A lot of hams have expressed trepidation about winding and installing T1 on a QCX Mini, QCX+ or even the original QCX, since they’re all the same. T1 looks hard because there are four windings on one toroid. In this video, I wound T1 and installed it on the QCX Mini. All that’s left to do is solder it. Check the video below.
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The trickiest part of T1 is not winding the toroid, it’s getting all the wires in the right holes on the PCB. In the original QCX build instructions, you were supposed to install T1 after most of the other components were in place; the crowded board made it even more difficult to get the wires in.
In the QCX+ instructions, and carrying over to the QCX-mini, the order was changed; you now install T1 first on a nearly empty board that has only SMD components in place. That makes it much easier to get the wires in. The tradeoff (this applies primarily to the QCX+ because most of those have been replaced with SMD parts in the QCX-mini) is that you now have to be a bit more careful when you install the small components like resistors and capacitors to keep them flush against the PCB, because the board will no longer sit flat on your workbench as you solder those parts. It’s still a big improvement.
If you still have an unbuilt original QCX kit, I recommend installing T1 first as the instructions for the later kits call for. It won’t get in the way of doing the rest of the build.
I have not yet received my QCX-mini kit. But by all accounts it’s the quickest of the QCX versions to build because a lot of the components are SMD parts that are already on the board when you get the kit. All the fixed resistors and over half the fixed capacitors are pre-installed, along with many of the transistors and all the op amps.
If I counted correctly there are like 54 parts total on the mini not already installed. Five of them are toroids that took me about two and a half hours to wind– well four including T1. I already wound all but one of my toroids in advance so I should be able to knock it off in an evening once I get it. I didn’t have a T37-2 in my vast junk box collection of toroids but I am tempted to wind a T37-6 with a couple more turns on it instead and use that (it would work.. Probably better). That mix is more temperature stable so I sorta question the choice of the other one anyway for that inductor.
All toroids suck, but T1 is evil. That is going to be my motto going on. 🙂 I am going to stick to it. What’s evil is that there is no good way to tune it on a VNA in advance…
I never will get ham radio builders obsessions with toroids. They are used in places that simple air wound coils would work better all of the time. You rarely see them on commercial products unless you need stuff to cancel out like common mode chokes.
Air wound coils are the domain of VHF, where the small coios can be self supporting.
Most coios are wound on coil forms.
There is as a time when prewound coios were often used, but those had polystyrene supports. The one time I bought some about 1972, memory says they were expensive. If they arestill available, they are biund to be expensive.
Toroids provide self-shielding, useful for more compact equipment. Coils generally have to be built on something, and toroids seem a bit more available these days than coil forms.
And a lot of “coil winding” is actually broadband transformers, the toroid material allowing for that broadband. In the old days, everything was tuned circuits and you didn’t have much choice, now yiu can broadband except when you really need selectivity. It makes the end product easier to build.
Ryan,
Thanks for doing this. I order my QCX’s prebuilt so I do ‘t have to mess with the toroid winding any more (have wound enough in my long life) but I enjoy your blogs and videos. Hope all is well with you and your wife.
Dave K8WPE since 1960
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Thank you so much Dave for the feedback and the well wishes. 73 to you and your family as well 🙂