Coaxial Line Isolators.
ON7FU coaxial line isolators are compact high power potted Common-Mode Choke type 1/1 UNUNs.
These devices are a variant of the well known ON7FU 1/1 high power current baluns, built using the same high quality materials and proven construction standards.
They are intended to be placed in the coaxial transmission line of radio amateur HF antenna installations, to eliminate common-mode (outer shield surface) currents caused by non-perfect transitions of a-symmetric to symmetric media.
Such conditions are often found in HF antenna installations with non perfect balanced behavior, like Windom antennas, antennas in the vicinity of obstacles, end-fed wire antennas with the coaxial cable acting as counterpoise or verticals with less than perfect ground systems.
ON7FU line isolators are characterized by their high common-mode choke impedance over the specified frequency range, including the largest possible resistive part contribution.
Furthermore, a grounding terminal is provided, allowing for connection of one side of the isolator to a clean RF ground, thus forming an “L” configuration filter for sheath currents, and providing additional (secondary) lightning protection. This configuration results in higher TX common-mode current rejection ratios and higher RX noise rejection characteristics than the more complex, larger and heavier “multicore” / “multi-stage” solutions offered by other brands.
The Common-mode choke line isolators can be installed at any place in the coaxial feedline.
The most popular, convenient and recommended places however are at the bottom of the tower or at the building entrance.
When installed correctly, the line isolator will effectively avoid RF from entering your shack, possibly causing RF interference in your TRX and other electronic equipment in your house, as well as avoiding RF noise caused by digital electronic devices to reach the antenna and enter your wanted weak signal receive path in conducted emission mode.
Noise floor can effectively be lowered by several dB.
These single core line isolators are effective over the entire HF frequency range.
Using different types of ferrite material and by manipulating the number of windings, the CMC impedance maximum can be optimized over a decade of the frequency range.
As such, LOW band optimized and high HF optimized variants are available.
- Deployable frequency range: 1.5 – 55 MHz.
- Low HF optimized variant: 1,5 – 30 MHz (Optimized 1,5 – 14 MHz)
- High band optimized variant: 3,5 – 55 MHz (Optimized 7- 50 MHz)
- Nominal system impedance: 50 Ohms.
- Operation principle: Coaxial UNUN Common-Mode Choke.
- Max Power: 3 kW PeP @ VSWR < 2,0/1, (ICAS)
- Insertion loss: < 0.05 dB.
- Intrinsic VSWR: < 1.2 / 1
- SO 239 coaxial connectors. (N-type or 7/16 DIN optional)
- Polycarbonate enclosure / Stainless Steel hardware / Teflon isolated connectors.
- Mounting option included.
Price: 104 Euro.
- Option: N-connector (N-connector instead of SO239): + 6 Euro.
- Option: UL 508A Certified enclosure. For those requiring the best of the best. (Recommended for extreme environmental conditions): + 10 Euro.