Partnership between Stockcorner and ON7FU.


Early 2017, thanks to a few hints of some mutual customers, Stockcorner met ON7FU.


After a short meeting and exchange of information with Hugo, it was recognized that both companies needed a reliable “Antenna Tuner BALUN” in their product line.

ON7FU agreed to cooperate with Stockcorner, and based on his experience, supplemented with Stockcorners knowledge of high power automatic remote antenna tuners, a heavy duty tuner BALUN was defined.

Because of the delicate application, being deployment at a random impedance environment, key development goals were defined as highest possible common-mode impedance, high voltage withstand and low saturation sensitivity.

ON7FU built some prototypes, which were extensively tested by Stockcorner engineers. The test BALUNs were placed in different antenna setups, and stressed under most harsh operation conditions.

While testing continues, half 2017 results proved successful and a first series of products were built, which are now available through Stockcorner’s webshop exclusively for Stockcorner antenna tuner applications , or via the ON7FU website for general purpose applications.


JC-Balun : The best optimized balun for ladders line solutions. Just connect it between A and B of a JC-4s

Doublets or loops are often deployed on multiple frequency bands using an antenna tuner.

Often balanced transmission lines are chosen to feed such antennas, in order to ensure low losses, even under high VSWR conditions.

Two wire transmission lines only act truly symmetrically when driven by a perfect balanced source.

Most antenna tuners however are a-symmetrical  (unbalanced) with respect to ground.

Therefore a balanced to unbalanced network is needed to adapt both natures.

This function is perfectly accomplished by a good wideband common-mode choke type BALUN placed at the output of an a-symmetric antenna tuner.

As this BALUN is placed in a random impedance environment, it can be subjected to very high voltages or currents.

So the two wire transmission line on such BALUN needs to be designed for high voltage withstand, rather than for a 50 Ohms characteristic impedance.

To accomplish this, the Teflon insulated wires are additionally slipped in Teflon sleeves having a voltage withstand of 48 kV/mm.

This ensures that it will not arc over, even when positioned in a voltage node, as a result of e.g. an antenna being half wave resonant at some frequencies.

This BALUN is a special variant of the standard 1/1 Common-Mode Choke current BALUN wound with a two wire transmission line instead of a Teflon coaxial cable.

It is available with a coaxial input connector, as well as with screw terminals an input and output.

It can be deployed at the output of an a-symmetrical antenna tuner, at the transition between coaxial cable and balanced line in a G5RV configuration or even after a symmetrical antenna tuner to maximize symmetry and block any common-mode current that may be caused due to the inevitable unbalance in any antenna.

Constructed to the high quality standards  known in ON7FU Ferrite Application Products.



 Broadband transmission line transformer (Common-Mode Choke) with impedance ratio of 1/1.
 Transmission line winding designed for high voltage withstand.
 Frequency range: 1,5MHz tot 55 MHz,( depending on the version; see label on the product)
 Large ferrite volume, preventing saturation under high power conditions.
 Use of teflon insulated transmission line with high temperature resistance and high power / voltage withstand.
 Circuit installed in waterproof housing and impregnated / potted with synthetic resin.
 Maximum power: 1200W PeP. (ICAS)

 Water proofing IP 68

 Optinal version, optimized for the mid / high HF bands, using "Mix 43" ferrite toroid core. This version only on request.
 Variant optimized for the low HF bands, using "Mix 31" ferrite toroid core. This variant is sold in the Stockcorner Webshop.
 Custom versions on request.

Suitable for deployment at any position in the balanced feedline.
Use of the BALUN / Line Isolator beyond the specified frequencyor power range can destroy it and cause safety risks.
The product must be considered as a sub assembly, intended to be a part of an amateur radio antenna installation.
The product is exclusively intended for outdoor use, in a fire safe and explosion safe environment.
Compatible with JC-3s, JC-4s and similar antenna tuners.

M6 stainless steel wire terminals on input and output. 

IMG 2144



IMG 1980

IMG 1981


IMG 2146


For more detailed information on ON7FU BALUNs: see www.on7fuferriteapplications.com



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