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201. Re: [TowerTalk] Feedline (choke) question (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Mon, 29 Sep 2025 15:40:49 -0700
The original postulation from Brian, K6STI, was that connecting the shield of the coax to ground at a point where any common mode current might exist would shunt it to ground. I've claimed that's a f
/archives//html/Towertalk/2025-09/msg00116.html (17,297 bytes)

202. Re: [TowerTalk] Feedline (choke) question (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Tue, 30 Sep 2025 02:04:55 -0700
What you are describing is totally different than the original claim (and the subsequent discussion) that the earth is an RF sink.  What was the purpose in doing that? Yes, you can make the earth act
/archives//html/Towertalk/2025-09/msg00119.html (24,390 bytes)

203. Re: [TowerTalk] Feedline (choke) question (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Tue, 30 Sep 2025 09:43:15 -0700
I already answered that.  RF isn't DC ... it doesn't just flow to the earth and disappear.  It flows back and forth every half cycle. Whatever current flow may occur between the coax and ground is st
/archives//html/Towertalk/2025-09/msg00122.html (11,079 bytes)

204. Re: [TowerTalk] Feedline (choke) question (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Tue, 30 Sep 2025 12:21:02 -0700
Brian, I didn't say there shouldn't be any current.  I said there isn't any current that just goes to ground and stays there ... as in bleeding it off.  EZNEC doesn't show that either.  It just shows
/archives//html/Towertalk/2025-09/msg00125.html (11,338 bytes)

205. Re: [TowerTalk] Feedline (choke) question (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Tue, 30 Sep 2025 13:37:33 -0700
Possibly I missed it, but I don't see your EZNEC model.  I only saw the diagram.  Can you send me the model? Dave   AB7E Dave, I don't know what you mean by back and forth. In my model, the ground wi
/archives//html/Towertalk/2025-09/msg00127.html (11,350 bytes)

206. Re: [TowerTalk] Raised Radial Spacing (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Mon, 27 Oct 2025 21:33:19 -0700
The VOR is a very valid concept, and I've modeled it in a couple of different ways to investigate it.  I'm even thinking of building an 80m vertical based upon it so I don't have to string wires arou
/archives//html/Towertalk/2025-10/msg00083.html (14,766 bytes)

207. Re: [TowerTalk] Raised Radial Spacing (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Tue, 28 Oct 2025 17:23:14 -0700
Exactly so, Jim.  I don't know why Zero Five would think that's a good idea. Dave   AB7E On 10/28/2025 1:58 PM, Jim Brown wrote: On 10/28/2025 11:15 AM, n1bkb-- via TowerTalk wrote: While I have not
/archives//html/Towertalk/2025-10/msg00096.html (10,726 bytes)

208. Re: [TowerTalk] Raised Radial Spacing (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Mon, 3 Nov 2025 18:50:06 -0700
Most of a lifetime ago I was a component engineer at Collins Radio, and one of the products I was responsible for was a small ferrite core.  The manufacturer's rep explained the manufacturing process
/archives//html/Towertalk/2025-11/msg00017.html (8,844 bytes)

209. [TowerTalk] Oh the irony ... (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Fri, 28 Nov 2025 10:25:57 -0700
You respond to a message imploring you to edit the digest subject line by keeping the digest subject line. Dave   AB7E On 11/28/2025 10:16 AM, ARTHUR BERNSTEIN via TowerTalk wrote: Well guys, my mind
/archives//html/Towertalk/2025-11/msg00117.html (11,680 bytes)

210. Re: [TowerTalk] 6M yagi (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Tue, 2 Dec 2025 20:47:56 -0700
I can't think of any reason why an antenna would be "quieter" other than it having a tighter pattern, either horizontally or vertically, and therefore discriminates against background noise better. 
/archives//html/Towertalk/2025-12/msg00007.html (8,333 bytes)

211. Re: [TowerTalk] 1/4 wave vertical versus vertical dipole (was Choke on feed point of dipole) (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Tue, 13 Jan 2026 00:11:21 -0700
On top of that, based upon the modeling I've done over the years I've never found that a vertical dipole has any appreciable advantage over a 1/4 wave ground plane.  Certainly not enough to justify t
/archives//html/Towertalk/2026-01/msg00034.html (14,016 bytes)

212. Re: [TowerTalk] Choke on feed point of dipole (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Tue, 13 Jan 2026 12:09:02 -0700
"Assuming you have the height" That's the kicker, though, and it takes twice as much of it for relatively little additional performance.  I've modeled a 20m ground plane with four elevated radials an
/archives//html/Towertalk/2026-01/msg00039.html (13,086 bytes)

213. Re: [TowerTalk] Choke on feed point of dipole (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Tue, 13 Jan 2026 13:22:54 -0700
I know what those are.  It's another design from N6BT, who I believe used to own Force 12.  As I said in a different post, he also came up with the VOR that coils the bottom half of a vertical dipole
/archives//html/Towertalk/2026-01/msg00042.html (11,657 bytes)

214. Re: [TowerTalk] Choke on feed point of dipole (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Tue, 13 Jan 2026 14:53:16 -0700
I already explained all of that. Default ground specs were used.  (0.005/13 over Real/MININEC) The ground plane antenna had four 1/4 wave horizontal radials 4 feet off the ground.  The bottom of the
/archives//html/Towertalk/2026-01/msg00044.html (11,254 bytes)

215. Re: [TowerTalk] Choke on feed point of dipole (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Wed, 14 Jan 2026 07:57:58 -0700
FFS Jim, I know all about the effect of ground specs on vertical antenna performance and the difference with horizontal polarization.  I used the default specs BECAUSE I WAS ONLY MAKING A COMPARISON!
/archives//html/Towertalk/2026-01/msg00048.html (15,150 bytes)

216. Re: [TowerTalk] Terrain Modeling (was choke on vertical dipole) (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Thu, 15 Jan 2026 11:36:31 -0700
FEKO is supposedly a much more sophisticated modeling application capable of handling complex terrain and even 3D objects like cars (or tanks, for which I assume it was originally designed) and at on
/archives//html/Towertalk/2026-01/msg00063.html (14,618 bytes)

217. Re: [TowerTalk] Choke on feed point of dipole (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Thu, 15 Jan 2026 12:02:50 -0700
What is say is absolutely true, but in today's world it would be possible to actually quantify some of those things. For real time propagation it is hard to beat PSK Reporter's map of FT8 activity, a
/archives//html/Towertalk/2026-01/msg00066.html (13,670 bytes)

218. Re: [TowerTalk] Choke on feed point of dipole (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Thu, 15 Jan 2026 12:31:16 -0700
Last year I got interested in the Radio Jove project that monitors broadband RF emissions from Jupiter from about 15 MHz to 25 MHz. For that purpose I built a 5 element wire log periodic antenna and
/archives//html/Towertalk/2026-01/msg00071.html (17,785 bytes)

219. Re: [TowerTalk] propagation was Re: Choke on feed point of dipole (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Thu, 15 Jan 2026 13:09:10 -0700
Hhmmm ... that is a truly interesting idea and I think it could be accomplished without a ton of cost, although not with particularly great resolution.  Here's a few thoughts. 1.  PSK Reporter can pr
/archives//html/Towertalk/2026-01/msg00074.html (17,270 bytes)

220. Re: [TowerTalk] Choke on feed point of dipole (score: 1)
Author: David Gilbert <ab7echo@gmail.com>
Date: Thu, 15 Jan 2026 13:10:29 -0700
Good point! Dave  AB7E In all cases, a small oscillator (crystal controlled or something like the popular Silicon Labs programmable ICs) positioned between the two antennas could provide a reference
/archives//html/Towertalk/2026-01/msg00075.html (11,209 bytes)


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