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381. Re: Topband: Beverage Feed Line Choke Installation (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Mon, 01 Jun 2009 16:17:38 -0700
A real transformer certainly does break that current path. BUT -- any asymmetry between the windings, as well as any stray capacitive coupling between the windings, provides a path between windings f
/archives//html/Topband/2009-06/msg00014.html (8,630 bytes)

382. Re: Topband: Beverage Feed Line Choke Installation (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Mon, 01 Jun 2009 23:39:35 -0700
I understand your logic of creating a two-stage common mode filter with chokes and multiple ground rods, with each choke being a series element and each ground rod being a shunt element. When overkil
/archives//html/Topband/2009-06/msg00018.html (8,675 bytes)

383. Re: Topband: Beverage Feed Line Choke Installation (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Tue, 02 Jun 2009 10:09:40 -0700
Do A/B tests with the antenna connected, switching the chokes in and out of the circuit. Symptoms of good performance -- deeper nulls of off-axis signals and/or less noise. Should not affect the desi
/archives//html/Topband/2009-06/msg00021.html (8,925 bytes)

384. Re: Topband: Testing Soil Conductivity (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Sun, 07 Jun 2009 18:03:35 -0700
There are maps that show soil conductivity in the US. One is part of the FCC rules for AM broadcasting. That's important to the FCC only because it has a strong effect on ground wave propagation on t
/archives//html/Topband/2009-06/msg00034.html (7,404 bytes)

385. Re: Topband: Twin Lead Marconi Antenna (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Mon, 15 Jun 2009 09:42:39 -0700
I disagree. Radiation is the result of CURRENT. Your analysis assumes that current is evenly distributed along the wire. It is not! The high current parts of the antenna are still vertical. The addit
/archives//html/Topband/2009-06/msg00051.html (7,813 bytes)

386. Re: Topband: inverted L fed with coax (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Mon, 15 Jun 2009 23:31:03 -0700
It will work fine. SWR will be moderate, and loss in RG8 is negligible at 1.8 MHz. Heck -- Although I wouldn't recommend it, I've even tuned a vertical that was close to a half wave on 80 meters, fed
/archives//html/Topband/2009-06/msg00054.html (7,392 bytes)

387. Re: Topband: One acre arrays (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Wed, 17 Jun 2009 01:04:05 -0700
I agree with Lee. I would go for the best vertical you can do with a lot of radials AND the best RX you can do. When thinking about RX, consider that a long Beverage can be pretty non-invasive when i
/archives//html/Topband/2009-06/msg00061.html (7,398 bytes)

388. Re: Topband: Dual feed for Pennants (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Wed, 24 Jun 2009 10:46:55 -0700
To take the coax out of the equation, you simply need to apply monster multi-turn chokes to the coax. See the Cookbook in my tutorial for winding details. In this application, I would try to achieve
/archives//html/Topband/2009-06/msg00083.html (8,080 bytes)

389. Re: Topband: Common mode chokes (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Sat, 04 Jul 2009 11:22:23 -0700
Good work! Several comments. First, since your primary interest is HF, you'll get FAR more bang for the buck with WOUND chokes, as opposed to a string of beads. The reasons why are well documented in
/archives//html/Topband/2009-07/msg00007.html (8,921 bytes)

390. Re: Topband: Common mode chokes (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Sat, 04 Jul 2009 18:23:39 -0700
Good move. I haven't seen the Clifton thing, but it sounds like a good idea, for the reason noted in the previous post. Using what you have in the back room can be a useful starting point. ON4UN's de
/archives//html/Topband/2009-07/msg00010.html (9,510 bytes)

391. Topband: QRe: Common mode chokes (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Sun, 05 Jul 2009 07:56:30 -0700
He did not. He originated the concept of a string of beads common mode choke to decouple the feedline from the antenna. It makes complete sense that the ground should help a lot by forming a voltage
/archives//html/Topband/2009-07/msg00017.html (9,580 bytes)

392. Re: Topband: Common mode chokes (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Tue, 07 Jul 2009 08:28:39 -0700
Caution with that, Julius. The capacitance from one end of the choke to the other is a critical component of the choke. A conductive enclosure can change that significantly by lowering the resonant f
/archives//html/Topband/2009-07/msg00026.html (9,128 bytes)

393. Re: Topband: Common mode chokes (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Tue, 07 Jul 2009 12:01:06 -0700
not very easy. Virtually everything is plastic. There are use I can think of for the larger metal cans too. On 160M it's not critical because the wavelength is so long. Rule of thumb is within 1/20 w
/archives//html/Topband/2009-07/msg00028.html (9,225 bytes)

394. Re: Topband: Common mode chokes (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Tue, 07 Jul 2009 17:08:59 -0700
Yes, BUT -- when I mentioned an idea similar to that as the solution to mounting a matching network outdoors, my neighbor reminded me the UV from Old Sol attacks most plastic materials and turns them
/archives//html/Topband/2009-07/msg00030.html (9,011 bytes)

395. Re: Topband: Common mode chokes (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Wed, 08 Jul 2009 12:34:39 -0700
For a discussion of what causes common mode current, see http://audiosystemsgroup.com/RFI-Ham.pdf It's in the discussion that leads into Coaxial Chokes. For a Power Point slides on the same topic, se
/archives//html/Topband/2009-07/msg00034.html (9,500 bytes)

396. Re: Topband: Common mode chokes (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Wed, 08 Jul 2009 12:38:29 -0700
YES! That's been true of my ham shack and antenna farm for all my 54 years in ham radio. I suspect there may be two kinds of hams -- those who continually experiment and try to learn things, as we do
/archives//html/Topband/2009-07/msg00035.html (8,971 bytes)

397. Re: Topband: Common mode chokes (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Fri, 10 Jul 2009 09:16:08 -0700
Not necessarily. There is a common mode circuit through the coax shield to the chassis of the equipment to which it connects, and from there to the station ground, which itself can be noisy. It is im
/archives//html/Topband/2009-07/msg00038.html (10,480 bytes)

398. Re: Topband: Common mode chokes (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Mon, 13 Jul 2009 13:53:51 -0700
Yes, I would expect it to work quite well as an alternative to coax where you want light weight for travel and don't care about deterioration from UV. On the other hand, coax is probably more conveni
/archives//html/Topband/2009-07/msg00044.html (10,327 bytes)

399. Topband: f IRe: HELICALLY WOUND VERTICAL (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Thu, 16 Jul 2009 08:07:54 -0700
Yes. If you can do anything top loaded, by all means go for it. K6MM's idea in QST shows a way to get on 160 if you cannot easily do something better. And any antenna that you DO install will beat on
/archives//html/Topband/2009-07/msg00061.html (7,995 bytes)

400. Re: Topband: QEX article and T-vertical improvement (score: 1)
Author: "Jim Brown" <jim@audiosystemsgroup.com>
Date: Sun, 19 Jul 2009 21:53:42 -0700
Complexity and loss in the unun. :) Why not go further (that is, more toploading) and take the feedpoint impedance to 50 +JX. Now you can match it with nothing more than a capacitor in series that su
/archives//html/Topband/2009-07/msg00080.html (8,186 bytes)

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