OM0ET | Mini 9:1 UNUN transformer
The EndFed Random Wire Antenna
is very popular antenna due to its 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 never shouldn't be the lenght of the half wave of any band. That's why it's called a "random wire antenna".
This antenna design is feeded on one end of an antenna wire, which is very practical because this antenna wire can be used in horizontal or vertical plane. The EFRW (EndFed Random Wire Antenna) requires also a counterpoise.
A standard recommendation (see QST, March 1936, page 32, "An Unorthodox Antenna") is an 84' (25.6m) antenna wire and 17' (5.18m) long counterpoise.
In some emergency situations coaxial feedline can be used as a counterpoise and no extra wire need to be connected. In this case is recommended to use at least 5m long coaxial feedline or longer.
For it's simplicity and small dimensions is very popular for portable or SOTA activities, and also as a static-mobile antenna.
This Mini 9:1 UnUn can be used also as the base point of a vertical antenna with its random length (minimum lenght should be at least 6m).
- lightweight (only 50g)
- small dimensions (fits into your pocket)
- max. input power up to 50W
- easy and quick installation
- external tuner is on some bands required
The 9:1 UNUN construction
Has been used the FT82-43 material toroid with 9 trifilar winded turns of 0.5mm thick 3-color 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.
Antenna wire lengthsThe Random Wire EndFed antenna requires to cut one of NON halfwave lengths. Here is the table of some examples.
For more details about lengths you can also read here on very informative vk6ysf website here.
My YouTube videos about the Mini UnUn 9:1 Transformer and Random Wire EndFed Antenna