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Last night I started building my QDX. I got up to the point where I will wind the six LPF toroids, and thought that would a good place to take a break and get some sleep. Wow, this little guy is not for the impatient, the absent minded or the feint of heart!

As some of you know, I build/complete/repair/tune QCXs as a volunteer contribution to this QRP-Labs community, and have... how should I put it delicately...? "seen some things", especially with the Mini. I assure you I'm not exaggerating when I say that building kits that already have SMT devices is NOT as easy as you might think: SMT and through-hole parts are not good board-fellows. So in my capacity as self-appointed know-it-all, I would like to offer some advice to save some of you some heart-ache...

First and foremost, I know you are all as excited as eight year olds at Christmas to get your QDX working, but TAKE YOUR TIME!

Specifically:

1. Absolutely read all the instructions and understand them before you pick up the soldering iron. Do it for the whole project first, and then again before each step. Identify and lay out your parts - especially the capacitors, because the markings on them are miserably hard to read.
2. Make sure you have plenty of light, a magnifier of some kind, a clean iron, good solder, and sharp cutters and fine long nose pliers.
3. For each component, especially those that have one lead connecting to the ground plane, solder in one (the non-grounded) lead first, check the positioning on the top-side of the board, then finish off by soldering the grounded lead. The ground plane on the QDX is, like on the QCXs, very effective at wicking away heat from the iron, and that makes soldering grounded component leads quite challenging. Apply more force to the pad than to the lead to make sure that you heat the pad sufficiently to accept solder before cooking the part. Don't just cram solder onto the joint in an effort to spread heat: you'll end up with a big blob of solder and may?still have a hidden bad connection and a wire whisker.
4. Conversely, when soldering the 0.5mm coil wires, apply more pressure to the wire, not the pad. Don't even attempt to burn off the insulation: it won't work. Follow Hans' advice and use your side cutters to gently scrape off most of the insulation before attempting to solder the wires. When soldering the loops, snip off the tip/fold, unwrap the twists right down to the board, and put the soldering tip right between the two wires to solder them, splaying them slightly. That retains them well, and spreads heat to the wires and allows the insulation to burn off and flow away in the liquid flux.

5. Perhaps the MOST IMPORTANT note of all: pay attention to the SMT devices at all times.
5.1 When soldering through-hole components, and especially coil wires, be very careful to keep your iron tip away from the SMT devices: if you liberate them, they're difficult to get back in place, especially if your not accustomed to SMT work. Think about the approach angle of your soldering iron so you don't accidentally heat and liberate an SMT device
5.2 Similarly, be extremely careful clipping off through-hole lead ends: be VERY CAREFUL not to destroy SMT devices that are adjacent to the through hole pads. Choose your approach direction carefully.

6. When winding L4, the wire is thick and stiff, and you'll need to coax the wire around the inner edge of the toroid. Be careful not to scrape the insulation off the wire as you pull it through, and use long nose pliers to help form the turns evenly. As Hans advises, DO NOT pre-tin the wires: the through-holes in the board are only just big enough for the wire alone. Make sure the wire ends are squarely cut off - not crushed - and vertical as you push them through, or you'll have trouble. Give the wound inductor a look over to make sure the coils are tidy before you solder the ends.
7. In the instructions to make L12, Hans tells you to cut of 75cms of 28 AWG wire. Treat that guidance seriously. Make sure you don't use too much wire for the start and for the tap loops: make them no more than 3/4 inch, or you will run out of wire before you get to 41 turns.

That's it for now; I wanted to get this out ASAP, but I'll probably have more comments later: I want everybody to be successful in their own build experience. If you have any questions, ask. If you have observations of your own, please post them.

I am very tempted to create some detailed close-up videos of some of the particularly challenging steps. I have had at least one request to build a unit for a customer who is wise enough to know that he is not fresh enough to do it himself, so if there's any interest I'll use that/those opportunities to take some detailed videos on technique "for the good of the party".

Good luck with your QDXs :-)
--
Julian, N4JO.

Jilian
Thank You excellent information especially the " TAKE YOUR TIME!" tip.
It is so much easier to find issues by checking each step once completed rather than try to guess where the problem might be.

Julian,

Great writeup and thanks for everything you do for the members of this fine community of QRP enthusiasts!
This is by far my favorite Groups.io.....

Looking forward to my QDX build.

73
-Mike

Thanks Mike. It's really a reciprocal process: electronics may be my trade, but I'm really new into amateur radio, so I'm learning a lot from you guys who have been it for longer, in some cases, than I've even been alive. I'm just paying it back :-)
I'll finish off my QDX tonight, maybe push out some more notes, and then get back to some other commitments I'm tardy on...
--
Julian, N4JO.

I reached stage 2.11 yesterday before other matters intervened, so hopefully today will be the day...

These hints may be blatantly obvious but here goes.

1.? My first step was to remove the four SMD inductors for no better reason than I could do it with the board flat on my work surface at that point.? Tweezers were helpful for two but the others came off stuck to the ball of solder on the tip of my iron

2.? If you are concerned about how much wire you need for T1, then wind L14 first and put it aside until needed.? Then you know how much you have left.? The inventory says 50cm is supplied, but the length in my kit was a generous 60cm and I had 18 cm (say 7") left at the end of my 3:3 transformer despite leaving longer tails than Hans suggests.? So you will have plenty.

3. I have several tips of differing sizes for my soldering iron, so I changed to a larger one for T1 and L14 for better heat transfer - there is room to wield a bigger tip if you are careful.? I also increased the iron temperature from my usual 350C to 390C (sorry, if you work in Fahrenheit ask Mr Google).? Seems to have worked as both passed their continuity checks first time.??

4.? If you are in the position of having to buy solder for the build, go for 0.5mm (0.02") or thinner rather than the more standard 0.7mm or thicker.? Although you can build successfully with the thicker solder, it needs more care as it's all too easy to use too much solder and create blobs and bridges.?

5.? I haven't got there yet, but if you do no other pre-switch on checks, at least check that you don't have a dead short on the DC input.? All I will say is that melting insulation has a smell of its own......

And a note for those who are concerned about such things, my QDX (order 50300) left Hans on Thursday 28th, reached his local TNT depot in Izmir around midday on Tuesday 2nd and was handed over to me in southern England midday on Wednesday 3rd.? So no complaints there.??

Good luck and enjoy the build.

Chris? G4CWS



??

As excellent as Hans' build instructions are, I feel there is one page which could do with a bit of clarification.? That is the one dealing with winding the trifilar transformer T2.? It is absolutely critical that the start and end of the windings are identified along with the continuity checks with a multimeter. If you get a start of winding mixed up with an end, you will get no phase reversal going into the QSD inputs and it just won't work!? (Strictly speaking, this only applies to the centre-tapped secondary windings, the primary phasing is immaterial.)

I have roughly modified the pages from version 1.04 of the manual, to hopefully make this clear.? There's a couple of pictures attached...
--??
Peter Lee
G3SPL

When soldering through hole leaded components i was taught to place tip of iron, pre tinned, to the pad first, wait for 3 seconds, slide iron to junction of pad and lead, apply solder then slide tip of iron up component lead and away.?
I cringe when I see soldering where both iron and solder are both applied at the same time and then both are immediately removed from joint.?
Andy?
--
The universe is made up of Protons, Neutrons, Electrons but contains only one M0RON.

It also says to cut the three lengths of enamelled wire to 20cm. I did this, then with the screwdriver turned it 60 times, to find it was only long enough to get seven turns, possibly eight with short tails, on the toroid. Luckily I had a?filter kit untouched so raided that to try again, making the lengths 30cm, and this time there was about 5cm sans tails over after the ten turns. It might be wise to put 25cm as the length in the manual as it's always easier to remove than to add ;)

Robbie M1ROK

After winding, I used a slightly different method to hook it up that I thought was easier. Each to his own, of course, but I'll post my method in more detail later today. Essentially I solder in the three connections on the right side, then unwind the three connections on the left, ring them out to identify, then feed through and solder.
My unit is up and running as a WSPR receiver right now...


--
Julian, N4JO.

That's a very good tip to remove the four inductors before starting construction. ?It's a lot easier with no additional components on the board and the board able to lay flat on the desk.

Regarding the 0.6mm coil wires, I've always been able to burn off the enamel on every wire I've used before, even the 18swg (1.25mm) and 19swg (1.0mm) stuff used for winding big bandpass filters. ?It just means changing the tip on the soldering iron to a larger one for that specific purpose and then changing it back again to solder them in.

73 Keith G6NHU

--
QSO365 - My amateur radio blog:?

?

Yes! I was going to include that in my notes; thanks for bringing it up.
--
Julian, N4JO.

On Thu, Nov 4, 2021, at 12:02 PM, Julian N4JO wrote:

Yes! I was going to include that in my notes; thanks for bringing it up.

Hi Julian,

First off, Thank You for sharing your experiences they have been a great help.

For clarity, which posting are you referring to in the above message?? It is always helpful to include the name of the person addressed in the response so those of us who read things in received order know how to interpret it.? This response is an example that includes the quoted part of the message in question.? There are so many people on the server that it is always probable that another response was posted before you could hit your send button.

Again, thank you!
73
Evan
AC9TU

On Thu, Nov 4, 2021 at 12:12 PM, Evan Hand wrote:

For clarity, which posting are you referring to in the above message?? It is always helpful to include the name of the person addressed in the response so those of us who read things in received order know how to interpret it

Yup, you're absolutely right, Evan, and I should know better !

I was referring to Dave's (k2lyv) comment: "Also before soldering the power and USB connectors, insert the leads for the 200uF capacitor."
When I got to that point I realized it would have been much easier to solder the cap in at the same time as the connectors - taking care that the latter are square to the edge of the board, of course.

?And thanks for holding me to high standards :-)
--
Julian, N4JO.

It depends on the item with the largest thermal mass. For a grounded pad that's definitely the best way to go, but for a half mmm copper wire you'll be there all week and liberate the pad. In any case, allowing a small amount of solder onto the tip of the iron improves heat flow, and it also release some flux, which is what cleans the joint and allows bonding. But yes, the solder should certainly be removed before the iron!
--
Julian, N4JO.