Simon (G5SHO) recently built a 49:1 end fed half wave UNUN matching unit - Thank you to Jon G7NFK for his help with the parts information
2 No. FT240 x 43 Ferrite cores - Held together with a couple of dots of super glue and ready to be wrapped.
Nicely wrapped in a PTFE protective jacket and ready to be wound.
The hole drilled for the SO259, using a reamer tool to dress the edges and adjust for the fit of the socket.
SO259 fitted and secured in with 4 No. 3mm x 20mm bolts 4 No. washers and Nyloc nuts. Th M6 hole at the side ready drilled for the earth connection.
The holes in the top of the enclosure are drilled to M6 for the strain relief and the stud for the secondary connection to the transformer.
Once the transformer coils have been wound using 14AWG laminated transformer wire with 2 turns for the double wire and a further 12 turns of the single, the lacquer can be scrapped off and the ends tinned with solder.
The 3D printed backplate with the nylon tie wraps fitted can be fixed in place.
With the wound cores set to the correct positions for the wire outputs it can be firmly secured to the backplate using nylon non-conductive tie-wraps.
One by one the transformer wires can be connected. At the bottom are the connections to the SO259 from the 2 turns on the cores (primary), one to the centre pin with one (along with the secondary connection and a link for the ground connection) to the outer screen connection of the socket. These are connected to one of the retaining bolts with an extra lead off to the ground connection stud, all ring terminal connections are soldered for better connection.
With all the connections tightened and checked and the transformer wire dressed neatly in the enclosure, the transformer can now be tested with the Nano VNA to check the SWR readings.
As this is designed for 10 - 40 meters, at top band there will be a high impedance due to the 66 foot (20m) of antenna cable that would normally be connected for the half wave on 40 meters. To enable the test to be done successfully a 2450 Ohm resistor is connected between the output (top right) and the earth / counterpoise connection (bottom left).
This will simulate the 49:1 of the 50 Ohms cable 49 x 50Ω = 2450Ω
The initial SWR test look very encouraging although a little higher than they should be indicating an issue somewhere along the line. The results showed as follows:
Band Frequency SWR
40m 7.000 - 7.200 MHz 1.312
20m 14.000 - 14.350 MHz 1.370
15m 21.000 - 21.450 MHz 2.170
10m 28.000 - 29.700 MHz 2.580
After a little bit of fault finding I narrowed the high SWR readings down to a poor connection caused by the centre pin socket on the SO239 in the 49:1 that was not making contact properly with the plug.
I removed the socket and replaced it, rechecking all of the solder connections at the same time. Reconnected the test resistors and attached the nanoVNA.
An SWR of 1:1.09 is now being shown for the 7 - 7.2 MHz test.
The 49:1 reinstalled to the EFHW
With the antenna trimmed, first contact was 5&9 to Italy (some 890 miles) pretty pleased with that.
Update: Feb 12th 2023 - Contact between G5SHO and VK7RG 10,846 miles away in Tasmania - Signal report 4 & 4 on 14.217!! Really super happy with that.