Antenna counterpoises - Page 1
Forum section: electronics / rf-microwave

author: A.Z.
author_rank: Super Contributor
timestamp: August 31, 2021, 09:52:27 pm
content: Hi folks, I kept reasoning about an idea. maybe it's crazy or maybe not, and I can't decideAs you know, when it comes to endfed antennas or vertical ones, you will usually need a counterpoise or radials system to give the antenna its "other half"Now, such a system should usually be configured so that currents will have low impedance and the RF will use it instead of the coax feedline (yes, ok assuming we are using coax)Now... if you look at linear loading, you'll find that when you apply linear loading to a piece of wire, its impedance will decrease (down to around 13 Ohms)So, and here is the idea, if we put together an endfed counterpoise or a vertical radial system using linear loading we should obtain low impedance on those, which in furn would improve its efficiencySo... am I wrong or missing something ?

author: bob91343
author_rank: Super Contributor
timestamp: August 31, 2021, 11:30:36 pm
content: Define linear loading; otherwise your question seems like technospeak.

author: radiolistener
author_rank: Super Contributor
timestamp: September 01, 2021, 12:44:29 am
content: High impedance for endfed radiator happends due to unbalanced load.Counterpoise make it more balanced and as result it also reduce impedance at feeding point.The main issue with endfed radiator is unbalanced load.RF choke helps to reduce common mode currents on coax line, but cannot eliminate it at all.Unbalanced antenna radiator always suffers from common mode currents in transmission line.Even if you use RF choke and balun/unun, common mode currents are still there, just a little bit smaller.So, if you want to minimize common mode currents and noise interference in transmission line, it's better to use antenna with balanced radiator and use proper balun and impedance matching at feeding point.My opinion is that unbalanced antenna like endfeed radiator (Fuchs antenna and other clones) is just a bad choice for a noisy environment like city. But it can works good enough if you use it somewhere in the field or in the forest, as far as possible from any building, electrical equipment or mains line.

author: vk6zgo
author_rank: Super Contributor
timestamp: September 01, 2021, 02:30:51 am
content: Quote from: bob91343 on August 31, 2021, 11:30:36 pmThe simplest version of "Linear loading" normally appears as bends in the conductor, pshortening it.(Looking at the planform of the conductor, it looks like a square wave.)There are other versions, but what makes them "linear" is the absense of discrete reactive devices.

author: bob91343
author_rank: Super Contributor
timestamp: September 01, 2021, 04:32:38 am
content: So what is the configuration of this setup? Very hard to visualize with only esoteric terms for something that isn't all that common.

author: radiolistener
author_rank: Super Contributor
timestamp: September 01, 2021, 04:37:45 am
content: May be he's talking about an idea to fix impedance with help of radiator geometry modification. But I think geometry modification cannot help here. Just because it can fix reactive part of impedance at feeding point, but cannot fix active part of impedance which is very high for end-feed radiator.Also, end-feeding cannot improve antenna radiation resistance.On the contrary, it leads to a more complicated matching of antenna with transmission line and more power loss on heating.As I know, antenna radiation resistance can be improved with usingmetamaterialswhich has a special electromagnetic properties that doesn't exists in naturally occurring materials. Such material allows to reduce reactive field of antenna, it improves radiation efficiency for a shortened radiator. And this is used for VHF antennas, but for a short wave it looks very difficult and expensive (due to a large size). I don't hear about short wave antennas which utilize metamaterials properties.

author: A.Z.
author_rank: Super Contributor
timestamp: September 01, 2021, 07:06:26 am
content: Quote from: vk6zgo on September 01, 2021, 02:30:51 amexactly so, and here is an examplehttps://www.nonstopsystems.com/radio/antenna_80m_vertical-lin-loaded.htmnow, one of the effects of linear loading is the reduction of impedance for the linear loaded section, so what I am wondering isWould the idea of using a linear loaded counterpoise wire (for an endfed) or linear loaded radials (for a vertical) help improving their efficiency and, in turn, the antenna efficiency ?My reasoning is that, due to the lower impedance (around 13 Ohm) than the ones of the antenna and the coax, such a setup could also help improving CM issues (not pretending to eliminate them btw)

author: iMo
author_rank: Super Contributor
timestamp: September 01, 2021, 09:41:18 am
content: I've been using an EFHW in a city, and I built a couple for others. You do not need any counterpoise, the shielding of a coax coming from the transformer does the job. People usually underestimate the proper construction of the transformer and tuning of the antenna thus spreading an info "it is much worse than a balanced dipole".

author: A.Z.
author_rank: Super Contributor
timestamp: September 01, 2021, 09:44:51 am
content: Quote from: imo on September 01, 2021, 09:41:18 amOh ... you still have a counterpoise, your coax, and that's something I'd try to avoid at all costs, good chokes on the coax and a decent counterpoise could surprise you, anyhow that isn't the subject

author: iMo
author_rank: Super Contributor
timestamp: September 01, 2021, 09:54:28 am
content: You do not need a counterpoise with an end fed half wave dipole.Quote from: A.Z. on September 01, 2021, 09:44:51 amHow you could avoid any coax??And what is the subject of your thread called "Antenna counterpoises"??

author: A.Z.
author_rank: Super Contributor
timestamp: September 01, 2021, 11:10:27 am
content: Forget it and thanks anyway, found some pointers and I'm going to experimenthttps://forums.qrz.com/index.php?threads/linear-loaded-radials.198661/

author: A.Z.
author_rank: Super Contributor
timestamp: September 01, 2021, 12:11:48 pm
content: Quote from: A.Z. on September 01, 2021, 07:06:26 amAgain, in case I was unclear, the idea IS NOT to use loading (linear loading in this case) to shorten the radiator, but to use linear loading to lower an endfed counterpoise or some other antenna radials impedance, so not only being able to shorten the counterpoise/radials but also improving both the CMC and efficiency; was I clear enough now ?

author: radiolistener
author_rank: Super Contributor
timestamp: September 02, 2021, 09:43:10 pm
content: Quote from: A.Z. on September 01, 2021, 07:06:26 amI think linear loading cannot fix unbalanced load.The problem with end-feed antenna is that you're needs some matching circuit which needs to keep all energy which is reflected from feeding point due to high SWR. You will have high loss on such matching circuit.And this problem with high SWR is not a long wire. The root of cause is a small counterpoise, so you cannot fix it with long wire modification and keep a small size of counterpoise.This is the same as trying to carry two buckets of water one of which has a mass 10 kg and second one has 0.1 kg. You will always be tilted towards the heavier bucket and trying to change shape of heavier bucket cannot help hereQuote from: A.Z. on September 01, 2021, 12:11:48 pmin order to reduce impedance at feeding point, you're needs to increase size of a small counterpoise. Just because it's too small against the radiator, so even a small increase of counterpoise size leads to a very significant improvement, while attempt to change something for a long wire will not have a noticeable effect