Radio-Stuff Common Mode Choke (Broadband Balun)
The Radio-Stuff Common Mode Choke is based on the well-known Joe Reisert, W1JR, variation of the Guanella common mode transformer. It’s designed to effectively suppress common mode currents and reduce unwanted electromagnetic (EMI) and radio frequency interference (RFI) in your antenna system.
 
In simple terms, this choke helps reduce common mode currents as well as noise and interference. Many of our customers have reported a noticeable drop in receive noise after installing this product.
 
Performance & Build
Each choke comes standard with a Fair-Rite 240-43 core, offering excellent broadband performance from 80m through 10m. Detailed product sweeps are available for reference.
 
Key features include:
Custom Radio-Stuff PCB
Greater than -30 dB impedance across 80m–10m
Very low insertion loss combined with a low SWR
400W power handling capability
Rugged ABS sealed case with quality SO-239 connectors
 
Installation
This choke can be placed:
At the feed point of your antenna, to isolate it from your coax
Inside your shack, to block noise picked up on the outside of the coax before it reaches your transceiver
 
For best results, we recommend:
One choke at each antenna feed point
One choke in the shack between the antenna line and your transceiver/linear amplifier
For EFHW antennas, placing the choke about 0.05 wavelengths below the EFHW transformer if you are not using a counterpoise