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.
We specify impedance ratios as an output to input ratio where the output (or load) is given first and the input is given second (e.g. 100:50 (2:1) would mean a 100 ohm output and a 50 ohm input; a 25:50 (1:2) would mean a 25 ohm load and a 50 ohm input). Most all products use a 50 ohm input unless otherwise specified.
We have products that are available as kits for the do-it-yourself (DIY) person or fully assembled and tested units for the “Plug & Play” crowd.
Our impedance transformers are available using two different topologies: Binocular cores or toroid cores with multiple turns for increased effectiveness and wide band frequency transformations. We utilize single and multiple core transformers using high order windings when needed to extend product performance.
We rate the power ratings as watts PEP (Peak Envelop Power) with standard duty cycles for various modes. To determine the PEP rating required for your needs, see: Choke & Transformer Power Ratings
This website page serves as a link page to the frequency ranges of our impedance transformers configured as either baluns or ununs. You can click on a picture to go to the specific page about the products described in the picture.