This is a departure from the normal 1:1 Isolation/choke balun and utilizes a bifilar pair designed to maximize interwinding breakdown voltage. The "ts" model is specially configured to provide isolation between a remote tuner and antenna at the feedpoint. The studs on input and output make installation/insertion very easy. Note that primary use is with a multiband dipole fed with ladder line or twin lead. With wire antennas such as this being focused on the lower HF bands, choking impedance has been shifted to provide maximum performance on these bands.
Two of these baluns can also be used at the beginning and end of an extreme long run of ladder or open feedline to create ultra low loss feedline beginning and ending with 50 ohm coax. 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.
Note this balun may be ordered without an enclosure to upgrade the 1:1 balun in a tuner.
Click to Enlarge
Testing done with an AIM-4170c Network Analyzer
This balun is best utilized with a quality tuner that can provide matching over a wide impedance range. If you have a less expensive tuner with limited range, consider using the Model 4124 balun to reduce the required impedance match.
Design Criteria
- 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.
- This 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.
For a good graphical explanation of why this designs works well, read through Steve's (G3TXQ) website page
http://www.karinya.net/g3txq/tuner_balun/
Specifications:
This balun will handle continuous power of 5kw or 10kw intermittent and tolerate high SWR for extended periods.
It will not heat up at rated power, extended duty cycles or stressing load conditions.
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