Re: #qmx Antenna Tuner Can Kill PAs
#qmx
Hi Evan,
This is my take of QDX class D amplifier as an experiment. I am using FDT86256 mosfets instead of BS170. The driver is different than QDX. As I said it is just an experiment board. It is not open source yet as WIP.
Flir image is just to give a rough idea of binocular heat distribution.?
73
Barb WB2CBA
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Hi,
About a week ago in a project I simultaneously fired up two ProgRocks - each with 3 outputs enabled - from an 11-ish volt supply - this was from a 12.0 volt supply with two diode drops as the specs of the regulator clearly state a 12 volt maximum:? At nominal room temperature (about 70F/21C) one lasted about 15 seconds and the other about twice that time before the onboard regulators failed - and I watched this happen as their output suddenly disappeared on the scope:? In one unit the regulator failed through shorted, dumped full 11 volt supply voltage on the 3.3 volt bus and clamped the power supply and on the other (the one that failed first) the regulator output dropped to about 1.5 volts and is drawing very little current - I haven't checked to see if the post-regulator chips on this unit have survived.
What I learned from this is that in a typical environment - particularly if all three outputs of the ProgRock are enabled and loaded - that it's probably best NOT to run them above about 8 volts to minimize power dissipation.? I have since been running ProgRock 2 devices at 5 volts (using a 78M05 with 0.1uF caps on the input/output) without issue.
They would probably be just fine if you were to insert a 68-100 ohm, 1 watt resistor in series with a 12 volt supply to drop the voltage and dissipate the majority of heat rather than the on-board regulator.? If you DO plan to run them from a typical shack supply of 13-15 volts, I would probably add a 10 or 11 volt, 1 watt Zener between ground and the ProgRock V+ input ("after" the series resistor) in case during start-up the current is low enough that not enough voltage is dropped to keep the input to the regulator below 12 volts - or just use a fixed regulator like a 7805 - to keep them happy.
73,
Clint, KA7OEI
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Re: #qmx Antenna Tuner Can Kill PAs
#qmx
Barb,
Is the IR image off compared to the background?? The hole in the upper left corner is off by about the same amount as the two hot spots that could be the transistors.? It could be that the transistors are at a higher temperature than the picture shows.
Do you have the information for the amp published?? Is it open source?? I am curious about the transistor used and the overall design.
Thank you
73
Evan
AC9TU
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Re: #qmx Antenna Tuner Can Kill PAs
#qmx
That is my issue here. Class D and Class E amplifiers should have relatively little heat generated compared to AB1 or AB2 amplifiers, based on my understanding of relative efficiencies . I suspect the heat is not necessarily the issue, but is possibly a symptom caused by the circuit limitations....... unless I am seriously misunderstanding Class D and Class E amplifier efficiencies, which is certainly more that possible, as I am neither an engineer nor a physicist. Hence my comments about Rube Goldberg apparati for removing heat.?
Lee KX4TT
On Thursday, September 14, 2023 at 11:52:43 AM EDT, Ted 2E0THH <qrp@...> wrote:
Forgive me, but I have become slightly lost as to what we are chasing here.
73s Ted
2E0THH
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Done with the build and it wooorrksss :)) Have a strange issue with volume control
#qmx
Hey guys. I have just built my new QMX and it works just fine except the volume control.
I have read somewhere in the threads that it is a software issue and will be fixed on the next firmware, but if someone has other ideas i am all ears :)
Also to help other builders. You may experience no audio at all when you turn on your QMX, but if you rotate the volume knob the opposite way the audio comes to live.
So yeah. Quite challenging build, but if you are careful and read every line of the manual everything will be ok. Also There is a video "52 tips for building your QMX successfully" by Hans that is very helpful.
An advice from me. Dont solder the power connector before putting the control board on or there is a good chance that you wont be able to fit it. I had to de-solder the connector and fit it again. Some isolation tape is necessary? between the volume encoder and the + of the power connector or there will be fireworks :)
73 and have fun de LZ3OM
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Re: #qmx Antenna Tuner Can Kill PAs
#qmx
Ted,
I am a bit lost too! In previous posts there was an inquiry for heat map of BN43-202 binocular during tx so I had those flir photos of my design which guves similar tesult as QDX. I thiught this might guve an idea.?
73
Barb WB2CBA
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Mine runs cool.? Or at least, I haven't noted any heat of significance.? Low current draw if it's running right, should mean little heat.? Are you running it from USB or an external source?
Brock
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Re: #qmx Antenna Tuner Can Kill PAs
#qmx
Hi Barb
Assuming that the current consumption is per spec (c.650ma on TX) wouldn't you expect this sort of heatmap after a continuous 5 minute transmit?
It looks like the design is working just fine.
Forgive me, but I have become slightly lost as to what we are chasing here.
73s Ted
2E0THH
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Re: QDX transmit troubleshooting advice¡
Chris, & all here,
Here is a fun exercise:
Assume that no commutating diode is present at L14 in QDX, and that,
for convenience, the PA is drawing 1A through L14. Then at the moment
the last BS170 transistors switch off, a large V=Ldi/dt spike will
take the transistors to avalanche at 60 Volts. At that moment, 60
watts of instantaneous power (60V x 1A) is being dumped into the four
of them. It will last about half a microsecond in duration.
If 47 volt Zeners are intended to absorb the spike, the calculation
results in half an amp flowing to each zener, and 47 watts being
delivered to the pair. The Zener resistance will allow for
considerable elevation of the drain voltage above 47 volts, and the 60
volt avalanche spec may still be violated in spite of the presence of
the Zeners, assuming they can even handle the instantaneous power
dump.
Hans has shown through bench testing that high voltages are extremely
unlikely as the result of high SWR. Simulations done by Evan and I
agree with his bench testing. It seems the Zener diodes offer no real
value here, and that the L14 commutating diode is a better overall
protective solution. It can handle the L14 current easily, which
becomes more important under low Z / high SWR conditions.
More musings from one of those pesky nerds...
JZ KJ4A
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Show quoted text
On Thu, Sep 14, 2023 at 10:56?AM Chris <chris.rowland@...> wrote:
On 14/09/2023 12:49, Jerry wrote:
Which BS120 Fails?
My low band QDX has just failed for the fourth time. Each time only Q9 has failed (shorted D-S). No other parts have been replaced.
My high band QDX also failed once, also Q9.
Both are built as 9 volt version, power is via a linear LM317 regulator with 1 amp current limiting.
Any ideas why this one part is more stressed than others?
I have just added 1N4148 diodes as in the QMX schematic.
You do realise that the diodes between the source and drain of the BS170s in the QMX schematic (D503 and D504) are place holders for Zener diodes?
You need something like 1N4756 47V Zener diodes there.
The place for an 1N4148 is across the inductor that drives them, L502.
Chris, G5CTH
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On 14/09/2023 13:46, rogerlaw159@... wrote: On the subject of heat, the ProgRock2 gets very hot...too hot to touch. Is this usual? Roger, Fed with USB 5V? Mine takes around 30mA. Shows as a COM port? Mine seems cool but difficult to tell the way it is mounted. 73 Alan
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Re: QDX transmit troubleshooting advice¡
On 14/09/2023 12:49, Jerry wrote:
Which?BS120 Fails?
My low band QDX has just failed for the fourth time. ?Each time
only Q9 has failed (shorted D-S). ?No other parts have been
replaced. ??
My high band QDX also failed once, also Q9. ??
Both are built as 9 volt version, power is via a linear LM317
regulator with 1 amp current limiting.
Any ideas why this one part is more stressed than others?
I have just added 1N4148 diodes as in the QMX schematic.
You do realise that the diodes between the source and drain of
the BS170s in the QMX schematic (D503 and D504) are place holders
for Zener diodes?
You need something like 1N4756 47V Zener diodes there.
The place for an 1N4148 is across the inductor that drives them,
L502.
Chris, G5CTH
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Re: #qmx Antenna Tuner Can Kill PAs
#qmx
Sure thing, Chris. Simulation at 25 ohms (2:1 SWR) shows each BS170 dissipating about half a watt, so there is some margin. JZ On Thu, Sep 14, 2023 at 9:26?AM Chris KB1NLW via groups.io <chrisrey1@...> wrote:
John Z
Thanks for your response. Looks like steady state SWR of 3 will heat the BS170s to their PD limit, so I assume SWR <2 is OK.
Transients from an auto tuner that can be as high as SWR of 10 will cause transient power dissipation significantly higher than the allowable dissipation. Unfortunately we don't have sufficient thermal data on the BS170 to understand transient thermal response at the silicon chip in order to determine allowable SWR Transient time product.
Bottom line is Don't Use an Auto Tuner without reducing the transient at the QMX. Reduced power or attenuation between QMX and tuner.
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Re: #qmx Antenna Tuner Can Kill PAs
#qmx
I put together my class D PA inspired from QDX PA. It is using the same BN43-202 with 3:2 winding ratio. Here is FLIR images to give an idea of heat distribution over pa mosfets and BN43-202. This is on 20m, RF output 4.8 Watts after 5 minute continous TX. Masurements are in Celsius.
73
Barb WB2CBA
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Re: Intermittent Dit on QMX
Jim:
I'm trying to increase my CW speed, but I've fallen behind a little because of the T41 project. That said, using the Farnsworth method just proves that the way I learned Morse code for my Novice license back in 1953 was wrong! Counting dits and dahs will make any speed above 20wpm very difficult. Listening for patterns, or rhythms, is the way to go. I like the program by G4FON which has many options, including setting the Farnsworth spacing. W1AW uses Farnsworth for its practice sessions at speeds under 18wpm.
If you're trying to learn Morse, give the G4FON software a shot. It's free and quite good. Try starting at 25wpm with 10wpm spacing. Being able to copy 25wpm probably covers most CW operators.
Jack, W8TEE
On Thursday, September 14, 2023 at 09:52:15 AM EDT, Jim Strohm <jim.strohm@...> wrote:
Farnsworth!
I'm in a Morse?class right now, and we're learning characters at 25 WPM timing, and 5 WPM spacing.? That timing is a little bewildering to me, because I learned code 30 years ago at 20 WPM timing / 5 WPM spacing for my Novice exam and was at 15 / 15 sending and receiving on-air at my best back then.? I'm a little limited now by having only straight keys (SKs) here, so my next buy/build project will likely be a paddle key. ?
But I'm trying!? Learning to send left-handed will be the hardest part for?me.
Occasionally I used to get compliments on my CW proficiency at 15 / 10, especially?when people learned I was?SK-ing it.? I think taking band in high school helped.
If you're truly desperate, you can get a code sender / reader and pick a Farnsworth?timing you like.? Eventually you'll pick up code well enough to read it in your head and send it with an SK. ?
Almost everybody can learn code and get proficient.? It's easier than most of us seem to think.? Even kids can learn it, once they know their alphabet well enough to read Dr. Seuss.? My oldest daughter could read that well before she was 3.
73 Jim N6OTQ
On Thu, Sep 14, 2023 at 7:02?AM K9NUD-Steve < k9nud@...> wrote: Albert, good on you for using the QRP Labs rigs for this. I suggested as much a couple of days ago in a LICW post where the OP was asking for ideas for a code oscillator. Why bother when you can build an entire rig for $55 and get a great practice oscillator in the bargain? I saw some weirdness early on with my QMX keyer, but not since, and I don't recall specifically what it was.
Regarding speed, though, I'd recommend trying to practice at 20 WPM. If you get good at 12, you will eventually hit the wall trying to get past it since slower speeds allow you to count dits and dahs, whereas 20WPM forces you to learn the rhythm of the characters, and eventually words. Just leave lots of spacing early on, and you'll start locking in the characters. It might seem impossible, but stepping from slower to faster speeds is actually far more difficult.
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Re: Best ways to measure output power w/ an o'scope and access ground
¡°I was able to obtain a Mirage MP1 which was checked against an?accurate station monitor. ¡°
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Dave Morris that looks a good instrument ?I expect you have the manual but just in case (and because it could be of wider interest to others):
The circuit info is there, and uses ¡°established methods¡± quite frequently recreated in homebrew form too (with calibration and meter scale issues that not everyone would relish) ?
I think that an AD8307 style power meter (very simple to build or buy) fed by the fwd and rev outputs of an MP1 style coupler (again homebrew able without great difficulty) would greatly ease the meter scale and calibration issues by the way. ?
Again, the MP1 looks to me to be a well made and attractive power & swr meter, thanks for your posting ?Dave ?
73
Rod
G0VKX
12:43am?I?was able to obtain a Mirage MP1 which was checked against a accurate station monitor.?
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Re: Intermittent Dit on QMX
Farnsworth!
I'm in a Morse?class right now, and we're learning characters at 25 WPM timing, and 5 WPM spacing.? That timing is a little bewildering to me, because I learned code 30 years ago at 20 WPM timing / 5 WPM spacing for my Novice exam and was at 15 / 15 sending and receiving on-air at my best back then.? I'm a little limited now by having only straight keys (SKs) here, so my next buy/build project will likely be a paddle key. ?
But I'm trying!? Learning to send left-handed will be the hardest part for?me.
Occasionally I used to get compliments on my CW proficiency at 15 / 10, especially?when people learned I was?SK-ing it.? I think taking band in high school helped.
If you're truly desperate, you can get a code sender / reader and pick a Farnsworth?timing you like.? Eventually you'll pick up code well enough to read it in your head and send it with an SK. ?
Almost everybody can learn code and get proficient.? It's easier than most of us seem to think.? Even kids can learn it, once they know their alphabet well enough to read Dr. Seuss.? My oldest daughter could read that well before she was 3.
73 Jim N6OTQ
On Thu, Sep 14, 2023 at 7:02?AM K9NUD-Steve < k9nud@...> wrote: Albert, good on you for using the QRP Labs rigs for this. I suggested as much a couple of days ago in a LICW post where the OP was asking for ideas for a code oscillator. Why bother when you can build an entire rig for $55 and get a great practice oscillator in the bargain? I saw some weirdness early on with my QMX keyer, but not since, and I don't recall specifically what it was.
Regarding speed, though, I'd recommend trying to practice at 20 WPM. If you get good at 12, you will eventually hit the wall trying to get past it since slower speeds allow you to count dits and dahs, whereas 20WPM forces you to learn the rhythm of the characters, and eventually words. Just leave lots of spacing early on, and you'll start locking in the characters. It might seem impossible, but stepping from slower to faster speeds is actually far more difficult.
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On the subject of heat, the ProgRock2 gets very hot...too hot to touch. Is this usual??
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Re: #qmx Antenna Tuner Can Kill PAs
#qmx
I'll second the use of an absorptive bridge - about no contact with high mismatch that way.
Just don't go and leave it in the "tune" position and wonder why the replies are very few and spaced out so.? ?From experience, I'm afraid - QRPp by accident.
Ted K3RTA?
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Re: QDX transmit troubleshooting advice¡
On Thu, Sep 14, 2023, at 07:12 AM, Jerry wrote:
Which Final FET Fails?
My low band QDX has just failed for the fourth time. ?Each time only Q9 has failed (shorted D-S). ?No other parts have been replaced. ??
My high band QDX also failed once, also Q9. ??
Both are built as 9 volt version, power is via a linear LM317 regulator with 1 amp current limiting.
Any ideas why this one part is more stressed than others?
I have just added 1N4148 diodes as in the QMX schematic.?
Jerry, The diodes in the QMX schematic are Zeners, NOT 1n4148.? Also, the single 1n4148 for the QDX protection is across L14, the RF choke that feeds power to the finals.? My simulations have shown that the Zeners OR the commutating diode across L14 are good choices.? You do not need both.? The simpler solution is John's commutating diode.? The commutating diode could be a 1n4148.? I have only bench-tested the commutating diode. 73 Evan AC9TU
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Re: #qmx Antenna Tuner Can Kill PAs
#qmx
John Z
Thanks for your response. Looks like steady state SWR of 3 will heat the BS170s to their PD limit, so I assume?SWR <2 is OK.
Transients from an auto tuner that can be as high as SWR of 10 will cause transient power dissipation significantly higher than the allowable dissipation.? Unfortunately we don't have sufficient thermal data on the BS170 to understand transient thermal response at the silicon chip in order to determine allowable SWR Transient time product.??
Bottom line is?Don't?Use an Auto Tuner without reducing the transient at the QMX.? Reduced power or attenuation between QMX and tuner.? ?
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Barb WB2CBA
Lee
Ted 2E0THH
jjpurdum