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QMX low pass filter

 

My QMX transmits (low power around 0.5 watts) into my fan dipole tuned for the 80 and 40 COAs on all bands from 40m up, but trying on 80m causes an immediate current limit, which suggests a short in the low-pass filter network. Am I right in thinking that LPF0 is only used for 80m, whilst LPF1 and LPF2 are shared 60m,40m and 30m,20m respectively. This would point to a short in LPF0 components from the transmit bias source to ground.

I'll worry about the low output when I have nailed this problem!

And I will be using a dummy load for further tests! I just didn't have one available when my enthusiasm got the better of me...
Re: Qmx+ V1 dodo #QMXplus #supply

 

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Ivica
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The first thing I would do is, remove both SMPS boards and test them stand alone as attached file.
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73
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Ian G4GIR

----- Original Message -----
From: Ivica - YU1QRP via groups.io <yu1qrp@...>
Reply-To: <[email protected]>
Sent: 25/09/2024 07:53:23
Subject: [QRPLabs] Qmx+ V1 dodo #QMXplus #supply
So i finished my build since it was only weekend work it took 20 days.
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Carefully assembled section by section, after each section the work was inspected with magnifying glass and dvm for shorts.
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But it does not start on first power up.
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Pluged my USB-A to C cable (it is data cable works with other devices)
Adjusted voltage to 9V and current to 200mA and connected to QMX+, no current draw in off condition
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Pressed the the encoder aaaaand no start, device did not show in file manager neither it showed on dmesg output ( using linux os )
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Only change that is visible when encoder is presed is that power supply engages current protection at 200mA which i belive is way of just for starting the device.
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Measured the 3.3V regulator ic input is 5.5V and output when encoder pressed it shows under 1V.
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On other supply board both mosfet show 8.9v both on input or output pins of them in standby and 5.6v on encoder press.
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If i understood the start sequence right, processor needs to see 3.3V to start.
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So any tips where to start looking for error would be welcome.
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Re: Damaged resistor R520

 

Thanks Bojan and Steve
I have those values. Much appreciated
73
ZL1REY
Rey


On Wed, Sep 25, 2024 at 8:17?PM Steve G4EDG via <g4edg=[email protected]> wrote:
Hi Rey
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Looking at the circuit diagram R520 is a 49.9 ohm resistor, replacing this with a 5.1k would certainly affect the SWR readings.
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You might get away with using a 47 or 51 ohm through hole resistor. If you have a batch of 47 and 51 ohm through hole resistors measure each one and see if you have one at the edge of its tolerance range.
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Using the intended 49.9 ohm smd component would be ideal...even if you have to repair the PCB trace/pad with wire.
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Good luck
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Steve G4EDG?
Re: Damaged resistor R520

 

Hi Rey
?
Looking at the circuit diagram R520 is a 49.9 ohm resistor, replacing this with a 5.1k would certainly affect the SWR readings.
?
You might get away with using a 47 or 51 ohm through hole resistor. If you have a batch of 47 and 51 ohm through hole resistors measure each one and see if you have one at the edge of its tolerance range.
?
Using the intended 49.9 ohm smd component would be ideal...even if you have to repair the PCB trace/pad with wire.
?
Good luck
?
Steve G4EDG?
Re: Damaged resistor R520

 

Hi,
The value of a QMX R520 is 49R9 Ohm and not 5k1.
You can use two 100R in parallel or 56R and 470R in parallel.
--
73 Bojan S53DZ
Damaged resistor R520

 

Just completed build of the QMX mid bands. While installing T507, I accidently damaged R520 resistor (5.1K). I replaced it with a 4.7K thro hole resistor.
The radio powers up alright with all else working wine including Audio and RF sweeps normal. The SWR sweep however shows 2.6:1 on all bands. I have no doubt this is linked to the 4.7K resistor. Any suggestions on the best way forward. I do not have a 5.1K thro hole resistor. One of the pads has been damaged so an smd replacement is not an option.
Any suggestion is welcome please.
Re: Still no output on QMX

 

checked, Q508 is good. Thank you for the additional info.?
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James
Qmx+ V1 dodo #QMXplus #supply

 

So i finished my build since it was only weekend work it took 20 days.
?
Carefully assembled section by section, after each section the work was inspected with magnifying glass and dvm for shorts.
?
But it does not start on first power up.
?
Pluged my USB-A to C cable (it is data cable works with other devices)
Adjusted voltage to 9V and current to 200mA and connected to QMX+, no current draw in off condition
?
Pressed the the encoder aaaaand no start, device did not show in file manager neither it showed on dmesg output ( using linux os )
?
Only change that is visible when encoder is presed is that power supply engages current protection at 200mA which i belive is way of just for starting the device.
?
Measured the 3.3V regulator ic input is 5.5V and output when encoder pressed it shows under 1V.
?
On other supply board both mosfet show 8.9v both on input or output pins of them in standby and 5.6v on encoder press.
?
If i understood the start sequence right, processor needs to see 3.3V to start.
?
So any tips where to start looking for error would be welcome.
?
?
?
?
Re: QMX+ building progress has progressed, but...

 

They are extra material used to support during the PCB manufacturing.
If you look carefully you should see that they are partially cut through.
Unplug the front panel pcb from the main board and then you should be able to carefully snap the “ears” off with pliers - working the pliers back and forth along the line with a little bending force.
Obviously need to be a bit careful supporting the front board as it’s now built.
QMX+ building progress has progressed, but...

 

I noticed far too late in the process that my front-panel board has two "ears" to either side; picture attached.

It is clear from both the fact that the board does not fit into the enclosure thus, and looking closer at the pictures of the board in the manual, that these should not be present.

What is my easiest path to trimming them off without doing mischief at this stage of the process?!

Thanks!

Michael WD0OM
Re: L506 Winding Gap Improves Filter Sweeps

Paul
 

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I was just able to get 38 turns. ?You really have to squeeze the wires together in the inside, even the slightest gap and they won’t all fit. ?I don’t think that an overlapped turn or two will make any difference however.

On Sep 24, 2024, at 4:15?PM, Robert AD6XJ <91710robert@...> wrote:

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I'm winding toroids, like we all are I suppose, for QMX+. L506 calls for 38 turns on T37-6. I can only fit 36. The post I've replied to here suggest a gap is desirable. Should I change to 30ga wire or to a T50-6 core or overlap the 28ga (0.33mm) in some fashion? I have both the larger toroid and the smaller wire in my parts stash.
I'm open to all helpful suggestions,
Tnx 73 AD6XJ Robert
<photo-5.jpg>
Re: 50 Watt PA with KX3

 

Just remember to turn the power down on the KX3. The 50W PA is not meant to handle over 5 watts input. Bad things will happen including blowing up the IFR510 transistors and various diodes. Ask me how I know!
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Steve N9SZ
Re: #QMX Failed to turn on today after working perfectly before #qmx

 

Quick update on this repair:?
I fitted a replacement 5351 and replaced IC501 and IC502. The radio now receives well so I'm happy that the replacement 5351 is functioning. It's only putting out about half a watt so I'll wait till my replacement for IC503 arrives before testing further. I've not checked with the scope to see if IC503 is actually faulty but it's the next suspect in the chain so I'll swap it out anyway as I'm quite enjoying the challenge of the SMD soldering. To be honest, I really wasn't expecting the 5351 to go in so easily ?... Onwards (slowly) and upwards...
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T.B.C.
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Ronan
MM0IVR?
Re: QMX+ Low Power and higher SWR seep values on higher bands

 

The dip in your passband of the LPF is unfortunate, and you may try to move the windings a bit to see if you can reduce it.
But don't try to move the cut-off frequency down, since it is set to cut off just above 15M, which shares this filter.
Re: #QMXplus Issues with latest firmware 1.00_27 with newly built qmx+ #QMXplus

 

I am just following up here and responding to my message.? The issue I had was self inflicted .? When bringing up the QMX for the first time, I had the voltage set about 6.5V.? Now this should be OK for operation, however, it did affect the firmware load. This is the only thing I can think of that caused this issue.? I have reloaded 1.00_27 and had no issues.? All of the test screens look OK and no strangeness.?
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I think it was just a fluke.??
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73,? Chris w0anm
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Re: QMX (not-plus) power issue

 

Based on your power meter readings, if it were me based on my prior experience, I would suspect that one of the PA transistors has died.? One of mine died with a direct internal short which caused the excessive power draw during receive mode. Yours doesn't seem to be pulling as much power during receive (unless your power source readout is a little off) but it could have died a different way internally.
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I would, if it were mine, remove the display board, remove the heatsink washer, power it up (still attach a dummy load just in case), and feel if one of the 4 transistors is getting warm or hot. It shouldn't take long for a bad one to generate heat if shorted internally.?
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And if one is getting warmer than others, again in receive mode only, replace it. Then see if you are back in business with about double the power out that you've measured.
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But if no excessive heat is detected, I'd then remove them and test each one individually.
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I can't say why the diagnostics screen is telling a different and inconsistent story compared to your power meter. But if there is a hardware failure, then without being an expert myself I could guess that the diagnostics could be misreporting due to that failure.
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Stating the obvious ... you need to get that baby fixed and on the air! Fingers crossed.
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--
73
de Roy - KI0ER
Littleton, Colorado USA
Re: L506 Winding Gap Improves Filter Sweeps

Robert AD6XJ
 

I'm winding toroids, like we all are I suppose, for QMX+. L506 calls for 38 turns on T37-6. I can only fit 36. The post I've replied to here suggest a gap is desirable. Should I change to 30ga wire or to a T50-6 core or overlap the 28ga (0.33mm) in some fashion? I have both the larger toroid and the smaller wire in my parts stash.
I'm open to all helpful suggestions,
Tnx 73 AD6XJ Robert
QMX+ Low Power and higher SWR seep values on higher bands

 

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Hello

I am trying to decide a route to improve RF power on 20m band (now with 2,5w). 17 and 12 also very low at about 1,7w.

I noticed high SWR near 2.0 in the higher bands 20m up in the diagnostics, when connected to a dummy load.

Is this normal?

RF filter sweep looks decent on 20m, but this is my LPF sweep on 20m:

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Should I try to lower LPF filter curve??

This is achieved adding inductance value to one of the L515 or L516?

It will lower power on 15m as the LPF is shared?

Your help please.

Thank you

Luis

CU2IJ

-- 
Cordiais saudacoes,

Luis Antonio Mota Albergaria Pacheco
luis.a.albergaria@...
luis.a.albergaria@...
(+351) 962374276
Re: #QMX IC402 issue in combination with 50W PA? #qmx

 

Re: Still no output on QMX

 

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