Utilizing Mil Spec coax, this balun provides very high power ratings across all HF frequencies, creates windings that have extremely uniform impedance for excellent transformation and is still based on the tried and tested design of Dr. Jerry Sevick (W2FMI). By using our mounting plate or mounting clamp, the balun can be securely installed on a mast, boom or where ever you need it.
Sometimes called a choke balun or common mode choke, this 1:1 ratio current balun is the best for feedline isolation. 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. If you have a yagi you should be using one to balance the power to the driven elements and prevent the coax feedline from distorting your radiated pattern. If you have a vertical you should be using one to prevent the vertical element from using your coax as a radial and to decouple the feedline for reduced noise.
Here are plots of the same dipole with and without a balun. Notice how the pattern is distorted when the feedline is not being isolated with a balun:
Click to Enlarge
This balun is more than just high power. Tests show SWR is below 1.06 across the entire HF band, transformation is perfectly flat, return loss is typically 60-75 dbmw and choking impedance peaks at over 5k ohms. Please click on the graphs shown below to view the complete test results.
Tests completed utilizing AIM-4170c Network Analyzer and precision 50 ohm non inductive load
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
- Utilizes specifications of Jerry Sevick, W2FMI, the authority on baluns. This is his Guanella current balun design which he redesigned for higher power and efficiency.
- Custom mix toroid with low permeability allows broad frequency coverage. Toroid is coated with epoxy paint for added durability.
- This Isolation balun has significantly higher common-mode impedance and larger effective core area than other similar designs. It 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 upto 40 MHz. Power should not exceed 4kw from 40 to 54 MHz.
- SO-239 connectors are silver plated with teflon insulation.
- All hardware is stainless steel.
- Alternate connectors and mounting options are available in Accessories.
- Very high efficiency. Will not heat up or saturate like many of the typical cheap "choke" baluns.
- Balun is built installed in weatherproof 4" X 4" X 2" Nema Box which makes an excellent outdoor weatherproof enclosure.
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 fed with coax (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 exception ONLY applies to HALF WAVE CENTER FED DIPOLES WHEN USING A 1:1 BALUN AT THE FEEDPOINT.
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 additonal 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.
If you are using a vertical antenna you need to read this
If your antenna SWR is already low and you wish to reduce feedline radiation and improve reception, a feedline isolation balun is recommended. Adding one at the base of a vertical antenna will substantially reduce unwanted feedline radiation (RFI) by preventing your antenna from using the your coax feedline as a radial. This can also reduce the need for improved station grounding.
With a ground-mounted quarter-wave vertical, regardless of the radial situation, but especially with poor radial systems, there is the need for a feedline isolation balun to keep common mode currents off the feedline.
When quarter-wave antennas are constructed over a near perfect radial system, they have a feedpoint impedance of about 36 ohms. When they are constructed over a less than optimal radial-system there is a loss introduced into the feed system that adds to the 36-ohm figure. This improves the SWR but there is a loss in the efficiency of the antenna, signals transmitted and received have a higher take-off angle and often there is current introduced onto the feedline.
With my SteppIR vertical I use two of these baluns. One at the base of the antenna and another midway along the feedline after the near field of the antenna. You can also install the balun where it enters your shack if you would rather not break the feedline run. The balun balances the RF currents at the antenna, is terrific for keeping RF out of your operating environment and greatly reduces the noise inherent in a vertical by decoupling the feedline.
Benefits to Yagis
Another very useful application for a feedline isolator is installing them in series with a yagi antenna’s normal feed system. The proper location is between the antenna’s matching device/system and the feedline. Doing this will not affect the antenna and prevents the feedline from acting as part of the antenna. In beam installations, using a feedline isolator in series with the antenna’s feed system can substantially improve the antenna’s front-to-back and front-to-side ratios. It does this by providing the antenna with balanced current at the feedpoint and by effectively preventing the coax shield from acting as part of the antenna.
It is a seldom appreciated fact that feedlines which are not adequately decoupled can act as efficient vertical antennas that degrade an otherwise excellent radiation pattern. The addition of a quality feedline isolation ("choke") balun can significantly reduce feedline radiation and dramatically decrease RFI and TVI.
Yagi antennas especially, benefit from improved balanced drive and superior feedline isolation, but even simple dipoles benefit from properly selected and installed Feedline Isolation baluns. In addition, receiver noise may also be reduced by eliminating stray EMI picked up by the coax shield.
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