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Author Topic: vertical antennas  (Read 96297 times)
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KM1H
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« Reply #75 on: June 04, 2011, 07:03:14 PM »

There seems to be quite a difference for some places between those 2 maps but Im my expected 1 on both.
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k4kyv
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« Reply #76 on: June 04, 2011, 07:53:23 PM »

Hello Don.

I was just looking at the ground conductivity map of the US on the FCC site and wondering if you were in the 2mS/m part of TN. I don't exactly know which part of the State you're in, but it's obviously not that part in the east where it's really bad.

Scroll down to the 100 mi/200 km scale.


http://maps.google.com/maps?q=woodlawn+tn&oe=utf-8&rls=org.mozilla:en-GB:official&client=firefox-a&um=1&ie=UTF-8&hq=&hnear=0x8864d51e75b573ef:0x6b9d02d9f7fca55,Woodlawn,+TN&gl=us&ei=m8TqTZKECY72gAfWhYTYCQ&sa=X&oi=geocode_result&ct=image&resnum=1&ved=0CCEQ8gEwAA
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Don, K4KYV                                       AMI#5
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« Reply #77 on: June 04, 2011, 08:49:29 PM »

Not nit-pickin', Dave. It's been a while since I've delved into this and was assuming you knew something I hadn't heard before/yet. No offence intended. I was just interested in what it was you meant. Please don't read a slap where none was meant.

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K5UJ
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« Reply #78 on: June 04, 2011, 10:43:54 PM »

Dave, thanks for the g.c. information for the UK.  The FCC map of the US that is frequently published accompanying this topic in books is pretty old.  I have no idea how they obtained the data and how accurate it is.  As far as I know, it is all we have here, that is, until now.  I'll have to study that "atlas" source you put a link up for.   I think I am in a slightly above average location (probably wishful thinking) because I am in a low lying area near a river bank and the earth is moist most of the year.

Rob
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Sam KS2AM
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« Reply #79 on: June 04, 2011, 11:14:55 PM »

Hello Don.

I was just looking at the ground conductivity map of the US on the FCC site and wondering if you were in the 2mS/m part of TN. I don't exactly know which part of the State you're in, but it's obviously not that part in the east where it's really bad.

Scroll down to the 100 mi/200 km scale.


http://maps.google.com/maps?q=woodlawn+tn&oe=utf-8&rls=org.mozilla:en-GB:official&client=firefox-a&um=1&ie=UTF-8&hq=&hnear=0x8864d51e75b573ef:0x6b9d02d9f7fca55,Woodlawn,+TN&gl=us&ei=m8TqTZKECY72gAfWhYTYCQ&sa=X&oi=geocode_result&ct=image&resnum=1&ved=0CCEQ8gEwAA

and why are there five Woodlawns in Tennessee Don ?  ... lack of creativity   Tongue ?

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« Reply #80 on: June 05, 2011, 04:18:49 AM »

I’ve just found a very small version of the BBC ground conductivity map for the UK in an old 1966 copy of the RSGB Bulletin, and it doesn’t agree too well with the CCIR map for the UK. Granted, the CCIR would have had difficulty getting the regional detail on a map of that scale, but even so the shape of the high-conductivity region around Lincolnshire and Cambridgeshire is wrong and specified as much more conductive than on the BBC version.

Bud, don’t worry about offending me. If I’ve been sloppy and imprecise, I need to be pulled up about it. I ought to be more careful, especially on this forum with Steve always lurking. Oh, and never assume I know what I'm talking about. Like everyone else I sometimes get a bee in my bonnet about something, or other, but I'm wrong. There's an awful lot to learn in the world and I realize how little I know in total. It's humbling!

Don, thanks for the link to the map of your location. The relief, such as it is, makes it appear that you’re on the edge of the basin where the Cumberland River deposited some half-reasonable soil way back in time, and there’s low-conductivity rock between you and Nashville.

You’re also rather close to Paducah. That could be real bad news in the future!

Sam, “Woodlawn” seems to be a really popular name in the States. A couple of years ago, I traced a Peace Corps teacher I used to know when I was teaching on VSO (British Peace Corps) in Grenada way back, and he was teaching at a school of that name in Arlington, Virginia. “Springfield” and various other names seems to be repeated quite a lot throughout the States as well. I suppose the pioneers liked to remind themselves of where they originated. When I try to keep up with the news on the Caribbean island of Grenada, I often get the news for some place in Mississippi or Louisiana coming up instead. Lack of imagination, possibly; but could just be the adult version of a comforter - human nature’s a funny thing!

Dave.
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Dave,G3UUR
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« Reply #81 on: June 05, 2011, 09:57:21 AM »

I suppose the bottom line to all this is a quote from the Slab Bacon himself and I quote"Get as much wire in the air as high as you can, feed it with  open wire ladder line and a robusto tuna then go to town wid it!" Werks fer me whenever I upgrade to General.
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G3UUR
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« Reply #82 on: June 05, 2011, 02:08:17 PM »

That has been said many times, and goes back well before Slab said it. I don't think it's entirely true, though, since if you can get it high enough you can usually get away with less wire.

Dave.
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Dave,G3UUR
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« Reply #83 on: June 05, 2011, 03:59:46 PM »

For all practical purposes this seems to be the best remedy.I have a
smaller back yard (garden) like the above person in the almost same predicament.A flat top with about 200 ft of wire fed with ladder line
at around 40 feet will be the best I will be able to do.Forget verticals with  radials My xyl would murder me if I even suggested such a monstrosity Smiley
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« Reply #84 on: June 05, 2011, 04:31:47 PM »

Forget verticals with  radials My xyl would murder me if I even suggested such a monstrosity Smiley

Well, I have to admit that any time someone asks me how to get all my antennas on a 50 x 100 foot lot, I always tell them the first thing you have to do is make your marital status single.
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« Reply #85 on: June 05, 2011, 06:22:05 PM »

Yep the story of my life in a nutshell LOL Smiley
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G3UUR
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« Reply #86 on: June 06, 2011, 10:17:16 AM »

A flat top of 170 to 200 ft at a height of 40 ft is a good all-band antenna in my experience. I've used that arrangement at several of my previous locations with good success around the UK and Europe on 160, 80 and 40m. I did try a 240 ft top once and that was so much worse on 80m that I had to give up using it. Could never understand why, but others I've talked to who use similar antennas have found the same thing.

Dave.

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Dave,G3UUR
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Steve - K4HX
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« Reply #87 on: June 06, 2011, 10:44:50 AM »

I've never been to a town named Woodlawn but I've seen quite a few cemeteries with that name.

A 3/4 wavelength vertical will have a TO angle of something like 50 degrees. No, it's not NVIS, but not a bad angle for lots of non-DX type contact.
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« Reply #88 on: June 06, 2011, 12:13:54 PM »

Isn't there a minor lobe at a lower take-off angle as well, Steve?
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Dave,G3UUR
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k4kyv
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« Reply #89 on: June 06, 2011, 12:42:42 PM »

Forget verticals with radials My xyl would murder me if I even suggested such a monstrosity

What's the problem? A vertical, particularly a single mast (especially if you can get it to stay up unguyed) is probably the least imposing antenna structure you can erect, except maybe for a wire antenna with "natural" supports (trees). You don't have to tear up the lawn to bury the radials. Just clip them to the surface of the ground with stiff pieces of wire with hooks on one end, driven into the soil. This keeps the lawn mower from lifting the wire and getting tangled up with it. After a few weeks the wires will become invisible. Left undisturbed for a season or two, they will bury themselves, as thatch and sod form over the wire.

Regarding visible antennas on the property, whenever my wife grumbles about a radio project, I remind her that she knew about the radio long before she agreed to the marriage contract, and it was all part of a package deal.

I looked over those articles on radials in QEX, NCJ and the issue of QST in the footnotes, and interestingly, a full size quarter-wave vertical with just 4 to 8 short radials appears to be only 3-4 dB down from the same vertical with an optimum ground plane. The poor radial system can be compensated for by simply increasing power: "Ground Plane by Eimac". Of course, this doesn't work worth a hoot for a significantly shortened vertical; those little 16-ft commercially manufactured "No Radials Needed" verticals might perform reasonably well (with a big leen-yar) on 20 through 10m, but pretty well become dummy loads on 40 through 160.

I think the full wave vertical is supposed to have a very low angle minor lobe that might make it work for DX, but it is quite a few dB down from the main lobe, which is somewhere about 53° as I recall.  Minor lobes begin to become significant at about 5/8λ, which is why the 5/8WL broadcast verticals didn't prove satisfactory. They put out the maximum ground wave, but the high angle skywave radiation causes severe selective fading when it interferes with the ground wave.  This is known as the "fading wall". WSM had to chop about 80' off the tubular mast on top of the big Blaw-Knox tower to reduce a severe fading problem in Chattanooga.

"Woodlawn" is a very common name for graveyards all over the country. Here, it just happens to be the name (origin unknown) of the rural post office that delivers the mail; no official township with surveyed boundaries. There used to be little post offices scattered all over the countryside just a few miles apart, dating back to the days of horse-drawn vehicles, usually located in the rear of a grocery store or other business. About the time of WWII, they "consolidated" the little P.O.s into a few larger ones. Ours happened to be one of those that were saved to serve as a consolidated distribution point. When the grocery store was about to close (could no  longer compete with the big supermarkets in town), the P.O. purchased a plot of land next to the old one and erected a dedicated post office building, one of those little brick buildings with a flag out front that looks identical to millions of other small post offices all over the country. We don't have townships here; outside incorporated towns the only name for a community to go by is the name of the post office that serves it.  Many adjoining  communities still informally go by the name of the post office that used to be there but closed decades ago.  Some are downright funny, like Lickskillet, Possumtrot, Turtletown and Bucksnort. And of course, don't forget about the famous motel by the same name in Intercourse, PA.
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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« Reply #90 on: June 06, 2011, 01:06:24 PM »

If youre stuck on a small back yard then make all of it a ground plane by using the 2x2 or 2x4" welded, then galvanized and then green plastic dipped yard mesh sold at garden centers and box stores. See Freds version in another thread. Tack it down and maybe spread a inch of loam over it and the grass and its invisible and will function well for decades. As mentioned on here a few times it really improved my DX chasing at a prior QTH.

I know a guy who even buried it under his foundation and driveway during construction. A 100 x 100 lot is almost all a ground system and he gets out like gangbusters on 160/80 with a 43' stick. A couple of Slinky's along the lot lines give decent reception.

Carl
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w3jn
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« Reply #91 on: June 07, 2011, 06:10:59 PM »

For all practical purposes this seems to be the best remedy.I have a
smaller back yard (garden) like the above person in the almost same predicament.A flat top with about 200 ft of wire fed with ladder line
at around 40 feet will be the best I will be able to do.Forget verticals with  radials My xyl would murder me if I even suggested such a monstrosity Smiley

That's about what I use at my Mt Airy, MD QTH.  But I made it a fan dipole, with the ends spread a few feet and one pair of conductors a foot or so shorter than the others.  Works FB, and even puts an acceptable signal on 160 with the GPT-750 and K1JJ tuna.  There's a, ahem, fair amount of circulating current in that tuna on 160 though.  The vacuum variable has a bit of talkback  Grin
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« Reply #92 on: June 07, 2011, 07:55:05 PM »

I've never been to a town named Woodlawn but I've seen quite a few cemeteries with that name.


Did you start any arguments with the inhabitants? Just asking.
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KM1H
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« Reply #93 on: June 08, 2011, 12:07:55 PM »

I wonder if ground conductivity is better in a cemetery or is it a RF dead spot?  Roll Eyes Grin

Carl
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« Reply #94 on: June 08, 2011, 01:26:58 PM »

I guess, Carl, that might be determined by the ratio of wood to metal caskets?
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Steve - K4HX
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« Reply #95 on: June 08, 2011, 08:39:04 PM »

I was invited to a few garden parties.



I've never been to a town named Woodlawn but I've seen quite a few cemeteries with that name.


Did you start any arguments with the inhabitants? Just asking.
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« Reply #96 on: June 08, 2011, 09:34:12 PM »

I was invited to a few garden parties.



I've never been to a town named Woodlawn but I've seen quite a few cemeteries with that name.

Did you start any arguments with the inhabitants? Just asking.

Just remember you can't please everyone.....
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k4kyv
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« Reply #97 on: June 08, 2011, 11:42:52 PM »

I guess, Carl, that might be determined by the ratio of wood to metal caskets?

http://www.therealmofterror.com/gallery/main.php?g2_itemId=1888

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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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Steve - K4HX
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« Reply #98 on: June 09, 2011, 08:01:20 AM »

But it's all right now.

I was invited to a few garden parties.



I've never been to a town named Woodlawn but I've seen quite a few cemeteries with that name.


Did you start any arguments with the inhabitants? Just asking.

Just remember you can't please everyone.....
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WD8BIL
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« Reply #99 on: June 09, 2011, 08:47:26 AM »

Did you learn your lesson well, Steve?

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But it's all right now.
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