The Radio-Stuff Common Mode Choke (broadband Balun) is a replica of the Joe Reisert, W1JR variation of the Guanella common mode transformer. Designed to supress common mode currents and unwanted electromagnetic interference (EMI) or radio frequency interference (RFI) within your antenna system.
 
Simply put, this CMC is to suppress common mode currents and interference/noise on your coax.  Some of our clients have been amazed with the effect a CMC can have on receive noise. Please read our shop reviews.
 
As standard the choke is supplied with a Fair-Rite 240-43 core which gives good all round choking performance from 80m through to the 10-meter band.  See the product sweeps.

The 240-43 core offers.
Impedance greater than -30db across the 80m to 10m range.
Low insertion loss.
400w power handling capability.
ABS sealed case with quality SO239 connectors.
 
Please select 240-43 for the cheapest option, this will give you the best performance for the money.  
 
Other core types available see options. However, we recommend you use the 240-43 option unless you have a specific requirement. If you’re not sure what type of CMC you should have please contact us, remember were here to help.
 
This choke is designed to be placed either below your antenna, to isolate the antenna from your coax. In your shack to isolate your transceiver from noise picked up on the outside of the coax. 
 
Ideally you should have one CMC at each antenna feed point and one in the shack between the antenna before your transceiver/linear amplifier.
 
If you are using an EFHW you should place the CMC at .05 wavelength below the EFHW transformer.