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It is certainly worth some experimental effort. Somehow it needs to detect severe stress while not false alarming too often, as in FT modes quite annoying when rig decides not to transmit. I have many rigs with bs170 finals, zero failures but all these are Morse cw.?

Failure of si5351?? Perhaps you mean error in its quadrature.?

I don't know if this complexity makes sense versus reasonable derating of PA bias. One of my rigs did suggest some diodes to drop PA bias voltage, but I didn't do that. But for digital modes it may make sense to back down PA bias voltage.?

Curt

Just a thank you to Hans. I bought another of his excellent QCX+? and a 50w amp. Part of the process of transferring my bank account into his. They arrived very quickly, despite me not once asking on here as to where they were. His postal system is working very well and after an initial delay, it takes a day or two for packages to be picked up from his location, they arrived in the UK very quickly.

I can only wonder at the chaos that must have ensued recently with having to ship out some 500 new product kits. I would like to say a big thank you to the people who work with Hans. The kits are well packed and it can't be easy ensuring each kit has all the necessary components in it.

Hans and his employees are all doing a great job and have improved the QRP side of ham radio enormously. Some days I reckon they bump into themselves coming back the other way?????? >:-)

Reg??????????????????? G4NFR

Ken, Bob,
As a follow-on to my earlier note, I can confirm 'Mode' was set to 'None'.? I read somewhere that changing 'Handshaking' from 'default' to 'none' had been beneficial for the writer, but that made no difference here.

I changed port settings - 'USB' was available but that resulted in a different error:? invalid configuration.? So I tried typing dev/ttyUSB0 in full, which produced yet another error variant:? IOerror

My next step is to try the QDX with WSJT-X loaded onto a W10 laptop, which I don't normally have available, in the hope that it will at least allow me to confirm that I have a fully working QDX.? No reason at the moment to think otherwise.

Thanks again for your input and maybe someone else will be able to chip in with observations.

Chris? G4CWS?

I just like to share hat i have made a dualband 2m/10m QCX. No rocket science but a small internal transverter fits perfect in the case. I love those QCX’es!

Just adding some unscientific anecdotal evidence as I too experienced catastrophic failure of a BS170 while transmitting on 20m.? Same situation, lots of QSOs on 40m, switched over to 20m and heard a pop midway through the first transmission.??

Now I may also have been doing some other foolish things like trying to power it with a DC-DC buck converter (which to be fair didn't seem to be a problem on 40m), and I have not tuned my 20m dipole lately so it could well be there was lots of SWR.? I've since built a linear regulator and I'll check the antenna, but I'm still wary of trying 20m again.

Fortunately I was able to replace all 4 transistors and I seem to be back in business at full power.

Dennis

On Tue, Nov 9, 2021, at 11:44 AM, Steven Dick wrote:

The push-pull output stage can theoretically be damaged if the out of phase drives to the BS170 pairs become faulty for various reasons

Steven,

I do not understand the above statement.? As I look at the QDX PA circuit it seems that both of the output pairs could be on at the same time and have the same current through each pair as if the driver signal were out of phase as it should be.? For that period of time, the total current would be twice normal, but there is not a rail to rail issue as is the case for a totem type of output.? Leaving that current on for too long would cause damage to one or both sides of the push-pull output.? That could be the failure you are describing.? It could be caused by software when detecting the loss of the USB sound card connection and the processor does not shut down the TX signal soon enough to avoid a problem.? Or maybe leaves the Si5351 in a bad state like you are describing.? The point is that the phase relationship would be less of an issue as compared to letting a gate be turned on too long.? This might be supported by the fact that one side of the output seems to be damaged at a time.? All just speculation on my part.

As I see it, the high voltage on the BS170s can be caused by feedback from the antenna.? The instantaneous voltage or current could feedback through the transformer as a voltage spike across the drain/source connections of the MOSFET.

I do like the idea of current sensing and turning off the drive to protect the output devices regardless of the failure cause.? It does add cost and real estate to an already cramped board.

FWIW
73
Evan
AC9TU

Hello,
After a burnt of the old LM1117 regulator, I changed to a 78M05 and lot of other components (uP, diodes, Si 5351, 74ACT00, LCD,? and the 3 BS170)
I am blocked on the FST3253. When I have a signal on Z and W (180° phase shifted) of 7.02MHZ .. I have nothing at the output on X0-X3 , Y0-Y3. I changed the FST3253 and remove the resistances R5,R6,R8 and R9 .... Nothing ....
On the input, I have a DC component of 3.6V plus my RF signal .... at the output a DC component of 2V and no AC signal at 700Hz ...
I firstly don't understand why the DC component at the input isn't 2.5V .... and why these strange values at the output. I changed twice the FST, the 5V DC is ok, and the clocks signals from Si 5351 also .... It seems like the MUX is not working ???? Any idea to test it ??
Best 73,
Nico

I agree with this. Not having built one of the kits in a while, I'd
love to see if this could be paired with the Class C amplifier

Hi,

I would like to congratulate Jack W8TEE for his nomination as Microcontrollers Editor for CQ Magazine.

Like many excellent contributors we already have in this group, we are grateful to all who like to share their knowledge.

Best regards and 73.

--
Jeff | VA2SS

The QDX is a clever and beautiful design but I had some thoughts on protecting the BS170 output transistors. The push-pull output stage can theoretically be damaged if the out of phase drives to the BS170 pairs become faulty for various reasons.? A relatively low cost addition, perhaps in a future revision could be based on using a high side current monitoring device, such as the TI??which costs about 68 cents at Mouser in a 5 pin SOT-23 package.? Read the data sheet, but attached is the basic concept from the data sheet. It's essentially a differential op amp across a low value sense resistor. The voltage drop across that sense resistor is negligible if the right value is chosen and the right gain part is used (20, 50, 100, or 200V/V depending on part number.? Its output could drive the processor's built-in A/D and generate an interrupt if the measured load current of the output stage is too high and drive an auxiliary switch transistor? to pretty quickly remove power from the output stage. Certainly other parts are needed besides this chip, including filtering and a power switch, but it may be worth considering.? Many of the BS170 failures, I suspect, are excessive current draw due to a failure of the SI5351 driving the out of phase outputs driving the high current nand gates. A DC state of these outputs will cause a high current condition in the BS170s resulting in a failure.? I don't think overvoltage to the BS170s is a significant problem because the push-pull circuit has a lower peak voltage at the BS170s compared to say a QCX variant using a songle-ended class E output stage.? Thoughts.comments?

-Steve K1RF??

Steve
Interesting about the oscillation, presumably due to RF from the output getting back into the rig.? I wonder what your antenna arrangement is?? Is the outer of the coax "hot", perhaps, due to not having a balun on a dipole or whatever?? And where and what ferrites did you install?? I presume on the power and USB leads?? (PS jealous that you have a QDX to play with - I missed out!)
--
Peter Lee
G3SPL

On Donnerstag, 4. November 2021 09:12:18 -03 mweidle@... via
groups.io wrote:

I got my QDX by TNT today. Shipping started 30th October. Within 1
Week. I hopefully will start building the QDX up next weekend. 73 de
DL1SER

My QDX order #50419 was shipped by QRPLabs on 02/11/2021
and arrived today at my mailforwarder in Miami
09/11/2021, 10:26 not bad eh?
If everything goes according to the info I got from the forwarder I
ought to be able to collect it here at the office on Monday 13/11/2021

--
Eike Lantzsch ZP6CGE
01726 Asuncion / Paraguay

Well perhaps any ptt output circuitry could be implemented on an add on prototype board similar to that offered for qcx. But 200 milliseconds before transmit is only known within the PC, so no way for Hans to implement this is what I see.?

While the zener may protect some bipolar power amplifiers I am not sure it would do the same for mosfets. Someone could do the experiment ?? ?one huge problem, zener diodes might be scarce and likely cost a lot more than the mosfets.?

Do respect that Hans may need to sell a few thousand of these as is.?

Curt

On 09/11/2021 15:57, John AE5X wrote:

I made a few comparisons with my QDX on 40m in order to learn what input voltage is required to produced a desired output.

John,

I did something similar except I took the minimum input voltage to be that when the 5 volt regulator did not. This was about 6.5 volts. To reduce to 1 watt I cut the PA feed track and soldered in two IN4001s in series to L14.
I have the intention to use a separate regulator for the PA although really the QDX is not a QRPp rig.

On 09/11/2021 16:28, Fred Spinner wrote:

I wonder if it couldn't be protected from damage b

Fred,

I am not so worried about the 74ACT08 but a few failures of the driver IC of the QCX passed a spike through to other components. I remember a Si5351 and.. the processor.

73 Alan G4ZFQ

To add to the wish list would be the protection of the PA section.? Maybe Zener diodes as suggested by?Fred W0FMS in message #72455 for IC5.

73
Evan
AC9TU