, Willie N1JBJ On Aug 25, 2023, at 10:38 AM, John Z <jdzbrozek@...> wrote:
|
|
Dan, The QMX has a PMOSFET modulator that can gracefully ramp down the supply voltage to the power amplifier stage, under digital/MCU control. That circuitry is essential for the QMX wave shaping function and to it's future SSB functionality. It doesn't exist on QDX, and so a firmware solution for QDX is not possible. Is the inductive spike damaging transistors on QDX?? Hans and I have had a lively debate on that subject, with he of the opinion that the energy level is too low to do damage, and I of the opinion that it is responsible for some, perhaps many of the fails attributed to high SWR. A big problem in resolving the question is forensics: How do you know which mechanism is responsible? A dead part looks the same either way, and usually winds up in the trash! JZ KJ4A? On Fri, Aug 25, 2023, 10:12 AM Daniel Walter via <nm3a=[email protected]> wrote:
|
|
Hi Dan RF envelope shaping requires amplitude modulation capability for the PA. QDX does not? have this, QMX does.? 73 Hans G0UPL On Fri, Aug 25, 2023 at 5:12?PM Daniel Walter via <nm3a=[email protected]> wrote:
|
|
John,
|
|
Paul,
QMX has no spike voltage issue at end of transmission because of the built-in wave shaping system. Regarding Zeners for QDX, they may provide some protection against the hi-Z SWR case, but they are not a good solution to the inductive spike problem. At the moment the BS170 transistors turn off, there is approximately an amp +/- of current flowing through L14. That current will now go to the Zeners, where it most likely will be shared unequally as they are not identical. The datasheet for 1N4756A shows a maximum current of 95 mA. The voltage at the BS170 drains will be well above the Zener voltage of 47 volts, as that high current and the Zener diode resistance conspire to elevate it well above the BS170 breakdown spec. The diode instantaneous power will be very high, perhaps as much as 75 watts each for a very brief time.? These are not healthy conditions, either for the Zener diodes or the transistors. A commutating diode across L14 which is capable of handling the coil's current avoids all these problems. JZ KJ4A |
|
One thing that comes to mind when comparing the inductive spike at the drains between the TN/VN*06 and the BS170 - you saw a 120V spike with the former compared to 60V with the BS170 - is that the BS170 is not turned on all the way with a 5V drive while the *06 devices are more strongly turned on due to their lower gate thresholds. This was the primary reason I suggested the *06/*10 FETs. The lower gate threshold of the *06 FETs results in a higher drain current which builds a larger magnetic field in the inductor and therefore a larger inductive kick when the FET turns off. Regardless of what physical limitations in the BS170 are clamping the spikes at 60V, the *06 devices will produce a larger spike and will also produce more power output because they’re simply better switching transistors than the BS170 for the existing PA design. They also dissipate less power than the BS170 because Vds is smaller when they’re on. In any event, I certainly would not recommend allowing a spike over 60V so the clamp diode is a good addition. Long story short and with all other things being equal, the TN/VN*06 transistors are better suited to the existing PA design than the BS170. Others on this forum have found this swap to be very beneficial and I’ve yet to hear a complaint of any *06 devices blowing. Tony - AC9QY On Tue, Aug 8, 2023 at 7:01 AM mux_folder2001 <canthony15@...> wrote:
|
开云体育On QMX, it's been suggested to put a 47v zener from drain to ground on each side of the output transformer, to protect against high SWR over voltage. Wouldn't that also obviate the need for that commutating diode? Paul On 8/24/23 07:39, Jonathan Halterman
wrote:
I read this with interest a few weeks ago and would be interested in Hans' thoughts on a commutating diode across L14 and wondering if perhaps there might be a future revision to the QDX? |
|
An excellent note.
toggle quoted message
Show quoted text
Subtitle: "How to make Magic Blue Smoke even when you think you are safe." JZ KJ4A On Sat, Aug 12, 2023 at 1:24?PM mux_folder2001 <canthony15@...> wrote:
|
|
toggle quoted message
Show quoted text
From: [email protected] <[email protected]> on behalf of John Z <jdzbrozek@...>
Sent: Tuesday, August 8, 2023 7:48 AM To: [email protected] <[email protected]> Subject: Re: [QRPLabs] QDX Success story ?
Yes, agreed!
I think the fatal mechanism though is gate oxide punch through rather than avalanche, and that avalanche, if it is the lower voltage condition, actually somewhat protects the transistor by putting a higher failure energy demand on the inductor. The problem is, it can go either way. I have seen "walking wounded" failures of the BS170s where it is clear they are leaking drain current through a gate oxide pinhole and into the 74act08 driver chip. Things still work, but with degradation. It all depends on how big the punchthrough is and where it is. Large enough and the driver chip dies along with the BS170. JZ On Tue, Aug 8, 2023 at 9:31?AM mux_folder2001 <canthony15@...> wrote: > > Yes, exactly. This was the case with my antenna during rainy weather as measured with my nanovna. > > So, the manufacturer of these VN0606 and TN0106 may be binning 100 volt parts as 60 volts, maybe due to some other parameter. Who knows. > > Anyway, I am hopeful that time will demonstrate that the diode is all that I need. > > One thing to note is that the idea that avalanche for even a very short time will kill the device is not always the case. It appears to me that the BS170 is being hammered at every EOT into 50 ohms. > > Tony > ________________________________ > From: [email protected] <[email protected]> on behalf of John Z <jdzbrozek@...> > Sent: Tuesday, August 8, 2023 7:16 AM > To: [email protected] <[email protected]> > Subject: Re: [QRPLabs] QDX Success story > > That's quite a punch, Tony! > > Consider this: It gets worse when the load is at a low impedance. > > The drain currents go up sharply, and then so does the energy stored in the inductor, as the square of the current. > That magnifies the danger of the low Z/ high SWR case. > > JZ > > On Tue, Aug 8, 2023, 8:40 AM mux_folder2001 <canthony15@...> wrote: > > For good measure, here is the VN0606 drain picture. > > Tony > > ________________________________ > From: [email protected] <[email protected]> on behalf of mux_folder2001 <canthony15@...> > Sent: Tuesday, August 8, 2023 6:36 AM > To: [email protected] <[email protected]> > Subject: Re: [QRPLabs] QDX Success story > > Yes, that makes sense. I am still learning my new scope. I had it set to measure "Top" instead of "Maximum". You can see from the graticule scale that it is about 70 volts. BS170 drain picture attached (into dummy load, 9 volt build). > > Tony > AD0VC > ________________________________ > From: [email protected] <[email protected]> on behalf of John Z <jdzbrozek@...> > Sent: Tuesday, August 8, 2023 6:12 AM > To: [email protected] <[email protected]> > Subject: Re: [QRPLabs] QDX Success story > > Tony, > > My guess is that when you were running the BS170s and seeing a > flat-topped 60V you were observing avalanche breakdown of the BS170 > drain. Drain-gate oxide breakdown can also happen at that voltage. > > The TN0106 and VN0606 also have 60V breakdown specs, but the spec is a > minimum and actual breakdown may occur at substantially higher > voltage. > > In any case, you have seen first-hand what the inductive kick looks > like and what damage it is capable of inflicting. > > JZ KJ4A > > On Tue, Aug 8, 2023 at 8:01?AM mux_folder2001 <canthony15@...> wrote: > > > > The diode is a good idea I think. This is based not only on simulation but on measurements I have made with my scope. > > > > In my case, the loss of two or three sets of BS170 in my two QDX units led me to try different transistors. I ran the other transistors without any failures for months. But I was curious why the BS170s would fail and the TN0106 and VN0606 would not. Yesterday I got a new scope that allows me to see transients and I decided to look at the QDX with VN0606 transistors in it. To my surprise, the glitch at the end of a transmission was over 120 volts measured at the center tap. The transistor drains were similar. The spike was 100ns wide at the 60 volt level. And this is into a dummy load. The transistors must just be capable of dealing with this. > > > > I then replaced the transistors with BS170s and discovered another surprise. The spike was below 60 volts and had a broad flat (but ragged looking) top. > > > > Then I added the commutating diode and the spikes were gone. > > > > Right now my theory is that the BS170s are operating in a "make before break" mode which minimizes the di/dt. The VN0606 (and TN0106) might be in the "break before make" mode. The specific operating conditions might possibly allow the circuit to move between these two cases and the BS170s are just not capable of handling the over-voltage spike while the other transistors can. Just a theory mind you. I have not tried yet to make measurements to verify this. Prior to these measurements, I was thinking that the opposite would be the case, thus explaining why the VN0606/TN0106 did not fail. > > > > In any case, I am now running with BS170s again but with the diodes installed. We shall see how long this lasts. > > > > Tony > > AD0VC > > > > ________________________________ > > From: [email protected] <[email protected]> on behalf of John Z <jdzbrozek@...> > > Sent: Monday, August 7, 2023 6:14 AM > > To: [email protected] <[email protected]> > > Subject: Re: [QRPLabs] QDX Success story > > > > Simulations are here: > > > > /g/QRPLabs/message/105254 > > > > JZ > > > > On Mon, Aug 7, 2023 at 8:07?AM John Zbrozek <jdzbrozek@...> wrote: > > > > > > Hi Pierre, > > > > > > The diode simply is in parallel with the 47uH inductor L14, with the > > > orientation shown in the photo provided by Paul W9AC. Cathode towards > > > the power supply connection, anode to the transformer center tap. > > > Any of the diodes he mentioned? (1N4448, 1N4148, 1N914) will do a fine > > > job of absorbing the end-of-transmission voltage spike it produces. > > > I have used a 1N914. > > > > > > /g/QRPLabs/message/105256 > > > > > > Here you can see simulations with and without the diode present. > > > > > > On another thread, Evan, Hans and I explore the ability of QDX to > > > withstand SWR. It seems to have a reputation for SWR intolerance but I > > > think there is a case that the problem may actually be as described > > > above. > > > > > > /g/QRPLabs/message/106759 > > > > > > Regards, JZ KJ4A > > > > > > On Mon, Aug 7, 2023 at 7:46?AM Pierre FK8IH <jb.gallauziaux@...> wrote: > > > > > > > > Could you please elaborate: what diode, how did you connect it? A handmade schematic and a photo would be nice. > > > > 73 > > > > Pierre > > > > FK8IH > > > > > > > > > > > > > > > > > > > > > > |
Paul - AI7JR
to navigate to use esc to dismiss