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Date
Weekly Michigan QRP zoom chat

 

The meeting might be delayed. Standby.
Ed
AB8DF
Re: QMX+ - LPF array design question

 

¿ªÔÆÌåÓý

I think I figured this out myself. I used the scope to look at both sides of the LPF0 input diode during the start of a transmission. Sure enough, the diode is forward biased by several volts but it is only for 10-20ns at a time. Then I googled for the 1n4007 turn on time and found that they take about 1usec to start conducting. So they are also slow in the forward direction. Apparently SPICE is not modeling that property. Maybe I can find a tweak to the model to fix it.

Tony
AD0VC

From: [email protected] <[email protected]> on behalf of mux_folder2001 via groups.io <canthony15@...>
Sent: Wednesday, May 28, 2025 5:12 PM
To: [email protected] <[email protected]>
Subject: [QRPLabs] QMX+ - LPF array design question
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Let me start by saying there is no evidence that the situation I will describe is occurring or has ever occurred in a real QMX+. There is nothing here to worry about. It is most likely just something I am doing wrong so no panicking!

OK, I have set up a model of the entire QMX+ lpf array. I have figured out how to make the diode model give a long reverse recovery (Vp parameter). The issue is not with recovery though. I am seeing something that is clear and yet must be wrong. The situation is that I have LPF4 enabled and the others disabled (by switching the gate of the correct BSS123). I set up my source to drive a signal big enough to generate 5 watts out, roughly 22 volts peak. I set up the sim to run without signal for 10 millisecnds to give the simulation time to stabilize the various voltages, mainly the time needed to charge all of the lpf shunt capacitors in the disabled filters up to 12-.7 volts. At that point I discovered that it is a bad idea to simply switch on the 22 volt peak input signal full blast because it ends up creating a large enough input to forward bias the unused filters input diodes. Once the diodes switch on, they cannot turn off until the input signal stops (28MHz period is way less that TRR of the diode). Switching on the lpf0-3 filters puts a near short on the PA output and kills any chance of the doubler getting the reverse bias up above 22 volts so it is fatal.

OK, so maybe I need to "shape" the PA output. I "modulated" the input signal? amplitude with an RC charge and here is where I ran into the issue. If you do the math on LPF0 capacitors (4400 pf total) charging through a 470k resistor, it takes 5 milliseconds or more?to charge. What I found is that I had to use 5-6 milliseconds of "shaping" on the startup of the input signal in order to avoid tripping the LPF0. This seems too long to me but it looks like it is the way it is designed. Note that these diodes are OFF and get turned on by the large input. This has nothing to do with TRR (which is for ON->OFF transitions). This seems to mean that filter input amplitude transitions that rise above 12 volts must do so SLOWLY.?

Everything in the model seems to be doing what it should. The doubler doubles and the bias begins to rise when the input approaches 12 volts amplitude but it rises at different rates on the load side of the six 470k resistors with LPF0 being very slow and LPF6 being much faster. I have to raise the input amplitude slow enough to avoid turning on the LPF0 input diode.

So, where am I going wrong? I have never used a PIN diode but I THINK I understand how they are supposed to function as switch. Is there something that keeps them from turning on quickly?

Again, this is SURELY a red herring. But I would really like to make this work right so I have to ask.

Thanks,
Tony
AD0VC
Jeff, W1NC saved my QMX

 

Took more shipping time than anything else. awaiting the return.
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Other than some of my ham-fisted soldering, he reports a bad PCM1804. This would coincide with the symptoms I observed. All the tests he did, and explanations in the email I got this morning, seem like I'm good to go. So awesome to have a resource like Jeff to support the QRP-Labs community.?
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Can't wait to get it in hand!
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TU W1NC
QMX+ USB audio?

 

This is not directly a question for this forum, but somebody may have worked it out:
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First: my QMX+ USB audio works great into WSJT-x on my Windows PC.
Second: When WSJT-x is running on a Raspberry Pi 5, USB control of the rig works _but_, when I try to configure the audio, something strange happens. Under audio configuration, when I look for input devices, it show the QMX+ choices both as an alsa input device and an alsa output device. When I look for audio output devices, the QMX doesn't show up at all. Any ideas?
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I'm asking the same question in the wsjt forum.?
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Thanks!
--
Brent DeWitt, AB1LF
Milford, MA
Ladder Line

 

I use this: . 80-10m, continuous. ?Dipole up 70 feet, then ladder line goes to a 4:1 balun a short length of coax, then to an LG tuner to my rig. It was up for about 5 years, until an ice storm. ?Easily replaced with the pulleys in the trees. If I bought the 16AWG copper-stranded wire, it would have cost me more; here I got it assembled and shipped for about $175.00.?
73
Bob
WA2I
Re: Continuous tone on 14.053.5

 

There are some birdies it's a known issue.? I can see them very strong on 6m with a dummy load attached. I still have no problems using my QMX+ though.
Re: Programming Troubles

 

Thanks Ronald,
I just want to do CW.? I can't figure out how to set it up for straight key and save the setting. I also can't figure out how to set up memories for often used frequencies and save those settings.? Thanks in advance for any guidance you can supply.
73,
Dennis
Re: Blown Q504 - heat dissipation was not ok

 

check the screw for the terminal, i needed to file down the head of the screw a bit, coz it was pressing against the next IC and impossible to stand straight up.
CW / Rag Chew Practice Session

 

¿ªÔÆÌåÓý

Michigan QRP Club

My next CW practice session will be?May 30?at 18:00 EDT / 22:00 UTC on 20 meters.?Anyone and everyone is welcome. These practice sessions are? intended for operators who are new to CW or they need some practice. IT DOES NOT MATTER HOW POOR YOUR CW IS. Mistakes are OK. Poor fists are OK. Slow speed is OK. Really slow speed is OK. This practice is meant for you to improve your CW. I will do my best to adjust to your skill level. Operate at any power level. If several stations show up, I will operate as a round-table control station. I will do it as a round-table so everyone gets a chance to transmit. Please listen to my directions.

Details:
Date - May 30
Time -?18:00 EDT / 22:00 UTC
Band - 20 Meters

How to find me - I will find a clear frequency and call CQ. Go to the Reverse Beacon Network and search for my call sign AB8DF.


That will tell you what frequency I am on. Tune your station to that frequency and if you hear me give me a call. If there is a QSO in progress, please wait for a break in the action. Then send your call sign. If I hear you, I will invite you to join the QSO and start a round-table QSO.

Reply to this email if you have questions.

IT DOES NOT MATTER HOW POOR CW IS

Ed
AB8DF_._,_._,_
Re: QMX+ - Should there be resistance between T501 primary and secondary windings?

 

Hans changed the wording in the QMX+ manual. For the QMX, the manual says "there should be NO connection between A and B." whereas the QMX+ manual says "Check that there is NO DC continuity from the points marked A, and ground".

Charles - I would suggest ignoring any impedance reading and measure at DC...

72 de Russ, va3rr
Re: QMX+ - Should there be resistance between T501 primary and secondary windings?

 

Hello Charles.
Upon rereading the instructions, there is no mention of testing between A and B. I believe the continuity tests should be run separately (from A to A and from A to ground then from B to ground). Do not mix A and B.
--
Marc-Andre Gendron
VE2QVL
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Re: Michigan QRP Club Weekly Zoom Chat

 

The new time is too early for me. I was looking forward to joining you guys for another session:(
Re: High current draw on initial power up #qmx #troubleshooting

 

Results from the functional tests this morning, bizarre but also not the smoking gun I was hoping for

1.1 Vdd 3V Isupp 48mA
2 Vdd 0V Isupp 0A
3.1 Vdd 2V, ADC_3V3 0V, struggled to supply current (Even though the board has appeared to work fine when fully assembled)

In any event, no overcurrent event during those tests. Also took some pictures of PS #2 under a microscope, Q102 looks weird but all the pads are still connected

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Kaitlyn VA3KBY
Re: QMX+ Power Output

 

On Wed, May 28, 2025 at 08:16 PM, Larry- WA2VKG wrote:
The output power on several of the bands seems to be a bit lower than other results that I¡¯ve seen posted.? Is there any indication that something¡¯s wrong?? Should I be getting more power?
Some bands share a lowpass filter and their adjustment will trade off power between them. You can pick up one band but another may suffer.
Having tested several ham-grade power meters against my Keysight power sensor/meter and seen errors as high as +/-20%, it is possible that the difference their results and yours? is measurement error.
Other possibilities are different operating voltages; some folks' "12V" is closer to 13.8V, which will affect power output.??
Your results look like they are comparable to others'. The station at the other end will never know the difference.
Remember,?
"If you compare yourself with others, you may become vain or bitter..." Max Ehrmann
73, Don N2VGU
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Re: Release of version 2.0 of ABS solution for QMX+ (Automatic internal antenna tuner, internal battery and internal speaker with audio amp) #PSU #QMXplus #audio #ABS #ATU

 

Thanks to Hans, ABS is now featured in QMX+ Mods page:
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--
73,
Sardar (AC8L, 4K6SA, VA3DUA).
Re: Blown Q504 - heat dissipation was not ok

 

¿ªÔÆÌåÓý

Yes Bruce,

That¡¯s what makes a hobby a hobby¡­¡­ One can go as far as one desires. I remember my days in the RC plane hobby. Some folks had to improve every plane they built and the results were great and sometimes not so great but they ¡°did it¡±¡­¡­ themselves. ?


It¡¯s fun following some of those who persist and expand the boundaries. ?I just like to tinker and play radio. Today I ordered a Raspberry Pi and a learning kit so I can play with that for a while and upgrade my new zBitX when the gurus make improvements . I enjoyed what I learned years ago with a similar Arduino learning kit. ?At 80 I still am learning preparing for my ultimate shack in the here after. ?

While cleaning relatives grave stones at the cemetery I got my wife to agree to have my call and an antenna engraved on my stone when the time comes. ?That¡¯s an accomplishment (a win) for me. ?Ha!

Dave K8WPE


On May 29, 2025, at 6:38?AM, Bruce Akhurst <bruce@...> wrote:

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Hi Dave?

I see several different and non- converge-able groups here:?

Some know what they are doing,? Some don't .? ?Some can read and follow instructions, Others clearly less so.? ? ?Some go astray - but a surprising number / % of kits are successfully built/operated 'within limits'? by 'beginners' so well done Hans
??
Some like to see if a bunch of innocent? BS170's will do 10W Digimodes? and embrace the idea of an unplanned desktop BBQ/ FET firecrackers? as 101% fun along the way. .? ? ?(They probably have a car with a loud exhaust and ruined engine too)?

Some firmly in the first group probably pay too much attention to those in the second group ..? ?

Some have real-world experience / qualifications in Electronics / RF design /production but still find the QRP labs projects a really nice package/starting point for other things??

Some will successfully modify designs for Extra Features, Increased Convenience,? Increased Reliability etc?

but again it's all optional? ? ? ?

It's a free world . .
Re: Blown Q504 - heat dissipation was not ok

 

Hi Dave?

I see several different and non- converge-able groups here:?

Some know what they are doing,? Some don't .? ?Some can read and follow instructions, Others clearly less so.? ? ?Some go astray - but a surprising number / % of kits are successfully built/operated 'within limits'? by 'beginners' so well done Hans
??
Some like to see if a bunch of innocent? BS170's will do 10W Digimodes? and embrace the idea of an unplanned desktop BBQ/ FET firecrackers? as 101% fun along the way. .? ? ?(They probably have a car with a loud exhaust and ruined engine too)?

Some firmly in the first group probably pay too much attention to those in the second group ..? ?

Some have real-world experience / qualifications in Electronics / RF design /production but still find the QRP labs projects a really nice package/starting point for other things??

Some will successfully modify designs for Extra Features, Increased Convenience,? Increased Reliability etc?

but again it's all optional? ? ? ?

It's a free world . .
Re: QMX+ Power Output

 

I found that tuning with a power meter is better than using the low pass filter traces in diagnostics. Simply put, the scale and resolution of the graph are good to have a rough idea of performance, but not detailed enough for tuning.
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My tuning method is to attach the radio to an external power meter and then a dummy load. I have a variable power supply and I set it for 9 volts for my 12 volt build to lessen the power. I go key down and adjust the spacings on the low pass filter for max power on a band. Since most filters cover multiple bands, I cycle though all the bands affected by that filter to balance output between them or set it to favor the band I prefer.?

My approach to actually turning the coils is to start by checking the spacing between the PCB and the toroid and make sure those wires aren¡¯t crossed or all over. That is a quick way to lose power. If it¡¯s bad, I get out the soldering iron and try pulling it tighter while melting the connection. After that I start spreading and bunching the coils on the toroid as a whole. Once I get max power from that approach, I try doing that again on the second toroid. Once both have max power, I will some times tinker with moving single or small groups of coils to fine turn the inductance. Usually this isn¡¯t necessary. Since I take mine portable a lot, once I have everything happy, I use hot glue to hold things in place so it won¡¯t move in transport.?

I¡¯m currently on the road and just have my QMX with me right now so I can¡¯t share my power output, but all bands are roughly 4 to 5 with 160 and 6 meters being outliers (160 high and 6 meters low).?
Re: Blown Q504 - heat dissipation was not ok

 

¿ªÔÆÌåÓý

Anyone doing thermal imaging of the output transistors during key down (low power without the washer). Might be very interesting if one can get detail with a better than Harbor Freight thermal camera. ?

My thoughts are just run lower power to keep them cooler but then that is not acceptable to some in this group. ?An extra watt or even two is worth the risk.?

Am I way off base here? ?I see all sorts of other discussions about output failure.?

Dave K8WPE


On May 28, 2025, at 5:57?PM, Chris KB1NLW via groups.io <chrisrey1@...> wrote:

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I did my own tests many months ago and posed numerous results.? The bottom line was that voltage spikes are the most likely cause of BS170 failures.? The harmonic power reflections from the LPF cause peak voltages that often exceed the BS170 max voltage ratings.? This is exacerbated with poor SWR and is even true with a perfect SWR on 160m and 80m.
Stop worrying about heat. Worry more about making sure there are no loose connections to the antenna.? A high voltage spike can kill a BS170 faster than SWR protection can operate.?
Re: QMX+ Power Output

 

I was studying pages in the WIKI and noted the following remark:
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"Sweeps using TX mode may use a bit more current than normal transmitting."
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Larry, keen observation.
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I do notice that 12M & 17M are NOT so different from each other.
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Good luck
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