Snap On End Fed Feed Line Choke for Non-Resonant and End Fed Half Wave Antennas, RG8X, RG8, up to 38 dB common mode suppressionProduct DetailsMPN: SOFLCSNAP 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.
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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 15%$16.95Super-Choker™ Common Mode Feed Line Chokes
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.
Sometimes you need a high power common mode choke that is super effective and the Super-Choker™ products fill this need very well. All Super-Choker™ chokes use multiple turns through ferrite cores for higher choking impedance compared to our multi-bead sleeve chokes which only use one turn through multiple cores. Different ferrite mixes and turns ratios are used to optimize choking impedance in the selected product frequency range.
Super-Choker™ chokes are manufactured with 1/2″ 52 ohm coax cable (rated for full amateur radio legal limit of 1500 watts continuous (or the capacity of the coax cable at the selected frequency – good for over 5KW on 4 MHz into a matched load for example) with PL-259 connectors that can be connected to your coax feed line with simple double female barrel connectors.
Super-Choker™ chokes are ideal for high power stations and are very effective for keeping common mode current off the feed line on verticals, dipoles, and loop antennas at their feed point and also for choking coax lines at the station input to reduce common mode noise picked up by the outside of the coax braid between the feed point and the station entrance.
Ferrite core kits are available separately if you want to supply your own coax feed line.
Super Choker™ Case History:
I run an 80 meter loop antenna about 30 feet in height and have previously been using a coaxial balun common mode choke of 25 turns of RG-213 on a 6 inch form attached about 6 feet under the corner feed point of the loop (configured in a triangle). Using a Dentron 3000 antenna tuner I was able to tune all the ham bands and the lowest SWR was about 1.4 on most bands. The antenna feed line was led away from the corner of the loop and was not under the loop. Feed line length was about 105 feet as measured on the Aim 4170-TDR function.
I first placed a Super Choker™ 8010 at the antenna tuner leaving the coaxial balun in place. As I retuned the antenna tuner, the first thing I noticed was that I could now tune down to 1.1:1 on 80, 40 and 20 meters and I could not do that before. The noise level which had been running about S7 on 40 meters during the day had dropped to about S6 on my TS-870 receiver. I was pleased that the reflected power was now almost nil and the noise level was lower.
I then took the next step and replaced the coaxial balun and Super Choker 8010 with a Super Choker™ 16040 in series with a Super Choker 4010 for maximum choking power from 80-10meters. The antenna tuning was about the same but now the SWR was 1.0:1 on 80-10 meters and the noise level on 40 was down to S5. I tuned up on 20, 15 and 10 meters and worked a couple of JA’s and noticed that the noise level on 10 and 15 was not even S1 – something I had not experienced before on the 5 acre plot of land we call home.
What a welcome relief to find such a simple solution to RF feedback I had experienced and I got a lower noise level to boot!
Now to plan that 160 meter loop! I wonder what Krusty ole Kurt would use?
Bob, AK6R