Re: SMD chip rework equipment
First watch several YouTube videos about diy smd replacement.? Google will give you many options.? ?There are a few different methods,? and you will want to educate yourself on them to decide how you want to do it.? Then purchase the requisite tools and supplies (they don't need to be expensive, but don't get the cheapest ones, either).? Then practice several times using discarded circuit boards (from old phones or electronics) with components comparable to what you want to work on - practice both removal and replacement.?
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Then go for it.? That's what I did, and have since successfully done several smd rework tasks.? But I have also sometimes lifted pads and had to repair them, even after some experience,? so you need to be very patient and careful.?
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Stan
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Re: QCX 50W PA multibanding?
#50wpa
Further, from AN006 ?
"The highest frequency
(10m band LPF) must go in slot 1, closest
to the RF output from the relay board. If you have at least Rev 5 of the relay PCB, the highest
frequency LPF is always in circuit. This provides improved attenuation of VHF harmonics."
?
One of the guys in my radio club is building a legal-limit LDMOS amp which uses the same scheme.
73, Don N2VGU?
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Re: QCX 50W PA multibanding?
#50wpa
On Sun, Feb 23, 2025 at 04:26 PM, ok4rm wrote:
I cannot just take some 5.3 MHz lowpass and put it as-is after the original 7 MHz lowpass because the input shunt capacitor of the appended LPF would add to the output capacitor of the original LPF and that would result in a mess.
Actually, Hans' Ultimate Lowpass Filter kit does just that, puts the highest filter always inline and switches lower-frequency ones in series with it:? " This relay-switched LPF board kit can have up to five additional LPF's plugged in, permitting the??to sequence between 6 bands (including the LPF on the main U3 board)."
I have successfully cascaded filters and while the result may not have been textbook-perfect due to filter interactions it got the job done.??
It would not be difficult to do an experiment, you will need the filters in any case, just hook 'em up and see.
?
73, Don N2VGU
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Re: QCX buzzing sound on key down
One thing to check is that your power supply voltage is not drooping at keydown below a level that supports proper operation.? My QMX will squeal if the battery voltage gets too low during transmit.? Think of it as a low battery alarm :-).
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Brien - KE7WB
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On Sun, Feb 23, 2025 at 01:23 PM, Tech Guy wrote:
ud buzzing on key down at times. It is not transmitting then. If I power off and on it usually goes away and sounds ok
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Re: QMX new build showed up as USB but unresponsive after firmware transfer
On Sun, Feb 23, 2025 at 03:41 PM, Florin wrote:
- wielding the DMM probes while the radio is powered up is a bad idea most likely
I used to reverse-engineer cell phones and other devices and my best solution is to use multiple colors of AWG28 wire-wrap wire and a fine-tip iron to tap the circuit nodes I want to measure.
This has 8 colors and 250 meters will last a long time: ?
It is also great for PCB repairs and alterations.
I use hot melt or Krazy-type glue to tack down the wires someplace close so that it is not easy to snag one and rip up a trace, then tape down the free ends spaced so that they cannot short together as you connect to them.
It takes a little prep time and forethought, but I was working with irreplaceable prototypes and stealthily-obtained items so care was paramount.? Nice ham radios deserve care, too.
73, Don N2VGU
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Re: SMD chip rework equipment
Unless you plan on doing a lot of it get friendly with the local laptop repair shop?
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Otherwise?
Quality soldering iron
Background heat table?
Excellent (ideally stereo) magnification/light
Fume extraction, static protection?
Decent hot air gun (no not the cheapest one)?
Assorted pads and kapton tape to protect surrounding components?
picks, hooks pins and lots of cocktail sticks?
Solder paste. ?Rework flux, desolder braid
Cleaner, UV varnish, thin enamelled wire?
Drills, grinders, scalpels etc?
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A ton of old boards to learn/practice on.
i do mean a lot before you work on anything valuable?
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Ps. ?Different people will do the same task in quite different ways so it’s not a ‘one way only’ process. ? You’ll want to find techniques YOU can use confidently and successfully. ? ?
Like I say I use loads of toothpicks for small component installation, ‘back-flip’ removal and hole clearance to name just a few . . ?Others do it other ways. ??
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SMD chip rework equipment
In anticipation of future needs. I've yet to attempt anything with more than three leads, so I was curious what SMD chip removal and replacement methods, techniques, and equipment those in the know would recommend for the home hobbyist.?
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Re: QCX 50W PA multibanding?
#50wpa
Yep, in RX path it has almost the same effect. Theoretical insertion loss of the standalone LPF (with ideal C and L) calculated by LTspice is 0.01 dB worse than the big combo. So in reality it will be the same in and out.
Jindra?
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On Mon, Feb 24, 2025 at 12:11 AM, ok4rm wrote:
Hmm, it looks interesting:
- to make an "appendix LPF" that would work for both 3.6 and 5.3 MHz does not seem to be possible
- however, adding an elliptical PI-network C-L-C, sort of an "extra stage", seems to work for 3.6 MHz:?
?
first shunt capacitance: 727 pF (680+47), together with the 270 pF output capacitance in the PA it makes 997 pF
inductance: 1.77 uH (19 turns on T50-2), and 270 pF in parallel with it makes a parallel resonant circuit at 7.2 MHz
output capacitance: 727 pF (670+47)
?
This combination should suppress 7.2 MHz by 50-60 dB (resonance is critical and there might be tolerances in capacitor values as well as winding). Optimum values are slighly different by 2 to 3 pF but impact is insignificant (order of 0.001 dB according to simulation).
?
Now I have to check how will this appendix behave standalone in the "opposite direction", i.e. transceiver in RX, PA is bypassed and RX signal goes only through this LPF. But I think it should be fine. Tomorrow or on Tuesday I will try this. Unfortunately I think I have no BNC connectors in the drawer.
?
73 Jindra
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On Sun, Feb 23, 2025 at 10:26 PM, ok4rm wrote:
I like this idea, Don. I built the PA for 7 MHz (for emcomm this would be the highest band).? For the other two bands, 60 meters and 80 meters, I could perhaps live fine with just one simple elliptical lowpass aimed at suppressing 7 MHz.? 10 and 14 MHz are out of the game in this case.
?
Two ideas:
- in LTspice I was unable to design a lowpass that would work fine for both 80 and 60 meters (in OK we have the WARC 15-15 segment, i.e. 5351.5 to 5366.5 15W PEP) - 7 MHz is too close to 5.3 so 2nd harmonic suppression was not great, despite the assumption that push-pull amp creates relatively weak 2nd harmonic. 3rd harmonic of both 3.6 (central spot of all digital mods on 80m) and 2nd harmonic of 5.3 should be well suppressed by the original lowpass. So I need to resolve just the 2nd harmonic from 80 meters (7.2) and whatever else above that is attenuated is a bonus.
- I cannot just take some 5.3 MHz lowpass and put it as-is after the original 7 MHz lowpass because the input shunt capacitor of the appended LPF would add to the output capacitor of the original LPF and that would result in a mess. So the "appendix" LPF must be designed as "continuation" of the original built-in LPF. But that should be easy with LTSpice.
?
I will try to simulate this, build it, and if it works I will post it here.
?
73 Jindra
?
?
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On Fri, Jan 5, 2024 at 01:25 PM, Donald S Brant Jr wrote:
To keep it simple in an emergency situation you could just use outboard lowpass filters, swapping them manually as needed.? ?Put your highest-band filter in the box (always inline) and add lower-band ones when required.??
Instead of "...and a small SMPS giving ~ -300 volts to shut down 1N4007..."? ?you could just tap and rectify/voltage-double the RF output.? This would guarantee always having sufficient voltage to bias your diodes off.
73, Don N2VGU
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Re: QCX 50W PA multibanding?
#50wpa
Hmm, it looks interesting:
- to make an "appendix LPF" that would work for both 3.6 and 5.3 MHz does not seem to be possible
- however, adding an elliptical PI-network C-L-C, sort of an "extra stage", seems to work for 3.6 MHz:?
?
first shunt capacitance: 727 pF (680+47), together with the 270 pF output capacitance in the PA it makes 997 pF
inductance: 1.77 uH (19 turns on T50-2), and 270 pF in parallel with it makes a parallel resonant circuit at 7.2 MHz
output capacitance: 727 pF (670+47)
?
This combination should suppress 7.2 MHz by 50-60 dB (resonance is critical and there might be tolerances in capacitor values as well as winding). Optimum values are slighly different by 2 to 3 pF but impact is insignificant (order of 0.001 dB according to simulation).
?
Now I have to check how will this appendix behave standalone in the "opposite direction", i.e. transceiver in RX, PA is bypassed and RX signal goes only through this LPF. But I think it should be fine. Tomorrow or on Tuesday I will try this. Unfortunately I think I have no BNC connectors in the drawer.
?
73 Jindra
?
On Sun, Feb 23, 2025 at 10:26 PM, ok4rm wrote:
I like this idea, Don. I built the PA for 7 MHz (for emcomm this would be the highest band).? For the other two bands, 60 meters and 80 meters, I could perhaps live fine with just one simple elliptical lowpass aimed at suppressing 7 MHz.? 10 and 14 MHz are out of the game in this case.
?
Two ideas:
- in LTspice I was unable to design a lowpass that would work fine for both 80 and 60 meters (in OK we have the WARC 15-15 segment, i.e. 5351.5 to 5366.5 15W PEP) - 7 MHz is too close to 5.3 so 2nd harmonic suppression was not great, despite the assumption that push-pull amp creates relatively weak 2nd harmonic. 3rd harmonic of both 3.6 (central spot of all digital mods on 80m) and 2nd harmonic of 5.3 should be well suppressed by the original lowpass. So I need to resolve just the 2nd harmonic from 80 meters (7.2) and whatever else above that is attenuated is a bonus.
- I cannot just take some 5.3 MHz lowpass and put it as-is after the original 7 MHz lowpass because the input shunt capacitor of the appended LPF would add to the output capacitor of the original LPF and that would result in a mess. So the "appendix" LPF must be designed as "continuation" of the original built-in LPF. But that should be easy with LTSpice.
?
I will try to simulate this, build it, and if it works I will post it here.
?
73 Jindra
?
?
?
On Fri, Jan 5, 2024 at 01:25 PM, Donald S Brant Jr wrote:
To keep it simple in an emergency situation you could just use outboard lowpass filters, swapping them manually as needed.? ?Put your highest-band filter in the box (always inline) and add lower-band ones when required.??
Instead of "...and a small SMPS giving ~ -300 volts to shut down 1N4007..."? ?you could just tap and rectify/voltage-double the RF output.? This would guarantee always having sufficient voltage to bias your diodes off.
73, Don N2VGU
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Re: QMX new build showed up as USB but unresponsive after firmware transfer
On Sun, Feb 23, 2025 at 09:41 PM, Florin wrote:
If I'm not mistaken the only SMPS available for purchase separately were for REV 1 boards,
Florin, no, the available spare SMPS boards are good for all QMX revisions. And these boards are with some changed elements compared to REV 1 to enhance the robustness.
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And congratulations to your new build!!!
?
73 Ludwig
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Re: QCX 50W PA multibanding?
#50wpa
I like this idea, Don. I built the PA for 7 MHz (for emcomm this would be the highest band).? For the other two bands, 60 meters and 80 meters, I could perhaps live fine with just one simple elliptical lowpass aimed at suppressing 7 MHz.? 10 and 14 MHz are out of the game in this case.
?
Two ideas:
- in LTspice I was unable to design a lowpass that would work fine for both 80 and 60 meters (in OK we have the WARC 15-15 segment, i.e. 5351.5 to 5366.5 15W PEP) - 7 MHz is too close to 5.3 so 2nd harmonic suppression was not great, despite the assumption that push-pull amp creates relatively weak 2nd harmonic. 3rd harmonic of both 3.6 (central spot of all digital mods on 80m) and 2nd harmonic of 5.3 should be well suppressed by the original lowpass. So I need to resolve just the 2nd harmonic from 80 meters (7.2) and whatever else above that is attenuated is a bonus.
- I cannot just take some 5.3 MHz lowpass and put it as-is after the original 7 MHz lowpass because the input shunt capacitor of the appended LPF would add to the output capacitor of the original LPF and that would result in a mess. So the "appendix" LPF must be designed as "continuation" of the original built-in LPF. But that should be easy with LTSpice.
?
I will try to simulate this, build it, and if it works I will post it here.
?
73 Jindra
?
?
?
On Fri, Jan 5, 2024 at 01:25 PM, Donald S Brant Jr wrote:
To keep it simple in an emergency situation you could just use outboard lowpass filters, swapping them manually as needed.? ?Put your highest-band filter in the box (always inline) and add lower-band ones when required.??
Instead of "...and a small SMPS giving ~ -300 volts to shut down 1N4007..."? ?you could just tap and rectify/voltage-double the RF output.? This would guarantee always having sufficient voltage to bias your diodes off.
73, Don N2VGU
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QCX buzzing sound on key down
I have a loud buzzing on key down at times. It is not transmitting then. If I power off and on it usually goes away and sounds ok on my receiver. The finals have been replaced and power is about 4.5 watts. SWR is about 1.4 and battery is 12v. It’s random. It’s easier to fix if something stays broken. Microcontroller issue? I might have a spare but this was built several years ago. The fact that it just makes a loud buzzing sidetone with no iambic keying even though it’s selected puzzles me. After rebooting it usually works. Another transistor in the keying circuit questionable? Waveforms looked ok. May need to look again.
73s John N4HNO
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Re: QCX 50W PA multibanding?
#50wpa
You are right, Don. I think I wrote this before having read Hans' description of the method to obtain negative bias for 1N4007 in the manual. I guess I was exhausted by the building process and at the same time excited by how well it worked, so I stopped reading early :)
?
Jindra
?
On Fri, Jan 5, 2024 at 01:25 PM, Donald S Brant Jr wrote:
To keep it simple in an emergency situation you could just use outboard lowpass filters, swapping them manually as needed.? ?Put your highest-band filter in the box (always inline) and add lower-band ones when required.??
Instead of "...and a small SMPS giving ~ -300 volts to shut down 1N4007..."? ?you could just tap and rectify/voltage-double the RF output.? This would guarantee always having sufficient voltage to bias your diodes off.
73, Don N2VGU
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Re: Using WSJT-X 27.7.0-rc8 "FYI"
When I select QMX and hit the init button the program faults/crashes and closes every time.? TS480 works fine.?
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Re: QMX new build showed up as USB but unresponsive after firmware transfer
Some learnings and a success (eventually, with another build)
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Finally had time to wrap up this topic, so I will provide an update for anyone facing the same issues as I did. Hopefully this helps some poor soul going through what I did.
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My initial build had 2 solder joints that needed touching up: an SMPS GND pin on the main board, and one pin on the LCD potentiometer. Unfortunately while trying to debug the GND connection on the SMPS while powered on, I believe I may have shorted some connection with one of the DMM probes, which caused damage to ?one of the diodes on the board. This resulted in the radio not powering up at all after that. Symptoms included popping in the headphones while the power button was pressed, rig powering on only for the duration while the button was kept down and then powering off immediately on releasing it.
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I decided to replace the SMPS boards. If I'm not mistaken the only SMPS available for purchase separately were for REV 1 boards, so because of that plus an abundance of caution I ordered a new QMX kit, with the idea to do a better job on a second try.
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Today I started building the second kit and a few hours later I got to the step where you plug it in and hope for the best. It connected to the computer, I loaded the firmware and it rebooted to a fully working rig! I've yet to test it for power output because my antenna only has an SO-239 connector and I haven't got any BNC lying around, but I'm glad the learnings from the first build transferred over to a successful one. And now I have spare parts too in case I need that.
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My takeaways from this whole experience are:
- solder joints can look perfect yet still not make contact
- wielding the DMM probes while the radio is powered up is a bad idea most likely
- this is not an easy kit to build (today I had an accidental soldering iron slip which put solder across 3 pins of a close proximity IC. Almost had a heart attack but after 15 minutes of struggling with the iron and a sewing needle, I managed to break the short without damaging anything else)
- despite it being challenging, after the first try you really can go full speed on building this kit. I recommend you keep going even if at first it might have been a failure
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Many thanks to all those who shared their advice and thoughts in this thread, and despite me not having proper equipment for many of the testing procedures suggested, they've all helped me sort out what to look for in my second build, even before applying power.
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Re: QMX+ power & transmit current vs input voltage plots
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A question for Hans:
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Can the 5351 clock generator operate at 70MHz and be phase modulated fast enough to generate SSB??
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Tony
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Re: BASIC programs - Did I miss it?
It is working on U4B :)
73 DE muhsin TA1MHS
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Re: BASIC programs - Did I miss it?
No you did not miss it - I'm sure there will be lots of posts about it when it does appear, so you won't miss it.
It will be after SSB.
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Re: QDX - I/Q mode and SSB firmware
There are no issues in listening to SSB.? You can hear USB directly on the QDX audio output, or SSB via IQ mode using any SDR software (all of them that I am aware of support SSB).
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Donald S Brant Jr
Brien - KE7WB
Bruce Akhurst
Richard Dyer