Hi All

I think I know the answer to this but before I actually do it can I have confirmation from someone who either knows or at least fully understands the circuit better than me.? I don't want to damage anything.??

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I want to key my Juma PA100-D amplifier with my QMX.? The Juma T/R signal is to ground the tip of the plug.? My understanding of the QXM is that it has +5V and active-ground options on its PTT with active-ground on the tip.? So do I just wire the interconnect lead tip to tip and screen to screen, ignoring the ring?? Then the QMX active-ground grounds the Juma T/R input and the amp is keyed?? (I normally use KX3 which is ring to tip so it looks like I can't use the same interconnect lead).? I also recall some posts recently about the need for an intermediary FET switch rather than keying an amp directly?? Does that only apply if the changeover relay is getting its power via the keying line?? The Juma has a relay changeover but the power for the relay presumably comes from the amp itself rather than the keying line from the QMX if that's just acting as a switch to ground?

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Hopefully its a quick thumbs up and I can make the lead.? I'm planning to use it in the SKCC WES this afternoon testing a prototype UMPP mini straight key I've been developing over the hols.?

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Thanks and 73

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Peter GM0EUL?

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No reason why it wouldn't work. Just keep in mind that you won't be able to read it if you turn off the backlight.?

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73, Dan? NM3A

Hi Tony,

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Alan has some good advice- be a bit wary of everything you read. That said, there are a lot of helpful hints on this forum.?

I will try to address some of your questions as I just completed a Rev 1 QMX build yesterday. This was my 6th QMX build, 3 of which were Rev 1.?

First, I believe the latest Rev 1 assembly manual is 1.00j. No need to print the manual again, but review the latest with your 'g' version and make whatever changes you see. I usually print out individual pages where there are significant differences and paste them over whatever manual you have. I make specific documentation in writing on my manual so I have a reference for that radio. Most of the time that is just a check mark to indicate that I completed that section.?

Second, print out the T501 PA Transformer Manual. This is where you need to make the decision to wind for 12V (3:2 primary to secondary) or 9V (3:3 p to s) and which type of winding to use. As the type of winding is less important for low band (80-10 m) builds, I simply used the conventional winding, but you can use any appropriate one. Make sure you scrape the enamel for all the leads before soldering. This applies to all the other toroids and transformers, too. If you have extra 28 ga enameled wire, you can use that instead of the 0.6 mm wire suggested for this transformer. QRP Labs is using 28 ga (0.3 mm) for everything in the latest kits as it doesn't make any performance difference and it's easier to use.?

Third, read the 20 Meter Sensitivity Modification on the QRP Labs web site to get an understanding of how this issue was addressed. The description for building is correct in the 1.00j manual (section 2.10) and you can follow that with no problem. There is one mistake in the manual at Section 2.10, Step 8: When you test for continuity, Pin 6 will NOT show continuity as Pin 6 is connected to the hole that was skipped in step 5.?

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Fourth, Hans descriptions are excellent and you can follow them with confidence. However, I do have a few areas where I deviated from the manual.?

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I installed X201 (section 2.15) before I installed the LPF toroids (section 2.12) as it can be difficult to install later. The jumper across pins 2 & 4 of X201 can be installed. Make sure the jumper doesn't short anything else. If you never intend to use an external amplifier, you need not install the jumper at all.?

Make sure you check the 5V SMPS board for a short between Q103 and Q104 (section 2.31 step 6, see photo). It is essential that you correct this short if it is present. Also, a very small number of builders had an early failure of C107, probably due to component variance and the low headroom (6.3v rating in a 5v circuit)- I was one of those. You may want to consider changing that to a 10v rated capacitor. If you are concerned about either of these issues, the simplest solution is to contact Hans' website and order a set of new SMPS boards. Both issues have been resolved on the replacements.?

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Be careful when placing the top nut on each of the SMPS mounting screws. It is easy to damage close by parts. Don't try to turn the nut; hold the nut and turn the screw to tighten it. The nylon spacer nut will strip and become a true spacer. Earlier manuals suggested reaming out the spacer nuts beforehand and that is what I did.?

The USB-C connector is missing a couple of 5.1k resistors on early QMXs. The only time this is an issue is if you connect to a computer with a USB-C to USB-C cable. In many cases, the computer will not recognize the QMX. The simple fix is to use a USB-A to USB-C cable and a USB-A to C adapter or hub on the computer side. The other fix is to add the two resistors, but be warned; this requires good surface mount soldering techniques.?

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Preset the contrast trimmer (R305, section 2.21) fully CCW after installing. The LCD contrast will likely be spot on without further adjustment.?

Keep in mind that the only protection for high SWR is the firmware disconnect if you set it. So use some sort of resistive bridge to transmit through when tuning your antenna system. This applies to both manual and automatic antenna system tuners. Alternatively, you can power it with much lower input voltage while tuning or you can use the SWR Test under Hardware Tests in the menu while tuning the antenna system.?

Have fun! This is a great radio. It's my go-to radio for my portable operations.?

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73, Dan? NM3A

Hi Gert,

I built my QMX+ with a blue LCD because I prefer a blue LCD and it matches my 40m QCX+ .

Attached? photos with backlight on and backlight off.

73,

Malcolm EI8FH

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hi
Blue LCD looks sexier, not under the Sunlight
73 DE muhsin TA1MHS

I’m sure the blue display will work fine, but it wouldn’t be readable with the backlight off.

Only applies if you want to save a little on the supply current…

What revision is your QMX? ? Rev 3 & rev 4 versions sometimes have bad pcm1804 chips. ?There are many, ?many failure modes in those chips. ?One of the failure modes is similar to what you describe. ?What do the scans look like for A/D converter in Putty after it’s used for a while??

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73
Jeff Moore
W1NC

Do you have any ferrite beads you can put on the USB cable, or a different cable to try? Sounds like it could be RF being picked up on the cable.

On Fri, Jan 10, 2025 at 07:20 PM, Curt wb8yyy wrote:

Well your design might work for a rig that never leaves the house. Maybe.?

How does it know where it is?

On Fri, Jan 10, 2025 at 05:40 PM, Adam wrote:

Interesting that you say that the regulators get "a bit warm" (which I
understand: safe to touch, won't burn you).

Not really checked, but it doesn't seem excessive.

I assume there's no magic in using a larger (TO-220) chip vs DPAK with a
large ground plane. The chip inside is similar, the power dissipated is
the same, the heatsinking area is larger with a ground plane than with
TO-220 with a chopped tab. So my ground plane should be actually colder
than your chip, yet it gets to around 80°C, and DPAK (measured at the tab)
to around 90°C...

No magic involved.? I was using TO220 style chips because they were through hole.

Of course not immediately. But slowly, steadily, over the course of maybe
minutes, it gets there and settles.

What current draw do you have on your 3V3 rail? Mine is around 100 mA.

I guess mine is about the same.

BTW, I ran my QMX with these power supplies for 1.5 hour (without a case).
Nothing exploded. So I guess the regulator can handle it. I'm worried
about capacitors -- how long till they fail in this temperature (they're
directly on the ground plane, touching it, actually being pressed to it by
the display)...

I see you're using tantalum ones, maybe I should switch to that as well.

I used what I had.

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You seem quite concerned with reliability, are you planning to operate 24/7 in an inaccessible place?

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I routinely turn the power down, for bench testing 7 to 8 V is enough.

I built a QMX ? 20-10m version and the transmit portion works fine with about 4 watts out on 10m.

When I initially power on the radio, the receiver starts picking up FT8 signals with WSJT-X decoding them. However after 45 seconds the signals disappear and a high noise level begins to be heard. ?
I have to power on and off again to get that 45 seconds of good signals.?
any suggestions on where to start looking for the problem. ?(I have been doing the standard check on solder bridges and cold solder joints).

thanks

Ron H

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Hello Joshua many thanks for the overview.

If you could send the circuit of the input of the amp to get a good swr i would be very happy.

Thanks again for the overview.

73 hanz

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btw?

the ps for the amp us homebrew?

Great, SSB working now !!

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Has there been an "official" announcement ?

I don't recommend running it over 12V to get more power.? I believe Hans when he says that you significant increase risk of damage to finals, etc.? Morse code only may be a bit more forgiving due to its low duty cycle, but FT8 and other digital modes have long carrier-on times that are already stressful.?

You can likely achieve a bit more power if you really want by internal tuning adjustments to the LPFs for your lowest power bands - but I wouldn't bother.? The difference between 3W and 5W is less than 1/2 an s-unit at the receiving station, which most won't even notice.? ?One of my first QMX contacts was to New Zealand from Utah with 3.2 watts.? You will have more impact on your signal strength by making sure your antenna is efficient.?

This is the Version 1 Kit. I just don’t have the time to put it together. Comes with the following:

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QMX+ Kit

Case

Development Board

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Price - $160.00 Shipped?

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Please contact me off list.

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73

John W9QP

Would a blue LCD as in the QCX+ work in the QMX+ ?

Looks better I think ?

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So, having had a few hours to play around with this great little rig, I am wondering what most folks are seeing for output. I am running the 60-15m version and see no less than 3 watts or better across all the bands. I think that is pretty good. I could likely get it to 5 watts easily but it would mean 12.5 to 12.7 volts. I normally run resonate, purpose built antennas, but still, those little mosfets can only take so much, and what's a few hundred milliwatts between friends?? :).

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So, interested to hear what others are running (pwr/voltage) and what your experience is.

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As an aside, I was surprised to see the LSB/USB option and being able to open the rig up beyond the 300 hz filter. It sounds really, really good on SSB.

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Hats off to Hans for his incredible work. My faith in soldering has also been restored :)

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Scott

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