Here's my understanding of common-mode current on coax feedline with an EFHW: An UNUN feeding an EFHW is unbalanced by design. For an attached coax cable, the cable shield's inner surface and center conductor's outer surface carry differential currents. But the cable shield's outer surface can carry a common-mode current. The common-mode current may be induced by near-by electrical devices (motors, dimmer switches, etc.) induced via the unbalanced nature of the antenna feed, induced by the EM near-field of the fed antenna, induced by the EM near or far-field of a relatively close high-powered RF emitter, or all four sources (i.e., a multi-source or composite current). For the EFHW antenna, the "counterpoise" current is a common-mode current (i.e., it flows on the outer surface of the shield.) This common-mode current can be greatly attenuated by placing a "common-mode choke" (e.g., multi-turns of coax wrapped around a toroid) between the transmitter/receiver and feedline. Ken WA8FCI
@rickeaston32282 жыл бұрын
My definition of counterpoise is that it is anything that functions as a RF ground. It's relationship with earth ground is determined by how it is mounted in relation to ground. You could call the ground side of a dipole a counterpoise. You could also call the hot side of a dipole a counterpoise because it works like a radiating ground the same as the other side. The term "RF gound" is confusing because it sounds like a dc ground but it isn't. For all purposes, an RF ground is just something where RF energy will flow. If it radiates, it does not matter. What matters is that RF current will flow into it and has an RF impedance.
@mxv20152 жыл бұрын
Thank you Dave, you are a great teacher.
@henryleaball45152 жыл бұрын
For quarter wave radials at full length, the formula is for a quarter wavelenghth (234/f (MHz). You quoted the numbers for a half wavelength... - AL7W
@davecasler2 жыл бұрын
Good catch! Thank you.
@jonmcadams54012 жыл бұрын
Thank you for a very informative video linking several topics about antennas. Would you consider doing an additional video or QST "Ask Dave" answer discussing the relationships between SWR, antenna resonance, and antenna efficiency? Much appreciated!
@jamaciadog56032 жыл бұрын
Dave, thanks for all your videos.
@Soupie622 жыл бұрын
This is the first time I wished I could give a video TWO thumbs up (or even 3).
@sleeve8651Ай бұрын
Well Dave, if the products of a common current traveling back down the feed line towards the transmitter, are made up of the same components as the original, ( AC ), then where as they don't go thru some metamorphosis, and not knowing their names, Differential, or Common mode why doesn't the transformer allow those like components to pass, equally, and free of interference ? How would a, " Dumb Choke ", know the difference ?
@tonypoloney87212 жыл бұрын
I have an MFJ 931 artificial counterpoise attached to a junior g5rv. The meter shows full current when transmitting. My shack is on second floor (loft), so cannot use a ground due to distance to transceiver. I don't see any improvement in rf tx rx performance though. Many thanks for your excellent videos. You are a great teacher.
@javelinjim46992 жыл бұрын
Hi, I’ve been watching your channel for a couple of years, really informative, thank you! My question is specifically on EFHW antennas. I have a Vibroplex shortened 80/10 which uses a coil as an inductor trap and loading for the 80m section, but this only gives a narrow 75KHz usable bandwidth without a tuner. The antenna is a half wave on 40m from the coil to the feedpoint. I use the outer braid as a counterpoise and have a 1:1 choke about 55 feet from the feedpoint and a lighting arrestor a few feet further away at about 65 feet from the feed point. Does the counterpoise (coax braid) radiate as powerfully as the radiating wire? I’m thinking that on 40,15 and 10m the full half wave length of the radiator will allow the wave to form on those bands but for 80m outside the narrow bandwidth provided by the coil, some of the signal may be forming on the counterpoise? I may have this all wrong! Always learning in this hobby! Thank you, Jim 73 from the UK
@davecasler2 жыл бұрын
In general, the counterpoise doesn't count as the radiating part of the antenna, but each situation is different.
@DaDitDa2 жыл бұрын
You're correct. Ken WA8FCI
@mattb7406 Жыл бұрын
Would love to see if gauge of wire matters for radials. I see alot of 18awg radials, but there is alot of 26awg. That is a huge difference. for portable use with couple dozen radials, thinner would be better and cheaper BUT is 26awg as effective as 18awg. If not, by how much?? negligible? like 15watts vs 20 watts or is it like 15watts to 45 watts?
@NickWindhamАй бұрын
Generally, thicker guage is better.
@beowolfso.6096 Жыл бұрын
Thank you for the video. What location of a vertical antenna is where most of the radiating takes place?
@timmyers34286 ай бұрын
does the counterpoise have anything to do with SWR, or does it just affect Rx?
@NickWindhamАй бұрын
It increases Rx and decreases SWR significantly, when done well.
@aloisiosimoni1652 жыл бұрын
David what’s the importance of the capacitance, in a transmission antenna? Thanks.
@danielwietchy10372 жыл бұрын
You make me muse about things Ham. I like that Dave.
@alm138 Жыл бұрын
what would happen if u put 4 long wires on the endfed n s e w and a counterpoise in each direction??? would that work?
@jimheitman40332 жыл бұрын
Is it true that with hand held radios, the operator is the counterpoise?
@samgrieg25422 жыл бұрын
scary isn't it. you can feel RF bite through your sweaty palm with only 5 watts out. Imagine some Chinese hh's advertising 15 watts.. woohoo. Cooking time.
@dougtaylor77242 жыл бұрын
I thought a counterpoise was usually a piece of coax tuned for capacitance
@vinniec52862 жыл бұрын
I have an EFHW with no counterpoise and a 50 foot coax. In a previous video (last year I believe) you were somewhat adamant about the fact that you needed to use a counterpoise with EFHW. In this video you said you don't need one because your 50 foot coax acts as one. I am curious as to why you changed your position? Am I remembering this wrong? I have watched almost all of your videos, so I apologize that I cannot recall which one it was. Thank you for what you do.
@W9HJBill2 жыл бұрын
For an EFHW, the length of your counterpoise need only be 0.05 of a wavelength. Odds are, if you have pretty much any length of coax on an EFHW, you don't need a separate wire for a counterpoise, the shield on your feed coax will work. So just make sure you don't put a choke right next to the transformer. I've tried adding a dedicated counterpoise to my 80-10 EFHW, which has 70 feet of LMR-400 feeding it, and it made zero difference.
@DominicMazoch2 жыл бұрын
The title of this vid is a great pun!
@daveengstrom92504 ай бұрын
I was "with you" until you used the phrase "something for the antenna to work against.". Say that in a more descriptive way, please
@titaniummaster15322 жыл бұрын
So knowledgeable…..
@bushboy822 жыл бұрын
What is a ground counterpoise?
@robertharden4092 Жыл бұрын
A counterpoise is an antenna for your antenna .is what a really old ham told me once. I never argued with him I said ok sounds good to me.
@MI7DJT2 жыл бұрын
Still proud that you voted for Biden Dave? It wouldn't surprise me if you were lmao.
@kylefreemason Жыл бұрын
How do you know Dave voted for Biden?
@Mr.Robert12 жыл бұрын
12 minutes of a boring topic time to unsubscribe. To each his own. Where's all the commentary. Antennas I know very well matter of fact. I use to install and tune them for my friends years ago. Then the pagers came out followed by the prepaid cellphone still to this day. People don't know the difference between prepaid and postpaid Duh. I remember full quarter wave on cars for AM. Town of mayberry if you want to have a look. Sheriffs car.
@tonypoloney87212 жыл бұрын
Sooner you unsubscribe the better.
@Tonylovesjazz2 жыл бұрын
10 Subscribers...Easy to take potshots...'Nuff Said'. Hope you get better. God Bless.