SNAP On Feed Line Choke
Each end fed antenna needs a feed line choke at the radio end of the coax to stop the antenna common mode current (on the coax braid) from getting into the radio when transmitting and also to stop RFI common mode noise when receiving. A
simple easy to adjust in different places along the coax used as a counterpoise is the snap on ferrite core with a 1" ID (hole) installed as shown in the picture. (coax not included, but you can use RG-8X size for 5 turns and RG-8X size for 3 turns).
Add the Feed line choke (part # SOFLC) to your end fed antenna today today and stop the pesky RFI from getting into your radio and causing RFI, audio distortion or unexpected operation!
NOTE: Coax shown in picture is NOT INCLUDED and is shown as an installation example only. If you want a pre-wound choke check part# JC-1-1500-3 or JC-1-1500-6.
For non-resonant end fed antennas placement of the choke from 10-50 feet away from the antenna feed point to use the coax braid as the counterpoise (since these antennas are really off center fed dipoles with the short side using the coax braid as the count5erpoise. Wind 8-10 turns thru center for an effective 3-30 Mhz choke.
For End fed Half Wave antennas place 3-10 feet from antenna feed point to act as short counterpoise for these voltage fed antennas. Use 8-10 turns.
TECH NOTE: SNAP On Chokes for 80 and 160 meter end fed antennas
If you use RG-8X size cable, use 2 SOFLC if you have 5-6 turns thru the center of each.See picture on left as an example of how to wind the cable.
Measure 40 feet from the matching unun and then wind 6 turns thru the center of the SOFLC.Close it up and then wind an additional 6 turns thru another SOFLC placed adjacent to the first one and on the radio station side of the coax.See picture to left.
If you use LMR-400 or 1/2" coax cable you will only get 3 turns thru the snap on choke and you will need an additional choke (with an additional 3 turns) in series to provide enough choking on 40 and 80 meters. Part# SOFLC.
In lieu of the 2 chokes shown above, you may also use a F400-31 ring (3” ID) with 6 or more turns which provides a much higher common mode suppression and better antenna tuning on 80 meters. See picture for winding example.
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.