Hi,
Note the higher impedance windings go through the copper tube. This is an attempt to increase the coupling between the tube single turn and the wire turns. transmission lone devices inherently have close coupling of the windings but transformer devices will not, even with a good core.
Test your device with a resistive load and if the SWR is less than 1.25:1 across the range it will be qood for QRP.
I have been playing with some cores and revisiting work I did several years back on 1:1 and 1:4 transmission line transformers. I have built a 9:1 unun and a 9:1 current balun. Both do a very good job from 1.8 to 30 MHz and 3 to 50 MHz respectively. I can’t measure the losses as they are too low for my instruments to show. I usually build two and connect back to back with the rig on the input and an absorbing watt meter on the output. The resolution is a couple of percent.
I’ve also built a 49:1 transformer. It shows up to 2:1 swr from 3 to 30 MHz when connected to a resistive load of 2,500 ohms. This seems to be par for the course. I need to build a second one to see if it is efficient.
The reason for less than a perfect match is primarily the leakage of flux as not all turns see the same flux. At the higher frequency end some capacitance compensation brings the ratio back to near where it should be. This is necessary due to the distributed capacitance between turns.
Some of the cores I use are type 42 ferrite and others are unknown being bargains bought for a low price. I wind 8 turns of 100 ohm wire transmission line on the core and test it as a 4:1 device. If the results look OK then I put it in my Good box. CAT5 cable has 100 ohm balanced transmission lines inside. Cut off a m length and strip out a pair, Really good for medium sized ratio devices.
73
Ron
VK3AFW