Re: Topband: My Turn For a Brain Pick - Sanity Check
On 6/12/2013 3:34 PM, Tom W8JI wrote: I can't think of a reason to pick 90 degrees as a target value, unless it is a system designed to protect something on groundwave that happens to be straight in line with the elements. I agree. For me, the primary design objectives are maximizing forward gain, beamwidth, and gain bandwidth. I don't care about F/B. 73, Jim K9YC All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
Right. There's some discussion of this in the ON4UN book, where I found the Christman matching. As published there, it's 84 degrees of 50 ohm line in each element, plus 71 degrees of 50 ohm line in the element facing the desired forward direction,change directions by switching the 71 degree section. It is critical to understand that a 71 degree line does not necessarily delay phase 71 degrees. Also, if the lines to the elements are not multiples of 90 degrees, those lines will alter phase relationship between the two elements based on the impedance mismatch on the lines. Since the elements in a two element unidirectional array have grossly different impedances, and since the lines to the elements are not multiples of 90 degrees, phase delay and current distribution changes in the element feedlines themselves are different. This means we cannot look at the system and conclude anything. Along the same note, almost every Ham transmitting antenna setup I have seen does not have the phase shift and current ratios the builders or designers think. It's common to think a hybrid gives 90-degrees phase shift, that a 3/8th line gives 135 degrees delay, and other similar thingsbut that rarely is true. It might, but a cardioid with a null at zero degrees elevation straight off the back is a pretty poor pattern for skywave use, as well as for gain. Gain increases and the effective or useful F/R ratio increases significantly when phase shift between the elements is some value greater than 90 degrees. I can't think of a reason to pick 90 degrees as a target value, unless it is a system designed to protect something on groundwave that happens to be straight in line with the elements. 73 Tom All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
On 6/12/2013 10:10 AM, Jim GM wrote: What kind of gain readings are you getting now? We didn't measure gain, but we did measure F/B. Gain is rather difficult to pin down. Even F/B is tricky -- there was at least 6dB of QSB on the rear setup (with the 71 degree line traded to the other element). Measurement distance was 5 miles mid-afternoon. BTW -- many thanks for all the helpful ideas. 73, Jim K9YC All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
On 6/12/2013 10:18 AM, Jim GM wrote: Sounds like your gearing up for Field Day. If so where are you going to set up? With the K6MI "Chews Ridge Gang," about 50 miles E of Monterey, CA. We do QRP battery. 73, Jim K9YC All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
I guess 90 degree phase shift might result in a cardioid pattern? Charlie, K4OTV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Wednesday, June 12, 2013 2:58 PM To: topband Subject: Re: Topband: My Turn For a Brain Pick - Sanity Check > Christman phasing is at 71 degrees? I was thinking 90 degree phasing. > Whats the reasoning for this? Optimum phasing of two verticals 1/4 wave apart is never 90 degrees, unless the user for some reason wants a single-point zero-angle null and less than maximum gain. Optimum element current delay for Ham use is always more than 90 degrees, and generally around 110-120 degrees, with 1/4 wave spacing. Making things more complex, phase shift in a delay line is never the line length unless the line is either 1/4 wave long or a multiple of 1/4 wave, or the line has a reasonably well-matched termination. With that in mind, a 71 degree long line might produce considerably different phase shift than the electrical line length, and the user probably wants phase to be some other value than 90 degrees (if the user understands arrays and patterns). 73 Tom All good topband ops know how to put up a beverage at night. _ Topband Reflector All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
On 6/12/2013 11:58 AM, Tom W8JI wrote: Christman phasing is at 71 degrees? I was thinking 90 degree phasing. Whats the reasoning for this? Optimum phasing of two verticals 1/4 wave apart is never 90 degrees, unless the user for some reason wants a single-point zero-angle null and less than maximum gain. Optimum element current delay for Ham use is always more than 90 degrees, and generally around 110-120 degrees, with 1/4 wave spacing. Making things more complex, phase shift in a delay line is never the line length unless the line is either 1/4 wave long or a multiple of 1/4 wave, or the line has a reasonably well-matched termination. With that in mind, a 71 degree long line might produce considerably different phase shift than the electrical line length, and the user probably wants phase to be some other value than 90 degrees (if the user understands arrays and patterns). Right. There's some discussion of this in the ON4UN book, where I found the Christman matching. As published there, it's 84 degrees of 50 ohm line in each element, plus 71 degrees of 50 ohm line in the element facing the desired forward direction,change directions by switching the 71 degree section. 73, Jim K9YC All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
Christman phasing is at 71 degrees? I was thinking 90 degree phasing. Whats the reasoning for this? Optimum phasing of two verticals 1/4 wave apart is never 90 degrees, unless the user for some reason wants a single-point zero-angle null and less than maximum gain. Optimum element current delay for Ham use is always more than 90 degrees, and generally around 110-120 degrees, with 1/4 wave spacing. Making things more complex, phase shift in a delay line is never the line length unless the line is either 1/4 wave long or a multiple of 1/4 wave, or the line has a reasonably well-matched termination. With that in mind, a 71 degree long line might produce considerably different phase shift than the electrical line length, and the user probably wants phase to be some other value than 90 degrees (if the user understands arrays and patterns). 73 Tom All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
Read and envy: http://shakespeare-military.com/masts.asp They take Visa and Mastercard! Tim N3QE -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Jim GM Sent: Wednesday, June 12, 2013 1:19 PM To: topband Subject: Re: Topband: My Turn For a Brain Pick - Sanity Check I have seen some thing like those military surplus mast sections. I believe the ones I saw were made by Shakespear. I think this is the same company that made those good trout fishing rods and reels like the one I have. Sounds like your gearing up for Field Day. If so where are you going to set up? -- Jim K9TF All good topband ops know how to put up a beverage at night. _ Topband Reflector All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
I have seen some thing like those military surplus mast sections. I believe the ones I saw were made by Shakespear. I think this is the same company that made those good trout fishing rods and reels like the one I have. Sounds like your gearing up for Field Day. If so where are you going to set up? -- Jim K9TF All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: My Turn For a Brain Pick - Sanity Check
Very fine Jim. What kind of gain readings are you getting now? Christman phasing is at 71 degrees? I was thinking 90 degree phasing. Whats the reasoning for this? -- Jim K9TF All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: BOG antenna
I have a simple switchable coaxial BOG running NE-SW. I have often noticed that it is not bothered much by rain. In fact, I would consider this a valid "selling point" of the BOG. Having said that, even on a rainy day, the longer 2-wire beverage up about 5' still hears slightly better (even with the rain static). Wonder how many others have observed the same? If you avoid sharp points or things that encourage corona discharge on antennas, or getting them close to or aimed at tall objects that have corona, the p-static will greatly diminish or go away. I get no p-static at all on my bare-wire above-ground Beverages, except on one that points at my tall towers and is a few hundred feet from the towers. They stay dead quiet for p-static, except of course anything will hear the lightning noise from storms. All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: BOG antenna
Hi Bruce, I have a simple switchable coaxial BOG running NE-SW. I have often noticed that it is not bothered much by rain. In fact, I would consider this a valid "selling point" of the BOG. Having said that, even on a rainy day, the longer 2-wire beverage up about 5' still hears slightly better (even with the rain static). 73, Mike N1TA Original Message Subject: Topband: BOG antenna From: "Bruce" Date: Tue, June 11, 2013 11:25 pm To: >>Wonder how many others have observed the same? All good topband ops know how to put up a beverage at night. _ Topband Reflector
