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How do you ground a EFHW? Google says you have to use a counterpoise. How do you do that? Google says a counterpoise is just some radials. How long should it be? I did an experiment to try and use a earth ground but there was no difference.

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A voltage-fed antenna, like an EFHW, does not need a ground for radiation purposes, (and neither do other half wave antennas, but that's a different discussion), it needs it for high voltage DC shunting generated by static, or lightening protection; you should ground your coax shield with accepted practices.

This a decent video about the grounding & bonding: https://www.youtube.com/watch?v=IJVJjgI2YbM

Regarding the counterpoise, an EFHW would not use "ground" as a counterpoise, rather, since an EFHW has a high impedance at the feed-point compared to the low impedance output of modern radios, and the low impedance of coax, both usually 50 Ohm, an impedance transformation must be done at the feed-point; this can be done a couple of ways. Most people use a 49:1 or 64:1 UnUn, and some use a lumped LC circuit, any still others use a 1/4 wave balanced feed matching stub to get the impedance transformation needed to feed an EFHW (see J-Pole antenna).

If you use an UnUn, you will likely have/need a short counterpoise on the shield side of the UnUn coax feed. This is usually calculated to be: 0.05 x the wavelength of the center/resonant frequency of the antenna. Given this, some operators simply choke the coax at a distance of 0.05 x (wavelength of the operating frequency) from the UnUn feed-point and use that short unchoked section of the coax shield as the counterpoise. Others choke the coax at the UnUn feed-point and use a 0.05 x (wavelength of the operating frequency) length of wire, that is at least 90 degrees off the antenna direction. Either way, if you wanted to ground this type of setup at the antenna end of the coax, you would place your grounding wire on the coax-choke side of this arrangement, not the choke-UnUn side; if you used the coax as the choke, it would be a little more challenging, mechanically, because you'd have to strip back the coax insulation to get to the shield. Also, using strictly the coax as a choke (winding it into a coil) is not generally a good idea unless you do a calculation that considers the capacitive effects of the coax, because you are creating an LC circuit with that method, and you may not get the desired effect. A much better solution is using ferrite beads on the coax, or making a choke using a ferrite toroid and coax:

Coax-Ferrite Toroid Choke

A written description of the schematic would be:

Antenna|UnUn|Counterpoise|Choke|Coax & optional Ground Wire on shield side of coax.

If you are feeding an EFHW with an impedance transforming LC circuit, which you can calculate here: https://leleivre.com/rf_lcmatch.html you do not need a counterpoise. I would still use a choke as pictured above, and ground your coax at some point.

A written description of that schematic would be:

Antenna|LC Circuit|Choke|Coax & optional Ground Wire on shield side of coax.

A written description of the J-Pole schematic would be:

Antenna|1/4 wave Parallel Feed Stub|Choke|Coax & optional Ground Wire on shield side of coax. Some folks ground the bottom of the U-section of the J-Pole because it is the theoretical 0 voltage point on the antenna matching stub, I never have, because it is the maximum current point of the matching stub. Of the impedance matching methods, this is my least favorite because it is the least flexible, and it adds a 1/4 wavelength to the overall antenna length, that does nothing except distort the radiation pattern.

Keep in mind that single-point grounding is the only acceptable practice these days, and requires you to attach any wire that you are using for a ground, directly to the utility's ground, at either your AC supply for the building you're in, or the actual ground rod the utility is using, outside your home. This is why some operators don't ground their coax until it reaches their structure (home/shack) and all their coax cables go through a "grounding plane", where all coax shields coming into the structure, are bonded to a piece of metal that is in-turn, grounded to the utility's ground, at either the circuit breaker panel, or the utility's ground rod; in my view, this is actually the preferred method of grounding coax that is outside the structure.

As a side note, the coax shield can act like an antenna an carry undesired RF, into your shack, and into your radio's receiver. Some consider this another reason to ground your coax shield, since it might, slightly, help shunt some RF off of the coax shield, but in a high RF noise environment, like an urban area, the best way to prevent stray RF currents on the coax shield from affecting your receiver, a choke should also be put in-line directly at the radio's coax jack.

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