< back N5DUX's Ham Resources

QCX Build Tips


Toroids

I found the QCX manual from QRP-Labs to be extremely in depth. Unfortunately I found the toroid winding steps to be lacking a small piece of helpful information: the approximate length of wire needed for each toroid.
The length of each wire is taken from this wonderful toroid resource over at KitsAndParts.com. (Thanks to W8DIZ for reminding me about it!)
I hope you find the following information helpful.
Lengths are approximate. Be sure to give yourself a little margin of error. You don't have to be 100% exact on the measurement, you just dont want to run out of wire!

Should you run out or need more wire, the wire in the kit is #28 awg enamel-coated magnet wire.

Be sure to check the values of the toroids you've wound before soldering them in place.
I use a cheap LC meter I got off eBay long ago. There are also "transistor tester" kits you can build but many cheap multimeters can be found online that do inductance measurement.

T1 Toroid (transformer)

These lengths are very approximate.
I added the total number of turns and determined total length. Then added ~12" to the total to provide for 2" lengths (down and back) for the twisted loops between the Primary and S1 and S2.
Be extra sure to read and re-read the transformer directions before cutting or soldering anything!
BandToroidTurnsLength
PrimaryS1S2S3
80mT50-2
Red
55568~70" total
60mT50-2
Red
55546~56" total
40mT50-2
Red
55538~50" total
30mT50-2
Red
44430~44" total
20mT50-2
Red
33330~40" total
17mT50-2
Red
33322~36" total

L4 Toroid

BandToroidValueTurnsLength
80mT37-2
Red
2.3uH2414"
60mT37-2
Red
2.3uH2414"
40mT37-2
Red
1.0uH1610"
30mT37-2
Red
0.78uH149"
20mT37-2
Red
0.40uH107"
17mT37-2
Red
0.32uH97"

L2 Toroid

From Low Pass Filter kit
BandToroidValueTurnsLength
80mT37-2
Red
3.0uH2716"
60mT37-2
Red
2.3uH2414"
40mT37-6
Yellow
1.7uH2414"
30mT37-6
Yellow
1.3uH2012"
20mT37-6
Yellow
0.90uH1711"
17mT37-6
Yellow
0.67uH1510"

L1 & L3 Toroids

From Low Pass Filter kit
BandToroidValueTurnsLength
80mT37-2
Red
2.3uH2515"
60mT37-2
Red
2.3uH2314"
40mT37-6
Yellow
1.0uH2113"
30mT37-6
Yellow
0.78uH1912"
20mT37-6
Yellow
0.40uH1611"
17mT37-6
Yellow
0.32uH139"