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Thanks Hans, a self calibration feature would be great. My QMX+ is just under 1W on 6m and I would like a bit more, that is quite a lot under spec..

Thanks for all your efforts..

73 Dave G4FAW?

Of course there are more possible reason for non perfect output from IC503 without a load and worse with BS170, a faulty IC or a wobbly voltage supply.

73 Ludwig

On Mon, Jul 8, 2024 at 06:37 AM, Greg Walsh wrote:

Sorry for the delay but family matters over the weekend.

Hi Greg, this is important.

And I needed some time to think about your last post.

The outputs from IC503 are better. How about the waveforms, something like rectangular (with smooth slopes)? Is the TX frequency the largest part of the waveform?

Decrease of the output may point to the frequency response of the probe or the measurement situation or it could point to a load connected to the output. Who knows.

Could you check please some resistance values:

1. S, G and D of each BS170 position to GND. Use the GND in the centre of the BS170 and use your DMM in both directions. Don't change something before.
2. Lift the leg of L502 towards T501 to isolate T501. Check the resistance values from D to GND of each BS170 position.
3. If you have an element tester please check capacity from the open pad from L502 to GND. But don't change the solders of T501!

About the photos attached and with some markers.

Some of the solders are looking a bit strange, far away from a smooth surface.

BS170 pins_answer1:
red - unwanted tin ball?
blue - for exact measurement cleaning would be good (washing the flux away)
yellow - a circle structure around the soldered wire, cold solder?

T501 end 1_2_answer1:
red - the enamel wire comes with 45° from the PCB. It seems to be very close to the GND plane.

T501 end 2_answer1:
yellow - see about strange solder above
red - the wires are twisted. Was there enough room in the hole to put the twisted wires through the PCB? The solder looks wide, maybe to wide? Could it be the tin is touching the GND plane only isolated by the thin green silk screen?

Btw I've found no information about your power supply.

Good luck and I hope you will find something to improve.

73 Ludwig

Hi Ludwig
Sorry for the delay but family matters over the weekend.? I've done many measurements and am reasonably certain either the 'scope or the probes are limited in bandwidth.? See my notes and findings below...

Could you check

1. the region of the BS170 for unwanted things, (See pix attached.? All pads and soldering look fine and check ok)
2. T501 and the area around,? (see pix attached.? I rewound this in case I had made a mistake but the original looked fine and the replacement performs the same)
3. the PIN diode system of the LPF section,? (I tested each diode, checked the configuration and voltages at each point.? All are per the document.)
4. the G, S and D voltage at Q508 for RX and TX,? (TX G=0, D=10.6, S=0; RX G=3.3, D=0, S=0)
5. the frequency response of your oscilloscope with the actual probe (e. g. checking a fast clock signal from the QMX).? (I used the three CLK's 0,1&2 with both probes and got the same results across 1.8MHz to 50MHz.? All 3 signals produced the same waveforms on each band.? Good square waves on 1.8, 3.5 and 7MHz and the waveform got progressively more round until at 50 MHz the signal was a sinewave.? I think the probes may be part of the problem.? I have ordered a better quality (bandwidth) probe.?

For No 1 and 2 it would be fine to show detailed photos. (Pix attached) For No 3 you will find information reading this document from the QRP Labs Wiki (section PIN diode switching). It's for QMX but simple to expand for QMX+.

It would be also fine to remove all BS170 and check the signals from IC503 for different bands.? I removed all BS170's and made the following measurements:

Voltage measurement p-p (with scope)				?	?	?	?
?	?	1.8MHz	14MHz	28MHz	50MHz	?	?
Q503,505 gates		?	5V?	4.2	1.3V	IC503 outputs
Q504,506 gates		?	5V?	4.2	2.0V	No FETs in circuit	?
IC501 pin 4		3.8V	3.5V	3.0V	2.4V	?	?
IC502 pin 4		3.8V	3.5V	3.0V	2.3V	?	?
?	?	?	?	?	?	?	?

The step next is a visual check of the capacitors from "+12V" to GND and from VCC to GND.? I checked all caps on both rails visually and with a DMM where possible and all appear ok.

To get a better impression of your system:

• which power supply do you use? See pic
• which dummy load do you use?? See pic

Apart from having to replace Q507, I'm unsure how to proceed.? Maybe a better probe will give more meaningful readings/measurements.
Regards, Greg.

Hi Greg,
interesting news. So for 1.6 MHz no more negative voltage at the gates and 50% duty cycle. This looks fine.
So something was caused by the switched drain voltage / current. But how came this into the gate circuit, by the chanel to gate capacity??? Or is there a wrong coupling between the drain and the gate circuit??? Questions but no answer.

But for 28 MHz it's terrible, both with all FET and with two FET removed. Nothing to be seen what looks like a 28 MHz signal.

Going back to your post from Jul 3th. The drain voltage was going up to around 61V. Assuming the supply voltage was 12 V this was 5 times of the supply!!! Checking my QMX the drain voltage was in the region of the supply voltage. Your high value looks like produced by a resonant circuit with a high real part of the impedance, not near 50 ohm.

Could you check

1. the region of the BS170 for unwanted things,
2. T501 and the area around,
3. the PIN diode system of the LPF section,
4. the G, S and D voltage at Q508 for RX and TX,
5. the frequency response of your oscilloscope with the actual probe (e. g. checking a fast clock signal from the QMX).

For No 1 and 2 it would be fine to show detailed photos. For No 3 you will find information reading this document from the QRP Labs Wiki (section PIN diode switching). It's for QMX but simple to expand for QMX+.

It would be also fine to remove all BS170 and check the signals from IC503 for different bands.

The step next is a visual check of the capacitors from "+12V" to GND and from VCC to GND.

To get a better impression of your system:

• which power supply do you use?
• which dummy load do you use?

Sorry for this lot of work.

73, Ludwig

Hi Ludwig
Your reply inspired me to make the gate measurements - The first 4 meaurements were with the FET's in circuit but for comparison I removed Q504 and Q506 and remeasured them.? The 1.8 MHz waveforms were the same as first measured (approx 5V pk), so have not included them, but the 28 MHz waveforms were certainly different in amplitude.? (The smoother waveform at 28 MHz may be partially due to the 'scope and probe's frequency response).
I hope the file names are sufficiently descriptive.
I'll have a look at the duty cycle shortly.
Regards
Greg

Greg, sorry to read about the damage.
But you could check now the gate waveforms without working BS170. (Of course the gate capacity is "working".) Now there is no possible feedback from drain current to the gate circuit.

From my post before:

The voltage is >= 1V for around 70% of the period. The part of the waveform with voltage around 1 V is wrong.

It would be interesting to know if the input duty cycle of IC503 is equal to the wrong output duty cycle. But maybe without drain voltage the wrong duty cycle is not wrong anymore?

73 Ludwig

Hi Ludwig.? Thank you for the analysis.? To answer your first 3 questions:
The GND lead was clipped to the bnc output connector
The ground lead is approx 150mm
The original BS170's are in circuit.
Unfortunately while looking for the waveforms you asked for, I must have shorted the +ve at the BS170's as they have no Drain voltage so I think Q507 has been destroyed as there is 11.5V on its Source, nearly 11.5V on its Gate and 0V on its Drain.? So at this stage I have ordered a replacement AOD403 from Digikey and it will probably take a week or so to be delivered.
Thank you for your help to date and I will update when I have replaced the AOD403.
Regards
Greg

Hi Greg,

fine pictures except the content.

The waveforms looking strange to me. Lets have a look at 1.8 MHz. The gate voltage is going down to -2V! Why negative? I guess not from the IC503. The voltage is >= 1V for around 70% of the period. The part of the waveform with voltage around 1 V is wrong. The drain voltage is low when the FET is ON. The duty cycle is around 70% for both groups. It looks like the FET are switched on by gate voltages >= 1V, so for 70% of the period. An overlapping ON is bad.

For 28 MHz the FET are between ON and OFF all the time. The gate voltage stick at a medium value and couldn't go to LOW and HIGH. Something is blocking "large" voltage alterations.

So I have some more questions:

1. Where did you clip the probe GND to the QMX?
2. How long is the ground lead from the probe to the QMX?
3. Do you use the original BS170 from the kit?
4. Could you show waveforms at the connection T501 - L502, at the other side of L502 and at the secondary winding of T501 for both bands?
5. Could you show detailed photos from the PA and from T501 from both sides to see the windings

73, Ludwig

Success (so far). I replaced IC503 and now have a nice 5v TTL level signal out on both sides. BS170s not installed yet. Waveform attached.
This was on 20m. I tried 6m and it was bit lower amplitude at 4v. But still much better than before.
The IC501 and IC502 XORs also have a nice clean output now.
Onward..

--
Randy, N4OPI

Hi Ludwig
Attached is a file with the pix inserted.? The file names explain which each is.? I hope they're helpful.
Regards
Greg

I am seeing similar indications out of IC503 with my just completed QMX+.?
It was working fine for a couple of hours on 20m at 4.3w. Tried tuning up on 10m and power out went to 0w. Switched back to 20m and still no output.
Having been through this and with a handful of spare BS170s, I just clipped them out and started looking at IC503. I'm getting a wonky output from one pair of the gates (C&D) and only 2v P-P. Good and bad traces attached..
The output of IC501 is also a bit weird compared to IC502 but I'm thinking this may be caused by a bad gate within IC503.
I will be replacing IC503 tomorrow. If all looks well I'll plug in a new set of BS170s and see how it goes.
--
Randy, N4OPI

On Tue, Jul 2, 2024 at 02:32 AM, Greg Walsh wrote:

It is the output voltages from the ExOR gates and the AND gates that concerns me as the lower the voltage output, the lower the RF output from the BS170's.?

Greg,

it looks like an increasing load to IC503 produced by the PA. The higher load may affect also the load to IC501 and IC502.

Could you show the waveforms at G and D of each group of BS170 (with DC, not only AC) at let's say 1.8 MHz and 28 MHz?

73, Ludwig

Bi Ludwig
Thank you for the reply.? The probe is a PP-150 which came with the oscilloscope.? I have used it for a few years.
Its bandwidth (@10:1) is 100 MHz.? The probe compensation allows the square wave calibrator to show a good squarewave with no ringing.
The input impedance is 10Mohm/18.5pF.
It is the output voltages from the ExOR gates and the AND gates that concerns me as the lower the voltage output, the lower the RF output from the BS170's.? The measured RF output is within a few 10ths of a Watt as shown on the puTTY Terminal.? Both measurements decrease at the same rate to 0 @ 6m.
Any help you can give would be appreciated.
Regards
Greg

On Mon, Jul 1, 2024 at 09:29 AM, Greg Walsh wrote:

These were p-p voltages with a 100MHz oscilloscope.

Greg,

• what is the bandwidth of your probe?
• Did you use a 10:1 probe, well compensated?
• What is the input capacity of your probe?

73, Ludwig

I recently completed a QMX+ kit.? The firmware loaded, switch on current 90mA.? I used the puTTy terminal programme to look at all the parameters/values that the QMX+ should exhibit.

I found that power output was as follows:

?

160m???????????????????? 5.85W (calculated – oscilloscope across dummy load)

80m?????????????????????? 4.66W

60m?????????????????????? 1.9W

40m?????????????????????? .75W

30m?????????????????????? .36W

20m?????????????????????? 0.2W

17m?????????????????????? .07W

15m?????????????????????? .2W

12m?????????????????????? .04W

11m?????????????????????? .03W

10m?????????????????????? .04W

12m?????????????????????? 0W

?

I first suspected that the filter toroids or the transformers may have been incorrectly wound but subsequent checking (firmware sweeps, rewinding T501 and T507, attaching a Nanovna to each RF & LPF ?showed they were fine).

My concern rose when I looked at some voltages.? The CLK voltages were all ok but on measuring the outputs of IC’s 501, 502 and 503 from CLK2 input gave some interesting results.? These were p-p voltages with a 100MHz oscilloscope.

?

IC501 (74AHC1G86D)

??????????????????????????????? 1.8MHz???????????????? 14MHz????????????????? 28MHz? ??????????????? 50MHz

Clk2 input??????????? 4.7????????????????????????? 4.8????????????????????????? 4.9????????????????????????? 5.0????????? (Pin1)

Pin4 output??????? 4.2????????????????????????? 3.5????????????????????????? 2.8????????????????????????? 2.7

?

IC502 (74AHC1G86D)

Clk2 input??????????? 4.7????????????????????????? 4.8????????????????????????? 4.9????????????????????????? 5????????????? (Pin1)

Pin4 output??????? 4.2????????????????????????? 3.5????????????????????????? 2.8????????????????????????? 2.8

?

IC503 (74ACT08D)

Pins2,5,10,13????? 3.3????????????????????????? 3.3????????????????????????? 3.3????????????????????????? 3.3????????? (From TX 3.3V)

Pins 8,11????????????? 7.4????????????????????????? 4????????????????????????????? 1.6????????????????????????? .4??????????? (gates of Q503/Q505)

Pins3,6????????????????? 7.4????????????????????????? 4????????????????????????????? 1.7????????????????????????? .6??????????? (gates of Q504/Q506)

?

Q503/Q505

Drain???????????????????? 63V??????????????????????? 20V??????????????????????? 4V?????????????????????????? 0

?

Q504/Q506????????

Drain???????????????????? 65V??????????????????????? 19V??????????????????????? 6V?????????????????????????? 0

?

There are no passive components in this part of the circuit so my conclusion is that IC’s 501, 502 and/or 503 do not have the High Frequency response they should.

Are the IC’s faulty or is there something else I should check.? Some expert help here is needed.

?

Greg, ZL4GW

Hello Hans
Thank you for your comments. I will probably not make any optimization attempts because, as you write, there may then be dips in the other two bands.
the QMX is the third device you have built, I previously built QDX High and Low Band

Many Thanks
Bernd