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Feed line choke windings - coax or wire?

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JHNC:
I am planning to construct a feed line choke for a 9:1 end fed wire antenna. Research reveals that using this type antenna, the coax outer braid is used by the antenna as the counterpoise.  I am getting RF in the shack despite having a separate wire counterpoise attached the toroid. I have 2 questions on construction:

1. I have seen examples of choke toroids wrapped using both coax [RG-58 in this case] and toroids wound with stranded wire, as is the toroid in the 9:1 transformer. www.earchi.org/92011endfedfiles/Endfed6_40.pdf I am wondering, but cannot find any information, as to whether a choke toroid should be wrapped using coax or 2 lengths of insulated wire. It seems to me that using coax for the choke toroid is the best method as I am trying to keep as much RF off of the outer braid as possible. Using insulated wire seems to be best for the 9:1 toroid as we are trying to transfer as much power to the radiating wire as possible. Am I correct here?

2. Using either coax or insulated wire, I have seen some 9:1 toroids and choke toroids wound with a "crossover" at the 1/2 way point, that is; for a 12 turn toroid, 6 turns are wound, then the coax or wire is passed thru the center of the toroid and the last 6 turns wound in the opposite direction. I believe the reasoning had to do with reducing capacitance issues [?].
Any thoughts or guidance on this?

A.Z.:
Start by carefully reading the following

http://www.karinya.net/g3txq/chokes/

https://www.dj0ip.de/rf-cmc-chokes/different-kinds-of-chokes/

then decide, keep in mind that, to tame CMC on all HF bands you will probably need more than one choke

My usual "all rounder" is a choke wound around an FT240-43 using 17 or 18 turns of RG-174 with windings "Joe Reisert" style (that is a cross turn)

Notice that, with an endfed you will NEED a counterpoise AND a choke so, please, add a counterpoise to that antenna, it may be just a run of insulated wire dropping down to ground and laid down there, but you'll need it to both allow the choke to work and allow the endfed to radiate properly

Also, if possible, keep the antenna (the feedpoint too) as high and "in the clear" as possible

Oh, and since we are at it, here are some additional notes which may be of help

https://www.eevblog.com/forum/rf-microwave/putting-up-a-random-wire-antenna/

HTH



Wallace Gasiewicz:

Are you saying that you are using a 9:1 transformer with your end fed antenna?
If so, what is your standing wave? Can you measure the impedances of your antenna at the frequencies used?
A "choke" is typically used just to reduce "common mode" RF that is traveling down the shield of coax and this type of choke can just  several wraps of the feed line coax around a plastic pipe, commonly called an "ugly balun".  Usually 3-4 inch PVC pipe. You can also use a toroid. Since the feedline coax shield is used as the "counterpoise" the feedline choke is usually near the transmitter, but this means the rest of the coax is radiating and is in the shack itself.
So part of the antenna is actually in the shack.

A.Z.:

--- Quote from: Wallace Gasiewicz on December 07, 2021, 12:23:38 pm ---
Are you saying that you are using a 9:1 transformer with your end fed antenna?
If so, what is your standing wave? Can you measure the impedances of your antenna at the frequencies used?
A "choke" is typically used just to reduce "common mode" RF that is traveling down the shield of coax and this type of choke can just  several wraps of the feed line coax around a plastic pipe, commonly called an "ugly balun".  Usually 3-4 inch PVC pipe. You can also use a toroid. Since the feedline coax shield is used as the "counterpoise" the feedline choke is usually near the transmitter, but this means the rest of the coax is radiating and is in the shack itself.
So part of the antenna is actually in the shack.

--- End quote ---

well, if it isn't an EFHW which needs a 49:1 UnUn but a well "calculated" endfed, there's nothing strange in using a 9:1, no "magic" just a matter of using a wire length which in NOT resonant (neither 1/4 nor 1/2 or multiples), that way, with a proper antenna wire length, the impedance (on ham bands)  could be handled by the 9:1 UnUn and transformed to something which is "near" to the characteristic impedance of the feedline, at that point, an antenna matching unit (an L match works fine in own experience) will make the transmitter happy, then... ok, in RX an endfed isn't exactly the best, but... pair it with an RX ONLY loop and the results will be surprising

JHNC:
Wallace Gasiewicz: When I refer to the 9:1 toroid, I am referring to the antenna's internal toroid. Please refer to the link for details of construction.A.Z.: I will review your links and will be back if I have any further questions
Thanks to you both for the replies.


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