Why Current Baluns are superior to Voltage Baluns
Voltage Baluns
Voltage baluns try to force equal voltages into the output terminals. This would be fine providing the load was perfectly balanced, as this would imply equal currents into each terminal. Unfortunately, this does not occur in the real world of antennas. If there is even a small imbalance, feedline radiation will occur.
Voltage baluns work more like conventional transformers where the energy is coupled through the core. Core saturation, core heating, and balance quality are usually worse with voltage baluns.
Current Baluns
Current baluns try to force equal currents into each terminal, regardless of the differences in impedance. If the load is an antenna, this is exactly what we are trying to achieve. The feedline is presented with equal but opposite currents in each conductor and the nett result is minimal feedline radiation.
Based on the above facts alone, we can say the best type of balun to use with an antenna system is the current balun. However, there are also other advantages of the current balun. As well as providing better balance, the current balun is also more tolerant to variations in load impedance, has a better bandwidth, and more often has lower loss.
When adequate isolation exists between input and output ports, current baluns transfer energy by efficient transmission line mode. This also means a higher power rating for a given core area due to less core flux.
Standard vs. Tuner baluns
All of our baluns are based on the renowned designs of Jerry Sevick (W2FMI-sk), Joe Reisert (W1JR) et al. and have seen thousands of hours service in the field through our own in-house testing and that of our beta testers.
Our standard range of baluns are designed and optimised for specific impedances on both input and output ports. As an example, our standard 4:1 baluns are optimized for 200:50 ohm impedance ratios. They can be used for other impedances, however, power handling capability will be reduced as SWR increases.
Tuner baluns are used as the interface between coaxial line and open wire feeder. They are designed to withstand exceptionally high breakdown voltages using Teflon insulated, polyimide coated wire. They also have very high common mode impedance to maintain input to output isolation even with extreme loads.
Unfortunately, until very recently, most baluns within antenna tuners were 4:1 voltage types. Testing and experiments by various engineers has proven the best balun for this particular application is usually a current type with a 1:1 ratio.
Balun Enclosures and Potting
We have subjected our baluns to literally thousands of hours of field testing over the last few years. We have learned quite a lot about enclosures and their Ingress Protection (IP) Ratings. Many enclosures have a very good IP rating provided the extra holes added to the case for mounting connectors, through bolts etc. are also added in such a way as to preserve the enclosure’s original IP rating. This means proper gaskets, O-rings etc. must be used on the additional holes. Unfortunately this can be time consuming and expensive to implement correctly and, in most instances, is not done at all. This, of course, lowers the effective IP rating of the enclosure and can allow moisture and contaminants to penetrate. Given the right conditions of temperature and humidity, air transfer from the atmosphere to inside the enclosure can lead to the formation of water droplets (condensation) on the internal components.
An alternative method of ensuring the internals are protected is to use a carefully selected potting compound. Some epoxy based potting compounds cure to a hard state, which is unsuitable in this application. The internal components of the balun must be able to expand and contract as it warms up and cools down. Failure to allow flexibility with temperature change usually leads to cracking of the brittle ferrite material.
We have sourced a flexible, mining grade RTV potting material, highly suitable for potting baluns. All our baluns are potted with this compound to ensure full protection even from the harshest environments.
Connections
All of our baluns use corrosion resistant stainless steel hardware for the output connections. The high power baluns in the larger enclosure also use a silver plated, Teflon insulated SO239 socket with gold flashed center connection.
Part Numbers and Pricing
All of our balun products begin with the prefix BL
The second number is the PEP power rating (eg. 250 = 250watts; 1000 = 1000watts etc.)
The third number is the balun ratio (eg. 4 = 4:1; 1 = 1:1 etc.)
The suffix T identifies the balun as a Tuner Type balun.
Standard Types:
BL1000-1 1:1 1000w PEP, 50 ohm, 1.8-55MHz $ 65.00
BL5000-1 1:1 5000w PEP, 50 ohm, 1.8-55MHz $110.00
BL1000-4 4:1 1000w PEP, 200-50 ohm, 1.8-55MHz $ 75.00
BL2000-4 4:1 2000w PEP, 200-50 ohm, 1.8-55Mhz $125.00
Tuner Types (T suffix):
BL250-1-T 1:1 250w PEP, 1.8-55MHz $ 65.00
BL500-1-T 1:1 500w PEP, 1.8-55MHz $ 85.00
BL1000-1-T 1:1 1000w PEP, 1.8-55MHz $100.00
BL2000-1-T 1:1 2000w PEP, 1.8-55MHz $125.00
BL3000-1-T 1:1 3000w PEP, 1.8-55MHz $150.00
Typical Performance Specifications
Frequency range – 1.8 to 55MHz
Input SWR with matched load (Standard baluns) <1.5:1
Typical matched insertion loss << 0.2dB.
Generally, power handling capability is reduced and losses increase as SWR increases.
Enclosure Dimensions and Weight (approximate)
Enclosure A – 65 x 59 x 38mm; 200g:
BL1000-1, BL1000-4, BL250-1-T, BL500-1-T
Enclosure B – 116 x 90 x 58mm; 600g:
BL5000-1, BL2000-4, BL1000-1-T, BL2000-1-T, BL3000-1-T
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