1:1 ATU Current Balun 1 - 54 MHz 5kW - #1171
|Manufacturer: Balun Designs|
This is a departure from the normal 1:1 Isolation/choke balun and utilizes a bifilar pair designed to maximize interwinding breakdown voltage. The balun functions to transform balanced to unbalanced feedline for the transition to coax while providing high levels of choking impedance to stop common mode currents from entering equipment. This balun is not wound with a 50 ohm pair as the design goal is to maximize inter-conductor breakdown voltage. Primarily used to transform ladder line, twin lead or window line feeding antennas such as multiband dipoles (doublet) and/or multiband loops.
With wire antennas such as this being used primarily on the lower HF bands, choking impedance has been shifted to provide maximum performance on these bands. However, this ferrite mix still provides excellent common mode control on the upper HF bands where very high choking impedance levels are not as critical.
The model 1171ts is specially configured to provide isolation between a remote tuner and antenna at the feedpoint such as a random wire being fed against ground. The studs on input and output make installation/insertion very easy. The balun may also be ordered without an enclosure (1171x) for upgrading the balun in a tuner.
This balun is best utilized with a quality tuner that can easily match a wide impedance range. If you have a less expensive tuner with limited range, consider using the Model 4114 balun to reduce the required impedance match and thereby assist the tuner. It is best installed outdoors to minimize the chance of RF entering the operating position from the balanced feedline.
My thanks to Owen (VK1OD) for his recommendation and assistance with this design. Click on the graph below to view the full choking impedance curve.
Click to Enlarge
Testing done with an AIM-4170uhf Network Analyzer
For a good graphical explanation of why this designs works well, read through Steve's (G3TXQ) website page
- T match antenna tuners perform quite poorly if the resistive component of load impedance is very low, even worse if there is also a high capacitive reactive component. This is a common load found in shortened dipoles fed with open wire line.
- The traditional approach is to use a 4:1 balun on such antennas, but antenna tuner loss is worse with low resistive loads.
- The need to tolerate high voltages occurs when the balun happens to be located near a differential voltage maximum.
- High common mode impedance for effective reduction of common mode current.
- Balun is intended for use with an antenna tuner which will manage SWR and transformation mismatches.
- Differential insertion loss is not a significant parameter in this application, the dissipation in a current balun is primarily from the common mode current which is installation dependent and not easily predicted.
| Core Material
|| Custom mix ferrite from Fair Rite Products optimized for low frequencies.
Cores are coated and sealed for long term durability.
| Winding Type
|| Stacked dual core, bifilar pair 1:1 current balun provides larger effective core.
| Winding Material
|| Heavy gauge Essex polyamideimide Allex 240 Winding Wire wire inserted in teflon tubes.
Breakdown voltage in excess of 10kv
| Power Rating
|| 1 to 35 MHz - 5kW, 10kW intermittent. 35 to 54 MHz - 5kW.
All ratings at resonance. High SWR will reduce power handling ability.
|Useable Frequency|| 1 to 54 MHz
| Insertion Loss
|| Less than .02db
|| SO-239 connectors are silver plated with Teflon insulation.
Studs and eyebolts are 1/4 inch.
Alternate connectors and Mounting Options are available in the Accessories section.
||All Stainless Steel|
| Enclosure Type
|| NEMA rated 4x marine grade junction box for outdoor installations.
Cover has neoprene gasket for weatherproof integrity.
|| 4x4x2 inches for main body of unit
| Additional Info
|| Very high efficiency (98-99%).
Will not heat up or saturate at like many of the "less expensive" designs.