50:450 ohm (9:1) Balun or Unun Core Kit, 1.8-30 MHz, 250 watts PEP, end fed, T2FD antennaProduct DetailsInput ohms/Output ohms: 50 in, 450 outFrequency Range < 2:1 SWR (MHz): 1-31PEP Power Rating (watts): 250Model BA-9-250 is a 9:1 balun/unun kit (assembly from parts supplied required) used to translate a 50 ohm input up to 450 ohms at RF power levels up to 250 watts PEP when used with a matched load. With a matched 450 ohm load the SWR over the frequency range 1.8 to 30 MHz is shown in the following table measured with an AIM 4170 network analyzer. Notice that the conversion from 450 to 50 ohms is very consistent from 1-31 MHz and SWR is less than 2:1 over most of the range allowing easy tuning by most radio internal antenna tuners or an external tuner. Graph is for a 9:1 unun often used with long wire or end fed antennas.
Radio Club idea:
Buy 10 for a club do it yourself construction project - you can learn something about winding impedance transformers and also build an end fed antenna (just add wire).
Typical SWR curve for this project:
HF 1-61 MHz coax feed line common mode chokes
Model BA-9-250 is a 9:1 balun/unun kit (assembly from parts supplied required) used to translate a 50 ohm input up to 450 ohms at RF power levels up to 250 watts PEP when used with a matched load. With a matched 450 ohm load the SWR over the frequency range 1.8 to 30 MHz is shown in the following table measured with an AIM 4170 network analyzer. Notice that the conversion from 450 to 50 ohms is very consistent from 1-31 MHz and SWR is less than 2:1 over most of the range allowing easy tuning by most radio internal antenna tuners or an external tuner. Graph is for a 9:1 unun often used with long wire or end fed antennas.
Radio Club idea:
Typical SWR curve for this project:
1:1 feed line Chokes (also known as feed line current chokes, common mode chokes, line isolators, current mode chokes, and 1:1 baluns/ununs) are available in kit form or assembled form in a weatherproof Current Unun and Balun Enclosure which we call a CUBE™. All 1:1 chokes are ferrite based and are designed for 50 ohm coaxial cable input and 50 ohm output. 1:1 Ferrite toroidal or bead chokes have a higher choking impedance than our popular Sleeve Chokes and various models are available for specific frequency ranges and power levels.
1:1 Chokes are useful for choking common mode currents that may flow on the exterior of the coax cable shield while allowing the signals on the interior of the shield and the center conductor to flow unaffected and keeping the common mode current on the antenna. They isolate the coax shield and prevent it from becoming part of the antenna system.
1:1 Chokes are useful between balanced lines for center fed dipoles at their fundamental frequency (468/f (MHz), beam antennas with a 50 ohm balanced driven element, G5RV, loops, yagis, NVIS antennas, mobile installations, portable antennas and anywhere common mode current (or RFI) is a problem. They are also helpful between transmitter and linear amplifier or between linear amp and antenna tuner or as isolation chokes where higher choking impedance is needed (in the range of 2K-7K ohms).
1:1 Chokes are also very useful as feed line current chokes at the “radio end” of the antenna (we call them coax noise filters) where they choke/filter common mode current induced onto the coax shield from radiated waves (from your antenna, and other sources such as DSL routers, computer devices, plasma TVs, etc. originating in your house or your neighbor’s house). For RFI issues see RFI/EMI Solutions for general use or for specific radios and devices.
For best results we recommend a 1:1 choke at the “antenna end” of the coax and a coax noise filter at the “radio end” of the coax. (A side benefit is a reduction in noise level caused by common mode currents). 1:1 chokes are also available as Sleeve Chokes (Slip on or Snap on) for ease of installation and light weight on the antenna.