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This balun is new to the Balun Designs lineup and is for those of you with tough RFI, SWR and/or RF in shack problems. Building on the original 1:1 design by Dr. Jerry Sevick, this balun has two (2) stacked cores to maximize choking impedance on HF bands from 1- 35MHz. By utilizing Mil-Spec coax, the SWR, Transformation and power handling are excellent while providing a choking impedance that exceeds 10,000 ohms. Even on 80m the choking impedance is over 3,500 ohms. Please click on the graph shown below to see the complete results.
Sometimes called a choke balun or common mode choke, this 1:1 ratio current balun is the best for feedline isolation and choking. It has the widest operating frequency range, lowest core stress and provides the best overall balance of any balun for given cost, size, and weight.
Additional Models & Photos:   
Design features:
Utilizes specifications of Jerry Sevick, W2FMI, the authority on baluns. This is his Guanella current balun design which he modified to provide higher efficiency. By utilizing a new toroid mix, the bandwidth of his design has been increased.
Stacked toroids with low permeability allows broad frequency coverage. Toroid is coated with epoxy paint for added durablity.
This Isolation balun has significantly higher common-mode impedance which exceeds 10,000 ohms. The larger core area is much more effective than types with ferrite beads, ferrite bars or wound air-core coax.
Windings are Mil Spec 50 ohm coax rated 19kw @ 1mhz, 9kw @ 10 Mhz and 3.5kw @ 50 Mhz. Silver coated braid and center conductor. Solid Teflon dielectric.
Typical insertion loss is less than 0.2 dB
Power handling of 5kw continuous / 10kw intermittent upto 35mhz. May be used to 50 mhz with minimal reduction in efficiency.
SO-239 connectors are silver plated with teflon insulation.
All hardware is stainless steel
N connectors and Alternate Mounting Options are available in the Accessories section.
Very high efficiency. Will not heat up or saturate like many of the typical cheap current baluns.
Balun is built installed in weatherproof 4" X 4" X 2" Nema Box which makes an excellent outdoor weatherproof enclosure.
Regardless of the antenna you're using, an isolation balun can provide numerous advantages
- Preventing unwanted RFI by eliminating feedline common mode currents and radiation
- All power goes to the antenna, improving efficiency
- Reduces noise or EMI picked-up by your coax shield
- Power is balanced between driven elements of antenna
- Can help overcome a less than optimal ground
Noise Reduction
While the most common advice is to improve the station's RF ground, the root of the problem is in the poor isolation of the feedline from antenna currents. If your goal is to reduce feedline radiation and improve reception by reducing noise, feedline isolation baluns are an excellent choice. Adding an additional isolation balun at the point where the feedline exits the near field area of the antenna will substantially reduce unwanted feedline radiation and reception of EMI without the need for improved station grounding.
One Exception!!!
It must be pointed out that a 1:1 balun should never be used on the second harmonic of a half-wave center-fed dipole (like an 80 meter dipole being used on 40 meters). The impedance can be as great as 10,000 ohms creating very high voltages which can bring about voltage breakdown and/or excessive heating. This does not apply to OCF dipoles or center fed dipoles using ladder line.
NOTE: Although this balun will tolerate very high SWR, efficiency drops markedly if your SWR is 4:1 or above.
This isolation balun will handle continuous power of 5kw and tolerate high SWR for extended periods.
It will not heat up or saturate at rated power, under extended duty cycles or stressing load conditions. |
