Miniature Antenna UNUN or BALUN Transformer for Receivers
The BALUN types offer GALVANIC ISOLATION too, because the ground lead of the transformer is not connected to receiver's ground.
Choose from 1:1, 2:1, 4:1, 9:1, 16:1, 25:1 and 36:1 impedance ratios - NEW: 49:1 Added wound on a FT50-43 ferrite core working from 3.5-21 MHZ
With a Gas Plasma Discharge Tube for overvoltage protection
My friend Thanasi, SV1JO, told me the idea first. He has a Yagi beam antenna for operating on 10/15/20 m bands and he needed an easy way to operate his receivers at lower frequencies with a 10 meters long wire or so. After a couple of tries with hand-wound BAL-UNs we realized we cannot achieve and guarantee the bandwidth a Mini-Circuits transformer can provide. There are models starting from 15 KHZ and ending at 250 MHZ! It is not easy winding a BALUN working on such a wide bandwidth. So we decided to take advantage of the guaranteed performance Mini-Circuits transformers offer and we prepared a universal small PCB module with an SMA connector for the 50 Ohms port and screw terminal fixtures (solder lugs) for the high impedance port. This side is protected with the overvoltage protection Gas Plasma Discharge Tube since this side has the exposed long wire attached. For proper protection, it is recommended to connect the GND terminal to a ground point.
The PCB dimensions are only 41 x 19 mm and its material is a durable 1.6 mm thick FR4, gold plated.
For permanent installations, one can use a small plastic or metal enclosure to fully protect the module.
Now, depending on the antenna used, you may need a different impedance ratio from a receiver BALUN.
For example, loop antennae may need 2:1, another antenna type 2:1 or 4:1 and for long wires 9:1 or better, 16:1.
You can directly connect the 50 Ohms port to a receiver or through a preamp (LNA).
Today, December 2019, both for UNUNs and BALUNs, the following configutrations are available:
1:1 Using the ADTT1-6+ transformer, working from 15 KHZ - 100 MHZ (-3 dB points).
2:1 Using the T2-1T-KK81+ transformer, working from 70 KHZ - 200 MHZ (-3 dB points).
4:1 Using the T4-6T-KK81+ transformer, working from 20 KHZ - 250 MHZ (-3 dB points).
9:1 Using the TX9-1+ transformer, working from 1 MHZ - 200 MHZ (-3 dB points).
16:1 Using the T16-6T-KK81+ transformer, working from 30 KHZ - 75 MHZ (-3 dB points).
25:1 Using the TT25-1-KK81+ transformer, working from 20 KHZ - 30 MHZ (-3 dB points).
36:1 Using the T36-1-KK81+ transformer, working from 30 KHZ - 20 MHZ (-3 dB points).
49:1 Using a wound FT50-43 ferrite core, working from 3.5 MHZ - 20 MHZ
Ordering: Please send us an email to tell us which ratio you need and which PCB (Green for BALUN and Red for UNUN). The BALUN PCB can be easily modified to make an UNUN by simply grounding one of the wires in the BALanced side. The UNUN PCB can be modified to a BALUN by cutting the ground connection of the grounding wire at the BALanced side.
Most of the transformers used have a center tap either on the primary or on the secondary winding and help for making more impedance transformation combinations possible. You need to modify the circuit for doing this, since the center taps are not connected.