OM0ET | Mini 49:1 UNUN transformer
Mini 49:1 UNUN
The EndFed Half Wave Antenna
is very popular antenna due to the very simple installation and handy design which can achieve many HAM bands without or with the tuner. All depends just on the lenght of the wire which have to be the lenght of the half wave of any band. That's why it's called a "half wave antenna".
It's actually a classic half wave dipole antenna, but this one is feeded on the end of an antenna wire instead of in center, which is very practical because this antenna wire can be very easy used in horizontal or also in vertical plane. The EndFed Half Wave Antenna doesn't requires a counterpoise which makes it even more practical and no other wires are needed to connect.
For it's simplicity and small dimensions is very popular for portable or SOTA activities, and also as a static-mobile antenna.
This Mini 49:1 UnUn can be used also as the base point of a vertical dipole antenna with its half wave length.
Yes, we can use this antenna also as a multiband dipole, when harmonic resonant frequencies allowes us to work also on some other bands.
An example: if you cut your wire for 40m band, antenna will resonate on 40M, 20M and 15M bands without tuner and with tuner also on 10M band. The lenght of the wire for 40M band should be around 20.7m or 67.9ft.
- lightweight (only 50g)
- small dimensions (fits into your pocket)
- max. input power up to 50W
- easy and quick installation
- no counterpoise
- external tuner is on some bands required
The 49:1 UNUN construction
Has been used a FT82-43 material toroid with 2 primary and 14 secondary turns of 0.5mm thick enamelled solid copper wire.
Transformer partsSmall BNC-F socket is used for quick and simple connection to your coaxial feedline. Housing is made of the solid 25mm wide PVC tubing. The radiator wire is simply connected under the wing nut so no screwdriver is required. Simple and easy installation.
Update: 100pF/10kV primary capacitor has been added
"Added capacitor improves higher frequency UNUN performance and compensates for UNUN primary leakage" - K1RF.
"Capacitor flattens SWR at higher frequencies" - WA7ARK
Antenna wire lenghtsThe End Fed Half Wave antenna requires to cut one of halfwave lenghts. Here is the table of some examples:
My YouTube videos about the Mini UnUn 9:1 Transformer and Random Wire EndFed Antenna