Coax Jumper Choke - RG-8X - RFI Range: 1.8-65 MHz, -30 dB Noise Reduction, 1.5KW PEP, Magnetic Loop, Antenna ChokeProduct DetailsMPN: JC-1-1500Country/Region of Manufacture: USASimple Jumper Feed Line Choke
The simplest, most cost effective feed line choke is a ferrite ring installed as shown in the picture (at the antenna feed point) to stop feed line radiation or at the radio end of the coax to suppress common mode coax noise current on the coax braid.
Improves antenna pattern by preventing your dipole from becoming a tripole
Suppresses pesky coax braid radiation and RFI
Reduces coax braid common mode current up to -30 dB ( 6 "S" units) on receive
Use one choke for each antenna feed line
Add a double female barrel connector to act as an "extension" of the existing coax.
Magnetic Loop Users: use 1 JC-1-1500 at the antenna feed point to keep all of transmit power on antenna and another at radio end to remove common mode noise received on the coax braid.
Need the ring only and not the jumper, select F240-31-1 as the part #.
Question: Assuming the JC-1-1500 uses mix 31, why is the effective range 1.8-65MHz instead of 1-300MHz?
Answer: Look at measurement chart to see the answer - it takes at least -12 dB of common mode rejection to see/hear a noticeable difference with and without choke. Yes the spec for mix 31 say it is good to 300 mhz but at that frequency the CMRR is very small and hasn't much of effect on common mode rejection. Also when you form a choke with coax your are actually creating a parallel tuned circuit at a certain resonant frequency determined by the coax capacitance of approximately 28 pf/foot and the inductance of the coil. The graph shown that the max CMRR is roughly -30 dB between 1-21 MHz and slightly less as you go higher in freq (the resonant freq of the JC-1-1500 is roughly 10 MHZ and broad banded by the use of the ferrite). Above 6 meters CMRR becomes low so as not to be very effective. If you want to use the choke on higher bands you need to change ferrite mix and the number of turns of the choke so the center resonant freq is higher.
Ferrite are in reality frequency dependent resistors and the specs say they have a resistive component above 1 mHz and under 300 mHz but the resistance (or CMRR) has to be high enough to be effective. We publish the effective range so you know what to expect when used.
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RG-8X Coax Jumper Cable with PL-259's on each end - 3 feetRG-8X Coax Jumper Cable with PL-259's on each end - 3 feetSKU RG-8X-3List price $19.95 Save 25%$14.95HF 1-61 MHz coax feed line common mode chokes
Simple Jumper Feed Line Choke
The simplest, most cost effective feed line choke is a ferrite ring installed as shown in the picture (at the antenna feed point) to stop feed line radiation or at the radio end of the coax to suppress common mode coax noise current on the coax braid.
Improves antenna pattern by preventing your dipole from becoming a tripole
Suppresses pesky coax braid radiation and RFI
Reduces coax braid common mode current up to -30 dB ( 6 "S" units) on receive
Use one choke for each antenna feed line
Add a double female barrel connector to act as an "extension" of the existing coax.
Magnetic Loop Users: use 1 JC-1-1500 at the antenna feed point to keep all of transmit power on antenna and another at radio end to remove common mode noise received on the coax braid.
Need the ring only and not the jumper, select F240-31-1 as the part #.
Question: Assuming the JC-1-1500 uses mix 31, why is the effective range 1.8-65MHz instead of 1-300MHz?
Answer: Look at measurement chart to see the answer - it takes at least -12 dB of common mode rejection to see/hear a noticeable difference with and without choke. Yes the spec for mix 31 say it is good to 300 mhz but at that frequency the CMRR is very small and hasn't much of effect on common mode rejection. Also when you form a choke with coax your are actually creating a parallel tuned circuit at a certain resonant frequency determined by the coax capacitance of approximately 28 pf/foot and the inductance of the coil. The graph shown that the max CMRR is roughly -30 dB between 1-21 MHz and slightly less as you go higher in freq (the resonant freq of the JC-1-1500 is roughly 10 MHZ and broad banded by the use of the ferrite). Above 6 meters CMRR becomes low so as not to be very effective. If you want to use the choke on higher bands you need to change ferrite mix and the number of turns of the choke so the center resonant freq is higher.
Ferrite are in reality frequency dependent resistors and the specs say they have a resistive component above 1 mHz and under 300 mHz but the resistance (or CMRR) has to be high enough to be effective. We publish the effective range so you know what to expect when used.
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.